ALBERT

Notes: The dark reaction of NOx and H2O vapor in 1 atm of air was studied for the purpose of elucidating the recently discussed unknown radical source in smog chambers. Nitrous acid and nitric oxide were found to be formed by the reaction of NO2 and H2O in an evacuable and bakable smog chamber. No nitric acid was observed in the gas phase. The reaction is not stoichiometric and is thought to be a heterogeneous wall reaction. The reaction rate is first order with respect to NO2 and H2O, and the concentrations of HONO and NO initially increase linearly with time. The same reaction proceeds with a different rate constant in a quartz cell, and the reaction of NO2 and H218O gave H18ONO exclusively. Taking into consideration the heterogeneous reaction of NO2 and H2O, the upper limit of the rate constant of the third-order reaction NO + NO2 + H2O → 2HONO was deduced to be (3.0 ± 1.4) × 10-10 ppm-2-min-1, which is one order of magnitude smaller than the previously reported value. Nitrous acid formed by the heterogeneous dark reaction of NO2 and H2O should contribute significantly to both an initially present HONO and a continuous supply of OH radicals by photolysis in smog chamber experiments.

Notes: Absorption spectra of the superoxide ion have been studied in dimethylformamide (DMF) and acetonitrile (AN). It was found that the superoxide ion existed in equilibrium with an ion pair in AN (Keq = 20M-1, Bu4N+ is the cation) and as “free” (solvated) ion in DMF. The addition of DMF caused the destruction of an ion pair in AN. The addition of the proton donors HX (water or ethanol) to the \documentclass{article}\pagestyle{empty}\begin{document}${\rm O}_{\rm 2}^{\overline {\rm .} }$\end{document} solutions in DMF and AN caused the formation of new ion pairs (Bu4N+\documentclass{article}\pagestyle{empty}\begin{document}${\rm O}_{\rm 2}^{\overline {\rm .} }$\end{document})2HX. The equilibrium constants of these ion pairs were determined in DMF and AN.

Notes: The kinetics of the reaction of the superoxide ion with ethyl acetate have been studied in DMF, AN, and their mixtures. It was shown that the rate constants depend on the ethyl acetate concentration, which indicates the formation of an intermediate in this process. Equilibrium constants for the process of the intermediate formation and the rate constants for its decay have been determined. It is concluded that aprotic solvents affect mainly the stage of the intermediate decay in this reaction.

Notes: The gas-phase equilibrium and rate constants for the isomerizations of 1,3,6-cyclooctatriene (136COT) to 1,3,5-cyclooctatriene (135COT) [reaction (1)] and bicyclo[4.2.0]octa-2,4-diene (BCO) to 135COT [reaction (-2)] have been measured between 390 and 490 K and between 330 and 475 K, respectively. The rate constant of reaction (1) obeys the Arrhenius equation \documentclass{article}\pagestyle{empty}\begin{document}$$k_{\rm 1} = 10^{10.93 \pm 0.08} {\rm exp}[- (115.9 \pm 0.7{\rm kJ}/{\rm mol})/RT]{\rm s}^{ - 1}$$\end{document} The corresponding equilibrium constant is given by the van′t Hoff equation \documentclass{article}\pagestyle{empty}\begin{document}$${\rm In K}_{\rm 1}^{\rm 0} = (0.24 \pm 0.04) + (13.78 \pm 0.15{\rm kJ}/{\rm mol})/RT$$\end{document} The strain energy of the 136COT ring is calculated to be 31.7 kJ/mol, based on the known value of 37.2 kJ/mol for 135COT, and ΔHf0(298 K) for gaseous 136COT is 196.3 kJ/mol. The rate constant of reaction (-2) obeys the Arrhenius equation \documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm - 2}} = 10^{12.38 \pm 0.23} {\rm exp}[(- 106.9 \pm 1.5{\rm kJ}/{\rm mol})/RT]{\rm s}^{ - 1}$$\end{document} The equilibrium constant for 135COT ⇆ BCO fits the van′t Hoff equation \documentclass{article}\pagestyle{empty}\begin{document}$${\rm In K}_{\rm 2}^{\rm 0} = (- 1.20 \pm 0.02) - (0.40 \pm 0.07{\rm kJ}/{\rm mol})/RT$$\end{document} The strain energy of the BCO skeleton is calculated to be 108.3 kJ/mol, and ΔHf0(298 K) for gaseous BCO is 183.3 kJ/mol.

Notes: The azoethane-sensitized thermal reaction of isobutene has been studied at 526-565 K. The initial concentrations of azoethane and isobutene were in the ranges of 1.40-10.5 × 10-4 and 6.78-26.6 × 10-4 mol/dm3, respectively. From the initial rates of formation of ethane and 2-methylpentane the heat of formation of the 2-methyl-2-pentyl radical was determined. The result obtained is ±Hf0(2-methyl-2-pentyl) = 0.8 ± 2.0 kcal/mol. The entropy of the radical, obtained from statistical mechanical calculations and experimentally, is S0(2-methyl-2 pentyl) = 92.8 ± 1.5 cal/mol°K. The results support the high heat of formation of the t-butyl radical suggested by different authors.

Notes: The gas-phase thermal isomerization of hexachlorocyclopropane to hexachloropropene at 208-283°C is first order and unaffected by changes in the surface-to-volume ratio or by the addition of iodine, tetrachloroethylene, and oxygen. The first-order rate constants fit the Arrhenius equation \documentclass{article}\pagestyle{empty}\begin{document}$${\rm log}k({\rm s}^{ - 1}) = (15.74 \pm .022) - (45,660 \pm 526)/4.576T$$\end{document} The reaction was interpreted as an unimolecular process taking place with chlorine atom migration. A comparison of the reactivities of several chlorocyclopropanes is made.

Notes: The rates of elimination of 5-chloropentan-2-one and 4-chloro-1-phenylbutan-1-one in the gas phase have been determined in a static system, seasoned with allyl bromide, and in the presence of the chain inhibitor propene. The reactions are unimolecular and follow a first-order rate law. The working temperature and pressure ranges were 339.4-401.1°C and 46-117 torr, respectively. The rate coefficients for the homogeneous reactions are given by the following Arrhenius equations: for 5-chloropentan-2-one, log k1(s-1) = (13.12 ± 0.88) - (207.8 ± 11.0)kJ/mol/2.303RT; and for 4-chloro-1-phenylbutan-1-one, log k1(s-1) = (12.28 ± 1.09) - (185.2 ± 12.0)kJ/mol/2.303RT. The carbonyl group at the γ position of the C—Cl bond of haloketones apparently participates in the rate of pyrolysis. The five-membered conformation appears to be a favorable structure for anchimeric assistance of the C=O group in the gas-phase elimination of chloroketones.

Notes: Vinylacetylene was pyrolyzed at 300-450°C in a packed and an unpacked static reactor with a pinhole bleed to a quadrupole mass spectrometer. The reactant and C8H8 products were monitored continuously during a reaction by mass spectrometry. In some runs, the products were also analyzed by gas chromatography after the run. In these runs CH4, C2H6, C3H6, and C2H4 were also detected.The reaction for vinylacetylene removal and C8H8 formation is homogeneous, second order in reactant, and independent of the presence of a large excess of N2 or He. However, C8H8 formation is about half-suppressed by the addition of the free-radical scavengers NO or O2. The rate coefficient for total vinylacetylene removal is 1.7 × 106 exp(-79 ± 13 kJ/mol RT) L/mol · s. The major reaction for C4H4 removal is polymerization. In addition four C8H8 isomers, carbon, and small hydrocarbons are formed. The three major C8H8 isomers are styrene, cyclooctatetraene (COT), and 1,5—dihydropentalene (DHP).The C8H8 compounds are formed by both molecular and free-radical processes in a second-order process with an overall k ≃ 3 × 108 exp(-122 kJ/mol RT) L/mol · s (average of packed and unpacked cell results). The molecular process occurs with an overall k = 8.5 × 107 exp (-118 kJ/mol RT) L/mol · s. The COT, DHP, and an unidentified isomer (d), are formed exclusively in molecular processes with respective rate coefficients of 4.4 × 104 exp(-77 kJ/mol RT), 1.7 × 105 exp(-89 kJ/mol RT), and 3.1 × 109 exp(- 148 kJ/mol RT) L/mol · s. The styrene is formed both by a direct free-radical process and by isomerization of COT.

Notes: The product quantum yields in the photolysis of 2,2,4,4-tetramethyl-3-pentanone have been measured in homogeneous solvents of different viscosities, in micellar solutions of cetyltrimethylammonium chloride and sodium dodecyl sulfate, and in dioctadecyl ammonium chloride vesicles.The product quantum yield in n-heptane was found to be 1. This value decreases to 0.5 in paraffin oil as a consequence of geminate recombination. In the presence of free radical scavengers, the extent of geminate disproportionation can be evaluated from the yields of isobutene and 2,2-dimethyl propionaldehyde. From these yields and the geminate recombination yields the total amount of geminate processes and the disproportionation-to-combination ratio for caged radicals are estimated. It is found that micelles provide the most efficient cages. In these media only about 10% of the radicals avoid cage processes. The disproportionation-to-combination ratio of tert-butyl and pivaloyl radicals was found to be extremely media dependent. The measured values ranged from about 0.2 in paraffin oil to 0.8 in cetyltrimethylammonium chloride micelles.

Notes: Kinetics of the thermal decomposition of acetic acid vapor dilute in argon have been studied over the temperature range of 1300-1950 K in a single-pulse shock tube. The acid was found to decompose homogeneously and molecularly via two competing firstorder reaction channels at nearly equal rates, to form methane and carbon dioxide on the one hand, and ketene and water on the other. Fall-off behavior has been taken into account and limiting high-pressure rate constants for both channels have been derived. Ketene was found to decompose both unimolecularly to methylene radicals and carbon monoxide and also by a radical reaction with CH2 to form ethylene and carbon monoxide. The rate constant derived for the unimolecular reaction was found to be in good agreement with an earlier shock tube measurement by H. G. Wagner and F. Zabel [Ber. Bunsenges Phys. Chem., 75, 114 (1971)]. The bimolecular reaction of ketene to produce allene and carbon dioxide, important in lower temperature reaction systems, has been found to be unimportant under the present conditions. A computer model for the decomposition kinetics involving 46 reactions of 21 species has been found to simulate the experimental yield data substantially. Sensitivity analyses have been used to identify reactions which make important contributions to the overall mechanism and yields of major products. Methylene radicals play important roles in determining yields of major species.

Notes: The abstraction of hydrogen/deuterium from CH3CH2Cl, CH3CHDCl, and CH3CD2Cl by photochemically generated ground-state chlorine atoms has been investigated over the temperature range of 8-94°C using methane as a competitor. Rate constant data for the following reactions have been obtained:The temperature dependence of the relative rate constants ki/kj was found to conform to the Arrhenius rate law, where the stated error limits are one standard deviation:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 /k_2 = (1.099 \pm 0.015)\exp [(429 \pm 2)/T] $$ $$ k_1 /k_r = (1.422 \pm 0.026)\exp [(1113 \pm 3)/T] $$ $$ k_2 /k_r = (1.295 \pm 0.029)\exp [(684 \pm 3)/T] $$ $$ k_3 /k_r = (1.177 \pm 0.025)\exp [(717 \pm 4)/T] $$ $$ k_4 /k_r = (1.115 \pm 0.023)\exp [(732 \pm 2)/T] $$ $$ k_5 /k_r = (0.978 \pm 0.020)\exp [(985 \pm 2)/T] $$\end{document} and kr is the rate constant for the reference reaction (CH4 + Cl → CH3 + HCl). The β secondary kinetic isotope effects (k2/k3/k4) are close to unity and show a slight inverse temperature dependence. Both preexponential factors and activation energies decrease as a result of deuterium substitution in the adjacent chloromethyl group. The trends are well outside the limits of experimental error.

Notes: The reaction between ozone and carbon monoxide was reinvestigated in the range of 80-160°C. The previously reported rate law -d[O3]/dt = ka[O3][CO] + kb[O3]2 was confirmed and simulated using a mechanism based on an impurity-initiated chain reaction. When the CO was sufficiently purified, kb tended to zero and ka reduced to the value expected for the thermal decomposition of O3. Subsequent reactions of O atoms with CO produced chemiluminescence which was used to measure k3 for \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm O}\,\, + \,\,{\rm CO}\,\,\mathop {\longrightarrow}\limits^{\rm 3} \,\,{\rm CO}_{\rm 2} \left( {^3 B_2 } \right) $$\end{document} as 10-14.0±0.3 exp[-(1630 ± 325)/T] cm3 molecule-1 s-1. The implications of this are discussed.

Notes: The thermal decomposition of azoisopropane (AIP) was studied by detailed product analysis in the temperature and pressure intervals 498-563 K and 0.67-5.33 kPa. Besides the predominant termination and hydrogen-abstraction reaction of the 2-propyl radical, the decomposition is characterized by a very short chain process. The following rate constants were determined from the measurements\documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{rcl} \log (k_1 {\rm /s}^{ - 1} ) &=& (16.3 \pm 0.2) - (199.9 \pm 1.6){\rm kJ mol}^{ - 1} /2.3RT \\ \log (k_4 /k_3^{1/2} {\rm dm}^{{3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm mol}^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm s}^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. \kern-\nulldelimiterspace} 2}} ) &=& (4.1 \pm 0.3) - (52.5 \pm 3.0){\rm kJ mol}^{ - 1} /2.3RT \\ \log (k_5 /k_3^{1/2} {\rm dm}^{{3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm mol}^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm s}^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. \kern-\nulldelimiterspace} 2}} ) &=& (2.4 \pm 0.1) - (27.6 \pm 1.3){\rm kJ mol}^{ - 1} /2.3RT \\ k_2 /k_3 &=& 0.51 \pm 0.02 \end{array}$$\end{document} for the following reactions:

Notes: Chlorocyclopropane has been produced by addition of CH2(1A1) and CH2(3B1) to chloroethene. CH2 was generated by the photolysis of ketene at 313 and 366 nm. Chlorocyclopropane was formed in a chemically activated state, had an energy content between 378 and 427 kJ/mol, and reacted in three parallel channels to 3-chloropropene, cis- and trans-1-chloropropene. As secondary reactions elimination of HCl from the chemically activated primary products occurred to form allene and propyne. The apparent rate constants for the isomerization and elimination reactions are reported. The results of RRKM calculations including distribution functions for the activated chlorocyclopropane and a stepladder model for the deactivation support the proposed reaction scheme.

Notes: The kinetics of OH reactions with furan (k1), thiophene (k2), and tetrahydrothiophene (k3), have been investigated over the temperature range 254-425 K. OH radicals were produced by flash photolysis of water vapor at λ 〉 165 nm and detected by timeresolved resonance fluorescence spectroscopy. The following Arrhenius expressions adequately describe the measured rate constants as a function of temperature (units are cm3 molecule-1 S-1): k1 = (1.33 ± 0.29) × 10-11 exp[(333 ± 67)/T], k2 = (3.20 ± 0.70) × 10-12 exp[(325 ± 71)/T], k3 = (1.13 ± 0.35) × 10-11 exp[(166 ± 97)/T]. The results are compared with previous investigations and their implications regarding reaction mechanisms and atmospheric residence times are discussed.

Notes: The reactions of ground-state S(3PJ) atoms with thiirane, methylthiirane, and trans-2,3-dimethylthiirane have been studied by flash photolysis-VUV kinetic absorption spectroscopy. From the analysis of the S(3PJ) decay plots the following rate constants were determined: (1.4 ± 0.2) × 1013, (2.7 ± 0.3) × 1013 and (4.0 ± 0.2) × 1013 (in cm3 mol-1 s-1 units) for thiirane, methylthiirane and trans-2,3-dimethylthiirane, respectively, showing an upward trend with increasing methylation.

Notes: NO Abstract.

Notes: An examination of the results of measurements of the forward and reverse rate constants for the reaction \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm H} + {\rm C}_{\rm 2} {\rm H}_{\rm 6} \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\rightarrow\over {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} {\rm H}_{\rm 2} + {\rm C}_{\rm 2} {\rm H}_{\rm 5} $$\end{document} shows that agreement between the kinetics and the thermochemistry is achieved only through use of a value of ΔHf(C2H5) = 28 kcal mol-1. This system therefore provides further support for the recent measurement of this quantity.

Notes: The very low pressure reactor (VLPR) technique has been used to measure the bimolecular rate constant of the title reaction at 300 K. The rate constant is given by log k1 (1/mol s) = (11.6 ± 0.4) - (5.9 ± 0.6)/θ the equilibrium constant has also been measured at the same temperature and is given by K1 = (5.6 ± 1) × 10-3 and hence log k-1 (1/mol s) = 9.5 ± 0.1. The results show that the reaction Br + t—C4H9 → HBr + i—C4H8 is unimportant under the present experimental conditions. Assigning the entropy of t-butyl radical to be 74 ± 2 eu which is in the possible range, the value of K1 gives ΔH°f (t-butyl) = 9.1 ± 0.6 kcal/mol-1. This yields for the bond dissociation, DH° (t-butyl-H) = 93.4 ± 0.6 kcal/mol. Both of these values are found to be in good agreement with recent VLPP studies.

Notes: Kinetics of the basic hydrolysis of glyceryl trinitrate (TNG) were investigated in CO2-free aqueous calcium hydroxide solutions. The hydrolysis reactions were carried out in a temperature controlled reactor vessel with provision for continuous N2 sparging of the reaction mixture. TNG hydrolyzed via second-order reaction at 25°C, 18°C, and 10°C. The activation energy of the hydrolysis reaction of TNG was calculated from the kinetic data and found to be equal to 27.53 kcal/mol. The major products of the hydrolysis of TNG in solution of calcium hydroxide were calcium nitrate and calcium nitrite, accounting for approximately 50% of the degradation products. The minor identified products such as calcium oxalate and nitrate esters amounted to approximatey 6% of the products. The remaining 30% of the isolated products was a mixture of calcium formate, a nitrate ester, and unidentified volatiles, polymerlike substances, and other organic residue.

Notes: Results obtained from the photolysis of ketene with acetylene strongly support the formation of C3H3 radicals in the title reaction. Stationary state studies are interpreted in terms of the reaction \documentclass{article}\pagestyle{empty}\begin{document}$${\rm C}_3 {\rm H}_{\rm 4}^{\rm *} \buildrel3\over\rightarrow{\rm C}_3 {\rm H}_3^ \cdot + {\rm H}^ \cdot$$\end{document} with a rate constant (109.8 s-1) which is compared to RRKM predictions. In pulsed laser induced decomposition experiments, recombination products involving C3H3 have been detected (some for the first time) and their formation modeled using step (3) with the same rate constant.

Notes: A readily applicable empirical formula is obtained for the collisional efficiency for energy transfer between a highly vibrationally excited reactant and a seasoned (usually quartz) wall, in terms of the molecular weight, potential well depth and dipole moment of the reactant. This expression is used to examine corrections due to nonunit wall collision efficiency in the high-pressure rate parameters obtained from very low-pressure pyrolysis experiments. It is found that these corrections are up to ca. ±5 kJ/mol in the high-pressure activation energy and a factor of ca. 2 in the high-pressure frequency factor, for molecules with molecular weight less than ca. 100 and where experiments are carried out at temperatures exceeding 1000 K.

Notes: The rate constants for reactions (4) and (5) were determined at room temperature by pulsed laser photolysis and time resolved mass spectrometry. A description of the experimental setup is given. CFCl2O2 radicals were generated by photolysis of CFCl3 at 193 nm in the presence of an excess of oxygen, using an excimer laser. The rate constant for reaction (4), determined under different experimental conditions is: \documentclass{article}\pagestyle{empty}\begin{document}$$k_4 = 1.6{\rm }(\pm 0.2) \times 10^{ - 11} {\rm cm}^{\rm 3} \cdot {\rm molecule}^{ - 1} \cdot {\rm s}^{ - 1}$$\end{document} The rate constant of reaction (5) was determined in the pressure range of 1-12 torr, using oxygen as the buffer gas. The reaction is in its fall-off region and the parameters determined by using the semiempirical method of Troe, taking Fc = 0.6 are: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} k(0) = 3.5{\rm }(\pm 0.5) \times 10^{ - 29} {\rm cm}^{\rm 6} \cdot {\rm molecule}^{ - 2} \cdot {\rm s}^{ - 1} \\ k(\infty) = 6.0{\rm }(\pm 1.0) \times 10^{ - 12} {\rm cm}^{\rm 3} \cdot {\rm molecule}^{ - 1} \cdot {\rm s}^{ - 1} \\ \end{array}$$\end{document} The value of k(∞) is obtained from the low-pressure measurements and therefore the uncertainty on the actual high-pressure limit is higher than the error limits quoted above. The results are compared with those reported for similar reactions.

Notes: Potassium persulfate oxidizes triphenylphosphine to triphenylphosphine oxide in 60% aqueous acetonitrile. It has been suggested that the oxygen of the product, triphenylphosphine oxide, might originate from solvent water, following nucleophilic attack on an intermediate phosphonium ion. We have investigated the origin of the oxygen in the oxidation of triphenylphosphine by potassium persulfate in 60% aqueous acetonitrile containing 20% [18O]water. The product was analyzed by using the 18O isotope effect in 31P NMR spectroscopy. The magnitude of the 18O isotope-induced shift was determined by synthesizing triphenylphosphine [18O]oxide and was found to be 0.038 ppm upfield. The product of the oxidation reaction in 20% [18O]water displayed no 18O isotope effect. The origin of the oxygen in the oxidation reaction is the persulfate ion, consistent with an alternative mechanism involving nucleophilic attack by water at the sulfur atom of a phosphonium peroxysulfate intermediate.

Notes: It is shown how kinetic electron spin resonance spectroscopy with intermittent radical generation can be used to obtain rate constants of various simultaneous reactions in systems containing more than one kind of transient radicals. The technique is applied to reactions of tert-butyl [(CH3)3Ċ] and isopropylol [(CH3)2ĊOH] radicals generated by photolysis of di-tert-butyl ketone and acetone in 2-propanol/acetone mixtures. It yields the rates of generation of the two radicals, the rate constants for their self- and crossterminations and for the reaction of tert-butyl with 2-propanol. The extent of diffusion control of the termination constants is discussed.

Notes: Trifluoro-t-butoxy radicals have been generated by reacting fluorine with 2-trifluoromethyl propan-2-ol: \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm \dot F} + {\rm CF}_3 {\rm C}({\rm OH})({\rm CH}_3)_2 \to {\rm HF} + {\rm CF}_3 {\rm C}({\rm \dot O})({\rm CH}_3)_2 $$\end{document} Over the temperature range 361-600 K the trifluoro-t-butoxy radical decomposes exclusively by loss of the —CF3 group [reaction (-2)] rather than by loss of —CH3 group [reaction (-1)]: The limits of detectability of the product CF3COCH3, by gas-chromatographic analysis, place a lower limit on the ratio k-2/k-1 of ca. 75. The implications of these results in relation to the reverse radical addition reactions to the carbonyl group are discussed along with the thermochemistry of the reactions.

Notes: The gas-phase reaction of CF3 with HCN has been examined over a wide conversion range using CF3I as a thermal and photolytic source of radicals. Quantitative and qualitative results show a significant increase of the specific rate constant for the hydrogen abstraction reaction relative to CF3 recombination when reaction is carried out under ultraviolet irradiation. This “extra” formation of the reaction product, CF3H, has been assigned to the participation of iodine in this system through the formation of a (I-HCN) intermediate. Arrhenius parameters obtained for the addition mechanism of I to HCN do not seem to conform to a single reaction step, on the contrary, they correspond to a more complex reaction scheme.

Notes: Small low residence time flow tube reactors made of alumina and used as molecular beam sources are described. In these reactors, gas mixtures are rapidly heated and brought to reaction. The composition of the gas leaving the reactor is analyzed by molecular beam mass spectroscopy. For quantitative simulation of the reacting gas flow, the theory of one-dimensional compressible flow with friction, heat transfer, and chemical reaction is brought into a form suitable for practical computation. The system has been applied to study the thermal decompositions of O3 and N2O. The experimental results on both reactions can be well modeled by homogeneous reaction mechanisms with accepted rate constants. Heterogeneous reaction steps are shown to be unimportant.

Notes: The yield of benzene in the reaction of 1,4- and 1,3-cyclohexadiene with OH radicals in the presence of oxygen was determined using H2O2 and CH3ONO as OH radical sources. Both in the H2O2 and the CH3ONO systems, the yield of benzene from 1,4-cyclohexadiene was 15.3% and the yield from 1,3-cyclohexadiene was 8.9%. On the basis of the obtained yields, the rate constant for allylic hydrogen abstraction per C—H in cyclohexadiene was determined to be 3.8 × 10-12 cm3 molecule-1 s-1. The branching ratio of the hydrogen abstraction to overall reaction for 1-butene and 1-pentene was estimated to be (25-14)% by applying the obtained rate constants. The result was in good agreement with the branching ratio determined directly by use of the discharge flow photoionization mass spectrometer by Biermann, Harris, and Pitts [4].

Notes: The photolysis of carbon tetrachloride in the presence of a number of organosilicon compounds has been investigated in the gas phase. The products obtained from the photolysis experiments were those expected from a chain reaction in which trichloromethyl radicals abstract hydrogen atoms from the organosilane. Arrhenius parameters for hydrogen atom transfer were determined relative to those for trichloromethyl radical combination. The activation energies for the reaction of methyl, trifluoromethyl, and trichloromethyl radicals with organosilicon compounds are compared and the results rationalized in terms of polar effects.

Notes: Calculations of low-pressure limit, third-order rate constants are presented for the association reactions A + O2 + N2 and A + OH + N2 (A = Li, Na, K) over the temperature range 200-2000 K and a comparison is made with the available experimental data.

Notes: The photooxidation of formaldehyde in CH2O—O2, oxygen-lean mixtures was studied in the temperature range 298-378 K. H2 and CO formation and the loss of O2 proceed by a chain mechanism, which between 328 and 378 K follows the previously suggested kinetics [1] with one modification. The reaction HO2 + CH2O ⇄ HO2CH2O (5) is now assumed to be reversible and ΔH5° is estimated to be between 14 and 19 kcal/mol. The relative yields of the chain formed H2 and CO and of the consumed O2 remained constant over the entire temperature range indicating that the relative efficiencies of the HO reactions: HO + CH2O → H2O HCO† (7), HO + CH2O → H2O + HCO (8) and HO + CH2O → HOCH2O (9) are temperature independent.

Notes: The kinetics of OH reactions with 1-4 carbon aliphatic thiols have been investigated over the temperature range 252-430 K. OH radicals were produced by flash photolysis of water vapor at λ 〉 165 nm and detected by time-resolved resonance fluorescence spectroscopy. All thiols investigated react with OH at nearly the same rate; k(298 K) = 3.2-4.6 × 10-11 cm3 molecule-1 s-1, -Eact = 0.6-1.0 kcal/mol, A = 0.6-1.2 × 10-11 cm3 molecule-1 s-1. CH3SH and CH3SD react with OH at identical rates over the entire temperature range investigated. We conclude that the dominant reaction pathway is addition to the sulfur atom.

Notes: Relative rate constants for the reaction of OH radicals with a series of α,β-unsaturated carbonyls have been determined at 299 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with propene of 2.52 × 10-11 cm3/molec·s, the rate constants obtained are (× 1011 cm3/molec·s: acrolein, 1.83 ± 0.13; crotonaldehyde, 3.50 ± 0.40; methacrolein, 2.85 ± 0.23; and methylvinylketone, 1.88 ± 0.14). These data, which are necessary input to chemical computer models of the NOx-air photooxidations of conjugated dialkenes, are discussed and compared with literature values.

Notes: It is shown that, by deliberate activation of the reaction vessel, heterogeneous reaction at the wall can be made to dominate chain termination in a complex gas-phase reaction. For a homogeneous process, characterized, as is often the case, by multiple terminations, this has the effect of simplifying the mechanism and allowing explicit solution of the relevant steady-state equations so that the rate constants of some individual steps can be evaluated without assumption as to the values of those of others.The pyrolysis of propane, in the vicinity of 500°C, has been used as an example of this approach. Enhancement of the wall activity leads to the reaction providing, almost exclusively, chain termination. As a result, rate constants for the initiation step can be directly determined. The results of this study provide the Arrhenius equation \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_1 (s^{ - 1}) = 16.71 \pm 0.54 - 83400 \pm 1950{\rm cal}/{\rm mol}/2.303RT $$\end{document} In combination with current thermochemical values this result gives k-1 = 1013.40 cm3/mol·s which, in turn, implies, via the geometric mean rule, kEt-Et = 1012.9 cm3/mol·s for ethyl-ethyl recombination, in good accord with the most recent determinations and compatible with the newly proposed value of the enthalpy of formation of ethyl.The first-order wall constant k8 has been evaluated as k8〈104.2 s-1. This appears to be the first occasion on which a wall constant has been evaluated from data for a high-temperature complex gas reaction.

Notes: The initial rates of formation of the major products in the thermal reactions of ethylene at temperatures in the neighborhood of 800 K have been measured in the presence and absence of the additives neopentane and ethane. It has been shown that in the absence of the additive the main initiation process is while in the presence of neopentane and ethane the following additional initiation processes occur: From the ratios of the rates of formation of the major products in the presence and absence of the additive the ratios kN/k1 and kE/k1 were measured over the temperature range of 750-820 K. Taking values from the literature for kN and kE, the following value was obtained for k1: \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_1 ({\rm L}/{\rm mol} \cdot {\rm s}) = 11.27 \pm 0.6 - \frac{{64,200 \pm 2000}}{{2.3RT}} $$\end{document} Previous results using butene-1 as additive were rexamined and shown to be consistent with this measurement. From this measurement the following values were derived: ΔHf(C2H3) = 63.4 ± 2 kcal/mol and D(C2H3—H) = 103 kcal/mol.

Notes: An empirical approach to the kinetic investigations of photo-initiated liquid-phase chlorination of benzene is presented. Reaction order and the reaction constants for chlorine consumption and for the production of hexachlorocyclohexane isomers were evaluated from experimental data.

Notes: Thermochemical analysis of the electron capture process of SF6 leads to a rate constant for the reverse process \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm SF}_6^ - \mathop \to \limits^2 {\rm SF}_6 + e^ -,k_2 = 1.5 \times 10^{13 - 31.4/\theta } {\rm s}^{{\rm - 1}} $\end{document}, where θ = 2.303RT, in kcal/mol. The electron affinity of 32±3 kcal/mol is deduced from the observed bimolecularity of the capture process down to 0.1 torr Ar bath gas and estimated entropies of SF6 and SF6-. The capture process is discussed from the view point of the formation of a metastable SF6- electron (SF6·eL-) Langevin complex which appears to have a lifetime of about 2 × 10-13 s. Curve crossing from the SF6·eL- complex to vibrationally excited (SF6-)* appears to have a normal rate and A factor. This is interpreted to indicate near-resonant coupling between the orbiting electron and the vibronic motions of SF6, together with similarity in structure of SF6 and SF6-. It is shown that the apparent slowness of thermal electron ejection from SF6- is a result of an unfavorable equilibrium constant rather than a slow rate.

Notes: The kinetics of oxidation of methyl phenyl sulfoxide by chloramine-T (CAT) has been studied in buffered ethanol-water (1:1 v/v) of pH 7.0. The reaction was found to follow no simple-order kinetics. A possible mechanism is suggested involving three rate-controlling steps: (1) the reaction between RNHCl (R = CH3C6H4SO2) and the sulfoxide, (2) the disproportionation of RNHCl, and (3) the reaction between RNCl2 and the sulfoxide. A mixed-order rate law is derived as rate/[C][SO] = k1 + Kdk2[C]/[SA]. The rate law is found to be obeyed for the meta- and para-substituted phenyl methyl sulfoxides also. The ρ value is obtained using Hammett's σ constants. The ρ values obtained for the attack of both RNHCl and RNCl2 with the sulfoxides are almost the same, showing that both are converting the sulfoxide to the same intermediate. A chlorinium ion transfer is suggested.

Notes: The vacuum decomposition of sucrose and cellobiose has been observed in the 150-250°C temperature range. The predominant decomposition product of both sugars is H2O with less than 5% CO, CO2, CH2O, CH3CHO, CH3OH, and C2H5OH formed. The detailed rates and temperature dependences suggest that with the possible exception of C2H5OH, the minor products are formed in secondary reactions of the dehydration products. Further it is shown that the so-called “melting with decomposition” of a sugar is in reality a high-temperature dissolution of the disaccharide in the eliminated water.

Notes: The kinetics of the cerium(IV) oxidation of glycolic acid have been studied in the medium HClO4—Na2SO4—NaClO4 at varying organic substrate (HL), hydrogen, and bisulfate ion concentrations at 25.0°C and ionic strength 2.0M. Under the experimental conditions used (0.03 ≤ [H+] ≤ 0.5M; 0.02 ≤ [HSO4-] ≤ 0.1M; 0.01 ≤ [HL] ≤ 0.1M) the observed pseudo-first-order rate constant kobs has been found to follow the complex expression where the values of the various constants have been estimated by a nonlinear least-squares method. According to this expression the oxidation process occurs significantly through three simultaneous pathways. Moreover three equilibria involving cerium(IV) and HSO4- (or SO42-) ions are important from a kinetic point of view, whereas only two equilibria involving the corresponding complexes with the organic substrate are predominant.

Notes: The gas-phase elimination of ethyl 3-methylbutanoate and ethyl 3,3-dimethylbutanoate has been studied, in a static system, over the temperature range of 360-420°C and in the pressure range of 71-286 torr. The reactions are homogeneous, unimolecular, and follow a first-order rate law. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for ethyl 3-methylbutanoate, log k1 (s-1) = (12.70 ± 0.36) - (202.5 ± 4.4) kJ/mol/2.303RT, and for ethyl 3,3-dimethylbutanoate, log k1 (s-1) = (13.04 ± 0.08) - (207.1 ± 1.0) kJ/mol/2.303RT. Alkyl substituents at the acyl carbon of ethyl esters yield very close values in rates. Consequently it is rather difficult to offer some conclusion concerning the effect of these substituents.

Notes: The gas-phase reaction CH3SH + I2 has been studied spectrophotometrically over the temperature range of 476-604 K. It was found that the reaction undergoes H abstraction by I at ≤575 K, leading to the formation of MeSI and followed by a secondary reaction which leads to the formation of MeSSMe: Taking into consideration the effect of reaction (2), the equilibrium constant K1 (554 K) has been evaluated to be 0.025 ± 0.004. This value was combined with the estimated values S2980 (CH3SI, g) = 73.7 ± 1.0 eu and 〈ΔCp1,5540〉 = 0.87 ± 0.3 eu to obtain ΔH1,2980 = 4.03 ± 0.73 kcal/mol. This yields ΔHf2980 (CH3SI, g) = 7.16 ± 0.73 kcal/mol when combined with known thermochemical values for CH3SH, HI, and I2. A kinetic study was vitiated by the concurrent heterogeneous reaction of MeSH and I2 at lower temperatures and the rather complicated chemistry occurring at elevated temperatures. However, attempts at measuring rate constants at 554 K lead to a lower limit of ΔHf2980 (CH3S·, g) ≥ 29.5 ± 2 kcal/mol when an estimated value of A = 1010.8 ± 0.2 L/mol·s for the reactionc is used. DH2980 (CH3S-I) is estimated to be 49.3 ± 1.7 kcal/mol. The bond strengths of some divalent sulfurs and the reaction mechanisms are discussed. A crude estimate of DH0(H-CH2SH) = 96 ± 1 kcal has been obtained from the kinetic data.

Notes: The kinetics of the oxidation of dimethylsulfoxide by oxohydroxoosmate(VIII) complex ions in alkaline media follow pseudo-first-order disappearance in Os(VIII). The values of the observed pseudo-first-order rate constant are linearly dependent on initial dimethylsulfoxide concentrations in a fortyfold range, and increase with increasing [OH-], leveling off at higher relative [OH-]. The results are interpreted in terms of outer sphere interactions involving dimethylsulfoxide and various species of the Os(VIII) complex. The more nucleophilic dihydroxotetraoxoosmate(VIII) ion reacts about 50 times faster than the trihydroxotrioxoosmate(VIII) species.

Notes: The rate coefficient of the reaction \documentclass{article}\pagestyle{empty}\begin{document}$$(2){\rm H}_2 {\rm CN} \to {\rm H} + {\rm HCN}$$\end{document} has been determined in the temperature range of 2700-3500 K using a shock tube technique. C2N2—H2—Ar mixtures were heated behind incident shock waves and the early-time CN history was monitored using broad-band absorption spectroscopy. The rate coefficient providing the best fit to the data was \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm k = (7}{\rm .5}_{ - 2.0}^{{\rm + 2}{\rm .5}} {\rm)} \times {\rm 10}^{{\rm 13}} {\rm cm}^3 /{\rm mol} \cdot {\rm s} $$\end{document} in good agreement with extrapolations of previously published low-temperature results.

Notes: The photolysis of azocyclopentane in the presence of cyclopentane-carbon tetrachloride mixtures has been investigated in the gas phase. Product analysis data have been used to determine the Arrhenius parameters for the reactions \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {(4)_C - {\rm C}_5 {\rm H}_{9.} + {\rm CCl}_4 \to _C - {\rm C}_5 {\rm H}_9 + {\rm CCl}_{3.} } \hfill & {k_4 = 10^{9.0 \pm 0.6} {\rm exp}[- (10.3 \pm 1.0){\rm kcal}/{\rm mol}/{\rm RT}]} \hfill \\ {(6){\rm CCl}_{3.} + _C - {\rm C}_5 {\rm H}_{10} \to {\rm CCl}_3 {\rm H} + _C - {\rm C}_5 {\rm H}_{9.} } \hfill & {k_6 = 10^{8.4 \pm 0.4} {\rm exp}[- (10.0 \pm 0.7){\rm kcal}/{\rm mol}/{\rm RT}]} \hfill \\ \end{array}$$\end{document} The rate data for chlorine atom abstraction from CCl4 by the cyclopentyl radical were compared with available data for other alkyl radicals in both the gas and the solution phases. The results indicate that the rate constant for chlorine atom abstraction in the gas phase is fairly insensitive to the nature of the attacking alkyl radical and that the activation energy for a secondary radical is about 4 kcal/mol higher than the corresponding reaction in the solution phase.

Notes: The Ce(IV) oxidation of the five-, six-, and seven-membered ring α-hydroxycycloalkanecarboxylic (C5, C6, and C7) acids to the corresponding cyclic ketones has been studied in acidic perchlorate media. The data may be interpreted in terms of a mechanism which involves fast preequilibrium complexation steps between Ce(IV) and the hydroxy acids, yielding two complexes which differ only by a proton. Complexation is followed by rate-determining decarboxylation to an intermediate (free radical?), which reacts quickly with another Ce(IV) to give products. Of the two proposed complexes, the protonated one is virtually unreactive. The C7 ring acid is oxidized more rapidly than the C6 acid, which, in turn, is oxidized faster than the C5 acid.For comparison, the oxidation of the five-, six-, and seven-membered ring cyclic alcohols to the corresponding cyclic ketones by Ce(IV) in acidic perchlorate was also studied. The order of reactivity is cyclopentanol 〉 cycloheptanol 〉 cyclohexanol. The differences in observed reactivities between the hydroxy acids and the cyclic alcohols are explained in terms of differences in transition state structure.The stepwise hydrolysis constants of Ce(IV) leading to Ce(OH)3Plus; and Ce(OH)22+ were determined. In the case of the hydroxy acids, evidence is in favor of Ce(OH)3+ as the reactive ceric species in aqueous acidic perchlorate media.

Notes: The oxidation of propionaldehyde has been investigated in a 1-L Pyrex reactor at total pressures of 50-120 torr and temperatures 553-713 K. Detection of reactants and products was principally by molecular beam mass spectrometry, although certain species could only be measured by gas-chromatographic analysis. At 553 K the yield of water was ∼83% of the propionaldehyde consumed, leading to the conclusion that OH is the principal chain carrier near the beginning of the negative temperature coefficient region. Many oxygenated organics (CH2O, CH3CHO, C2H5OH, C2H5O2H, CH3O2H) and C2H4 are formed during the oxidation process. These oxidation products are consistent with the important role of O2 addition to C2H5 radicals at 553 K followed by subsequent reactions of the C2H5O2 radical. As the temperature is increased, the product concentrations smoothly change to a much simpler distribution in which C2H4, H2O2, and CO are the dominant products.

Notes: The kinetics of decomposition of “oxohydroxonickel(IV)” [Ni(IV)] with concomitant intramolecular electron transfer to produce hexaaquanickel(II) and dioxygen in aqueous acid solutions show pseudo-first-order dissappearance of the Ni(IV). The pseudo-first-order rate constants for the acid decomposition (kad) satisfy \documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm ad}} = k_{\rm d} {\rm K}_{{\rm MH}} [{\rm H}^ +]/(1 + {\rm K}_{{\rm MH}} [{\rm H}^ +])$$\end{document} where KMH and kd refer to the equilibrium protonation constant and the decomposition constant of the protonated species of the Ni(IV) respectively. The values of KMH and kd in aqueous medium at 45°C and μ = 2.0M are 25.5 ± 1M-1 and (1.7 ± 0.1) × 10-5 s-1, respectively.The kinetics of the intermolecular electron transfer from dimethyl sulfoxide (DMSO) to the Ni(IV), producing Ni(H2O)62+ and dimethyl sulfone as products, have been investigated by monitoring the formation of Ni(H2O)62+. The pseudo-first-order rate constants for the electron transfer kobs are linearly dependent on [DMSO]0 or [H+], attaining limiting values at higher relative [DMSO]0 or [H+], in accordance with \documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm obs}} = \frac{{[{\rm DMSO}]_0 }}{{1 + K_{{\rm MH}} [{\rm H}^ +]}}\left({\frac{{k_{1{\rm x}} K_{1{\rm c}} }}{{1 + K_{1{\rm c}} [{\rm DMSO}]_0 }} + \frac{{k_{2{\rm x}} K_{2{\rm c}} }}{{1 + K_{2{\rm c}} [{\rm DMSO}]_0 }}} \right)$$\end{document} where K1c and K2c represent the formation constants of the precursors involving DMSO and the unprotonated and one-protonated Ni(IV) species, respectively, and k1x and k2x are the corresponding decomposition rate constants of the precursors. The values of K2c and k2x are (2.3 ± 0.1) × 104M-1 and 19 ± 1 s-1, respectively, at 45°C and μ = 1.0M. Results are interpreted in terms of probable mechanisms involving (1) a rate-determining decomposition of the protonated Ni(IV) followed by rapid product formation steps, and (2) precursor complex formation between DMSO and the unprotonated or the protonated species of the Ni(IV) followed by rate-determining decomposition with electron transfer.

Notes: The formation of methyl iodide was determined by radiochemical methods and by massspectroscopic analyses in mixtures of Ar-CH4-I2 and Ar—CH4—I2—O2, heated by a reflected shock wave to temperatures of 830-1150 K. The rate of formation of CH3I was consistent with the chain mechanism \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} {\rm I} + {\rm CH}_4 \to {\rm CH}_3 + {\rm HI} \\ {\rm CH}_3 + {\rm I}_2 \to {\rm CH}_3 {\rm I} + {\rm I} \\ \end{array}$$\end{document} where the indicated rate constant for reaction between I and CH4 is given by k2(cm3/mol · s) = 1014.17 exp(-32.9 ± 0.8 kcal/mol/RT). No effect on the reaction rate by the presence of O2 was detected. However, in one experiment at 1097 K with 3.86 mol % O2 the formation of CH2O was indicated by the mass-spectroscopic analysis, presumably from the reaction of O2 with CH3.

Notes: The rate constants for the protonation of “free” (that is, solvated) superoxide ions by water and ethanol are equal to 0.5-3.5 ×10-3M-1·s-1 in DMF and AN at 20º. It has been found that the protonation rates for the ion pairs of \documentclass{article}\pagestyle{empty}\begin{document}${\rm O}_{\rm 2}^{\overline {\rm .} }$\end{document} with the Bu4N+ cation are much slower than those for “free” \documentclass{article}\pagestyle{empty}\begin{document}${\rm O}_{\rm 2}^{\overline {\rm .} }$\end{document}. It is suggested that the effects of aprotic solvents on the protonation rates of \documentclass{article}\pagestyle{empty}\begin{document}${\rm O}_{\rm 2}^{\overline {\rm .} }$\end{document} are mainly due to the fact that the proton donors form solvated complexes of different stability in these solvents.

Notes: The dispersion of a pulse of O(3P) atoms in flowing helium has been analyzed by a modification of Taylor's method in order to determine the diffusion coefficient. Atoms of O(3P) were produced in a flowing stream of helium by a pulsed microwave discharge of molecular oxygen. After traversing a known length of the flow tube, the arrival time distribution of the O(3P) atoms was obtained using a mass spectrometer. The value obtained for D0 at 294 K, where D0 = D[He], is (2.40 ± 0.06) × 1019 cm-1 ·s-1, which corresponds to a diffusion coefficient of (731 ± 18) cm2/s at 1 torr. In addition to D0, analysis of the arrival time distributions gives an estimate of the mean flow velocity for O atoms in helium. There was no significant difference between the value of the velocity found this way and that obtained from the mean bulk gas flow measurement. Thus for this system there is no evidence for a chromatographic effect for O(3P) atoms on the walls of the flow tube.

Notes: The hydrolysis of 2,4,6-trinitrophenyl acetate was studied in the presence of several carboxylic bases and tertiary amines. Carboxylic bases pyridine and imidazole react as nucleophilic catalysts, while 2,4-dimethyl and 2,4,6-trimethyl pyridine react as general-base catalysts. The nonlinear structure-reactivity correlations (log kcat versus log kOH and log kcat versus pK of the leaving group) for the series of aryl acetates are discussed, and it is suggested that there is a change in transition-state structure along the series.

Notes: No ABSTRACT.

Notes: Absolute rate coefficients for the reactions of the hydroxyl radical with ethane (k1, 297-300 K) and propane (k2, 297-690 K) were measured using the flash photolysis-resonance fluorescence technique. The rate coefficient data were fit by the following temperature-dependent expressions, in units of cm3/molecule·s: k1(T) = 1.43 × 10-14T1.05 exp (-911/T) and k2(T) = 1.59 × 10-15T1.40 exp (-428/T). Semiquantitative separation of OH-propane reactivity into primary and secondary H-atom abstraction channels was obtained.

Notes: The reaction SO + SO →l S + SO2(2) was studied in the gas phase by using methyl thiirane as a titrant for sulfur atoms. By monitoring the C3H6 produced in the reaction \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm S} + {\rm CH}_3\hbox{---} \overline {{\rm CH\hbox{---}CH}_2\hbox{---} {\rm S}} \to {\rm S}_2 + {\rm C}_3 {\rm H}_6 (7) $\end{document}, we determined that k2 ≃ 3.5 × 10-15 cm3/s at 298 K.

Notes: Relative rate constants for the gas-phase reactions of OH radicals with a series of cycloalkenes have been determined at 298 ± 2 K using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with isoprene of 9.60 × 10-11 cm3 molecule-1 s-1, the rate constants obtained were (X 1011 cm3 molecule-1 s-1): cyclopentene 6.39 ± 0.23, cyclohexene 6.43 ± 0.17, cycloheptene 7.08 ± 0.22, 1,3-cyclohexadiene 15.6 ± 0.5, 1,4 cyclohexadiene 9.48 ± 0.39, bicyclo[2.2.1]-2-heptene 4.68 ± 0.39, bicyclo[2.2.1] 2,5 heptadiene 11.4 ± 1.0, and bicyclo[2.2.2] 2 octene 3.88 ± 0.19. These data show that the rate constants for the nonconjugated cycloalkenes studied depend on the number of double bonds and the degree of substitution per double bond, and indicate that there are no obvious effects of ring strain energy on these OH radical addition rate constants. A predictive technique for the estimation of OH radical rate constants for alkenes and cycloalkenes is presented and discussed.

Notes: The isomerization of 1-hexene on 70/80 mesh HY zeolite was studied at 200°C. The observed reaction products are formed via a variety of processes including double bond shift, cis-trans isomerization, skeletal rearrangement, cracking, hydrogen transfer, polymerization, cyclization, and coke formation. By applying the time-on-stream theory, the products have been classified as primary, secondary, or both, according to their OPE curves on product selectivity plots. 2-Ethyl-1-butene, which is present as an impurity in the feed, is found to react about 30 times faster than 1-hexene. Both 2-hexenes and 3 hexenes are formed primarily from 1-hexene, while 3 methyl 2 pentenes and 3-methyl-1-pentene formed from 2-ethyl-1-butene. The ratio of the initial rate of deprotonation to that of hydrogen shift in these reactions is ∼15 and ∼100, respectively. All products of skeletal rearrangement are observed to be secondary. Cracking products are produced mainly from precoke, which is also the source of hydrogen in the formation of paraffins. A detailed reaction network along with its associated mechanisms are presented and discussed.

Notes: The photochemical decomposition of peroxomonosulfate (PMS) in the presence and absence of 2-propanol at 25°C was found to obey an overall first-order rate - d[PMS]/dt = kφ[PMS]. In the absence of 2-propanol, the quantum yield ≤ for the decomposition of PMS was found to depend upon the concentration of PMS at [PMS] 〉 2 × 10-M, and is independent of concentration at [PMS] 〉 2 × 10-2M. The quantum yield in the presence of 2-propanol was found to be 3.03 at [PMS] = 1 × 10-2M and 4.45 at higher concentrations of PMS. In the pH range of 2-9.0 the quantum yield was found to be independent of pH, and the overall rate constant kφ was found to be 6.49 × 10-3 s-1 and 1.68 × 10-3 s-1, respectively, in the presence and absence of isopropanol. A suitable chain mechanism is proposed and explained.

Notes: Aqueous bromine reacts with alkyl-sidechain amino acids through a series of steps resulting in the formation of the corresponding alkyl aldelydes and nitriles. The kinetics and the mechanism of the interaction of bromine with alanine are examined. The products and the rates of this reaction are dependent in a complex way on the initial reactant concentration and pH. Acetaldeyde production is favored at low bromine-to-alanine ratios, low bromine concentrations, and pH values above 6. The first-order rate constant for the formation of acetaldelyde from alanine under these conditions is k4 = 1.98 × 1015 e-22,500/RT min-1. At higher concentration the nitrile is formed through a bromoimine intermediate. Under most conditions the nitrile appears to form from a catalyzed decomposition of the bromoimine which is too fast to be followed by the methods used in this study. However, residual amounts of the bromoimine decay by a slower first-order mechanism. The rate constant for this slower reaction in the case of alanine at pH 6.8-6.9 and alanine concentrations of 1 × 10-4M is k6 = 1.75 × 105 e-10,400/RT min-1.

Notes: The reactions where Y = CH3 (M), C2H5 (E), i—C3H7 (I), and t—C4H9 (T) have been studied between 488 and 606 K. The pressures of CHD ranged from 16 to 124 torr and those of YE from 57 to 625 torr. These reactions are homogeneous and first order with respect to each reagent. The rate constants (in L/mol·s) are given by \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm NMBO}} = - {{\left( {26530 \pm 80} \right)} \mathord{\left/ {\vphantom {{\left( {26530 \pm 80} \right)} {4.576T + \left( {6.05 \pm 0.03} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {6.05 \pm 0.03} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm XMBO}} = - {{\left( {28910 \pm 130} \right)} \mathord{\left/ {\vphantom {{\left( {28910 \pm 130} \right)} {4.576T + \left( {6.32 \pm 0.05} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {6.32 \pm 0.05} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm NEBO}} = - {{\left( {26150 \pm 120} \right)} \mathord{\left/ {\vphantom {{\left( {26150 \pm 120} \right)} {4.576T + \left( {5.85 \pm 0.05} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {5.85 \pm 0.05} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm XEBO}} = - {{\left( {28560 \pm 120} \right)} \mathord{\left/ {\vphantom {{\left( {28560 \pm 120} \right)} {4.576T + \left( {6.07 \pm 0.05} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {6.07 \pm 0.05} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm NIBO}} = - {{\left( {26560 \pm 80} \right)} \mathord{\left/ {\vphantom {{\left( {26560 \pm 80} \right)} {4.576T + \left( {5.57 \pm 0.03} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {5.57 \pm 0.03} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm XIBO}} = - {{\left( {28350 \pm 100} \right)} \mathord{\left/ {\vphantom {{\left( {28350 \pm 100} \right)} {4.576T + \left( {5.47 \pm 0.04} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {5.47 \pm 0.04} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm NTBO}} = - {{\left( {28920 \pm 50} \right)} \mathord{\left/ {\vphantom {{\left( {28920 \pm 50} \right)} {4.576T + \left( {5.86 \pm 0.02} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {5.86 \pm 0.02} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm XTBO}} = - {{\left( {32890 \pm 120} \right)} \mathord{\left/ {\vphantom {{\left( {32890 \pm 120} \right)} {4.576T + \left( {6.19 \pm 0.05} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {6.19 \pm 0.05} \right)}} $$\end{document} The Arrhenius parameters are used as a test for a biradical mechanism and to discuss the endo selectivity of the reactions.

Notes: The technique of laser photolysis of alkyl and perfluoroalkyl iodides at 266 nm followed by time-resolved detection of the 1.3-μm emission from I*(2P1/2) has been used to measure the rate constants for deactivation of I* by CH3I, C2H5I, CF3I, and CH4. The recommended values are (2.76± 0.22) × 10-13, (2.85 ± 0.40) × 10-13, (3.5 ± 0.5) × 10-17, and (7.52 ± 0.12) × 10-14, respectively, in units of cm3 molecule-1 S-1.

Notes: The reactions of labeled N15NO+ with CO, NO, O2, 18O2, N2, NO2, and N2O have been investigated using a tandem ICR instrument. In each case the total rate coefficient, product distribution, and kinetic energy dependence were measured. The results indicate that very specific reaction mechanisms govern these reactions. This conclusion is suggested by the lack of isotopic scrambling in many cases and by the complete absence of energetically allowed products in almost all of the systems. The kinetic energy studies indicate that most of the reaction channels proceed through an intermediate complex at low energies and via a direct mechanism at higher kinetic energies. Such direct mechanisms include long range charge transfer and atom or ion transfer.

Notes: The reaction of CH4 + Cl2 produces predominantly CH3Cl + HCl, which above 1200 K goes to olefins, aromatics, and HCl. Results obtained in laboratory experiments and detailed modeling of the chlorine-catalyzed polymerization of methane at 1260 and 1310 K are presented. The reaction can be separated into two stages, the chlorination of methane and pyrolysis of methylchloride. The pyrolysis of CH3Cl formed C2H4 and C2H2 in increasing yields as the degree of conversion decreased and the excess of methane increased. Changes of temperature, pressure, or additions of HCl had little effect. In the absence of CH4 C2H4 and C2H2 are formed by the recombination of ĊH3 and ĊH2Cl radicals. With added CH4 recombination of ĊH3 forms C2H6, which dehydrogenates to C2H4 + H2. C2H4 in turn dehydrogenates to C2H2 + H2. While HCl, C, CH4, and H2 are the ultimate stable products, C2H4, C2H2, and C6H6 are produced as intermediates and appear to approach stationary concentrations in the system. Their secondary reactions can be described by radical reactions, which can lead to soot formation. ĊH3 - initiated polymerization of ethylene is negligible relative to the Ċ2H3 formation through H abstraction by Cl. The fastest reaction of Ċ2H3 is its decomposition to C2H2. About 20% of the consumption of C2H2 can be accounted for by the addition of Ċ2H3 to it with formation of the butadienyl radical. The addition of the latter to C2H2 is slow relative to its decomposition to vinylacetylene. Successive H abstraction by Cl from C4H4 leading to diacetylene has rates compatible with the experimental values. About 10% of Ċ4H5 abstracts H from HCl and forms butadiene. Successive additions of Ċ2H3 to butadiene and the products of addition can account for the formation of benzene, styrene, naphthalene, and higher polyaromatics. The following rate parameters have been derived on the basis of the experimentally measured reaction rates, the estimated frequency factors, and the currently available heat of formation of the Ċ2H3 radical (69 kcal/mol): \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {\mathop {{\rm C}_{\rm 2} }\limits^. {\rm H}_{\rm 3} \mathop {\longrightarrow}\limits_{\left( {\rm M} \right)}^{39} {\rm H}\,\, + \,\,{\rm C}_{\rm 2} {\rm H}_{\rm 2} } & {\log k\left( {1\,{\rm atm,}\,{\rm 1300}\,{\rm K}} \right)\, = \,5.2\, + \,0.3\,s^{ - 1} } \\ \end{array} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {{\rm C}_{\rm 2} {\rm H}_{\rm 4} \, + \,\mathop {{\rm C}_{\rm 2} }\limits^. \,\mathop {\longrightarrow}\limits^{17} \,\mathop {{\rm C}_{\rm 4} }\limits^. {\rm H}_{\rm 7} } \hfill & {E\, \ge \,2\, \pm \,2\,{{{\rm kcal}} \mathord{\left/ {\vphantom {{{\rm kcal}} {{\rm mol}}}} \right. \kern-\nulldelimiterspace} {{\rm mol}}}\,} \hfill \\ {\mathop {{\rm C}_{\rm 2} }\limits^. {\rm H}_{\rm 5} \, + \,{\rm C}_{\rm 6} {\rm H}_{\rm 6} \,\mathop {\longrightarrow}\limits^{40} \,\mathop {{\rm C}_{{\rm 12}} }\limits^. {\rm H}_{{\rm 11}} } \hfill & {E\, = \,11\, \pm \,2\,{{{\rm kcal}} \mathord{\left/ {\vphantom {{{\rm kcal}} {{\rm mol}}}} \right. \kern-\nulldelimiterspace} {{\rm mol}}}} \hfill \\ \end{array} $$\end{document}

Notes: The kinetics of fast elementary recombination of neutral ketyl radicals of benzophenone and its four derivatives (BPH⋅), the dismutation of benzophenone radical anions, the disproportionation between BPH⋅ and stable nitroxyl radicals, (), and the electron transfer have been investigated in both individual solvents and binary mixtures of different viscosities. Reaction (1) for unsubstituted BPH in water, water glycerol, and n-hexane is controlled by diffusion with 2k1 ≃ kdiff. In aliphatic alcohols and toluene, which form solvation complexes with BPH⋅, reaction (1) is diffusion-enhanced and activation-controlled, respectively, with 2k1 〈 kdiff. In a viscous solvent such as 1-propanol-glycerol mixture (100 ≲ η ≲ 450 cP) reaction (1) is diffusion-controlled. Reaction (2) in alkaline 1-propanol and alkaline 1-propanol-glycerol mixture is activation controlled. The rates of reactions (3) and (4) for benzophenone radicals and nitroxyl radicals of the imidazoline series decrease as the viscosity of the water-glycerol and 1-propanol-glycerol mixtures is increased. The reactions are molecular mobility limited; nevertheless, the numerical values of k3 (k4) are 2-6 times as small as the corresponding kdiff values due to the low steric factor of the reactions (therefore called pseudodiffusion-controlled reactions). The theoretical estimates of k3 (k4) are in good agreement with the experimental results. The elimination of spin forbiddance in the process of radical recombination in viscous solvents is discussed.

Notes: The approximations developed to determine the energy distribution function of molecules activated above energy decomposition threshold, from experimental data, have been tested. The approach involved the theoretical (RRKM) calculations of “pseudoexperimental” data for a variety of activated energy distributions. (Single or double Gaussian representations were used in all cases.) Subsequently the algorithms mentioned were applied in order to recuperate the original (i.e., input) energy distributions from these pseudoexperimental data. The results obtained provide strong evidence in favor of the validity of the algorithms and illustrate the necessary requirements for their applications. A trend toward lower accuracy as the energy distributions move to higher energies has been observed. Evidence of the influence of the distribution width is also reported. The origins of the approximation errors have been studied, and ways for further improvement are suggested.

Notes: The autooxidation of retinyl acetate and methyl retinoate was investigated in chlorobenzene at 45°C. The rates of thermal initiation in the retinyl acetate solutions were measured, and a value was determined of the rate constant for the reaction of oxygen with retinyl acetate (RH + O2 → R· + HO2·): kio = (1.3 ± 0.2) × 10-5 L/mol · s. The number of moles of oxygen absorbed per mole of polyene depends on the substrate concentration. A kinetic scheme for the methyl retinoate autooxidation was proposed which takes into account the isomerization of primary peroxy radicals, and the rate constants for different elementary reactions were estimated. The partial rate constant for “allylic” hydrogen abstraction from retinyl acetate was estimated to be ≥ 1.65 × 103 L/mol · s. A probable propagation sequence was proposed for the autooxidation of retinyl acetate.

Notes: Rate constants for the self- and cross-termination of the isopropylol radical [(CH3)2ĊOH] and its anion [(CH3)2ĊO-] in aqueous solution are determined by kinetic electron spin resonance. Whereas the self-termination of the neutral radical occurs close to the diffusion-controlled limit, the cross- and self-terminations involving the anion are slower and reflect effects of charge repulsion and steric constraints by solvation.

Notes: The unimolecular decomposition of methyl nitrite in the temperature range 680-955 K and pressure range 0.64 to 2.0 atm has been studied in shock-tube experiments employing real-time absorption of CW CO laser radiation by the NO product. Computer kinetic modeling using a set of 23 reactions shows that NO product is relatively unreactive. Its initial rate of production can be used to yield directly the unimolecular rate constant, which in the fall-off region, can be represented by the second-order rate coefficient in the Arrhenius form: \documentclass{article}\pagestyle{empty}\begin{document}$$k_1 = 10^{17.90 \pm 0.21} \exp (- 17200 \pm 400/T){\rm cm}^{\rm 3} {\rm mol}^{ - 1} {\rm s}^{ - 1}$$\end{document} A RRKM model calculation, assuming a loose CH3ONO≠ complex with two degrees of free internal rotation, gives good agreement with the experimental rate constants.

Notes: Using a relative rate technique, rate constants for the gas phase reactions of the OH radical with n-butane, n-hexane, and a series of alkenes and dialkenes, relative to that for propene, have been determined in one atmosphere of air at 295 ± 1 K. The rate constant ratios obtained were (propene = 1.00): ethene, 0.323 ± 0.014; 1-butene, 1.19 ± 0.06; 1-pentene, 1.19 ± 0.05; 1-hexene, 1.40 ± 0.04; 1-heptene, 1.51 ± 0.06; 3-methyl-1-butene, 1.21 ± 0.04; isobutene, 1.95 ± 0.09; cis-2-butene, 2.13 ± 0.05; trans-2-butene, 2.43 ± 0.05; 2-methyl-2-butene, 3.30 ± 0.13; 2,3-dimethyl-2-butene, 4.17 ± 0.18; propadiene, 0.367 ± 0.036; 1,3-butadiene, 2.53 ± 0.08; 2-methyl-1,3-butadiene, 3.81 ± 0.15; n-butane, 0.101 ± 0.012; and n-hexane, 0.198 ± 0.017. From a least-squares fit of these relative rate data to the most reliable literature absolute flash photolysis rate constants, these relative rate constants can be placed on an absolute basis using a rate constant for the reaction of OH radicals with propene of 2.63 × 10-11 cm3 molecule-1 s-1. The resulting rate constant data, together with previous relative rate data from these and other laboratories, lead to a self-consistent data set for the reactions of OH radicals with a large number of organics at room temperature.

Notes: The kinetics of the oxidation of lactic and atrolactic acids by ceric sulfate have been studied in the medium HClO4-Na2SO4-NaClO4 at 25.0°C and ionic strength 2.0 mol dm-3 over a wide range of organic substrate (HL), hydrogen and bisulfate ion concentrations. The redox reactions proceed significantly through three simultaneous paths involving intermediate complexes between the reactive cerium(IV) species and the organic substrate according to the following expression \documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm obs}} = \frac{{(b[{\rm HSO}_4^ -] + c[{\rm HSO}_4^ -]^2 + [{\rm H}^ +]){\rm [HL]}}}{{\{ f_1 [{\rm HSO}_4^ -]^3 + d_1 [{\rm HSO}_4^ -] + e_1 [{\rm HSO}_4^ -]^2){\rm }[{\rm H}^ +]\} + A'[{\rm HL}]}}$$\end{document} where kobs indicates the observed pseudo-first-order rate constant, b and c are rate constants relative to that for the path associated with the term [H+] in the numerator, and A' is a quantity depending on the [H+] and [HSO4-] concentrations. Moreover, three equilibria involving cerium(IV) and HSO4- (or SO42-) ions are important from a kinetic point of view, the cumulative equilibrium constants being in the ratios β1: β2: β3 = d1: e1: f1. The present data are compared with those obtained previously for the cerium(IV) oxidation of glycolic acid and the substituent effects discussed.

Notes: A kinetic study of oxidation of hydroxylamine by bromate ion in acid sulfate solution using spectrophotometric and potentiometric methods is reported. Oxidation of hydroxylamine to nitrate is quantitative and followed competitive, consecutive, and auto catalytics steps characterized by induction periods. In the slow rate limiting step, hydroxylamine on reaction with HOBr (k1′) forms an intermediate I, which further reacts fast with second molecule of HOBr (k2′) giving nitrite. Nitrite reacts with HOBr (k3′) yielding the final product nitrate. Nitric acts as an autocatalyst also and its initial addition decreased the induction periods. In excess of hydrogen ion concentration all the reaction steps follow second-order kinetics. All the second-order rate constants are reported and the reaction mechanism is proposed.

Notes: Mixtures of NH3 and N2O dilute in Ar were heated behind incident shock waves in the temperature range 1750-2060 K. A cw ring dye laser, tuned to the center of an OH absorption line in the ultraviolet, was used to monitor OH concentration profiles by absorption spectroscopy. Infrared emission was used to follow N2O (at 4.5 μm) and NH3 (at 10.5 μm) concentration - time histories. The early-time NH3 and OH concentration profiles were sensitive to the rate constants of the reactionsleading to the following best-fit expressions for k2 and k3:k2 = 1013.34±0.3 exp(-4470/T) and k3 = 1013.91±0.2 exp(-4230/T) cm3 mol-1 s-1. The results of this study combined with previous low-temperature data suggest a significant non-Arrhenius behavior for both k2 and k3.

Notes: The thermal decomposition of azoisopropane (AIP) was studied in the presence of various quantities of propylene in the temperature and pressure intervals 498-553 K and 3.33-5.33 kPa. The inhibition functions relating to formation of the products were determined; these proved a good basis for interpretation of the formation of the secondary decompositon products of AIP. The experimental data support the conception that the βμ radical - radical reactionoccurs. The product of this is not stable; its decomposition is one of the sources of the secondary products. The ratio of the rate constants was determined for the following reactions:

Notes: The photooxidation of acrylonitrile, methacylonitrile, and allylcyanide in the presence of NO was studied in parts per million concentration using the long-path Fourier transform IR spectroscopic method. The stoichiometry of the OH radical initiated oxidation of methacrylonitrile was established as \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {{\rm OH}} \right) + {\rm CH}_{\rm 2} = {\rm C}\left( {{\rm CH}_{\rm 3} } \right){\rm CN + 2NO + 2O}_{\rm 2} \mathop {\hbox to 20pt{\rightarrowfill}}\limits^{1.0} {\rm HCHO + CH}_{\rm 3} {\rm COCN + 2NO}_{{\rm 2}} + \left( {{\rm OH}} \right) $\end{document}. The yield of HCHO for acrylonitrile and allylcyanide was found to be ca. 100 and 80%, and the stoichiometric reactions were assessed to proceed, \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {{\rm OH}} \right) + {\rm CH}_{\rm 2} = {\rm CHCN + 2NO + 2O}_{\rm 2} \mathop {\hbox to 20pt{\rightarrowfill}}\limits^{1.0} {\rm HCHO + HCOCN + 2NO}_{\rm 2} + \left( {{\rm OH}} \right) $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {{\rm OH}} \right) + {\rm CH}_{\rm 2} = {\rm CHCH}_{\rm 2} {\rm CN + 2NO + 2O}_{\rm 2} \mathop {\hbox to 20pt{\rightarrowfill}}\limits^{0.8} {\rm HCHO + HCOCH}{\rm 2} {\rm CN + 2NO}_{\rm 2} + \left( {{\rm OH}} \right) $\end{document}, respectively. These results revealed that the reaction mechanism for these unsaturated organic cyanides are analogous to that of olefins.

Notes: Rates and thermodynamic data have been obtained for the reversible self-termination reaction: \documentclass{article}\pagestyle{empty}\begin{document}$${\rm R}^ \cdot + {\rm R}^ \cdot \mathop{\buildrel\longleftarrow\over\longrightarrow}^{2k1}_{2k_{-1}}D $$\end{document} Involving aromatic 2-(4′dimethylaminophenyl)indandione-1,3-yl (I), 2-(4′diphenylaminophenyl)indandione-1,3-yl (II), and 2,6 di-tert-butyl-4-(β-phthalylvinyl)-phenoxyl (III) radicals in different solvents. The type of solvent does not tangibly affect the 2k1 of Radical(I), obviously due to a compensation effect. The log(2k1) versus solvent parameter ET(30) curves for the recombination of radicals (II) and (III) have been found to be V shaped, the minimum corresponding to chloroform. The intensive solvation of Radical (II) by chloroform converts the initially diffusion-controlled recombination of the radical into an activated reaction. The log (2k-1) of the dimer of Radical (I) has been found to be a linear function of the Kirkwood parameter (ε - 1)/(2ε + 1), the dissociation rate increasing with the dielectic constant of the solvent. The investigation revealed an isokinetic relationship for the decay of the dimer of Radical (I), an isokinetic temperature β = 408 K and isoequilibrium relationship for the reversible recombination of Radical (I) with β° = 651 K. For Radical (I) dimer decay In(2k-1) = const + 0.8 In K, where K is the equilibrium constant of this reversible reaction. The transition state of Radical (I) dimer dissociation reaction looks more like a pair of radicals than the initial dimer. The role of specific solvation in radical self-termination reactions is discussed.

Notes: The thermal decomposition of SO2 and of the primary dissociation product SO have been studied in shock waves by the uv absorption technique. The controversy about SO2 dissociation data from uv absorption signals was resolved and attributed to the extensive overlap of SO2 and SO uv absorption spectra. The derived rate coefficients are k1/[Ar] = 1015.6 exp(-420 kJmol-1/RT) cm3mol-1 s-1 (temperature range 3000-5000 K) for SO2 dissociation, and k3/[Ar] = 1014.6 exp(-448 kJmol-1/RT) cm3 mol-1 s-1 (temperature range 4000-6000 K) for SO dissociation. Anomalously high values of the apparent collision efficiencies βc in SO2 dissociation are attributed to marked contributions from excited electronic states.

Notes: 5-Methyl-hexanone-2, 3-methyl-pentanone-2, and hexanone-2 have been decomposed in comparative rate single pulse shock tube experiments. The mechanism of decomposition involves the breaking of carbon-carbon bonds as well as molecular processes involving 6-center complexes. The following rate expressions at 1100 K have been obtained: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{rcl} k(3{\rm - methyl - pentanone - 2} \to {\rm CH}_{\rm 3} {\rm \dot CO} + {\rm sC}_4 {\rm H}_9 .) = 10^{16.4} \exp (- 38,300/T)/{\rm s} \\ k(5{\rm - methyl - hexanone - 2} \to {\rm CH}_{\rm 3} {\rm \dot CO} + {\rm iC}_4 {\rm H}_9 .) = 10^{16.6} \exp (- 40,600/T)/{\rm s} \\ k(5{\rm - methyl - hexanone - 2} \to {\rm CH}_{\rm 3} {\rm COCH}_{\rm 3} + {\rm iC}_4 {\rm H}_8) = 10^{12.56} \exp (- 31,600/T)/{\rm s} \\ k({\rm hexanone - 2} \to {\rm CH}_{\rm 3} {\rm COCH}_{\rm 3} + {\rm C}_3 {\rm H}_6) = 10^{13.28} \exp (- 32,400/T)/{\rm s} \\ \end{array} $$\end{document} These results lead to ΔHf(CH3ĊO) = - 13.8 kJ and ΔHf(CH3COCH2·) = - 12.6 kJ at 300 K. They are compared with existing literature values and some generalizations are made with regard to the stability of carbonyl compounds.

Notes: Kinetics of the incorporation of mercury(II) ion in tetra (p-trimethylammoniumphenyl)porphine have been investigated in aqueous solution at 30.0°C and 0.2 M (NaNO3) ionic strength. The reaction was found to be first order each in mercury(II) and the porphyrin. The forward (formation) and the reverse (dissociation) rate constants were found to be 1.9 ± 0.2 × 103 M-1 s-1 and 7 ± 2 × 106 M-1 s-1, respectively. Kinetics of zinc(II) incorporation in tetra(p-trimethylammoniumphenyl)porphine catalyzed by mercury(II) were also investigated. This catalysis is explained in terms of steady-state formation of mono mercury(II) porphyrin followed by zinc(II) displacement of mercury(II) ion from the porphyrin. Such a mechanism also illustrates the importance of porphyrin core deformation to metal incorporation.

Notes: The absolute rate constant for the OH + HCl reaction has been measured from 240 to 295 K utilizing the techniques of laser/flash photolysis-resonance fluorescence. The HCl concentrations were monitored continuously by ultraviloet and infrared spectrophotometry. The results can be fit to the following Arrhenius expression: \documentclass{article}\pagestyle{empty}\begin{document}$$k_1 = (4.6{\rm } \pm {\rm }0.3){\rm } \times {\rm }10^{ - 12} \exp [- (500{\rm } \pm {\rm }60)/T{\rm cm}^3 /{\rm molecule} \cdot {\rm s}$$\end{document} The rate constant values obtained in this study are 20-30% larger than those recommended previously for modeling of stratospheric chemistry.

Notes: The reaction \documentclass{article}\pagestyle{empty}\begin{document}${\rm Br} + {\rm CH}_3 {\rm CHO}\buildrel1\over\rightarrow{\rm HBr} + {\rm CH}_3 {\rm CO}$\end{document} has been studied by VLPR at 300 K. We find k1 = 2.1 × 1012 cm3/mol s in excellent agreement with independent measurements from photolysis studies. Combining this value with known thermodynamic data gives k-1 = 1 × 1010 cm3/mol s. Observations of mass 42 expected from ketene suggest a rapid secondary reaction: \documentclass{article}\pagestyle{empty}\begin{document}$${\rm Br} + {\rm CH}_3 {\rm CO}\buildrel2\over\rightarrow[{\rm CH}_3 {\rm COBr}]^* \buildrel3\over\rightarrow{\rm HBr} + {\rm CH}_2 {\rm CO}$$\end{document} in which step 2 is shown to be rate limiting under VLPR conditions and k2 is estimated at 1012.6 cm3/mol s from recent theoretical models for radical recombination. It is also shown that 0 ≤ E1 ≤ 1.4 kcal/mol using theoretical models for calculation of A1 and is probably closer to the lower limit. Reaction -1 is negligible under conditions used.

Notes: The effect of pressure on the rate constant of the OH + CO reaction has been measured for Ar, N2, and SF6 over the pressure range 200-730 torr. All experiments were at room temperature. The method involved laser-induced fluorescence to measure steady-state OH concentrations in the 184.9 nm photolysis of H2O-CO mixtures in the three carrier gases, combined with supplementary measurements of the CO depletion in these same carrier gases in the presence and absence of competing reference reactants. The effect of O2 on the pressure effect was determined. A pressure enhancement of the rate constant was observed for N2 and SF6, but not for Ar, within an experimental error of about 10%. The pressure effect for N2 was somewhat lower than previous literature reports, being about 40% at 730 torr. For SF6 a factor of two enhancement was seen at 730 torr. In each case it was found that O2 had no effect on the pressure enhancement. The roles of the radical species HCO and HOCO were evaluated.

Notes: The extinction coefficients and the decay kinetics of I2-. and (SCN)2-⋅ have been characterized over the 15-90°C-temperature range. The extinction coefficients of I2-⋅ at 385 and 725 nm were determined to be 10,000 and 2560M-1 cm-1, respectively, based on the extinction coefficient of (SCN)2-⋅ at 475 nm being equal to 7600M-1 cm-1. At these three wavelengths, all extinction coefficients were constant over the temperature range studied. The rate of decay of both I2-⋅ and (SCN)2-⋅ was found to be a function of I- and SCN- concentration, respectively, as well as temperature.

Notes: The pyrolysis kinetics of several ethyl esters with polar substituents at the acyl carbon have been studied in the temperature range of 319.8-400.0°C and pressure range of 50.5-178.0 torr. These eliminations are homogeneous, unimolecular, and follow a first-order rate law. The rate coefficients are given by the Arrhenius equations: for ethyl glycolate, log k1 (s-1) = (12.75 ± 0.30) - (201.4 ± 3.8) kJ/mol/2.303RT; for ethyl cyanoacetate, log k1 (s-1) = (12.19 ± 0.18) - (191.8 ± 2.1) kJ/mol/2.303RT; for ethyl dichloroacetate, log k1 (s-1) = (12.62 ± 0.36) - (193.9 ± 4.3) kJ/mol/2.303RT; for ethyl trichloroacetate, log k1 (s-1) = (12.27 ± 0.09) - (185.1 ± 1.0) kJ/mol/2.303RT. The results of the present work together with those reported recently in the literature give an approximate linear correlation when plotting log k/k0 vs. σ* values (ρ* = 0.315 ± 0.004, r = 0.976, and intercept = 0.032 ± 0.006 at 400°C). This linear relationship indicates that the polar substituents affect the rate of elimination by electronic factors. The greater the electronegative nature of the polar substituent, the faster is the pyrolysis rate. The alkyl substituents yield, within experimental error, similar values in rates which makes difficult an adequate assessment of their real influence.

Notes: Mathematical modeling was used for the kinetics of gas-phase propane oxidation at 586, 613, and 658 K and pressures 172 and 250 torr. The reaction mechanism involving branching by decay of the peracetyl peroxy radical, and oxygen-containing products formed on decay of the RO4 radical is discussed. Fair agreement between calculated and experimental results on the kinetics and accumulation rates of reaction products was obtained.

Notes: The termolecular rate constant for the reaction Cl + NO2 + M has been measured over the temperature range 264 to 417 K and at pressure 1 to 7 torr in a discharge flow system using atomic chlorine resonance fluorescence at 140 nm to monitor the decay of Cl in an excess of NO2. The results are\documentclass{article}\pagestyle{empty}\begin{document}$k_1^{{\rm He}} = 9.4{\rm } \times {\rm }10^{ - 31} \left({\frac{T}{{300}}} \right)^{ - 2.0 \pm 0.05} {\rm cm}^6 {\rm s}^{ - {\rm 1}}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$k_1^{{\rm N}2} = (14.8{\rm } \pm {\rm }1.4){\rm } \times {\rm 10}^{ - 31} {\rm cm}^6 {\rm s}^{ - 1}$\end{document} at 296 K where error limits represent one standard deviation. The systematic error of k1 measurements is estimated to be about 15%. Using a static photolysis system coupled with the FTIR spectrophotometer the branching ratio for the formation of the two possible isomers was found to be ClONO(≥75%) and CINO2(≤25%) in good agreement with previous measurements.