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  • 1
    Electronic Resource
    Electronic Resource
    Micellar effects on the alkaline hydrolysis of N-alkyl-4-cyanopyridinium ions. An example of micelle-induced regiochemical selectivity (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 207-216 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The rates of the reaction of N-alkyl-4-cyanopyridinium (RCP) ions [alkyl = CH3 (MCP), n-C4H9 (BCP), n-C8H17 (OCP), n-C12H25 (DCP)] with OH- ion in water are independent of chain length and RCP concentration up to 0.001 M. The ratios of the concentrations of the reaction products, N-alkyl-4-pyridone (P) and N-alkyl-4-carboxamidopyridinium (A), P/A, are similar for all substrates. In water the P/A ratios increase with pH, reaching a plateau value of ca 2 at pH ≥ 13. Added salts slightly decrease the reaction rate and do not affect the P/A ratios. In aqueous solutions, addition of dioxane increases both rates and P/A ratios. Micelles of hexadecyltrimethylammonium bromide (cetyltrimethylammonium bromide; CTAB) and 3-(N,N-dimethyl dodecyl ammonium)propane-1-sulphonate (SDP) catalyse the alkaline hydrolysis of OCP and DCP and increase the yield of pyridone with BCP, OCP and DCP. In micellar CTAB and SDP the attack of OH- on RCP occurs almost exclusively at the 4-position of the pyridinium ring. Sodium dodecyl sulphate micelles inhibit the reaction and produce small changes in the P/A ratio. The regiochemical selectivity produced by micelles, leading to a preference for the attack of OH- at the pyridinium ring, was rationalized in terms of the low effective dielectric constant at the micelle-water interface.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040403
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  • 2
    Electronic Resource
    Electronic Resource
    Short communication. Synthesis and properties of 4-cyano-1-(7-carboxyheptadecyl)pyridinium bromide: A probe of the ionic composition near the surface of positively charged micelles (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 643-646 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 4-Cyano-1-(7-carboxyheptadecyl)pyridinium bromide (CCHP) was synthesized using standard procedures. The rates and product distribution of the reaction between OH- ion and CCHP are very similar to those previously obtained with alkyl-substituted 4-cyanopyridinium ions. The effect of hexadecyltrimethylammonium bromide micelles on the rate and product distribution of CCHP indicated that the cyanopyridinium ring of this compound is distal to the surface of the micelle. CCHP constitutes a probe for ionic composition in the vicinity of positively charged micelles.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041010
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  • 3
    Electronic Resource
    Electronic Resource
    Micelle-induced change in the rate-limiting step of substituted benzoate ester thiolysis (1993)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 6 (1993), S. 7-14 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effect of hexadecyltrimethylammonium bromide (CTAB) micelles on the acid dissociation constant of para-substituted benzenethiols, α-toluenethiol and n-heptanethiol was determined. The effect of CTAB on the rate of thiolysis by the thiols was measured using para-substituted p-nitrophenyl benzoates. The effects of micelles were analysed using a pseudophase ion-exchange (PIE) model. The Brønsted plot for ester thiolysis showed discontinuity at the pKa of the leaving group in water and was linear in micelles. Micelles increased the Hammett ρ value for thiolysis of esters by α-toluenethiol from 2·08 to 2·68. The Hammett plot for the rection of benzenethiol with esters in water is linear with σ- and displays a ρ value of 0·87, whereas in micelles the plot is linear with σ and presents a ρ of 2·83. Taken together, these data indicate that micelles produce a change in the rate-limiting step of thiolysis of substituted benzoate esters, leading exclusively to rate-limiting thiolate attack. In micelles thiolysis may be concerted and the effect of the aggregate on the reaction mechanism can be ascribed to the interaction of the thiolate ions, and the transition states, with the head groups as well as a medium effect.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610060103
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of hexadecyltrimethylammonium bromide micelles on the hydrolysis of substituted benzoate esters (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 13-18 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The alkaline hydrolysis of nine para-substituted phenyl esters of para-substituted benzoates was studied in the presence and absence of hexadecyltrimethylammonium bromide (CTAB) micelles. The second-order rate constant for alkaline hydrolysis in CTAB micelles (K2m) was calculated using a pseudo-phase ion-exchange model. the substituent effect on the second-order rate constant in the aqueous phase (k2w) and on k2m was analysed using Hammett's σ ρ plots. The calculated ρ values in micelles were 0.8 unit. larger than those in water. The effective low dielectric constant in the micellar surface may be responsible for the general effect of increasing the sensitivity of reactions to the electronic effect of substituents in micelles.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040104
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  • 5
    Electronic Resource
    Electronic Resource
    Micellar catalysis of the intramolecular aminolysis of the β-lactam antibiotic cephaclor (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 19-24 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The rate of intramolecular degradation of cephaclor, involving the attack of the amino group at C-17 (N-18) on the β-lactam carbonyl, was increased up to 50-fold by neutral (polyoxyethylene-23 lauryl ether; Brij) and zwitterionic [3-(N-dodecyl-N, N-dimethylammonium) propane 1-sulphonate; (SDP)] micelles. The rate of OH- attack on cephaclor was increased 2-3-fold by Brij and SDP micelles. In the absence of micelles the rate of intramolecular degradation of cephaclor increased by up to 2-fold by addition of organic solvents. Distance calculations, based on the crystal structure of the antibiotic, showed that the intramolecular degration can only proceed in a conformation involving a cis-amide bond (N-14 - C-15). Micellar catalysis of the intramolecular degradation process was proposed to be due to the stabilization of the reactive conformation.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040105
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of hexadecyltrimethylammonium bromide micelles on the rate of oximolysis of esters (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 341-348 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two amphiphilic oximes, 10-phenyl-10-hydroxyiminodecanoic acid (oxime II) and 4-(9-carboxynonanyl)-1-(9-carboxy-1-hydroxyimino nonanyl)benzene (oxime III) were synthesized. The pKa values of oximes II and III and acetophenoxime (oxime I) and the rates of oximolysis of p-nitrophenyl acetate (NPA) and p-nitrophenyl octanoate (NPO) were determined in the presence and absence of micellar hexadecyltrimethylammonium bromide (CTAB). The rates of oximolysis increased by up to 3 × 104-fold in the presence of CTAB. Quantitative analysis of micellar effects, using an ion-exchange pseudo-phase model, allowed the determination of the second-order rate constants for the reactions of oximes I-III with NPA and NPO in the micellar pseudo-phase. The calculated rate constants in the micellar pseudo-phase were lower than those in water, demonstrating that the rate enhancements were due to substrate concentration in the micelles. Comparison of the rate constants in micelles and water suggests that the sites of reaction of oximes I-III with NPO and NPA are similar to those in bulk aqueous solution. Micellar incorporation of the hydrophobic oximes II and III does not lead to a major change in the nucleophilicity of the oximate anion.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050610
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