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  • 1
    Electronic Resource
    Electronic Resource
    Continuous operation of lipase-catalyzed reactions in nonaqueous solvents: Influence of the production of hydrophilic compounds (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 232-237 
    Details
    ISSN: 0006-3592
    Keywords: lipozyme ; esterification ; continuous reactor ; water activity ; organic solvent ; supercritical carbon dioxide ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In the field of biocatalysis in nonaqueous media, water has been identified as a crucial parameter which has to be carefully controlled. This article studies the continuous operation of a water-producing enzymatic reaction, here the esterification of oleic acid by ethanol in n-hexane catalyzed by LipozymeTM. The conversion decreased significantly over time, eventually coming to a lower steady-state level. This would be due to the accumulation of the produced water into the enzyme fixed-bed reactor, n-hexane being unable to evacuate this water out of the reaction vessel, because of the low polarity of this solvent. Therefore the conversion decreased until the produced water could be eliminated by the solvent achieving a steady state with a lower conversion. In supercritical carbon dioxide, a more hydrophilic solvent, steady state is at once obtained. This approach has been extended to reaction producing a hydrophilic compound, here glycerol during the transesterification between triolein and ethanol, and similar conclusions can be made. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 232-237, 1997.
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  • 2
    Electronic Resource
    Electronic Resource
    Water activity control: A way to improve the efficiency of continuous lipase esterification (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 60 (1998), S. 362-368 
    Details
    ISSN: 0006-3592
    Keywords: esterification ; continuous reaction ; water activity ; lipase ; organic solvent ; packed-bed reactor ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: During continuous lipase-catalyzed oleic acid esterification by ethanol in n-hexane, the oleic acid conversion, initially at 95%, decreases to 20% after 2 h. This decrease is caused by the accumulation of the water produced in the course of the reaction in the packed-bed reactor (PBR). In order to improve the PBR efficiency, it is necessary to evacuate the water produced. In this study, different approaches have been tested to control the water content in the PBR during continuous esterification. The first approach consisted in improving the water solubility by increasing the reaction medium polarity. The addition of polar additives to n-hexane, the use of more polar solvents, and the use of solvent-free reaction medium were tested as a means to favor the water evacuation from the PBR. First of all, the use ofn-hexane supplemented with acetone (3 M) or 2-methyl-2-propanol (1 M) enabled the conversion to be maintained at higher values than those obtained in pure n-hexane. The replacement of n-hexane by a more polar solvent, like the 5-methyl-2-hexanone, resulted in the same effect. In all cases, conversions at steady-state were always less than 95%, as obtained in pure n-hexane. This is explained by a decrease in the enzyme activity due to the increase in the medium polarity. Nevertheless, an increase in enzyme quantity allowed 90% conversion to be maintained during 1 week using 3 M acetone amended n-hexane. Good results (a steady-state conversion of about 80%) were obtained when esterification was carried out in a solvent-free reaction medium containing 2 M 2-methyl-2-propanol as a polar additive. The second approach consisted in the evaporation of the accumulated water by use of an intermittent airflow. Although this process did not enable constant esterification rate to be maintained, it did enable the initial conversion (95%) to be restored intermittently. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 60: 362-368, 1998.
    Additional Material: 4 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Continuous reaction-separation process for enzymatic esterification in supercritical carbon dioxide (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 43 (1994), S. 497-504 
    Details
    ISSN: 0006-3592
    Keywords: immobilized enzyme ; lipase ; esterification ; fatty acids ; supercritical carbon dioxide ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The study of enzymatic esterification by an immobilized lipase in supercritical carbon dioxide (SCCO2) and in n-hexane, described in our previous works, was extended to continuous operation in a tubular fixed bed. The modeling of the reaction vessel operation was achieved through the use of the simple plug flow model coupled with the appropriate kinetic equation. Comparison with experiments proved to be satisfactory. The study of the postreactional separation, an important feature when using SCCO2, was undertaken experimentally and good selectivities and product recovery were obtained. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260430610
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  • 4
    Electronic Resource
    Electronic Resource
    Complexes of 3,3′-Oxybis[(diphenylphosphino)methylbenzene] with Ni(II), Pd(II), Pt(II), Rh(I), and Ag(I). How Important is Backbone Rigidity in the Formation of trans-Spanning Bidenatate Chelates?? (1987)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 70 (1987), S. 158-170 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bidentate diphosphine ligand, 3,3′-oxybis[(dipenylphosphino)methylbenzene] (1) forms monomeric, trans-square-planar complexes MX2(1) (M = Ni, Pd, Pt; X = Cl-, Br- I-, and, in part, N3-, NCS-, CN-, NO3-) as well as Pt(H)Cl(1), Pt(H)Br(1), and RhCl(CO)(1). Polymeric species have been observed with substitutionally inert metal centres: trans-[PtCl2(1)]2 and cis-[PtCl2(1)]n (mean value of n ≈ 4-5) 31P-NMR, and selected IR and UV/VIS parameters are reported. Ligand 1 shows a marked preference for trans-spanning and monomeric chelate formation, despite its various degrees of freedom of internal rotation in the lignad backbone. The readily available ligand 1 as well as analogues with other donor atoms, therefore, appear useful in most potential applications of trans-spanning chelate ligands. The crystal structure of AgCl(1)·0.5 (CH3)2C=O·0.39 C6H12 (space group C2/c,a = 21.02 Å, b = 14.57 Å, c = 24.79 Å, β = 99.77°, V = 7531.4 Å3, Z = 8) confirms the presence of three-coordinate Ag(I), with a coordination intermediate between a trigonal-planar and a T-shaped geometry (P-Ag-P = 145.61(8)°).
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19870700120
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  • 5
    Electronic Resource
    Electronic Resource
    Base Hydrolysis of Pentaaminecobalt(III) Complexes: The [CoX(dien) (dapo)]n+ system. Part 2. Structure and reactivity of the pentacoordinate intermediate (1992)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 75 (1992), S. 1147-1171 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Base hydrolysis of optically pure mer-exo(H)- and mer-endo(H)-[CoCl(dien)(dapo)]2+ (A and B (X = Cl)), resp.; dien = N-(2-aminoethyl)ethane-1,2-damine; dapo = 1,3-diaminopopan-2-ol, kOH = (1.13 ±0.09)·105 M-1s-1 (A (X = Cl), kOH = (1.18 ± 0.11)·105M-1s-1 (B (X = Cl)); I = 1.0M (NaClO4 or NaN3)1, T = 298 K) is accompanied by retention of the mer-geometry and full racemization (99 ± 1%). It is shown this is not due to racemization of either reactants or products. This result, together with the fact that both A and B yield the same mer-exo(H)-product distribution, indicates the intermediacy of a pentacoordinate species II which is symmetrical (at least in the time average), viz. trigonal bipyramidal with a deprotonated (‘flat’) secondaryamine moiety. The H-exchange rates of the coordinated amine groups are consistent with this interpretation and indicate that loss of Cl- is the rate-determining step, in agreement with an SN1CB mechanism. The reactivity of the unsym-fac-exo(OH)- and unsy,-fac-endo(OH)-isomers C and D, respectively, is in sharp contrast: base hydrolysis is 3 orders of magnitue slower, and the reaction is accompanied by some change of coordination geometry (C, 23%; D, 10%, some inversion of configuration (C, 15%; D, 19%)); much lower acceleration of hydrolysis in base (106 vs. 1010). Azide competition during base hydrolysis of the mer-isomer A and B is quite large (R = [CoN3]∞/[CoOH]∞[N-3] = 1.4 ±0.2M-1, I= 1.0M, T = 298 K) and indicates that the coordinatively unsaturated intermediate II is highly selective. The ratios of exo(H)- and endo(H)-azide competition products A and B (X = N3), respectively, immediately after the substitution reaction (kinetic control) are independent of the engaged epierm A or B: 31.7 ± 0.9% of B (X = N3) and 68.3 ± 0.9% of A (X = N3, determined after ca. 10.t½ of the base hydrolysis). This is agreement with the effective site of deprotonation at the secondayr(central)-amine group of dien, cis to the leaving group X, and with a common set of intermediates. Epimerization of A and B (X = Cl, N3) is shown to proceed solely via the pentacoordinate (base hydrolysis) intermediate II, viz. the direct route involving a six-coordinate deprotonated intermediate is immeasurably slow. For the hydroxo products A and B (X = OH), the direct rotue may compete with the H2O-substitution(exchange) path which can occur by an internal conjugate-base process. The kinetically controlled distribution of complexes A/B (X = N3) is different from the quasi-thermodynamic one (19.1 ± 0.8% of B (X = N3) and 80.9 ± 0.8% of A (X = N3)). This is consistent with the differences in the base-hydrolysis rates of the reactants (kOh (A (X = N3))= (1.59 ± 0.04)·102M-1s-1; kOH (B (X = N3)) = (2.89 ± 0.22).102M-1s-1). Various aspects of the investigated reactions are discussed on the basis of the widely studied reaction of base hydrolysis of pentaaminecobalt(III) complexes. Also, the structure and reactivity of the pentacoordinate intermediate II are discussed in relation to various current models.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19920750417
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  • 6
    Electronic Resource
    Electronic Resource
    Origin of diastereoselectivity in the thermal [4+2] cycloadditions of dienophiles derived from Oppolzer's sultams: Steric vs. Stereoelectronic InfluencesPresented in part at the IXth Eur. Symp. Org. Chem., 18-23 June 1995, Warse, Poland.Dedicated to the memory of Professor Wolfgang von Oppolzer (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 146-172 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Comparative semi-empirical PM3 and ab initio STO 3-21G calculations on bornanesultam-derived dienophiles containing the structural moiety SO2—N—C(O)—X(α) = Y(β) suggest that, among the conformers of low energy, the thermodynamically less stable SO2/C(O)-syn,C(O)/X=Y-s-cis conformation is also reactive in terms of LUMO level and atomic coefficients. Furthermore, the X(α), Y(β) LUMO atomic coefficients are nonequivalent with respect to both X(α)-re and X(α)-si faces, and thus have, depending on the conformation, a matching or mismatching stereoelectronic influence with the co-operative steric effect. This dissymmetry is believed to result from the generalized anemone effect of the N lone pair, itself anomerically stabilized and directed, in the absence of crucial steric interactions, by the pseudo-axial anti-periplanar S=O bond. Five N-acyl-substituted bornanesultams arc discussed ((-)-1a: N-acryloyl, X=CH, Y=CH2; (-)-1b; N-crotonoyl, X=CH, Y=CHMe; (-)-1c: N-N′-fumaroyl, X=CH, Y=CH(C(O)-bornanesultam); 2a: N-glyoxyloyl, X=CH, Y=O; 2b: N-acylnitroso, X=N, Y=O). In this context, differences with toluenesultams 3 are pointed out. A previous report on N-(acylnitroso)-bornanesultam 2b is revisited, and the diastereoselectivity observed is shown to result from thermodynamic control.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800115
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  • 7
    Electronic Resource
    Electronic Resource
    Electrochemical Investigation of Potassium Heptacyanorhenate(III) in Aqueous Solution (1987)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 70 (1987), S. 375-380 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrochemistry of potassium heptacyanorhenate(III) in aqueous solution was studied by cyclic and by rotating disk voltammetry at planar microelectrodes. The results are consistent with a single, reversible electron transfer: Re(CN)3-7 + e⇄Re(CN)4-7 with E′0 = 643 mV vs. NHE. A single protonation equilibrium is observed: Re(CN)4-7 + H+⇄ Re(CN)7H3- with pK = 1.31 determined from combined voltammetric and pH data. The Re-CN bond appears to be kinetically inert, and none of the cyano complexes in other oxidation states of Re claimed in the literature was found in the potential range - 2 V to + 1 V.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19870700215
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  • 8
    Electronic Resource
    Electronic Resource
    Base Hydrolysis of Pentaaminecobalt(III) Complexes: The [CoX(dien) (dapo)]n+ system. Part 1. Syntheses, structures, configuration, and spectroscopy (1992)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 75 (1992), S. 1130-1146 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxygentation of aqueous solutions of CoIII in presence of stoichiometric amounts of N-(2-aminoethyl)ethane-1,2-diamine (dien) and 1,3-diaminopropan-2-ol (dapo) produces μ-peroxocobalt(III) dimers. Acid cleavage (HCI) yields mer-exo(H)-, mer-endo (H)-, unsym-fac-exo(OH)-, and unsym-fac-endo(OH)-[CoCl(dien)(dapo)]2+ (A-D)(X = Cl), resp. and unsym-fac-[Co-(dien)(dapo-N,N′,O)]3+ (G). Isomer seperation was achieved by fractional crystallization as ZnCl42- and ClO4- salts and by ion-exchange chromatography. The corresponding bromo, azido, nitrito-O, nitro-N, thiocyanato, hydroxo, and aqua complexes were also synthesized. Optically resolved samples were prepared for chiral compounds, and the complexes were structurally characterized by X-ray analyses (\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\it \Lambda} \limits^ \to $\end{document}(-)436(CD)-A (X = N3)), (\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\it \Delta} \limits^ \to $\end{document}(-)436(CD)-B). (X = N3), \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\it \Delta} \limits^ \to $\end{document} (+)436(CD)-B by their chiroptical properties, and by 13C-NMR spectroscopy supported by 1H-NMR, IR, CD, and UV/VIS spectroscopy. \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\it \Lambda} \limits^ \to $\end{document}(-)436(CD)-mer-exo(H)-[Co(N3)(dien)(dapo)](hydrogen di-O-benzoyl-L-tartrate)2.4 H2O crystallizes in the orthorhombic space group P212121, a = 7.676(1) Å, b = 19.457(1) Å, c = 34.702(2) Å. \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\it \Lambda} \limits^ \to $\end{document}(-)436(CD)-mer-endo(H)-[Co(N3)(dien)(dapo)] (hydrogen di-O-benzoyl-L-tartrate)2.2.75 H2O crystallizes in the triclinic space group P1, a = 8.062(3) Å b = 10.296(1) Å, c = 15.056(2) Å, alpha = 80.55(1)°, β = 85.18(2)°, γ = 89.10(2)°. \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\it \Delta} \limits^ \to $\end{document}(+)436(CD)-mer-endo(H)-[Co(N3)(dien)(dapo)](hydrogen di-O-benzoyl-L-tartrate)2. 5.75 H2O crystallizes in the triclinic space group P1, a = 7.742(1) Å, b = 10.014(1) Å, c = 18.045(2) Å, α = 99.57(1)°, β = 92.87(1)°, γ = 102.56(1)°. The absolute configurations of the three cations were determined unambiguously. Interconversions of the various isomers and derivatives and structural, configurational, and spectroscopic aspects are discussed in detail.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19920750416
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  • 9
    Electronic Resource
    Electronic Resource
    Base Hydrolysis of Pentaaminecobalt (III) Complexes: The [CoX(dien) (dapo)]n+ system. Part 3. The internal conjugate base mechanism (1992)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 75 (1992), S. 1172-1184 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Azide anation and racemization of optically pure mer-exo(H)- and mer-endo(H)-[Co(OH)(dien)(dapo)]2+ (A and B (X = OH), resp.; dien = N-(2-aminoethyl)ethane-1,2-diamine; dapo = 1,3-diaminopropan-2-ol) involve the same symmetrical pentacoordinate intermediate as the base hydrolyses of the corresponding mer-exo(H)- and mer-endo(H)-[CoX(dien)(dapo)]2+ species A and B, respectively, where X = Cl, Br, or N3. The kinetic parameters of the anation process are fully compatible with the independently measured competition ratio. The rate data reveal that substitution of OH- is unexpectedly fast, viz. it is not consistent with the usual sequence Br- 〉 Cl- 〉 H2O 〉 N3- 〉 OH-. This behavior is interpreted on the basis of an internal conjugate base mechanism which involves an amino-hydroxo/aminato-aqua tautomerism, viz. the reaction is actually an OH- -catalyzed substitution of [CoH2O(dien)(dapo)]3+ where deprotonation occurs effectively at the secondary-amine site NH of dien.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19920750418
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  • 10
    Electronic Resource
    Electronic Resource
    Inequivalence Magnetique Due a la Presence d'un Atome de Phosphore Asymetrique ou Pseudo-Asymetrique (1970)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 2 (1970), S. 141-157 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: In phosphinous esters of general formula R—PH(O)OR', the asymmetric phosphorus atom induces magnetic non-equivalence in geminal protons and methyl groups. When alkoxy groups also possess an asymmetric carbon, the presence of the two possible diastereoisomers in equal amounts is proven by 31P and 1H NMR.31P NMR reveals that the phosphorus atom in phosphonous esters R—P(O·C4H9-s)2 of racemic sec. butyl alcohol, is a centre of pseudo-asymmetry.
    Notes: Dans les phosphinates d'alcoyle R—PH(O)OR′, la présence de l'atome de phosphore asymétrique induit des inéquivalences magnétiques au niveau de protons ou groupes méthyles géminés. Si le reste alcoxy OR' comporte lui aussi un atome de carbone asymétrique, la résonance magnétique de 31P et de 1H, permet de mettre en évidence la formation des deux diastéréoisoméres attendus, en proportions égales.Par ailleurs, la résonance magnétique de 31P révèle le caractère de centre de pseudo-asymétrie de l'atome de phosphore dans les esters phosphoneux de l'alcool butylique secondaire.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270020207
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