caa a22 4500 378891901 CHVBK 20180305123456.0 cr unu---uuuuu 161128e20040315xx s 000 0 eng 10.1515/HF.2004.016 doi (NATIONALLICENCE)gruyter-10.1515/HF.2004.016 Polyoxometalate oxidation of non-phenolic lignin subunits in water: Effect of substrate structure on reaction kinetics [Elektronische Daten] [T. Yokoyama, H.-M. Chang, R. S. Reiner, R. H. Atalla, I. A. Weinstock, J. F. Kadla] The effect of lignin-biopolymer structure on the mechanism of its oxidative depolymerization by polyoxometalates (POMs) was investigated by reacting an equilibrated POM ensemble with a series of ring-substituted benzyl alcohols. Under anaerobic conditions in mixed water/methanol, observed pseudo-first order reaction rates (150°C) of 8.96 × 10−3 and 4.89 × 10−3 sec−1 were obtained for oxidations of 1-(3,4-dimethoxyphenyl) ethanol (1) and 1-(3,4,5-trimethoxyphenyl)ethanol (2), respectively. Organic products from the oxidation of 2 (95% recovery) indicate the reaction proceeds via successive oxidations of the benzylic carbon atom; aromatic-ring cleavage was not observed. A primary kinetic-isotope effect of 1.6 and 1.7 was observed for the reactions of 1 and 2 deuterated at the benzylic-carbon atoms. This combined with the relatively large activation energies, indicate that C-H bond breaking (either H-atom or proton-coupled electron transfer) occurs late along the reaction coordinate of the rate-determining step. Replacing the 4-CH3O-group in 2 by CH3CH2O- to give 1-(4-ethoxy-3,5-dimethoxyphenyl)ethanol (3), had a substantial effect on the temperature dependence of the observed reaction rate, suggestive of a possible change in mechanism. Copyright © 2004 by Walter de Gruyter GmbH & Co. KG Timber & wood processing nationallicence Biotechnology nationallicence Materials science nationallicence Yokoyama T. aut Chang H.-M aut Reiner R. S. aut Atalla R. H. aut Weinstock I. A. aut Kadla J. F. aut Holzforschung Walter de Gruyter 58/2(2004-03-15), 116-121 0018-3830 58:2<116 2004 58 hfsg https://doi.org/10.1515/HF.2004.016 text/html Onlinezugriff via DOI 1 research article jats NATIONALLICENCE 856 40 https://doi.org/10.1515/HF.2004.016 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Yokoyama T. aut NATIONALLICENCE 700 1- Chang H.-M aut NATIONALLICENCE 700 1- Reiner R. S. aut NATIONALLICENCE 700 1- Atalla R. H. aut NATIONALLICENCE 700 1- Weinstock I. A. aut NATIONALLICENCE 700 1- Kadla J. F. aut NATIONALLICENCE 773 0- Holzforschung Walter de Gruyter 58/2(2004-03-15), 116-121 0018-3830 58:2<116 2004 58 hfsg CC0 http://creativecommons.org/publicdomain/zero/1.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-gruyter