The H2O2-promoted oxidations of the non-phenolic beta -O-aryl-lignin model dimers 1-(3,4-dimethoxyphenyl)-2-phenoxyethanol (1) and 2-(4-methoxyphenoxy)-1-phenylethanol (2) catalysed by LiP at pH = 4.0 have been studied. The oxidation of 1 mainly leads to the corresponding ketone, indicating that the prevailing reaction of the intermediate radical cation 1(+.) is C alpha -H deprotonation. The oxidation of 2 forms 2-(4-methoxyphenoxy)2-phenylethanol (7, an isomer of 2), 2-phenyl-1,4-dioxaspiro[4.5]deca-6,9-dien-8-one (8) and products coming from the cleavage of the C-C bond gamma to the more electron rich ring. The formation of all these products can be rationalised by assuming that the main reaction of the intermediate 2(+.) is a nucleophilic attack of the alcoholic OH group on the ring bearing the positive charge. This leads to a spirocyclohexadienyl radical; which either is then oxidised to the dioxaspirodecadienone 8 or undergoes ring opening to give an alkoxyl radical from which the isomer of 2 and the C-C bond cleavage products may form. Support for this mechanism has been provided by a study of the oxidation of 4-MeOC6H4OCH2CD2OH and by comparing the results with those obtained when the alkoxyl radical 4-MeOC6H4OCH2CD2O . was generated from 4-MeOC(6)H(4)OCH(2)CD(2)OOt-Bu. The oxidation of 1 induced by the genuine one-electron oxidant potassium 12-tungstocobalt(iii)ate at pH = 4.0 confirms the results obtained with LiP However, under the same conditions, no fragmentation products were observed in the oxidation of 2, probably due to a fast oxidation, by potassium 12-tungstocobalt(iii) ate, of the spirocyclohexadienyl radical.

Baciocchi, E., Bietti, M., Gerini, M., Lanzalunga, O., Mancinelli, S. (2001). Oxidation of non-phenolic beta-O-aryl-lignin model dimers catalysed by lignin peroxidase. Comparison with the oxidation induced by potassium 12-tungstocobalt(III)ate. JOURNAL OF THE CHEMICAL SOCIETY. PERKIN TRANSACTIONS 2(9), 1506-1511 [10.1039/b101362i].

Oxidation of non-phenolic beta-O-aryl-lignin model dimers catalysed by lignin peroxidase. Comparison with the oxidation induced by potassium 12-tungstocobalt(III)ate

BIETTI, MASSIMO;
2001-01-01

Abstract

The H2O2-promoted oxidations of the non-phenolic beta -O-aryl-lignin model dimers 1-(3,4-dimethoxyphenyl)-2-phenoxyethanol (1) and 2-(4-methoxyphenoxy)-1-phenylethanol (2) catalysed by LiP at pH = 4.0 have been studied. The oxidation of 1 mainly leads to the corresponding ketone, indicating that the prevailing reaction of the intermediate radical cation 1(+.) is C alpha -H deprotonation. The oxidation of 2 forms 2-(4-methoxyphenoxy)2-phenylethanol (7, an isomer of 2), 2-phenyl-1,4-dioxaspiro[4.5]deca-6,9-dien-8-one (8) and products coming from the cleavage of the C-C bond gamma to the more electron rich ring. The formation of all these products can be rationalised by assuming that the main reaction of the intermediate 2(+.) is a nucleophilic attack of the alcoholic OH group on the ring bearing the positive charge. This leads to a spirocyclohexadienyl radical; which either is then oxidised to the dioxaspirodecadienone 8 or undergoes ring opening to give an alkoxyl radical from which the isomer of 2 and the C-C bond cleavage products may form. Support for this mechanism has been provided by a study of the oxidation of 4-MeOC6H4OCH2CD2OH and by comparing the results with those obtained when the alkoxyl radical 4-MeOC6H4OCH2CD2O . was generated from 4-MeOC(6)H(4)OCH(2)CD(2)OOt-Bu. The oxidation of 1 induced by the genuine one-electron oxidant potassium 12-tungstocobalt(iii)ate at pH = 4.0 confirms the results obtained with LiP However, under the same conditions, no fragmentation products were observed in the oxidation of 2, probably due to a fast oxidation, by potassium 12-tungstocobalt(iii) ate, of the spirocyclohexadienyl radical.
2001
Pubblicato
Rilevanza internazionale
Articolo
Sì, ma tipo non specificato
Settore CHIM/06 - CHIMICA ORGANICA
English
Con Impact Factor ISI
SIDE-CHAIN FRAGMENTATION; BOND-CLEAVAGE REACTIONS; PHANEROCHAETE-CHRYSOSPORIUM; AQUEOUS-SOLUTION; RADICAL CATIONS; CARBON ACIDITY; AROMATIC RING; MECHANISM; CHEMISTRY; PRODUCT
Baciocchi, E., Bietti, M., Gerini, M., Lanzalunga, O., Mancinelli, S. (2001). Oxidation of non-phenolic beta-O-aryl-lignin model dimers catalysed by lignin peroxidase. Comparison with the oxidation induced by potassium 12-tungstocobalt(III)ate. JOURNAL OF THE CHEMICAL SOCIETY. PERKIN TRANSACTIONS 2(9), 1506-1511 [10.1039/b101362i].
Baciocchi, E; Bietti, M; Gerini, M; Lanzalunga, O; Mancinelli, S
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2108/53743
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