879-67-4Relevant articles and documents
The aerobic oxidative cleavage of lignin to produce hydroxyaromatic benzaldehydes and carboxylic acids via metal/bromide catalysts in acetic acid/water mixtures
Partenheimer, Walt
body text, p. 456 - 466 (2009/12/01)
Roughly 30% of all woody plants is composed of lignin. Five different lignin samples, from wood and bagasse, were oxidized in air with a cobalt/ manganese/zirconium/bromide (Co/Mn/Zr/Br) catalyst in acetic acid as a function of time, temperature, pressure, and lignin and catalyst concentrations. 18 products were identified via gas chromatography-mass spectrometry (GC/MS). The most valuable products from lignin were 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, 4-hydroxy-3-methoxybenzaldehyde (vanillin), 4-hydroxy-3-methoxybenzoic acid (vanillic acid), 4-hydroxy-3,5-dimethoxybenzaldehyde (syringaldehyde) and 4-hydroxy-3,5-dimethoxybenzoic acid (syringic acid). 10.9 wt% of the lignin was converted to the aromatic products. By the use of model compounds we demonstrate that 1) the presence of the phenolic functionality on an aromatic ring does inhibit the rate of reaction but that the alkyl group on the ring still does oxidize to the carboxylic acid, 2) that the masking of phenol by acetylation occurs at a reasonable rate in acetic acid, 3) that the alkyl group of the masked phenol does very readily oxidize, 4) that an acetic anhydride/acetic acid mixture is a good oxidation solvent and 5) that a two-step acetylation/ oxidation to the carboxylic acid is feasible.
COMPETITION BETWEEN NUCLEAR AND SIDE-CHAIN SUBSTITUTION IN THE OXIDATION OF SOME ALKYLAROMATIC COMPOUNDS BY CERIUM(IV) AMMONIUM NITRATE AND COBALT(III) ACETATE
Baciocchi, Enrico,Rol, Cesare,Sebastiani, Giovanni V.
, p. 513 - 518 (2007/10/02)
The distribution between nuclear and side-chain substitution (N:S ratio) in the oxidations of m-methoxytoluene, 2-methylnaphtalene, mesitylene, and fluorene by cerium(IV) ammonium nitrate (CAN) and cobalt(III) acetate in acetic acid has been determined.The two oxidants exhibit remarkably different behaviours, the propensity for nuclear substitution being much stronger with CAN than with Co(OAc)3.For example, with m-methoxytoluene, CAN affords only products of nuclear acetoxylation, whereas Co(OAc)3 gives side-chain acetoxylation exclusively.The N:S ratio and the isomeric distribution for the CAN-induced reactions are consistent with a mechanism involving a common radical cation intermediate for the side-chain and nuclear substitution.The same mechanism might hold in the reactions with Co(OAc)3; however, in this case, the simultaneous operation of two different mechanisms is an additional possibility: a radical cation mechanism for the nuclear substitution and a hydrogen atom transfer mechanism for the side-chain reaction.
