The occurrence and reactivity of phenoxyl linkages in lignin and low rank coal

Nucleophilic substitution reactions by electron transfer

Lignin in straw and its applications as an adhesive

Dissection of lignin macromolecular configuration and assembly: Comparison to related biochemical processes in allyl/propenyl phenol and lignan biosynthesis

The basic mechanistic aspects of the photo- and radiation chemistry of lignin model compounds (LMCs) are discussed with respect to important processes related to lignin degradation. Several reactions occur after direct irradiation, photosensitized or radiation chemically induced oxidation of LMCs. Direct irradiation studies on LMCs have provided supportive evidence for the involvement of hydrogen abstraction reactions from phenols, β-cleavage of substituted α-aryloxyacetophenones and cleavage of ketyl radicals (formed by photoreduction of aromatic ketones or hydrogen abstraction from arylglycerol β-aryl ethers) in the photoyellowing of lignin rich pulps. Photosensitized and radiation chemically induced generation of reactive oxygen species and their reaction with LMCs are reviewed. The side-chain reactivity of LMC radical cations, generated by radiation chemical means, is also discussed in relation with the enzymatic degradation of lignin.

Photo- and radiation chemical induced degradation of lignin model compounds.

Ceric ammonium nitrate oxidative-cleavage reaction of some lignin model compounds. Role of the benzylic hydroxyl group

Role of the p-hydroxyl group in the nitrobenzene oxidation of hydroxybenzyl alcohols

The nitrobenzene and copper (II) Oxidations of 4-hydroxystilbenes 2 gave moderate yields of p-hydroxybenzaldehyde. No aldehyde was obtained in the absence of water. A Hammett Substituent effect study found a ρ value of — 0.48 versus σ for both the copper (II) and nitrobenzene oxidations. These results are consistent with a homolytic mechanism involving the benzylic hydroxyl groups of intermediate alcohols 1. A polar transition state in the rate-controlling cleavage of benzyl radicals is postulated to explain the σ dependence.

https://www.degruyter.com/view/j/hfsg.1988.42.issue-3/hfsg.1988.42.3.163/hfsg.1988.42.3.163.pdf

Substituent Effects in the Nitrobenzene and Copper (II) Oxidations of Some Hydroxystilbene Lignin Model Compounds

The conformations of five hydropyridazines in the solid state have been determined from their crystal structures. The results are compared with the conformations of these compounds in solution as analysed by interpretation of their 1H and 13C n.m.r. spectra Dihydropyridazine (1) adopts the twist-boat conformation in the solid state however, in accordance with the interpretation of 1H n.m.r. spectra tetrahydropyridazines, (2) and (3) adopt the half-chair conformation in agreement with that found for (2) and in contrast to that found for (3) in solution. Hexahydropyridazine (4) was found to adopt the chair conformation both in solution and in the solid state.

Stephen M. Dershem

Papers

Ceric ammonium nitrate oxidative-cleavage reaction of some lignin model compounds. Role of the benzylic hydroxyl group

Role of the p-hydroxyl group in the nitrobenzene oxidation of hydroxybenzyl alcohols

Substituent Effects in the Nitrobenzene and Copper (II) Oxidations of Some Hydroxystilbene Lignin Model Compounds

The conformation of some di-, tetra-, and hexa-hydropyridazines in the solid state

Role of the p-Hydroxyl Group in the Nitrobenzene Oxidation of Hydroxybenzyl Alcohols.