Reactions of some substituted phenols with chromyl and vanadyl chlorides

Abstract

. Can. J. Chem. 58,686 (1980). The oxidation of 2,4,6-tritertbutylphenol and several other alkyl and halophenois by CrO,Cl, and VOC1, was studied. The products of CrO,Cl, oxidation are mostly quinones and diphenoquinones, whilst those of VOCL, oxidation also include major amounts of dealkylated phenols and C-C coupled dimers. The product distributions are interpreted in terms of a mechanism involving phenoxyl radicals, ligand transfer from metal to radical, and either phenoxonium ions or metallate esters where there is sufficient electron withdrawal from the organic group for it to exhibit carbenium ion properties. The differences in behaviour between CrO,CI,, VOCI,, and CuCl, are attributed to different balances between the oxidation potential and Lewis acidity of the metal complexes. It is concluded that CrO,Cl, is not a good model for proposed ferry1 intermediate in heme oxidase systems since it induces 1 + 3 rather than 1 + 2 halogen shifts and an NIH shift that is best explained by carbenium ion-like intermediates. JOHN F. HARROD et ASHA PATHAK. Can. J. Chem. 58,686 (1980). On aetudie l'oxydation du tritert-butyl-2,4,6phenol et de plusieurs autres phenols alkyles et halogenes par CrO,Cl, et VOC1,. Les produits de l'oxydation par CrO,CI, sont principalement des quinones et des diphenoquinones alors que ceux resultant de I'oxydation par VOCI, comprennent egalement des quantitez appreciables de phenols desalkyles et des dimeres lies par une liaison C-C. On interprkte la repartition des produits en fonction d'un mecanisme qui fait intervenir des radicaux phenoxyles, des transferts de ligands du metal au radical et soit des ions phenoxonium ou des esters de type metallique dans lequel le groupe organique est suffisamment polarise pour exhiber les proprietes d'un ion carbenium. On attribue les differences de comportement entre le CrO,Cl,, le VOCI, et le CuCI, aux differents equilibres entre les potentiels d'oxydation et I'aciditC de Lewis des complexes metalliques. On a conclu que le CrO,Cl, n'est pas un bon modele pour I'intermediaire ferryle propose dans les systemes heme oxydase puisqu'il indui.t un glissement 1+3 d'halogtne plutBt que 1 4 2 et un glissement NIH qui s'explique mieux par un intermediaire de type carbenium.[Traduit par le journal]

The reaction of guaiacol with iron III and chromium VI compounds as a model for wood surface modification

“…The related reaction of phenols with chromyl chloride CRO2C12, the Etard reagent, has been investigated in more detail (Strickson and Brooks 1967;Strickson and Leigh 1968;Leigh and Strickson 1973;Harrod and Pathak 1980). In these studies the emphasis has been on the structure and mechanism of formation of low valent non-stoichiometric chromium coordination complexes of product quinones, but uncharacterized tars were the major products from the reaction of chromyl chloride with monosubstituted phenols.…”

“…Reaction with sodium borohydride in tetrahydrofuran or zinc in acetic anhydride was necessary to free oligomers from the polymeric complex. With regard to the mechanism of the chromyl chloride reaction with phenols, there is no doubt that free radical formation is an important step, but the exact oxidation and coordination states of the associated chromium species are unknown (Harrod and Pathak 1980). With both chromyl chloride and chromium trioxide lower valent chromium complexes of phenol oxidation products are obtained.…”