5457-60-3Relevant articles and documents
Electron transfer between protonated and unprotonated phenoxyl radicals
Omura, Kanji
, p. 858 - 867 (2008/09/19)
(Chemical Equation Presented) The reaction of phenoxyl radicals with acids is investigated. 2,4,6-Tri-tert-butylphenoxyl radical (13), a persistent radical, deteriorates in MeOH/PhH in the presence of an acid yielding 4-methoxycyclohexa-2,5-dienone 18a and the parent phenol (14). The reaction is facilitated by a strong acid. Treatment of 2,6-di-tert-butyl-4-methylphenoxyl radical (2), a short-lived radical, generated by dissociation of its dimer, with an acid in MeOH provides 4-methoxycyclohexa-2,5-dienone 4 and the products from disproportionation of 2 including the parent phenol (3). A strong acid in a high concentration favors the formation of 4 while the yield of 3 is always kept high. Oxidation of the parent phenol (33) with PbO2 to generate transient 2,6-di-tert-butylphenoxyl radical (35) in AcOH/H2O containing an added acid provides eventually p-benzoquinone 39 and 4,4′-diphenoquinone 42, the product from dimerization of 35. A strong acid in a high concentration favors the formation of 39. These results suggest that a phenoxyl radical is protonated by an acid and electron transfer takes place from another phenoxyl radical to the protonated phenoxyl radical, thus generating the phenoxyl cation, which can add an oxygen nucleophile, and the phenol (eq 5). The electron transfer is a fast reaction.
Reactions of some substituted phenols with chromyl and vanadyl chlorides
Harrod, John F.,Pathak, Asha
, p. 686 - 693 (2007/10/02)
The oxidation of 2,4,6-tritertbutylphenol and several other alkyl and halophenols by CrO2Cl2 and VOCl3 was studied.The products of CrO2Cl2 oxidation are mostly quinones and diphenoquinones, whilst those of VOCl3 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 CrO2Cl2, VOCl3, and CuCl2 are attributed to different balances between the oxidation potential and Lewis acidity of the metal complexes.It is concluded that CrO2Cl2 is not a good model for proposed ferryl 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.