Hammettcorrelations in the photosensitized oxidation of 4-substituted thioanisoles

S. M. BONESI, M. FAGNONI AND A. ALBINI

JOURNAL OF ORGANIC CHEMISTRY

American Chemical Society

Año: 2004 vol. 69 p. 928 - 935

0022-3263

Abstract: Singlet oxygen is quenched by a series of 4-substituted thioanisoles (methoxy to nitro), with rate constant kt = 7 x 106 M-1 s-1, close to the value observed for the myoglobin-catalyzed sulfoxidation of the same sulfides. Correlations with s (r = – 1.97) and with Eox (slope -3.9 V-1) are evidence for an electrophilic mechanism. In methanol sulfoxides are formed (85%) via an intermediate quenched by diphenyl sulfoxide; competing minor paths lead to arylthiols, arylsulfenic acid, and aryl sulfoxides. In aprotic solvents, the sulfoxidation is quite sluggish, but carboxylic acids (mostly<0.1 M) enhance the rate by a factor of <100. The protonated persulfoxide is formed in this case and acts as an electrophile with sulfides, again with a rate constant correlating with s (r = - 1,78).