title: Hammett correlations in the photosensitized oxidation of 4-substituted thioanisoles.
abstract: Singlet oxygen is quenched by a series of 4-substituted thioanisoles (methoxy to nitro), with rate constant k(t) = 7 x 10(4) to 7 x 10(6) M(-)(1) s(-)(1), close to the value observed for the myoglobin-catalyzed sulfoxidation of the same sulfides. Correlations with sigma (rho = -1.97) and with E(ox) (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 sigma (rho = -1.78).
authors.affiliation: Department of Organic Chemistry, University of Pavia, via Taramelli 10, 27100 Pavia, Italy.
authors.forename: Sergio M
authors.initials: SM
authors.lastname: Bonesi
authors.forename: Maurizio
authors.initials: M
authors.lastname: Fagnoni
authors.forename: Angelo
authors.initials: A
authors.lastname: Albini