Photolysis of tris(4-tert-butoxycarbonyloxyphenyl) sulphonium salts. A mechanistic study

Abstract

Tris(4-tert-butoxycarbonyloxyphenyl)sulphonium salts of the structure Ar3S+X–(X–: CF3SO3– or AsF6–) were irradiated with UV light in acetonitrile or dimethyl sulphoxide solution. Product analysis by ion pair chromatography (IPC), 1H NMR measurements and IR spectroscopy revealed that simultaneously bis(4-tert-butoxycarbonyloxyphenyl) sulphide, Ar2S, and a protonic acid (CF3SO3H or HAsF6) were formed. The latter catalyses the decomposition of the tert-butylcarbonate groups in the absence of water at room temperature. In the presence of water the acids dissociate, and H3O+ ions, thus formed, only catalyse the decomposition significantly at elevated temperatures (T > 70 °C). Therefore, photolysis products formed in the absence of water consist, apart from (4-HO–C6H4)2S, essentially of a mixture of salts of the ions: Ar2(4-HO–C6H4)S+, Ar(4-HO–C6H4)2S+ and (4-HO–C6H4)3S+. In addition to these products, (ButOCO2-C6H4)2S and an as yet unidentified product were formed when the irradiation was performed in the presence of water. Quantum yields (in the absence of water) determined by IPC are: φ[–salt]= 0.2 and φ[(4-HO–C6H4)2S]= 0.1.