Photochemistry of Dialkyl-4-hydroxyphenylsulfonium Salts

The photochemistry of dialkyl-4-hydroxyphenylsulfonium salts has received little attention in the literature. Recently, on the basis primarily of NMR data and analysis of the photolysis products, Crivello and Lam have proposed the following mechanism for the photolysis of these compounds which is related to that of the dialkylphenacylsulfonium salts. 

The key step in this mechanism involves the photoexcitation of the sulfonium salt which rapidly dissociates to form the resonance-stabilized ylide (V) and the solvated protonic acid. Recombination of these two products to form starting material via a thermal back reaction results in the establishment of a small steady-state concentration of ylide and protonic acid. As in the case of the dialkylphenacylsulfonium salts, solvents or monomers may play an important role in this mechanism by assisting in the removal of a proton from the excited sulfonium salt. 

---