Aryl dialkyl sulfonium salts

Another aspect of the reactivity of the sulfur atom is illustrated by a reaction done on thianthrene. Indeed, 8 is not sufficiently nucleophilic to be alkylated by methods that work well with dialkyl and alkyl aryl sulfides, although Saeva was able to alkylate it by reaction with -cyanobenzyl bromide and silver triflate <1986T6123>. The sulfonium salt 52 bearing a methyl group can be obtain by an acid-promoted reaction with methyl formate (Equation 4) <1998JCX37522>. 

Considerable variation in both the aryl and alkyl groups in the above structures can be tolerated while maintaining the photoactivity of these salts. Through the introduction of substituents and structural modifications, it is possible to manipulate both the spectral absorption characteristics and the photosensitivity of both types of photoinitiators. In addition to those sulfonium salts represented by structures III and IV, several related compounds such as alkylarylphenacylsulfonium salts and dialkyl-2-hydroxyphenylsulfonium salts have also been observed to be excellent cationic photoinitiators... 

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