MODEL STUDIES ON THE PHOTOCHEMISTRY OF PHENOLIC SULFONATE PHOTOACID GENERATORS

The mechanism of photodissociation and acid generation for three pheno lic sulfonate esters, ranging from alkyl, to benzyl, to aromatic, was investigated by laser flash photolysis and product studies. All the su lfonate esters studied showed the presence of phenoxyl and other compl ex radicals in the transient spectra. The formation of these complex t ransients indicates that the radical pair formed upon excitation of th e sulfonate can escape the solvent cage, and undergo further chemical transformations, it was observed that all of the sulfonate esters inve stigated resulted in the formation of acidic species. Photoproduct stu dies indicate that phenyl methanesulfonate and phenyl toluene-alpha-su lfonate undergo a photo-Fries type rearrangement and also produce a la rge excess of phenol with the corresponding sulfonic acid. Upon excita tion, phenyl toluene-a-sulfonate undergoes near quantitative SO2 extru sion, with the formation of no Fries rearrangement photoproducts; inst ead it was observed that the benzyl radicals, generated by SO2 loss, u ndergo a ''pseudo'' Fries rearrangement to form the ortho and para phe nylmethane isomers. Further, the SO2 photogenerated undergoes oxidativ e and hydrolytic processes to form sulfuric and sulfurous acids.