The photochemistry of α-aryl carboxylic anhydrides—II : Photolysis of some substituted phenylacetic anhydrides☆

Abstract The photolysis of phenylacetic acids and anhydrides with λ 254 nm was studied. The main product is bibenzyl, but with o - and p -methoxyphenylacetic anhydride, in addition substantial amounts of methoxybenzyl methoxyphenylacetates are formed. The photoreactivity of phenylacetic acid strongly reduces upon substitution of the phenyl ring, this in contrast to the behaviour of the corresponding anhydrides. The quantum yields for substrate conversion and product formation are reported. The mechanisms of the photo-formation of the products are discussed. Experimental evidence is presented to support the proposition that the ester formation occurs via a dipolar intermediate.