Successive photocyanation of highly chlorinated aromatic compounds

Successive photocyanation was found to be a general reaction when chlorinat ed aromatic compounds were photolyzed with sodium cyanide. The products wer e polycyanated hydroxychloro compounds with various degrees of chlorine rep lacement. Although the products from some substrates could be isolated, ide ntified, and characterized, most reactions proceeded with low regioselectiv ity, which limits their synthetic potential. Quantum yields of substrate di sappearance increased with the number of chlorine substituents on a substra te, and followed the expected relationship phi(-1) proportional to [CN-](-1 ). In some cases, phi depended also on the concentration of the chloro comp ound, indicating the involvement of excimers, although the major reaction c hannel appears to be S(N)2Ar*. Sensitization and quenching experiments esta blished the triplet excited state to be reactive for ail substrates tested.