SUCCESSIVE PHOTOSUBSTITUTION OF HEXACHLOROBENZENE WITH CYANIDE ION

We report a novel nucleophilic polysubstitution reaction of hexachloro benzene (HCB) with cyanide ion in acetonitrile/water. Successive photo cyanations of HCB occur with high quantum yield (phi(diss) --> 0.18) w ithout the need for an electron acceptor, to give as products pentacya nophenol, 4-chloro-2,3,5,6-tetracyanophenol, and a dichlorotricyanophe nol. The phenol functional group is introduced by competing hydrolysis of the polycyanochlorinated benzenes. Sensitization and quenching exp eriments indicate a triplet reactive excited state. Variation of [CN-] at constant [HCB] follows the expected relationship phi(diss) -1 prop ortional to [CN-](-1), but variation of [HCB] at constant [CN-] shows that the reaction becomes less efficient with increasing [HCB], consis tent with the formation of an unproductive excimer.