ON THE PHOTODECOMPOSITION MECHANISM OF ORTHO-DIAZONAPHTHOQUINONES

The mechanism for the photodecomposition of several omicron-diazonaphthoquinones has been examined in acetonitrile solution using time-resolved laser flash photolysis techniques. It is concluded that the Wolff rearrangement, which involves the formation of a ketene intermediate, can be regarded as a concerted process in the nanosecond time scale. It is suggested that the reaction of the ketene with water, which is well known to yield 3-indenecarboxylic acids, involves the intermediacy of a ketene hydrate. Pyridine, a molecule frequently employed as a carbene trap/probe, efficiently traps the ketene in these systems; this scavenging reaction can be employed as a probe for the study of the dynamics of ketene reactions, but in some systems it may represent a problem in carbene studies if the possibility of ketene reactions is not considered.