PHOTOCHEMISTRY OF UNSATURATED NITROGEN-CONTAINING COMPOUNDS .3. MECHANISM OF CIS- AND TRANS-STILBENE FORMATION FROM IRRADIATION OF BENZALAZINE

The direct irradiation of 4-methoxybenzalazine (9) in 2-propanol produces cis and trans isomers of stilbene, 4-methoxystilbene, and 4,4′-dimethoxystilbene; in addition, small quantities of benzalazine (1) and anisalazine (10) are also formed, cis- and trans-stilbene (2 and 3) and cis- and trans-4,4′-dimethoxystilbene (11 and 12) are shown not to arise from excitation of the small amounts of 1 and 10 produced photochemically. Irradiation of a mixture of 1 and 10 in 2-propanol also leads to cis and trans isomers of the unsubstituted, 4-methoxy-, and 4,4′-dimethoxystilbene systems; in this instance also the small amount of photochemically produced 4′-methoxybenzalazine (9) cannot account for cis- and trans-4-methoxystilbene (13 and 14) formed. Irradiation of trans-4-methoxystilbene (14) causes cis-trans isomerization but produces neither the stilbene nor the 4,4′- dimethoxystilbene system. Similarly, photolysis of a mixture of trans-stilbene (3) and trans-4,4′-dimethoxystilbene (12) gives none of the 4-methoxystilbene system. Irradiation of either benzalazine (1) with added trans-4,4′-dimethoxystilbene (12) or anisalazine (10) with added trans-stilbene (3) does not produce cis- or trans- 4-methoxystilbene (13 or 14). These results along with previously reported observation on azine photochemistry are interpreted as requiring the azine to stilbene transformation to be an intermolecular process initiated by direct interaction between two azine systems. Possible mechanisms for this process are proposed and discussed. © 1969, American Chemical Society. All rights reserved.