Photolysis of 1,2,3-selenadiazole. Formation of selenirene by secondary photolysis of selenoketene

Abstract

Irradiation of 1,2,3-selenadiazole together with diethylamine in solution at room temperature or at 150 K gives rise to N,N-diethylselenoacetamide in near quantitative yield, an indication of the trapping of selenoketene during photolysis. Experiments with ¹³C-labelled selenadiazole demonstrate lack of carbon randomization in the selenoketene. This excludes selenirene as potential precursor for selenoketene.

After irradiation of 1,2,3-selenadiazole in an EPA-glass or PVC-film at 77 K, carbon randomized selenoketene has been detected in up to 56% yield by i.r. spectroscopy and 78% yield by trapping with diethylamine; the yields are dependent on the experimental conditions. A reaction mechanism is suggested which involves reversible formation of selenirene by photolysis from selenoketene. This process does not occur in liquid solution because of the extremely small steady-state concentration of selenoketene during photolysis.