PHOTOCHEMISTRY OF ACYLAZIDES .7. AROYLAZIDE DECOMPOSITION BY PHOTINDUCED ELECTRON-TRANSFER

The decomposition of p-trimethylsilylbenzoylazide (1) is induced by th e photoexcitation of electron donors such as diphenylanthracene (DPA), pyrene (PY) and Michler's ketone (MK) in acetonitrile solution. Sensi tization of 1 by Py of DPA results in the formation of 4-trimethylsily lisocyanate (3) and (4-trimethylsilylphenyl)-5-methyl-1,3,4-oxadiazole (2), the product of the cycloaddition of the aroylnitrene to the solv ent. Sensitization by MK leads to 2 and 4-trimethylsilylbenzamide (4). Flash photolysis studies in conjunction with electrical conductivity measurements reveal the formation of ionic intermediates. Optical abso rption measurements indicate the transient existence of radical cation s of PY and DPA. In this way an earlier postulated electron transfer m echanism for the reaction of aroylazide with electronically excited el ectron donors was substantiated. Triplet states (for MK) and singlet s tates (for DPA and PY) are the reactive excited species. Moreover, fre e ions generated on irradiation of benzophenone in the presence of 1 i n 2-propanol are detected by electrical conductivity measurements. Fro m this it is concluded that electron transfer occurs from the dimethyl ketyl radicals to 1.