On the mechanism of photolysis of 4-phenyl-1,3,2-oxathiazolylio-5-oxide in ethanol : Evidence for ketene intermediates

Photolysis of 4-phenyl-1,3,2-oxathiazolylio-5-oxide (1) in ethanol in the presence of oxygen leads to benzonitrile (21%) and ethyl phenylglyoxylate (65%). Photolysis under an atmopshere of ¹⁵NO results in isotope exchange which is considered strong evidence for phenyl(nitrosothio)ketene (2) being in photolytic equilibrium with the starting material. In ethanolic solution saturated with nitric oxide the photolytic equilibrium is shifted towards the starting material resulting in formation of benzonitrile in 100% yield. Benzonitrile is formed by a competitive reaction route via benzonitrile sulfide.¹ Compound 2 does not undergo ethanolysis to ethyl(nitrosothio)phenylacetate (3). Ethyl phenylglyoxylate is probably formed via thiyl radical 6 resulting from homolytic scission of the SNO bond in ketene 2. Singlet molecular oxygen is present during photolysis of 1 but seems to be unimportant to the course of reaction.