Photo-oxidative cyanation of aromatics on semiconductor powder suspensions I: oxidation processes involving radical species

Illumination of platinized WO3 and TiO2 suspensions in CH3CN/H2O mixed solvents containing dimethoxybenzene (DMB) and cyanide leads to the formation of cyanoanisole together with side products. Laser flash photolysis of the transparent colloidal dispersions shows the formation of DMB+.. The amount of DMB+{radical dot} formed decreases in the presence of CN-, which indicates the competitive oxidation of DMB and Cn- rather than the reaction of DMB+{radical dot} and CN-. Using the electron spin resonance spin trapping technique we report for the first time evidence of CN{radical dot} and {radical dot}CH2CN radical formation in illuminated semiconductor suspensions. Use of dry CH3CN, DMB and (Bu)4+CN- decreases further the yield of cyanoanisole due to formation of a cyanated derivative of tributylamine which, in turn, originates from (Bu)4+ after cyanide oxidation to CN{radical dot}. © 1990.