Collect. Czech. Chem. Commun. 1986, 51, 358-367

Photocyanation of 3,4-dimethoxy-1-nitrobenzene. A quantitative study

Petr Kuzmič and Milan Souček

Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, 166 10 Prague


UV photolysis (365 nm) of 3,4-dimethoxy-1-nitrobenzene in the presence of potassium cyanide leading to 3-cyano-4-methoxy-1-nitrobenzene was subjected to a quantitative photokinetic study. The reaction exhibits a second order kinetics with respect to the nucleophile and is effectively quenched by molecular oxygen as well as 2,4-hexadienoic acid. The excited triplet lifetime of 0.9 microseconds was determined on the basis of the dependence of quantum yield on the nucleophile and quencher concentrations in 50% aqueous tert-butanol. The quantum yield of intersystem crossing is at least 0.38 in the same solvent; bimolecular rate constant for the interaction of triplet 3,4-dimethoxy-1-nitrobenzene with cyanide anion has the value of 5.6 . 108 l . mol-1s-1, which is approximately one half of the rate constant for diffusion controlled quenching. Quantum yield of the reaction is strongly dependent on the water content in mixtures with tert-butanol and increases from 0.04 in water to 0.68 in 88% tert-butanol.