PHOTOREACTIONS OF NITROANISOLES WITH CYANIDE ION . STUDIES OF PRODUCTS AND REACTION SEQUENCE

Irradiation of an aqueous solution of 4-nitroanisole and potassium cyanide in the presence of air affords 2-cyano-4-nitroanisole. Under the same conditions 2-nitroanisole gives a mixture of 4-cyano-2-nitroanisole and 6-cyano-2-nitroanisole, and 3-nitroanisole gives 3-nitrobenzonitrile. The preferred point of attack is therefore meta to nitro in each instance. The course of the reaction of 4-nitroanisole was probed by investigating the effect of oxygen on the system, possible interactions of cyanide with ground-state 4-nitroanisole, and rates and quantum yields as a function of cyanide concentration. It was concluded that cyanide intercepts photoexcited 4-nitroanisole with high efficiency, forming an intermediate of short lifetime which is oxidized by molecular oxygen to 2-cyano-4-nitroanisole. Competition experiments utilizing cyanide with pyridine, 2,4,6-trimethylpyridine, and iodide provide evidence that pyridine and cyanide compete for the same excited species of 4-nitroanisole, that pyridine converts the excited species to ground-state 4-nitroanisole (as well as yielding substitution products), that the quenching reaction is subject to steric hindrance, and that iodide quenches excited 4-nitroanisole. Data from these experiments in conjunction with data from previous studies are used to construct a table of relative reactivities for several nucleophiles toward photoexcited 4-nitroanisole. © 1969, American Chemical Society. All rights reserved.