Photoreduction of nitro-1,4-naphthoquinones in solution

The photolysis of 2,3-dichloro-n-nitro-1,4-naphthoquinones (nitroN’Q, n: 5 and 6) was studied in benzene and acetonitrile. The triplet states of both nitroN’Qs, which can be quenched by H-atom donating solvents, e.g. 2-propanol or 1-phenylethanol, were characterized by flash photolysis. Formation and decay of nitronaphthoquinone radicals, due to H-atom transfer, were observed; the reactivities of the donors were examined and the mechanistic aspects discussed. The photoreduction of 6-nitroN’Q in the presence of the donors is efficient in contrast to 5-nitroN’Q. The major product is considered to be 6-hydroxylaminoN’Q.