Carl Manning

The photoaddition of aliphatic amines to benzene

Primary, secondary, and tertiary aliphatic amines undergo photoaddition to benzene via photoexcitation of benzene to the S1 state. Primary amines give products of 1,2-, 1,3-, and 1,4-addition of the N–H bond, although the 1,3-adducts are derived from secondary photoreactions of the 1,2-adducts by way of hexa-1,3,5-triene intermediates. Secondary amines react similarly, but give only 1,2- and 1,4-adducts. The photoadditions of tertiary amines involve an α-C–H bond in the amine and occur 1,4- to the benzene ring, but little addition occurs in the absence of methanol or other proton donors. The mechanisms of these reactions have been investigated, and the findings are discussed : charge-transfer processes and both polar and radical intermediates appear to be involved.