Photochemical behaviour of dichloroanilines in water and formation of aminochlorophenoxazones

The main photochemical reaction of dichloroanilines (DCAs) is photohydrolys is, i.e. a substitution of Cl by OH involving a molecule of water, with ini tially a relative specificity. The quantum yields Lie in the range 0.015-0. 060. This reaction was previously reported for 3,4-DCA and 2,6-DCA, It is o bserved with all other isomers 2,3-DCA, 2,4-DCA, 2,5-DCA and 3,5-DCA. This reaction is not influenced by the presence of oxygen. in contrast to 2-chlo roaniline (2-CA), 2,4-DCA and 2,6-DCA do not lead to the contraction of the ring (formation of chlorinated cyclopentadiene carbonitrile). Surprisingly , 2,4-DCA neither reacts as 2-CA nor as 4-CA. A priority order in the site of substitution is deduced from the comparison between the six DCA isomers: meta > ortho > para. in other words, para and ortho substitutions are mino r pathways when the meta position is chlorinated. Moreover, the formation o f aminochlorophenoxazones was observed with 2,4- and 2,6-DCA. It results fr om the photochemical transformation of the aminochlorophenols initially for med. With 2,4-DCA, 2-amino-7-chlorophenoxazin-3-one was identified; with 2, 6-DCA, 2-amino-1-chloro- and 2-amino-1,9-dichlorophenoxazin-3-one are forme d. These reactions involve the intermediate formation of an o-benzoquinone monoimine. (C) 1999 Elsevier Science S.A. All rights reserved.