Syntheses of deep coloured aminonaphthoquinonoid dyes. Reaction of dichloronaphthazarins with 2-aminobenzenethiol and related compounds

The reaction of 2,3-dichloronaphthazarin 1a with potassium 2-amino-benzenethiolate gives the ring-closure product 10,11-dithia-5H,16H-5, 16-diazadinaphtho2,3a],2,3c]-1,4-naphthoquinone 9 in 86.2% yield together with small amounts of 5-hydroxy-6-chloro-7-thia-12H-12-azanaphtho2,3a]-1,4-naphthoquinone 8. Dye 9 is green in colour and absorbs infrared light at 727 nm. Oxidation of 9 by hydrogen peroxide gives 10,11-dithia-5H,16H-5,16-diazadinaphtho2,3a],2,3c]-1,4-naphtho-quinone-10,11-dioxide 14 which absorbs infrared light at 827nm. The reaction of 1a with 2-aminoethanethiol gives 5-hydroxy-6-chloro-7-thia-10-aza-8, 9,10-trihydrobenzo2,3a]-1,4-naphthoquinone 4 and 2,3-di-chloro-5-hydroxy-7-thia-10-aza-8, 9,10-trihydrobenzo2,3a]-1,4-naphtho-quinone 5 in yields of 14.2 % and 3.2 %, respectively.