Abstract
The structure of pigments derived from 2-chloro-(Pigment III) and 4-chloro-(Pigment I), and 2, 4-dichloro-1-naphthol (Pigment II), and the reactivity of some phenols and naphthols were investigated in the reaction mixture of diacetyl and 1, 1-pentamethyleneguanidine in alkaline medium. The structures of Pigments I and II were identical with 4-chloro derivative of Pigment A obtained from 1-naphthol as reported previously, and Pigment III was a para-isomer relative to the structure of Pigment I and II. It was found that Pigment III was also identical with 2-chloro derivative of Pigment B which could not be separated from 1-naphthol because of its instability. For the reactivity of phenols and naphthols, 1, 3-dihydroxy type such as 2-methyl- and 5-methyl resorcinol, 3, 5-dihydroxy benzoic acid, and 1, 3-dihydroxynaphthalene gave striking coloration in comparison with 1-naphthol, while 1, 2- or 1, 4-dihydroxy type, which is immediately oxidized to a quinone form, did not give positive coloration.
