Azomethine Type Tetrachloroisoindolinone Pigments

Commercially used tetrachloroisoindolinone pigments have the general chemical structure 39 [1]  

The synthetic route generally involves condensing two equivalents of 4,5,6,7-tetrachloroisoindoline-l-one derivatives with one equivalent of an aromatic diamine in an organic solvent. Suitable tetrachloroisoindoline-l-one derivatives are substituted in 3-position, which is occupied either by two monovalent groups (A) 

Primary starting materials for this condensation reaction are 3,3,4,5,6,7-hexa-chloroisoindoline-l-one (40) and 2-cyano-3,4,5,6-tetrachlorobenzoic acid methyl ester (41)  

40 directly reacts with a diamine to afford the desired pigment. Two pathways have been found effective for the synthesis of 40. Tetrachlorophthalimide may be chlorinated either 

41 reacts with ammonia or alkali alcoholate to form the corresponding activated compounds 43 and 44  

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Depending on in situ and post-synthetic treatment procedures, azomethine-type tetrachloroisoindolinone pigments may result in several crystal modifications, e.g., in a, p, and 6 types l Mono and disazomethine pigments featuring heterocyclic ring systems have also been claimed by several companies " l The heterocyclic structure 18 even features tivo pigment chromophores, namely the quinophthalone and the isoindolinone moieties. ... 

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