Azomethine-type isoindolinones

All isoindolinone pigments are characterized by the presence of the isoindolinone ring structure 1. 

ICI in 1946 was the first to take out a patent [1] on isoindolinone-type dyes and pigments, protecting products of the general formula 2, where each of the isoindolinone benzene rings contain up to two substituents (Rj, Rj), while R is derived from an aromatic or heterocyclic diamine. 

In the following years, EMdge and Ilnstead [2, 3] reported on the preparation of additional compounds represented by the general formula 2. The use of heterocyc-Uc diamines has also been reported to yield yellow dyes [3, 4], 

Although the initial products at ICI were mainly made from unsubstituted phthaUmide, the majority of their compounds were aU prepared by the condensation of a primary diamine with the corresponding 3-iminoisoindolinone derivative 3, affording in general yellow or orange pigments. 

Even as late as in the 1970s, Bitterli and Kehrer [5] reported the preparation of yellow isoindolinone pigments starting with unsubstituted (R, = H) and 

---

Formal replacement of the two hydrogen atoms at the 3-position by a substituted nitrogen atom yields an azomethine (>C=N-) linkage at this position - the ensuing product being conveniently referred to as an azomethine-type isoindolinone derivative. If, however, the two hydrogen atoms are replaced by an appropriately substituted carbon atom to yield a C=C double bond, the resulting semicyclic amidine derivative is classed as a methine-type isoindolinone. 

From a chemical standpoint, the azomethine-type isoindolinones 2 and 4 are derivatives of phthalimide, and may also be viewed as acylated exocyclic amidines with the acylamino group forming a part of the heterocycle. 

Monomeric and polymeric phenylene-bridged azomethine-type isoindolinone pigments have been prepared, e.g., by the reaction of intermediates such as 21 and 22 with appropriate aromatic mono and diamines . ... 

Methine isoindolinones of generic structure 23 can be prepared by the reaction of active methylene compounds with either phthalimides [e.g., 22], or iminoisoindoli-nones [e.g., 23], or a-cyanobenzoates by analogy with the methods described above for azomethine type isoindolinones. 

Further, stable 2 1 transition metal complex pigments 27 (C.I. Pigment Yellow 177) and 28 (C.I. Pigment Yellow 179), featuring six-ring chelates, have been prepared from methine and azomethine type isoindolinones l... 

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. ... 

In comparison with their azomethine analogs described above, methine-type isoindolinones have gained Htde significance as pigments, although bismethine iso-indoline pigments constitute commercially important yellow-to-red products [21]. 

By virtue of their high-performance properties, azomethine-type tetrachloro-isoindolinone pigments 5 find extensive application in general and high-grade... 

Yet another type of polycyclic azomethine isoindolinones, where the isoindolinone benzene ring is either linearly or angularly fused with other benzene rings, have also been reported. Yellow to orange bisazomethine pigments of structure 20 were synthesized from the corresponding naphthalene dicarboxylic acids and diamines in the presence of phosphorous pentachloride. ... 

---