Benzimidazolone finishing

Benzimidazolone pigments are used throughout the paint industry to lend color to all types of industrial finishes. 

Suzuki, E. M., and W. P. Marshall. "Infrared Spectra of U5. Automobile Origincd Topcoats (1974-1989) III. In Situ Identification of Some Organic Pigments Used in Yellow, Orange, Red, eind Brown Noiunetallic and Brown Metallic Finishes—Benzimidazolones." Journal of Forensic Sciences 42 (1997), 619-648. 

The properties described qualify benzimidazolone pigments for applications such as high quality industrial paints, including automotive finishes and special effect paints, plastics and high performance printing inks. The colorants are available in the form of powders, masterbatches, liquid dispersions, pastes and granules (see Table 10-4). 

Preparation of the benzimidazolone-dioxazine pigments usually involves a multi-step synthesis followed by finishing. A typical reaction scheme depicting the synthesis of the unsubstituted derivative, but which can be generalized for all other substituents, is shown in Figure 20-15. 

Hence, according to crystal engineering the ideal molecule would be the mixed methyl-ethyl compound 4c (R = CHj, R = QHs). However, this unsymmetical compound is difRcult to synthesize in pure form performing the synthesis with a 1 1 mixture of 1-methyl- and 1-ethyl-benzimidazolones results in a mixture of dimethyl (4b), methyl-ethyl (4c), and diethyl (4d) compounds in a ratio of 4b 4c 4d = 1 2 1. This ternary mixture forms a solid solution (mixed crystal). Upon syntheses the solid solution emerges as a dull crude material, which is isostructural to the 6-phase of 4b a subsequent finish in N-methyl-pyrroUdone or isobutanol causes a phase transition to the desired p-phase [21]. For organic compounds, such phase transitions from one ternary solid solutions to another without separation into the individual compounds have rarely been reported. 

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