Red Benzimidazolone Pigments - Coupling Component

Red benzimidazolone pigments, which cover the entire range of shades in the red and brown part of the spectrum, are based on the following general structure  

Rd and m represent the same atoms or groups as in the corresponding yellow pigments (Sec. 2.8.1.1). 

The coupling component 26 is prepared like a Naphthol AS derivative. 5-Ami-nobenzimidazolone is treated with 2-hydroxy-3-naphthoic acid chloride or with 2-hydroxy-3-naphthoic acid and phosphorus trichloride in an organic solvent (Sec. 2.1.2). 

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