Disazo (Bishydrazone) pigments based on pyrazolones

The most important classical orange organic pigments are disazopyrazolones, also referred to as diarylide oranges. The first pigment in this series, CI Pigment Orange 13, was discovered in 1910 although it was a further 20 years before it was introduced as a commercial product. Currently, two orange disazopyrazolones are extremely important industrial organic pigments, while two red products are of lesser importance. The products are structurally analogous to the disazoacetoacetanilides (diarylide yellows), which are discussed in a separate chapter. For example, they are symmetrical compounds that exist in the bis-ketohydrazone tautomeric form. The pigments also exhibit similar technical and color properties compared with disazoacetoacetanilide pigments, for example providing high color strength and transparency, features that determine their importance as printing ink pigments. They are manufactured in a process that parallels those used for the disazoacetoacetanilide (diarylide) yellows, but with coupling components containing the pyrazolone heterocyclic system, in place of acetoacetanilides.