Identification and analysis of diarylide pigments by spectroscopic and chemical methods

Abstract

Diarylide pigments are a class of colored organic disazo compounds prepared from substituted 4,4′,-diaminobiphenyls (1: X = Cl, CH₃, OCH₃; Y = H, Cl) and acetoacetanilide or its derivatives (2: R¹ = H, CH₃, OCH₃, Cl; R² = H,

CH₃, OCH₃, OC₂H₅, Cl; R³ = H, OCH₃, Cl). Diarylide pigments can be represented by the general structure, 3. The term ‘diarylide’ signifies a disazo compound whose azo groups are linked to an acetoacetarylide molecule, which is usually referred to as the coupler. Table 8.1 lists various diarylide pigments found in the Colour Index¹ and demonstrates the numerous permutations possible by changing the substituents. In addition, co-couplings are also prepared by the simultaneous reaction of two different couplers with the same aromatic diamine to form asymmetric pigments such as C.I. Pigment Yellow 174 and Yellow 188.