The crystal structures of three azonaphtharylamide pigments

The single crystal X-ray structures of three structurally related azonaphtharylamide pigments are reported. Two azo pigments derived from 4-amino-3-nitrotoluene as diazo component (1a and b) crystallize in the centrosymmetric space group P21/c while the third (1c), an analogue of 1b but derived from 2,5-dichloroaniline as diazo component, crystallizes in the chiral space group P212121. The compounds adopt the ketohydrazone tautomeric forms with intramolecular, but no intermolecular, hydrogen bonding. The application performance of the products is discussed in relation to the molecular and crystal structures. X-ray powder diffraction, supported by FTIR spectroscopic and DSC analysis, demonstrate that pigment 1a shows polymorphism. The application performances of the two polymorphs of this pigment are compared.