Preparation of Organic Pigments with γ-Alumina as a Core

Abstract

Red or yellow organic pigment with γ-alumina as a core was prepared by utilizing mechanochemical reaction. The method was as follows: By dry grinding the mixture of γ-alumina and aminobenzoic acids in a porcelain ball mill, aminobenzoic acids were introduced as aluminum salts in the active site appeared on broken face of γ-alumina. The organic groups on the surface of the ground sample were then derived to structures similar to sudan I [azo dyestuff, 1-phenylazo-2-naphthol] or tartrazine [Food Yellow No.4, trisodium salt of 5-hydrox1-(4-sulfopheny1)-4-(4-sulfophenylazo)-1 H-pyrazole-3-carboxylic acid] by diazotization and followed by coupling with 2-naphthol or 5-oxo-1-(4-sulfopheny1)-2-pyrazoline-3-carboxylic acid.
The mechanochemical reaction took place only between the active site of γ-alumina and carboxyl group of the aminobenzoic acid and not between γ-alumina and amino group. Aminobenzoic acids were not decomposed by the grinding. The prepared pigments had color similar to the corresponding sudan I (red) or aqueous solution of tartrazine (yellow).