METHOD FOR PRODUCING AZO COMPOUND

PROBLEM TO BE SOLVED: To provide a method for producing an azo compound e.g. forming low viscosity ink in using as printing ink without performing a conventional postprocessing step, wherein α-type crystal is converted into β-type, or a pigment-forming step. SOLUTION: This method is for producing N-(2,3-dihydro-2-oxo-1H- benzimidazol-5-yl)-3-hydroxy-4-[[2-methoxy-5-methyl-4-[(methylamino) sulphonyl]phenyl]azo]-2-naphthalenecarboamide of a crystalline structure having strong peaks at Bragg angle (2θ±0.2 deg.)=8.6 deg. and 26.9 deg., and weak peaks at Bragg angle = 10.5 deg., 12.9 deg., 14.0 deg., 14.8 deg., 17.2 deg., 21.7 deg., 22.3 deg., 23.7 deg. and 24.5 deg. based on a powder X-ray diffraction diagram of CuKα characteristic X-ray, wherein the method comprises dropping, at the same time, an aqueous solution of 1-amino-2- methoxy-5-methylbenzene-4-sulfonic acid methyl amide diazonium salt and an aqueous solution of 5-(2'-oxy-3'-naphthoyl-amino)-benzimidazolone into 40-70 deg.C water to perform coupling reaction.