Patent ID: 6864032

Claim:
A method for forming an azo colorant, wherein a coupler having a leaving group at a coupling position thereof and a diazo compound pound are used, and the method has a faster coupling reaction rate constant, measured by mixing equivalent amounts of an ethyl acetate solution containing an 8×10 −5 mole concentration of the diazo compound and an ethyl acetate solution containing an 8×10 −3 mole concentration of the coupler and a base with a stopped flow measurement device and by measuring change over time of an absorbance of the produced colorant and applying the resultant value to the following formula (1), than an azo dye-forming reaction between the diazo compound and a coupler having a hydrogen atom at a coupling position thereof: D {colorant}/ dt=k {diazo compound} formula (1) wherein k diotes the coupling reaction rate constant (s −1 ), t denotes time (s), {colorant} denotes a mole amount of the produced colorant, and {diazo compound} denotes an initial mole amount of the diazo compound (mol).