PURPOSE: To provide a new and further efficient process for preparing N- substituted-N'-phenyl-P-phenylenediamines useful for the preparation of pharmaceuticals and agricultural products.

CONSTITUTION: The compound of formula III e.g. N-methyl-N'-phenyl-p- phenylenediamine, is obtained by reacting a mixture of N-phenyl-p-quinoneimine of formula I and p-hydroxydiphenylamine in a mole ratio of (1.5:1) to (1:1.5)with a primary amine of the formula R1-NH2 [R1 is 1-20C alkyl, 6-8C cycloalkyl or formula II (R2 is H or CH3; R3 is 1-12C alkyl;(n) is 0 to 6)] in the presence of methanol at 15 to 130°C preferably room temperature to 65°C. A mole ratio of the mixture to the primary amine in the reaction mixture is generally in a range of (1:1) to (1:10) preferably (1:1) to (1:3).