PURPOSE: To obtain the titled compound useful as a herbicide in a short economically advantageously in high purity in high yield, by reacting a phenylacetic acid with a 2,2-dialkylbenzylamine under specific conditions by two steps.

CONSTITUTION: A phenylacetic acid shown by the formulaI(X1WX5 are halogen, H, 1W3C alkyl, 1W3C alkoxy, phenoxy, nitro, etc.; R1 and R2 are H, halogen, 1W4C alkyl, 1W4C alkoxyl, or cyano) is reacted with α,α-dialkylbenzylamine shown by the formula II(X6WX10 are halogen, H, 1W3C alkyl, 1W3C alkoxyl, trifluoromethyl, cyano, etc.; R3 and R4 are 1W4C alkyl) at 190W220°C until a conversion becomes 30W70%. The temperature of the reaction mixture is lowered and it is reacted at 180W190°C, to give the desired compound shown by the formula III. When the temperature difference before and after the reaction is ≥5°C, especially ≥10°C, the reaction is progrssed more effectively.