PURPOSE: To obtain the titled compound useful as a synthetic intermediate and sensitivity-improver for a color-developing agent for heat-sensitive recording material, with simple process in high yield, by reacting a 4-alkoxyphenylsulfonic acid derivative with a benzene derivative in the presence of a dehydrative condensation agent.

CONSTITUTION: The objective compound of formula III can be produced by reacting the 4-alkoxyphenylsulfonic acid derivative of formula I (R is lower alkyl; R1WR4 are H, halogen, lower alkyl, cycloalkyl or lower alkoxy; X is H or alkali salt residue) with the benzene derivative of formula II (R5WR9 are H, alkyl, thioalkoxy, aryl, etc.) in the presence of a dehydrative condensation agent (e.g. a mixture of polyphosphoric acid and methanesulfonic acid) at 0W150°C, preferably at room temperatureW100°C for several hours W several days.