PRODUCTION OF 3,3',4,4'-BIPHENYLTETRACARBOXYLIC ACID SALT

PURPOSE:To obtain the titled compound useful as a raw material of polymers, with easy separation and recovery of the reaction product, in high yield, by carrying out the dehalogenation dimerization of a 4-halogeno-orthophthalic acid salt with formic acid, etc. in the presence of a Pd-supported catalyst and a base. CONSTITUTION:The 4-halogeno-orthophthalic acid salt of formula I (X is halogen) is subjected to the dehalogenation dimerization using especially water as the solvent, in the presence of a catalyst prepared by supporting metallic Pd on a carrier, preferably Pd/C catalyst, etc. and a base such as KOH, and in the presence of formic acid or an alkaline aqueous solution at 70-150 deg.C under a pressure of