In the past, biphenyl dicarboxylic acid dialkyl esters have been produced by preparing corresponding biphenyl dicarboxylic acids by various known production processes and the esterifying the biphenyl dicarboxylic acids with alcohols.
As the conventional processes for producing the biphenyl carboxylic acids, there are known a process for causing coupling of a 3-bromo benzoic acid by a treatment with a KOH-methanol aqueous solution in the presence of a Pd/C catalyst (U.S. Pat. No. 2,809,210), a process for preparing a Grignard reagent from 4,4'-dichlorobiphenyl, then causing a reaction of the resultant reagent with CO.sub.2 (U.S. Pat. No. 2,508,022), a process for oxidizing 3,3'-dimethyl biphenyl by using potassium permanganate (Journal of American Chemistry; J. Am. Chem. Soc. 72, 3221 (1950)), a process for iodizing biphenyl, then causing a reaction of the resultant product with carbon monoxide (Japanese Unexamined Patent Publication No. 63-104942), and a process for oxidizing 4,4'-diisopropyl biphenyl with molecular oxygen (Japanese Unexamined Patent Publication No. 63-122645).
Further, as another process for producing the above-mentioned biphenyl- dicarboxylic acid, there is known the process for oxidizing 3,3',4,4'-tetramethyl biphenyl with molecular oxygen to synthesize 3,3'-dimethyl biphenyl-4,4'-dicarboxylic acid (Japanese Examined Patent Publication (Kokoku) No. 52-3377).
Nevertheless, these conventional processes for producing biphenyl dicarboxylic acid suffer from many defects, e.g., it is difficult to acquire the materials, extremely complicated and long steps are required, and there are many byproducts. Accordingly, all of the conventional processes in which biphenyl dicarboxylic acid is produced and then biphenyl dicarboxylic acid dialkyl esters are produced therefrom, have a poor practically in industrial terms.
Further, it was difficult to selectively manufacture 3,4,3',4'-substituted dimethyl biphenyl dicarboxylic acid dialkyl esters by the conventional processes or by processes provided by combinations of the same.