| abstract |
A biphenyltetracarboxylic tetraester, especially, 3,3',4,4'-biphenyltetracarboxylic tetraalkyl ester, is produced by bringing an orthophthalic diester, especially, orthophthalic dialkylester, into contact with a molecular oxygen-containing gas in the presence of a catalyst consisting of a mixture of a palladium salt with 2,2'-bipyridyl or a chelating reaction product of a palladium salt with 2,2'-bipyridyl, so as to promote oxidative coupling of the orthophthalic diester. |