Development of biphenyltetracarboxylic acid production process on a factory scale

3,4,3', 4'-Biphenyltetracarboxylic acid (s-BTC) derivatives are now widely recognized as a useful compound. The anhydride (s-BPDA) is a raw material f or polyimide which is the most heatproof resin, and it is known that the ca boxylate has unique functions as a plasticizer. Although it is supposed to be difficult to form biphenyl structure on a fac tory scale, there are two industrial methods. The first method is oxidative dimerization of dimethyl phthalate by palladium catalyst and the second is reductive dimerization of 4-chlorophthalic acid by palladium catalyst. In 1994, the latter process was established in our laboratory and then we s tarted the industrial production on hundreds tons per year according to the process flow diagram (Fig.2).