4-Chloro-o-xylene → 2,2'-Dichloro-4,4',5,5'-tetramethylbenzophenone

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Specific benzophenonetetracarboxylic dianhydrides preferred in this invention are readily available from commercial sources or synthesis. For instance, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (D1) is available from Aldrich Chemical Co., Inc. (1001 W. St. Paul Ave., Milwaukee, Wis. 53233). 2,2'-Dichloro-4,4',5,5'-benzophenone tetracarboxylic dianhydride (D2) is available from 4-chloro-o-xylene by Friedel-Crafts acylation with oxalyl chloride to give 2,2'dichloro-4,4',5,5',-tetramehtylbenzophenone, followed by oxidation with nitric acid and dehydration of the resulting tetracarboxylic acid as described by Falcigno, et al., J. Poly. Sci. 1992, 30, 1433.

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