Formation of Anhydrides and Their Reactions

The anhydride of 23-dicarboxypyrazine heated with hydrazine hydrate under various conditions gave some 5,8-dihydroxypyrazino[2,3- /]pyridazine (16) (1338-1340). Pyrolysis of the anhydride of 2,3-dicarboxypyrazine (14) at 830 at 0.05 mm through a silica tube gave an 80% yield of an approximately 1 1 mixture of maleonitrile and fumaronitrile and the mass spectrum of the anhydride (14) was consistent with the formation of the dehydropyrazine (17) (1341). 

3-Dicarboxy-5,6-dimethylpyrazine, heated with acetic anhydride, also gave the anhydride which with methanol gave 2-carboxy-3-methoxycarbonyl-5,6-dimethylpyrazine (654). 2,3-Dicarboxy-5-methylpyrazine anhydride was prepared similarly and on methanolysis and decarboxylation it gave 2-methyl-5(and 6)-methoxycarbonylpyrazines (1327). 

Tetracarboxypyrazine treated with acetic anhydride gave tetracarboxypyrazine dianhydride (1291, 1342). This condensed with p,p -diaminodiphenyl ether to give polyimides (18) which could be thermally processed at 40-280° in vacuo to give films having high thermal stability (1291, 1343). The preparation of polymers (resistant to thermal degradation) from tetracarboxypyrazine dianhydride and tetraaminopyrazine in polyphosphoric acid at elevated temperatures has been described (1180). 

6-Diamino-3-carboxy-5-chloropyrazine A, 7V-diphenylcarbamic anhydride (19), an active ester, has been prepared by addition of diphenylcarbamoyl chloride to 2,6-diamino-3-carboxy-5-chloropyrazine and triethylamine in dimethylformamide, (and other similar compounds were also prepared) (1330, 1344, 1345). This compound was better prepared from 2,6-diamino-3-carboxy-5-chloropyrazine and 

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