Dehydrogenation of piperazines to pyrazines

The dehydrogenation of piperazines to pyrazine was first achieved by Stoehr (32), who heated piperazine (87) or its hydrochloride with zinc dust or, better, zinc dust and lime to give a yield of approximately 10% pyrazine (88). Since that time a number of publications and patents has described the conversion of piperazines to pyrazines by heating at elevated temperatures with various catalysts usually containing copper chromite (464) but also with palladium-charcoal (465) and platinum on alkali-washed firebrick (466), and also with other reagents. Some of these preparations are summarized in Table II.11 (464-475). 

Dehydrogenations of piperazines to pyrazines have been described in Section II.6, and the conversion of piperazine over catalysts (e.g., CuO) to give mostly pyrazine (90-94%) has been studied (1718). The oxidation of 1,4-diphenylpiperazine with manganese dioxide in chloroform at 20° to yield A, A -diformyl-A(, -diphenyl-ethylenediamine has been reported (1719). Formylpiperazines have been reported as formylating agents. Thiophene, 1,4-diformylpiperazine, and phosphoryl chloride are reported to give 2-formylthiophene (1720). 

Cu-. [M THarshaw] Copper chromite cat yst for dehydrogenation of alcohols, decomposition of methanol, oxygen scavenging, dehydrogenation of piperazines to pyrazines, methyl ester hydrogenolysis and dehydrogenation. 

Ethylenediamine undergoes catalytic self-condensation (with loss of 2 Nil,) to give piperazine and subsequently (by dehydrogenation)pyrazine (Pt—AFO, 400°C —38% pyrazine)." ... 

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