Pt/Al2O3 catalysts in the synthesis of nitrogen heterocycles. Catalytic synthesis of pyrazines

A study was carried out on the use of Pt/Al₂O₂ catalysts in the synthesis of pyrazines via the dehydrogenation of piperazines, dehydrodeamination of diamines, and dehydrocyclocondensation of N-hydroxyalkyldiamines. In contrast to the current hypothesis of the intermediate formation of piperazine in the latter two reactions, evidence was found that these reactions proceed through initial dehydrogenation and the dehydrogenated intermediate then undergoes cyclization. Polyalkylpyrazines, formed by the alkylotion of the pyrazine ring by hydrogenolysis products, are the major side-products in all the reactions studied. Pyrazines may be obtained in high yield and satisfactory selectivity by selecting suitable modifiers, which enhance the dehydrogenation activity of the catalyst and suppress the hydrogenolysis of the C-N bond.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1516–1525, November, 1993.