Studies of Pyrazines, I. Pyrolyses of Substituted Pyrazines and Their Thermal Stabilities

The pyrolyses and thermal stabilities of 2,5-dialkylpyrazines (1a–e), 2,5-diethoxypyrazine (2), chloropyrazine (3), alkoxypyrazines (4a–c), alkylthiopyrazines (5a, b), and alkylaminopyrazines (6a–d) were studied by means of a mass spectrometer, by which the pyrolysates in the sample reservoir were analyzed. The temperature dependence of the molecular ions and/or fragment ions was also discussed. The thermal dehydrogenation from two α-methine groups makes the 1d molecule thermally sensitive. The other 2,5-dibutylpyrazines were more stable than it, except for the t-butyl derivative, 1e. Hydroxy- and aminopyrazine, 4a and 6a, were very stable. The alkoxypyrazines, 4b and 4c, and alkylthiopyrazines, 5, underwent the thermal elimination of olefine to yield hydroxy- and mercaptopyrazine respectively. The latter disproportionated to form dipyrazinyl sulfide (11). At 280 °C, no analogous reactions of alkylaminopyrazines 6b–d could be observed. The relative thermal stabilities of the compounds were as follows: 2, ...