QUINOXALINES (Benzopyrazines), in organic chemistry, heterocyclic compounds containing a ring complex made up of a benzene ring and a pyrazine ring (formula I.) ; they are isomeric with the cinnolenes, phthalazines and quinazolines. They are formed by the condensing ortho-diamines with 1-2 diketones (Hinsberg, Ann., 1887, 237, p. 327), the parent substance of the group (quinoxaline) resulting when glyoxal is so condensed, whilst substitution derivatives arise when a-ketonic acids, a-chlorketones, a-aldehyde alcohols and o-ketone alcohols are used in place of diketones.

/NH 2 OC-R ,N:C-R C 6 H 4 / + | =C 6 H 4 / | +2H 2 0. N NH 2 OC-R' N N:C-R' In a similar manner, diamino derivatives are formed when cyanogen is condensed with ortho-diamines, and these amino compounds readily pass into the corresponding dioxy derivatives when acted upon with dilute hydrochloric acid.

The quinoxalines are weak bases, and are stable towards oxidizing agents but are readily reduced to hydro derivatives. The tetrahydroquinoxalines are formed by condensing ortho-diamines with ortho-dihydroxy benzenes, and the keto-dihydro derivatives arise similarly by condensing mono-alkyl diamines with ketonic acids (Kehrmann and Messinger, Ber., 1892, 25, pp. 1628 et seq.).

The azonium bases (formula II.) of this series are produced when the dihydroquinoxalines (obtained by similar condensations from the mono-alkyl-ortho-diamines) are oxidized with ferric chloride.

/N:C-R' C 6 H,< I \N:i-R' I. Quinoxaline. II. Azonium bases.

Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)

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