Aromatic acyl derivatives of 5-aminopentanoic acid, obtained by the Beckmann rearrangement of cyclopentanone oxime, when dry-distilled with soda lime, barium oxide, sodium amide, or zinc dust, afford a mixture of partially hydrogenated 2-arylpyridines, together with water vapor, ammonia, and inflammable gas. Dehydrogenation of this mixture easily affords 2-arylpyridine. Soda lime is the most effective condensation agent for 5-benzoylaminopentanoic acid (I) and the effect decreases in the order of zinc dust, sodium amide, and barium oxide. The yield also decreases in the respective order of 50%, 30%, 12%, and 3%, calculated as 2-phenyl-3, 4, 5, 6-tetrahydropyridine (II). Dehydrogenation of (II) could best be effected by heating with palladium black, in the presence of safrole, at 170-180° for 4-5 hours, from which 2-phenylpyridine (III) is obtained in 90-95% yield. The picrates of (II) and (III) do not show any depression of the melting point on admixture.
Dry-distillation of (I) affords a non-basic substance, in 7-8% of the starting material, and this consists of biphenyl, acetophenone, and benzonitrile.
Dry-distillation of 5-
o- and -
p-toluamidopentanoic acid with soda lime affords 2-tolyl-hydropyridine in 40% yield, whose dehydrogenation easily gives the corresponding 2-tolylpyridine.
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