Preparation of 2-ethyl-3-methyl-1,4-diazine, useful as aroma, e.g. in food, involves reacting pentan-2,3-dione and ethan-1,2-diamine in aliphatic diol or triol containing alkaline salt, and catalytic dehydrogenation

摘要

In the preparation of 2-ethyl-3-methyl-1,4-diazine (I) by reacting pentan-2,3-dione and ethan-1,2-diamine in organic solvent (III) and catalytic dehydrogenation, (III) is a 3-5C aliphatic diol or triol containing an alkaline salt. The reaction mixture can be dripped directly into a solution of alkali hydroxide and (supported) sub-group 8 catalyst in (III) at 70-180 deg C. The product is separated by steam distillation. Preparation of 2-ethyl-3-methyl-1,4-diazine (I) involves (1) reacting pentan-2,3-dione (II) and ethan-1,2-diamine in (0.1-2):1 molar ratio in an organic solvent (III) at -30 to 60 deg C and (2) catalytic dehydrogenation of the resultant dihydropyrazine. The novel features are that (a) (III) is a 3-5 carbon (C) aliphatic diol or triol containing 0.001-5 wt.% alkaline salt with respect to (II); (b) the reaction mixture can be dripped directly into a solution of alkali hydroxide (IV) and a (supported) catalytic sub-group 8 element in (III) at 70-180 deg C; (c) the amount of (IV) is 0.2-3 molar equivalents with respect to (II) and the amount of catalyst 0.001-0.5 wt.% with respect to the amount of reaction mixture in stage (1); and (d) the product is separated by steam distillation.