Preparation of .alpha.,.beta.-diaminoacrylonitriles

A process for the preparation of an .alpha.,.beta.-diaminoacrylonitrile of the formula

• R.sup.3 R.sup.2 NC(R.sup.1).dbd.C(NR.sup.2 R.sup.3)CN I
• where R.sup.1, R.sup.2 and R.sup.3 are identical or different and independently of one another are each hydrogen or an organic group selected from the class consisting of alkyl, cycloalkyl, aralkyl of 7 to 12 carbon atoms or phenyl, each of said organic groups being unsubstituted or substituted by an inert group selected from the class consisting of nitro and alkoxy, and the organic radicals R.sup.2 may furthermore be bonded to one another to form a 6-membered or 7-membered heterocyclic ring, or R.sup.2 and R.sup.3 may be bonded to one another to form a 5-membered or 6-membered heterocyclic ring, which process comprises reacting in any sequence the component (A) with the components (B), (C) and (D) as follows:
• (A) an .alpha.-dicarbonyl compound of the formula R.sup.1 COCHO, where R.sup.1 has the above meanings, or a derivative which is converted to this carbonyl compound under the reaction conditions,
• (B) a salt of sulfurous acid or sulfur dioxide or a donor reagent which liberates sulfur dioxide under the reaction conditions,
• (C) an amine of the formula HNR.sup.2 R.sup.3, or an aliphatic diamine of the formula R.sup.3 HN--(CH.sub.2).sub.n 13 NHR.sup.3, where the alkylene chain may carry a further substituent R.sup.1, R.sup.1 and R.sup.3 having the above meanings and n being 2 or 3, or a derivative which is converted to such amine or diamine under the reaction conditions, and
• (D) liquid or gaseous hydrocyanic acid or a donor reagent which liberates hydrocyanic acid under the reaction conditions.