Preparation of 1-pyrazolines

A process for the preparation of a 1-pyrazoline of the formula I ##STR3## by oxidation of a 1,3-diaminopropane of the formula II in a reaction vessel ##STR4## where R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and R.sup.6 independently of one another are each hydrogen or alkyl of 1 to 3 carbon atoms, or two of the stated radicals which are bonded to the same carbon atom or to two adjacent carbon atoms together form an alkylene radical of 3 to 5 carbon atoms, in aqueous solution, which process comprises:

• simultaneously passing into said vessel a 10-30% strength solution of the diamine, an aqueous solution of hypochlorite containing from 5 to 22% by weight of hypochlorite ions and a 20-50% strength by weight aqueous solution of an oxidizing agent of the formula III
• R.sup.3 --O--O--H III
• where R.sup.3 is hydrogen, alkyl of 1 to 5 carbon atoms or an aliphatic acyl radical of 2 to 5 carbon atoms, in a molar ratio of hypochlorite to III of from 0.5:1 to 1.5:1, while stirring, and care is taken to ensure that the reaction temperature does not exceed 60.degree. C., and as soon as possible after complete conversion of the diamine the resulting pyrazoline is extracted at room temperature with a hydrophobic organic solvent which dissolves pyrazoline, and is distilled under reduced pressure at below 100.degree. C.