Acrylonitrile dimerization process

In a process for dimerizing acrylonitrile to obtain 1,4-dicyanobutenes, said process comprising dissolving acrylonitrile in an organic solvent capable of donating protons but substantially unreactive with respect to acrylonitrile and organic phosphorus (III) compounds;

• contacting the acrylonitrile with an organic phosphorus (III) catalyst compound at a temperature from 0.degree. to 120.degree. C. under substantially anhydrous conditions;
• the improvement characterized in that:
• (a) the catalyst is represented by the formula:
• ##STR3## wherein n is 1 or 2;
• R.sub.1 and R.sub.2 are each hydrogen, alkyl, aryl, cycloalkyl or heteroatom containing substituents;
• R.sub.3 is alkyl, cycloalky or aryl;
• and aryl moieties constitute at least 25% by weight of the catalyst
• (b) the catalyst constitutes 16% to 90% by weight of the reaction mixture and at least 28% of the volume of any co-solvent present, and
• (c) the rate constant is higher than obtained with an otherwise identical reaction mixture containing less than 16% by weight catalyst under identical conditions.