The catalytic dimerization of acrylonitrile .2. Activity and selectivity of homogeneous catalysts derived from substituted aromatic phosphinites and phosphonites

The incorporation of electron-releasing substituents into the para-positions of alkyl diarylphosphinites, Ar(2)POR, and dialkyl arylphosphonites, ArP(OR)(2), causes a marked increase in the rate of reaction compared with that of the unsubstituted derivatives in the catalysis of the linear dimerization of acrylonitrile in toluene/alcohol solution. The magnitude of the effect is approximately proportional to the electron-releasing capability of the substituent, This enhancement in rate is offset by an associated reduction in the selectivity to the desired linear dimer. However, optimisation of reaction conditions provides a satisfactory combination of rate and selectivity. In contrast, when electron-withdrawing substituents are incorporated into the ortho position of the aryl ring, there are distinct disadvantages in that the rate of dimerization is significantly reduced and the selectivity to the linear dimer is unacceptably low. The most promising catalysts, from both rate of reaction and selectivity considerations, are the bis-p-tolylphosphinite, (p-MeC(6)H(4))(2)POPri, the mixed phenyl p-methoxyphenylphosphinite, (p-MeOC(6)H(4))PhPOPr(i) at 60 degrees C, and the bis-p-methoxyphenylphosphinite, (p-MeOC(6)H(4))(2)POPri at 20 degrees C.