ADDITION-REACTION OF PHENYLPHOSPHINES TO STYRENES AS THE MODEL OF POLYADDITION - STUDY ON THE RATE-DETERMINING STEP AND SUBSTITUENT EFFECT

The addition reactions of phenylphosphine or diphenylphosphine to styrenes or alpha-methylstyrene were carried out to know the reaction mechanism and the transition state of the addition reaction. Phenylphosphine having two reactive hydrogens added to two styrenes, and the 1:2 adduct [phiCH2CH2P(phi)CH2CH2phi] of the anti-Markownikoff's structure was obtained in a 94% yield. But, a little amount of the by-product containing styrene-styrene unit was produced as compared with the reaction of thiophenol to styrene. Such a side reaction was suppressed by using alpha-methylstyrene instead of styrene. The kinetics of the addition reaction of the P-H group to the vinyl group was investigated in detail by the addition reaction of diphenylphosphine to styrene, to give scarcely by-product. The rate-determining step of the reaction was the chain transfer step between the intermediate carbon radical (phiCHCH2Pphi2) and diphenylphosphine. In the para substituent effect of styrenes on the chain transfer step, fairly good linear correlation was obtained with modified Hammett's equation including the resonance effect. The rate-determining step and the substituent effect on this reaction were found to be similar to those of the addition reaction of thiophenol to styrenes. The results were also compared with the polyaddition of phenylphosphine to 1,4-vinylbenzene or 1,4-diisopropenylbenzene.