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 styr enes or alpha-methylstyrene were carried out to know the reaction mech anism and the transition state of the addition reaction. Phenylphosphi ne having two reactive hydrogens added to two styrenes, and the 1:2 ad duct [phiCH2CH2P(phi)CH2CH2phi] of the anti-Markownikoff's structure w as obtained in a 94% yield. But, a little amount of the by-product con taining styrene-styrene unit was produced as compared with the reactio n of thiophenol to styrene. Such a side reaction was suppressed by usi ng alpha-methylstyrene instead of styrene. The kinetics of the additio n reaction of the P-H group to the vinyl group was investigated in det ail 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 (phiCHCH2 Pphi2) and diphenylphosphine. In the para substituent effect of styren es on the chain transfer step, fairly good linear correlation was obta ined 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 thiophen ol to styrenes. The results were also compared with the polyaddition o f phenylphosphine to 1,4-vinylbenzene or 1,4-diisopropenylbenzene.