Hammett Type Relationsphip for the Catalytic Effect of Metal Compounds on the Model Reaction of the Formation of Poly(ethylene terephthalate)

Abstract

Catalytic effect of some metal compounds on the transesterification of p-substituted methyI benzoate(MB)with ethylene glycol(EG)was investigatead in order to elucidate the characteristic of the catalytic effect of metal compound on the transesterification of dimethyl terephthalate with EG.
The transesterification of P-substituted MB with EG was carried out at 150C, and the quantity of formed methahol was observed Acetate of Ca, Mn, . Zn or Al was used as a catalyst. Dimethylbenzylamine was also used as a catalyst for comparison.
The rate constants of the tfansesterification with above catalysts were calculated.
It was found that the Hammett equation can fairly be apPlied for each catalyst, and p value was positive n all cases. Furthermore, it was found thatpvalue varies markedly. with a kind of catalyst, is the highest in the case of dimethylbenzylamine and decreases in the following order dimethylbenzylamine Ca acetate Mn acetate Zn acetat6e Al acetate.. This tedency may closely be related to the Lewis acid strengthy of the catalyst p value decreases with increasing Lewls acid strength of the catalyst.
Above result suggests that the effect of p-substituents becomes feebIe because a catalyst of metal compound acts as Lewis acid, and that the catalytic effect of the metal compound is the same as that due to an electron withdrawing substituent.