Synthesis And Antimicrobial Activity Of Long-Chian Esters Of P-hydroxybenzoic Acid

The esters of p-hydroxybenzoate (parabens) were low toxic, nonirritant, and effective in the wider pH range and have been widely used as antimicrobial preservatives.(1)The long-chian esters of p-hydroxybenzoic acid, such as heptyl ester of p-hydroxybenzoic acid, octyl ester of p-hydroxybenzoic acid, undecyl ester of p-hydroxybenzoic acid and lauryl ester of p-hydroxybenzoic acid, were synthesized by a direct esterification from 1-heptyl alcohol (1-octyl alcohol,1-undecyl alcohol,1-laurl alcohol), p-hydroxybenzoic acid and p-toluenesulfonic acid or Solid superacid as catalyst in benzene.(2) In this paper, three kinds of optimality condition were used in the catalyst reaction and after the comparison of the optimalized reaction conditions, we got to know as follows:The yields of all kinds of the esters of p-hydroxybenzoate were different. The optimum condictions for the reaction as follow. The temperacture of reactions was identical and it was 130～140℃. The time of reactions was also identica and it was 4 h. The alcohol and p-hydroxybenzoic acid in the mole ractio of reactions was different, such as 3:1,5:1,4:1. The quality of catalyst was also different, such as p-toluenesulfonic acid and p-hydroxybenzoic acid in the ratio 8.7%, solid superacid and p-hydroxybenzoic acid in the ratio of 3%.(3) The yields rate of a series of Paraben rised together with the rising number of atom of carbon in R-group, regardless of whether p-toluenesulfonic acid or solid super acid (SO42-/TiO2 andSO42-/Fe2O3) was used as catalysts. The same was to the effect of recrystalization. The variation of melting point was irregular and IR spectrum was normal. In addition, employing the super acid as catalyst had low pollution and the post treatment of reaction solution is simple.(4) The antimicrobial of long-chian esters of p-hydroxybenzoic acid were investigated by measuring the size of inhibition zone and the minimum inhibitory concentration (MIC). The experimental results showed that the antimicrobial capability would increase with the increasing of the number of carbons in R-group. They were able to eliminate most common putrefactive microorganisms, most effective on gram-positive bacteria, followed by yeast and fungi, while relatively weak on gram-negative bacteria. Among p-hydroxybenzoates investigated in this study, heptyl and octyl p-hydroxybenzoate have demonstrated the most effective inhibitions on yeast and fungi.