Esterification of oxidized ricinoleic acid with various alcohols to produce emulsifier and antimicrobial compounds

This study's objective was to synthesize esters of ricinoleic oxidation product. The esterification products were expected may act as emulsifiers and to have antimicrobial activity against Staphylococcus epidermidis and Propionibacterium acnes. Before esterified, ricinoleic acid was oxidized by KMnO₄. The success of the oxidation reaction was proven by determining iodine number. Esterification was carried out using ZnCl₂ as catalyst with various alcohols, namely methanol, ethanol, isopropanol, and 1-butanol. Mole ratio fatty acid to alcohol used in esterification was 1: 2. The ester products were characterized using FTIR and the conversion percentage were determined by titrimetric method. Emulsifier test also performed to determine the ability of ester product as emulsifier. The success of oxidation was proven by decreasing iodine number from 44.05 mg/g to 17.15 mg/g and increasing absorption intensity -OH group in FTIR spectrum. FTIR spectrum of ester products showed the presence of absorption of C = O ester groups at 1750-1735 cm^-1 and C-O-C at 1300-1000 cm^-1 which proved the success of esterification. Emulsifier test showed that esterification products can act as emulsifiers and the emulsions formed were stable up to 24 hours for water-in-oil emulsion (w/o). The best ability as an emulsifier was shown by methyl esters. Antimicrobial assay showed that all esters can inhibit the growth both bacteria, P. acnes and S. epidermidis. The largest inhibition zone obtained for butyl ester against P. acnes by 17 mm and methyl ester against S. epidermidis by 17 mm.