Metilasi Asam Galat Menggunakan Agen Metilasi Dimetil Sulfat (DMS) atau Dimetil Karbonat (DMC)

Abstract

Methylation of gallic acid has been conducted by the use of dimethyl sulfate (DMS) or dimethyl carbonate (DMC)  as methylating agents. Methylation of gallic acid using DMS was carried out by various methods, i.e. mild condition at ambient temperature, reflux and sonication. The best method was achieved by methylation under reflux yielded 48.9% efficiency of 3,4,5-trimethoxybenzoic acid.

            Methylation of gallic acid with DMC was performed with several variations on the type and amount of base and phase transfer catalyst (PTC). In addition, green methods sonochemistry and microwave irradiation have also been done. Unfortunately, the methylation of gallic acid failed to give 3,4,5-trimethoxybenzoic acid. Methylation of gallic acid using green reagent DMC gave high yield at mole ratio of gallic acid : DMC : K₂CO₃ : KI : PTC of tetrabuthyl ammonium bromide (TBAB) = 5 : 320 : 20 : 5 : 8 under reflux for 10 hours and produced 75.96% of methyl 3,4,5-trimethoxybenzoate. Atom economy of gallic acid methylation method using DMC is 37.95%, which is not very different from that of DMS method (30.47%). However, the methylation method using DMC produced by products, which  have the lower toxicity compared to that of methylation using DMS.