HIGHLY SELECTIVE MONOACYLATION OF SYMMETRICAL DIOLS CATALYZED BY METAL SULFATES SUPPORTED ON SILICA-GEL

Several 1,n-diols, ranging from 1,2-ethanediol to 1,16-hexadecanediol, were monoacylated with high selectivity by reaction with esters in the presence of metal sulfates or hydrogen sulfates, like Ce(SO4)2 and NaHSO4, supported on silica gel. Symmetrical secondary diols were also selectively monoformylated, by reaction with ethyl formate. This method of selective esterification is simple and practical. The yield of monoester depends upon both the composition and the volume of the solvent (an ester/alkane mixture). Unsupported NaHSO4 also catalyzed monoacylation, but the selectivity was less than in monoacylations catalyzed by the supported reagent. The selectivity can be explained by the following reasons: (1) monoacylated products are formed selectively because the diol, but not the monoester, is preferentially adsorbed on the surface of the catalysts, where esterification then occurs, and (2) thin diol layers are formed on the surface of the catalysts due to limited solubility of the diols in the solvent.