Synthesis and Characterization of Silica Sulphonic Acid from Rice Husk Ash and it use in the Synthesis of 4-Methylcoumarin Derivatives

Abstract

In this work, Rice Husk Ash Silica sulphonic acid materials(RHA-SO3H and RHA-SiO2/SO3H) were synthesized at ambient conditions from direct reaction of chlorosulphonic acid and RHA sodium silicate or post reaction of RHA silica(RHA-SiO2)and chlorosulphonic acid, respectively. The two materials were characterized by FT-IR spectroscopy and conventional volumetric acidity measurement. The FT-IR indicated the successful incorporation of sulphonic species to the silicate surface of both materials, but with higher extent in the silicate of post-modified method(RHA-SiO2/SO3H). This was further evident through acidity measurement and the results showed that the post-modified material exhibited , extremely, higher Bronsted acidity over the directly-modified material(RHA-SO3H). Synthesized RHA-SiO2/SO3H solid acid material was used to catalyze the synthesis of 4-methyl coumarin derivatives via Pechmann condensation reaction of phenols and ethylacetoacetate(EAA).Various reaction parameters were studied for the production of high yields of coumarin derivatives which include molar ratio, type of phenol, catalyst loading, reaction time and re-usability . Optimum yield of 99 % coumarin was obtained when conducting the reaction between resorcinol and EAA with molar ratio of 1:2 at 80 °C for one hour using 0.1 g of the synthesized catalyst. Moreover, RHA-SiO2/SO3H catalyst was found reusable for this reaction several times without any significant changes in its catalytic performance.