Reaction mechanism of salicylic acid from methyl salicylate
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Abstract
The esterification of salicylic acid (SA) using dimethyl carbonate (DMC) is reported for the first time. The reaction is studied in detail over zeolites Hβ, HZSM5 and HY in the temperature region 370–425 K in an autoclave under autogenous pressure. The molar ratio of SA to DMC, the reaction period and the weight of zeolite catalysts are varied. The SA conversion is over 90% for both Hβ and HZSM5 at 423 K. HY is not as effective a catalyst as the other two. Irrespective of the conversion levels the selectivity towards methyl salicylate is greater than 95%. A comparative study on the esterifying ability of DMC and methanol is reported. From the kinetic data, the energy of activation (Ea) for the esterification reaction using DMC over Hβ and HZSM5 is calculated to be 25 and 36 kcal/mol, respectively. A reaction mechanism for the esterification of SA with DMC over zeolites is proposed.