Vapour phase transesterification over solid acids for the synthesis of isoamyl salicylate

Abstract

The transesterification of methyl salicylate with isoamyl alcohol has been studied in vapour phase over solid acid catalysts for the synthesis of isoamyl salicylate. The catalysts used include simple oxides — Al₂O₃, SiO₂, ZrO₂ and mixed oxides ZrO₂-Al₂O₃ and ZrO₂-SiO₂. The effect of sulphation on the catalytic activity of the oxides and mixed oxides has also been investigated for this reaction. Catalytic activity studies have been conducted at 200^oC for two different flow rates, 5 and 10 mL/h to check the effect of the contact time of the reactants with the catalyst. All the catalysts used in the reaction have been found to be active for the formation of isoamyl salicylate via transesterification of methyl salicylate with isoamyl alcohol. SO₄²/ZrO₂-SiO₂ (2:8) has been found to be the most active catalyst with 63% conversion of methyl salicylate to isoamyl salicylate. SO₄^2-/ZrO₂, which exhibited good selectivity was chosen as the catalyst for optimisation of the reaction conditions to obtain better yield and higher selectivity of isoamyl salicylate. Optimum yield of isoamyl salicylate was obtained with the following reaction conditions: amount of catalyst = 0.5 g, calcination temperature = 550^oC, reaction temperature = 200 ^oC, preheater temperature = 250 ^oC, molar ratio of methyl salicylate to isoamyl alcohol = 1:1.