Vapour phase transesterification over modified ZrO₂-Al₂O₃ and ZrO₂-SiO₂for the synthesis of isoamyl salicylate

Abstract

Vapour phase transesterification of methyl salicylate with isoamyl alcohol in the presence of simple oxides, mixed oxides and their modified forms as catalysts was carried out. A systematic study was made with zirconia, alumina and silicaand the complete series of zirconia-alumina and zirconia-silica mixed oxides for 10-100% composition of zirconia, as well as the sulphate, phosphate and borate treated forms to identify the most suitable catalyst for this reaction.<b style=""> </b>All the catalysts used for the study exhibited catalytic activity for this transesterification reaction. The only side-product formed was phenol, apart from the primary byproduct methanol. The catalytic activity of zirconia, alumina and silica is in the range of 12 to 15%. There is a significant increase in the catalytic activity when these simple oxides are modified by sulphate, borate and phosphate ions. The trend in the increase in activity on modification is zirconia > alumina > silica. Among the anions, the trend in the increase in the activity is sulphate > phosphate > borate. However, the phosphated forms score over the sulphated forms for this reaction because (a) the activity of phosphated forms does not reduce with time on stream up to 2 h while there is a noticeable reduction in the catalytic activity of sulphated forms within 15 minutes from the start of the reaction and (b) there is no coke formation when the phosphated forms are used while sulphated forms lead to excessive coke formation and loss of reactants. The mixed oxide ZrO₂-Al₂O₃ of 20% ZrO₂ composition modified with phosphate ions is found to be the most suitable catalyst for this reaction.