Preparation of solid superacid catalyst Al2(SO4)3/ZrO2-TiO2 and its mechanism of borneol synthesis from pinene

Abstract

Natural borneol has enormous medicinal value (like clearing heat, detoxifying, relieving pain, and other effects) but has a low yield and high price. Compared with the natural extraction method to obtain borneol, a synthetic method has significant advantages such as high yield, environmental protection, and high economic benefits. In the synthesis method, the catalyst is the most key factor. In this study, two catalysts (SO₄^2-/ZrO₂-TiO₂ and Al₂(SO₄)₃/ZrO₂-TiO₂) with high catalytic performance and high positive selectivity were synthesized by impregnation method to synthesize borneol from α-pinene. The optimum synthesis conditions of SO₄^2-/ZrO₂-TiO₂ were as follows: n(Zr): n(Ti) = 3: 1, sulfuric acid concentration 2 mol/L, calcination temperature 550 °C, the yield of borneol was 68.14 %. Based on the preparation of catalyst SO₄^2-/ZrO₂-TiO₂, the optimum synthesis conditions of Al₂(SO₄)₃/ZrO₂-TiO₂ were as follows: the concentration of aluminum sulfate was 0.4 mol/L, the calcination temperature was 600 °C, and the yield of borneol was 74.58 %, Compared with the highest yield of 59.89 % reported in the existing literature, the performance is improved by 13.96 %. In addition, the mechanism of the esterification and saponification reaction of borneol has been in the blank stage. We used the density functional theory (DFT) to explore the reaction mechanism.