Alkoxylation of terpenes over tungstophosphoric acid immobilized on silica

Abstract

The alkoxylation of -pinene, -pinene and limonene with Cl-C4 alcohols (methanol, ethanol, 1-propanol and 1-buthanol) to -terpinyl alkyl ether was carried out in the presence of silica-occluded tungstophosphoric acid (PW@S) in liquid phase. Different linear and branched alcohols (C1 to C4 alcohols) are compared in relation to their activity for the heterogeneously catalysed alkoxylation of alpha-pinene. The PW@S material was an efficient, environmentally friendly heterogeneous catalyst for the liquid-phase alkoxylation of -pinene, -pinene and limonene into their more valuable ethers (-terpinyl alkyl ether), which are used as in perfume and cosmetic products, as in the pharmaceutical industry, as well as in the food industry for organic synthesis. The catalytic activity decreased with the increase of chain length of the linear alcohols, in the alkoxylation of -pinene, -pinene and limonene, which can be explained due to the presence of sterical hindrance and diffusion limitations inside the porous system of PW@S. The reactivity of the terpenes increases as follows: limonene <-pinene < -pinene. This behaviour can be explained due to the limonene to be a higher stability than the -pinene and -pinene. The pinenes have the angle strain of cyclobutane ring that make them more reactive than limonene. A decrease of the PW@S selectivity to the -terpinyl alkyl ether with the increase of chain length of the alcohols was observed. The catalyst (PW@S) can be easily recovered and reused.