Effects of the properties of SO4/ZrO2 solid catalysts on the products of transformation and reaction mechanism of R-(+)-limonene diepoxides

Transformations of limonene diepoxides on solid SO4/ZrO2 catalysts in dried methylene chloride at room temperature were investigated by varying the amounts of supported sulfate ions and zirconia polymorphs. A method for estimating acid centers from DRIFTS spectra of adsorbed pyridine on the solid catalyst in a dried methylene chloride solution has been developed. It is shown that the mechanism of diepoxide transformations is changed by varying the type and amount of acid centers. At a 0.9–3% level of sulfation, Lewis centers are mainly responsible for the initial cleavage of the 8,9-epoxy group of limonene diepoxides (route B). At higher contents of sulfate ions (up to 30 wt.% SO4), the key transformations proceed with cleavage of the 1,2-epoxy group (route A) and involve the Brønsted centers. The type of support affects the structural features of the sulfate ions, which govern the rearrangement of limonene diepoxides by route A or B. Transformation of limonene diepoxides on the Lewis centers formed on sulfated alumina follows mainly route A. The type of acid centers also affects the stereochemical composition of the product mixture.

The mechanism of diepoxide transformations at room temperature may be changed by varying the type and amount of acid centers on SO4/ZrO2. At a sulfation level of 0.9–3%, the products of the initial cleavage of the 8,9-epoxy group of limonene diepoxides were dominant. When the sulfo group content increased to more than 9%, the key transformations were those that started with cleavage of the 1,2-epoxy group. Figure optionsDownload as PowerPoint slide