Acid-catalysed rearrangement of fatty epoxides:perspectives in application of acid saponites

The ring opening of epoxidized fatty acid derivatives is a valuable transformation for the production of compounds functionalized on the alkyl chain. Rearranged epoxides could find applications as precursors of biopolymers, lubricants, polyurethane foams and casting resins.
A two-step process, starting from fatty acid methyl esters and based uniquely on heterogeneous and easily recoverable catalysts, is here proposed. The FAME methyl oleate is epoxidized in liquid phase with tert-butylhydroperoxide in batch reactor over Ti-grafted MCM-41. The transformation is optimized and the conversion attains >90% after 24 h, with selectivity >95% to methyl 9,10-epoxystearate. After separation of the organic product from the solid Ti-catalyst, the ring opening of the epoxidized fatty ester is performed in the presence of a protonic acidic saponite clay, obtained by exchanging a synthetic Na+ saponite in aqueous HCl solutions at different concentrations. The catalytic results for the nucleophilic addition of methanol to methyl epoxystearate show the good performance of different acid saponites in terms of activity. The saponite catalysts were also compared with other widely used heterogeneous systems, such as mesoporous ordered aluminosilicate Al-SBA-15 and a protonic Beta zeolite (H-BEA). Protonic saponites showed better results than H2SO4 too (0.45 mmol g-1), the typical industrial catalyst for this reaction.
The best result is obtained over the protonic saponite prepared with a mild pretreatment (ion exchange in aq. 0.01 M HCl): with methanol, after 5 min, 90% of the epoxide is readily converted into Me-methoxyhydroxystearate and Me-oxostearate.