Epoxidation of limonene and pinenes by dimethyldioxirane in microemulsions

Terpene epoxides such as limonene dioxide are known as a very important intermediates for developing biological resins such as non-isocyanate polyurethanes. Recently, the dimethyldioxirane (DMDO) epoxidation technique has attracted attention and studies are being carried out to epoxidize terpenes. This study focuses on the epoxidation of hydrophobic terpene such as limonene and pinene by DMDO generated in-situ in a microemulsion system, examining the efficacy of cetyltrimethylammonium hydrogen sulfate (CTAHS) as a surfactant to homogenize the limonene and pinene in the aqueous reaction medium. The application of CTAHS showed a significant advantage for the epoxidation reaction. 100% limonene dioxide (LDO) and α-pinene oxide yields are obtained with molar ratios of only 1.6 for oxone/limonene and 0.9 for oxone/α-pinene respectively, after 30 min. The application of CTAHS resulted in a significant reduction in acetone content so that it just plays the role of a catalyst; Only an acetone/water volume ratio of up to 1:9 was sufficient to obtain these results. The reaction volume is therefore completely reduced and the amount of oxone required is almost 50% less than with the conventional biphasic organic solvent/water reaction medium. The separation of the epoxides from the aqueous medium and the surfactant (CTAHS) is easily done by liquid-liquid extraction. The main advantages of this technology are the use of acetone as a catalyst, which can be recycled indefinitely, the high selectivity of the epoxides without any by-products and the exclusion of the use of any organic solvent.