Ultrasonic and Catalyst-Free Epoxidation of Limonene and Other Terpenes Using Dimethyl Dioxirane in Semibatch Conditions

Limonene dioxide is a key intermediate molecule for the development of biobased polycarbonates or nonisocyanate polyurethanes. In this work the epoxidation of limonene to limonene dioxide using in-situ-generated dimethyl dioxirane as the oxidizing agent under both conventional agitation and ultrasound has been compared. The time required to completely convert limonene to limonene dioxide with 100% yield using ultrasound was only 4.5 min at room temperature. In comparison, when conventional agitation using a magnetic stirrer is used, the required time to reach a 97% yield of limonene dioxide was 1.5 h. The epoxidation of α-pinene has also been studied using both agitation techniques. Epoxidation of α-pinene to α-pinene oxide under ultrasound required only 4 min with an obtained yield of 100%, while in comparison with the conventional method the reaction time was 60 min. As for other terpenes, β-pinene was converted to β-pinene oxide in only 4 min whereas farnesol yielded 100% of the triepoxide in 8 min. Carveol, a limonene derivative, was converted to carveol dioxide with a yield of 98%. In the epoxidation reaction of carvone using dimethyl dioxirane the conversion was 100% in 5 min, but only 7,8-carvone oxide was produced.