Époxydation du limonène
|Abstract:||Limonene has been highlighted as a key molecule for the development of bio-based polymers as an alternative to conventional monomers from petroleum sources, but the direct polymerization of this leads to low quality plastics. However, its epoxidation products such as 1,2-limonene oxide and limonene dioxide are essential to produce green polycarbonates and polyurethanes without the use of isocyanate, therefore the production of these two molecules becomes a major issue. First, the epoxidation of limonene was carried out using low coordination titanium catalyst supported on a SBA-16 mesoporous silica in the presence of TBHP in the decane as oxidizing agent. The conversion to limonene was 80% with a selectivity of 79% 1,2-oxide of limonene and 21% of 8,9-limonene oxide after 24 hours of reaction time. The reaction conditions were optimized, and the reaction should be carried out in the presence of 300 mg of the catalyst at 75 ° C in acetonitrile as solvent with a molar ratio TBHP / limonene of 11 / 6.2. However, the use of a titanium catalyst supported on a mesoporous silica has proved ineffective for the double epoxidation of limonene to limonene dioxide. Different alternatives have been considered in order to produce this molecule. A relatively green approach is to perform the double epoxydation under semi-continuous conditions using DMDO generated in situ by the reaction of acetone with an aqueous solution of Oxone® at room temperature. Two methods have been studied and compared. First, the reaction was carried out in a conventional biphasic water-organic solvent system phase at room temperature. Ethyl acetate was used as the organic phase. The conversion obtained under these conditions was 95% with a yield of 33% for limonene dioxide. When the same reaction was carried out in excess of acetone, the obtained conversion of limonene was 100% leading to 97% of limonene dioxide in only 1.5 hours. The conditions of the reaction have been optimized. The reaction must be carried out with a flow rate of Oxone® aqueous solution of 4 mL min-1 and a stoichiometric excess of 33% with a reaction time of 45 min at room temperature. On the other hand, the multiphasic nature of this reaction causes limitations in the mass transfer of DMDO from the aqueous phase to the acetone phase. Ultrasound has been used to accelerate the mass transfer. process of DMDO and thereby reduce the reaction time. The double epoxidation of limonene in the presence of ultrasound with a nominal power of 50W achieved a yield of 100% of limonene dioxide with a reaction time of only 4.5 min at room temperature. From these results, other terpenes have also been epoxidized to generalize the technique. Both isomers of pinene were converted to 100% in their respective epoxide in just 4 min. Farnesol, a tri-alkene, has been converted to 100% farnesol tri-epoxide in 8 min. Carveol, a derivative of limonene was converted to 100% after 5 min of reaction time. The diepoxide yield was higher than 95%. The by-products of the reaction consisted of both carveol monoepoxide and the presence of carvone was also detected. Carvone, another derivative of limonene, was also converted to 100% after 5 min of reaction time. Only 7,8-epoxide carvone, a monoepoxide, was produced.|
|Document Type:||Thèse de doctorat|
|Open Access Date:||24 January 2019|
|Collection:||Thèses et mémoires|
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