草酸/聚乙二醇低温共熔体催化α-蒎烯水合反应

Hydration ofα-pinene catalyzed by oxalic acid/polyethylene glycol deep eutectic solvents

以天然有机二元羧酸草酸(OA)作为氢键供体,各种聚合度的聚乙二醇(PEG)作为氢键受体,构建出羧酸功能化低温共熔体(DES),将其用于催化α-蒎烯水合制备α-松油醇的反应中。傅里叶变换红外光谱(FT-IR)、核磁共振氢谱(1H NMR)、热重分析(TGA)等表征证实了OA与PEG之间氢键的形成。DES中PEG组分的存在对其酸强度影响较小,但随PEG分子量和用量的增加,DES总酸量减小,从而降低其催化活性。研究表明,分子量最小的PEG200与OA制备的OA/0.6PEG200 DES具有较佳的催化α-蒎烯水合反应性能,在DES催化剂用量0.03 mol(以OA计),α-蒎烯用量0.06 mol,水用量0.3 mol,反应温度75℃,反应时间8 h的优化条件下,获得81.5%的α-蒎烯转化率及51.2%的α-松油醇选择性。催化剂相反应结束后静置冷藏过夜即可分层分离,且循环使用性能良好。该OA/0.6PEG200低温共熔体制备简单,原子经济性高,为一步法催化α-松油醇的清洁制备开辟了新路线。

A series of carboxylic acid-functionalized deep eutectic solvents(DES)were constructed by a natural organic dicarboxylic acid,oxalic acid(OA),as the hydrogen bond donor and the polyethylene glycol(PEG)with different polymerization degrees as the hydrogen bond acceptors,which are used in the hydration ofα-pinene to produceα-terpineol.Fourier transform infrared spectroscopy(FT-IR),proton nuclear magnetic resonance spectroscopy(1H NMR),and thermogravimetric analysis(TGA)were used to prove the hydrogen bonding between OA and PEG.It is found that the presence of PEG has a less impact on the acid strength of DES.However,an increase in both molecular weight and dosage of PEG results in a decrease in total acidity and catalytic activity.Among them,OA/0.6PEG200,a DES catalyst prepared by PEG with the smallest molecular weight,exhibits a favorable catalytic performance.Under an optimal reaction condition with 0.03 mol of DES(based on OA),0.06 mol ofα-pinene,0.3 mol of water,at 75℃for 8 h,anα-pinene conversion of 81.5%and anα-terpineol selectivity of 51.2%are obtained.The catalyst phase can be separated by refrigerating overnight after reaction and reused directly with relatively stable catalytic performance.Thus,OA/0.6PEG200,as a DES catalyst prepared by a simple and highly atom economical process,will offer a clean catalytic route for the one-step production ofα-terpineol.