在Br(o)nsted酸性功能化离子液体中室温无溶剂合成长链脂肪酸甲酯

该文以N-甲基咪唑、苄基氯、硫酸、氯磺酸为原料,经季铵化、离子交换、磺化3步反应合成了磺酸型Br(o)nsted 酸性离子液体:1-(4-磺酸基苄基)-3-甲基-咪唑硫酸氢根盐,通过FTIR、1HNMR对其结构进行了确证.以其作为反应介质与催化剂,考察了C4～C16的直链脂肪酸与甲醇的Fischer酯化反应,确定了最佳反应条件:n(酸):n(醇):n(离子液体)=1:1:0.1,反应温度25 ℃、反应时间3～4.5 h,产率84%～98%,产物气相色谱纯度≥96%.该法无需加热、分水,产物分离简便,离子液体经真空除水后可重复使用,循环使用3次,催化活性保持不变.

Solvent-free Synthesis of Long Chain Aliphatic Acid Methyl Esters in Br(o)nsted Acidic Ionic Liquids at Room Temperature

SO_3H-functionalized Br(o)nsted acidic ionic liquid:1-(4-sulfonic benzyl)-3-methyl-imidazolium hydrogen sulfate was synthesized and characterized.The synthesis of these ionic liquids by using N-methylimidazole,benzyl chloride,sulphuric acid,chlorosulfonic acid as the starting material via quaternarization,ion-exchange,and sulfonation reaction,their structures were confirmed by IR and 1HNMR.It was investigated that these ionic liquids could act as reaction media and the catalyst for the Fischer esterification of the long chain aliphatic acids with methanol.The optimum reaction conditions were:n(acids):n(methol):n(ionic liquids)=1:1:0.1,reaction temperature 25 ℃,reaction time 3～4.5 h,the isolated yields 84%～98%.This approach has advantages such as:it can be carried out smoothly at room temperature under solvent-free conditions,without heating and separating water,esters can be separated easily and high yields.The ionic liquid could be recovered easily and recycled three times without any significant loss in catalytic activity.