Br?nsted酸性离子液体催化缩醛化反应合成聚甲氧基二烷基醚

聚甲氧基二烷基醚(RO(CH2O)nR)具有高的十六烷值(CN)和含氧量,能显著改善柴油的燃烧特性,有效提高热效率,大幅减少碳烟和NOx排放,被认为是一种优良的环保型燃油组分.随着–R基碳链的增长,CN值、热值和闪点逐渐增大,密度和冷凝点逐渐降低.同时,该类化合物具有优异的溶解及渗透性能,能与许多有机溶剂互溶,低毒,可以用作溶剂或颜料分散剂.近年来,聚甲氧基二甲基醚(CH3O(CH2O)nCH3,PODEn,DMMn)的制备及应用研究受到广泛关注,而对封端基团(–R)碳数大于1的多醚类化合物的研究鲜有文献报道.本文以Br?nsted酸性离子液体为催化剂,对甲醛和二乙氧基甲烷或脂肪醇(碳数 ≥2)缩醛化反应制备聚甲氧基二烷基醚的反应性能进行了研究,考察了离子液体结构和酸性对其催化性能的影响.结果表明,–SO3H功能化的离子液体MIMBs]HSO4在催化三聚甲醛与二乙氧基甲烷的缩醛化反应中表现出最好的催化活性.考察了催化剂用量、原料配比、反应温度、反应压力和反应时间等因素对反应性能的影响,并得到了最佳反应条件,在n(MIMBs]HSO4):n(DEM1):n(HCHO)=1:80:80,140°C下反应4 h,甲醛转化率达到了92.6%,DEM2–8选择性为95.1%.考察了不同甲醛源(三聚甲醛和多聚甲醛)与提供封端基团化合物(二乙氧基甲烷、乙醇、丙醇和丁醇)的缩醛化反应.结果发现,在反应过程中不生成水或不引入水的条件下,具有更高的反应转化率和产物选择性.分别采用静置分层和萃取实现了催化剂的分离与重复使用.推测反应机理认为,三聚甲醛首先在氢键作用下分解生成甲醛单体,甲醛和二乙氧基甲烷通过碳正离子反应机理实现了DEMn的链增长.

Br?nsted-acidic ionic liquids as efficient catalysts for the synthesis of polyoxymethylene dialkyl ethers

Acetalation of formaldehyde (HCHO) with dialkyl formal or aliphatic alcohol to prepare polyox-ymethylene dialkyl ethers (RO(CH2O)nR, n ≥ 1) catalyzed by Br?nsted-acidic ionic liquids has been developed. The correlation between the structure and acidity activity of various ionic liquids was studied. Among the ionic liquids investigated, 1-(4-sulfonic acid)butyl-3-methylimidazolium hy-drogen sulfate (MIMBs]HSO4) exhibited the best catalytic performance in the reaction of diethox-ymethane (DEM1) with trioxane. The influences of ionic liquid loading, molar ratio of DEM1 to HCHO, reaction temperature, pressure, time, and reactant source on the catalytic reaction were explored using MIMBs]HSO4 as the catalyst. Under the optimal conditions of n(MIMBs]HSO4):n(DEM1):n(HCHO) = 1:80:80, 140 °C, and 4 h, the conversion of HCHO and selec-tivity for DEM2?8 were 92.6% and 95.1%, respectively. The MIMBs]HSO4 catalyst could be easily separated and reused. A feasible mechanism for the catalytic performance of MIMBs]HSO4 was proposed.