酸催化甘油与苯甲醛缩合制备六元环缩醛

Acid-Catalyzed Synthesis of Six-Membered Cyclic Acetal from Condensation of Benzaldehyde and Glycerol

比较了对甲苯磺酸(PTSA)、磷钨酸(PWA)、KHSO4和FeCl3催化对甘油与苯甲醛的缩合反应收率,及对产物中六元环缩醛5-羟基-2-苯基-1,3-二氧六环(1)与五元环缩醛4-羟甲基-2-苯基-1,3-二氧五环(2)比例的影响。当以环己烷为带水剂及苯甲醛与甘油的摩尔比为2∶3的情况下,KHSO4为催化剂的缩合产物(1+2)收率较高,为96.8%;PTSA催化的缩合产物中,化合物1的比例最高(m(1)∶m(2)=48.6∶51.4)。室温下PTSA、PWA、KHSO4和FeCl3均可催化化合物2向化合物1的转化。在-20℃下,只有PTSA能催化化合物2向化合物1的转化。在-20℃,PTSA催化化合物2转化成化合物1a,并以晶体形式从苯(40%)-石油醚(60%)中析出。母液循环转化3次后,化合物1a的累计收率可达91.1%。

Based on the condensation reaction of glycerol with benzaldehyde,the effects of acid catalysts （ p-toluenesulfonic acid（ PTSA） ,phosphotungstic acid（ PWA） ,KHSO4 and FeCl3,respectively） on the yield of the condensation products and the mass ratio of 5-hydroxyl-2-phenyl-1,3-dioxane（ 1） to 4-hydroxymethyl-2-phenyl-1,3-dioxolane （ 2 ） were investigated. Comparison tests indicated that under the conditions of cyclohexane as water entrainer and n （ benzalhydehyde） ∶ n （ glycerol） = 2 ∶ 3,KHSO4 gave the best yield （ 96. 8%） of condensation products（ compound 1 ＋ 2） and PTSA yielded the highest proportion（ m（ 1） ∶ m（ 2） = 48. 6 ∶ 51. 4） of compound 1 in condensation products（ compound 1 ＋ 2）. At room temperature,PTSA,PWA,KHSO4 and FeCl3 all can,but at -20 ℃,only PTSA can catalyze the transformation of compound 2 to compound 1. Cis-5-hydroxyl-2-phenyl-1,3-dioxane （ 1a ） was isolated by the catalytic transformation of compound 2 with PTSA at-20 ℃ and crystallized from a mixture of V （ benzene） ∶ V（ ligroin） = 40∶60. Compound 1a was obtained by recycling the catalytic transformation of compound 2 in the mother liquor three times in a accumulative yield of 91. 1%.