柠檬醛及中间体的合成

以异戊烯醛和异戊烯醇为原料,经异戊烯酸催化缩醛化反应得到3-甲基-2-丁烯醛二异戊烯基缩醛,再经磷酸二氢铵催化消除反应得到顺/反-异戊二烯基-3-甲基丁二烯醚,并进一步热重排获得柠檬醛。研究了缩醛化反应条件和消除反应条件对转化率的影响。结果表明,以0.3%异戊烯酸为酸性催化剂,70～75℃共沸脱水反应8 h,异戊烯醛的单程转化率达到63%～64%,处理后可得含量为97.5%的3-甲基-2-丁烯醛二异戊烯基缩醛,收率96.8%;以0.2%～0.5%磷酸二氢铵为催化剂,100～130℃,2.66 kPa下反应并及时将反应产物蒸出,处理后得到含量为95.9%的顺/反-异戊二烯基-3-甲基丁二烯醚,收率97.0%。顺/反-异戊二烯基-3-甲基丁二烯醚在120～130℃重排反应1 h,其反应产物柠檬醛含量97.5%,收率90.2%。

Synthesis of Citral and Its Intermediates

Using prenal and prenol as precursors,3-methyl-2-butenal diprenyl acetal was obtained via an acetalization reaction using senecioic acid as catalyst.Then an elimination of 3-methyl-2-butenal diprenyl acetal catalyzed by ammonium dihydrogen phosphate yielded the cis/trans-prenyl-3-methyl-butadienyl ether.Further rearrangement of the elimination product through heating produced to the target citral.The conditions of acetalization reaction and elimination reaction were optimized.It was found that a conversion yield of 63%～64% for prenal could be achieved at 70～75 ℃ for 8 h with 0.3% senecioic acid as catalyst.After azeotropism treatment,the purity and yield of 3-methyl-2-butenal diprenyl acetal are 97.5% and 96.8%,respectively.Using 0.2%～0.5% ammonium dihydrogen phosphate as catalyst,the elimination reaction was carried out at 100～130 ℃ and 2.66 kPa.The cis/trans-prenyl-3-methylbutadienyl ether was distilled from the reaction batch and its purity and yield are 95.9% and 97.0%,respectively.The rearrangement reaction temperature was 120～130 ℃,the purity and yield of citral are 97.5% and 90.2%,respectively.