4-乙酰氧基-2-甲基-2-丁烯醛合成新工艺

New Process for the Synthesis of 4-acetoxy-2-methyl-2-butenal

研究了异戊二烯经与次氯酸加成、乙酸酐酯化和氧化三步反应合成4-乙酰氧基-2-甲基-2-丁烯醛的新工艺,总收率达到65%.用CO2控制异戊二烯-氯碱溶液体系的PH值,在加成反应温度0～5℃,反应时间5～6h时,1-氯-2-甲基-3-丁烯-2-醇和4-氯-3-甲基-2-丁烯-1-醇的总收率为72%;所得加成产物与乙酸酐酯化反应,1,2位酯化产物发生烯丙基重排,生成1-乙酰氧基-4-氯-3-甲基-2-丁烯.通过研究采用负载了高碘酸的离子交换树脂作催化剂,先期室温后期升温的反应工艺,使反应时间由原来24h缩短至5h,收率也提高到95%:再以TEMPO作催化剂,酯化产物1-乙酰氧基-4-氯-3-甲基-2-丁烯氧化成为4-乙酰氧基-2-甲基-2-丁烯醛,收率达97%.

A new process for the synthesis of 4-acetoxy-2-methyl-2-butenal was proposed which involves three steps - the addition reaction of isoprene with hypochloric acid, esterification of the additive results with acetic anhydride followed by allyl rearrangement of 1,2-position product, oxidation of the ester obtained to form the target C5-aldehyde, with an overall yield of 65%. The addition reaction of isoprene was conducted by controlling of the acidity with the adding carbon dioxide. When the reaction was operated under 0-5°C for 5-6 h, 1-chloro-2-methyl-3-buten-2-ol and 4-chloro-3-methyl-2-buten-1-ol was got in 72% yield. The acquired alcohol was esterified with diacetyl oxide and followed by allyl rearrangement to get 1-acetoxy-4-chloro-3-methyl-2-butene in 95% yield. During the esterification, a periodinic acid supported on cation exchange resin was used as catalysts, and the reacting temperature was 25-50°C, the time of esterification and rearrangement could be shortened from 24 h for the former process to within 5 h for the new process. Finally the 1-acetoxy-4-chloro-3-methyl-2-butene was oxidized by DMSO to get 4-acetoxy-2-methyl-2-butenal in 97% yield by using TEMPO catalyst.