Studies On Synthesis Of Citral From Isoprene

As an important product of organic chemical industry, citral can be widely used in medicine, pesticide, daily chemical and food industries. With continuous development of the functions, demands of citral are increasing year by year.In this paper, study about synthetic process of citral was described in detail. Then the paper focused on the preparation of citral with isoprene as the raw material and intermediates of the synthetic process were prenol and prenal.First, different synthetic routes were tried for the preparation of prenol and related process was optimized at the same time. There are three synthetic routes were described. A hydration process of isoprene and dilute sulphuric acid was tried for the synthesis of prenol. An esterification of isoprene and dichloroacetic acid and a saponification occurred one after another for the synthesis of prenol. A chlorination reaction of isoprene and concentrated hydrochloric acid, an esterification and a saponification occurred one by one for the synthesis of prenol. Among them, the third synthetic route was the best, because a better product yield and purity could be obtained under this route, and optimum reaction conditions of this route were: chlorination temperature was 10 oC, chlorination time was 6 h, molar ratio of isoprene and hydrogen chloride was 1:3.6, the additive amount of sodium chloride was 2.4 g, esterification temperature was 130 oC, molar ratio of isoprene and sodium formate was 1:1.5, saponification temperature was 100 oC, concentration of Na OH was 30%?m/m?, yield of prenol was 84% and purity was 89%.Second, prenal was prepared by oxidation reaction of prenol with different kinds of oxidants. Oxidants included two types, Mn O₂ and KMn O₄/Mn O₂. With this method, prenal was successfully prepared and optimization and improvement of related technology routes were also carried out. Optimum reaction conditions were: reaction solvent was CH₂Cl₂, oxidation reaction time was 13 h. Yield of prenal was 37% and purity was about 50%.Third, citral was prepared by a condensation reaction taking prenol and prenal as raw materials, and partial process conditions were improved at the same time. Yield of citral reached 21%.