The invention discloses a method for synthesizing trans-2-hexenal. The method includes steps of (1), adding acidic
ionic liquid into reaction flasks, completely dropwise adding vinyl ethyl
ether and
butyraldehyde mixed liquid into the reaction flasks at the temperatures of 0-25 DEG C, then heating systems until the temperatures of the systems reach 20-45 DEG C, carrying out stirring reaction for 1-6 hours, and carrying out reduced pressure
distillation after the reaction is completely carried out so as to obtain cyclization intermediates A; adding dilute
sulfuric acid aqueous solution and theintermediates A into reaction flasks, erecting
reflux oil and water layering devices, carrying out heating normal-pressure
distillation for 4-48 hours, and extracting upper oil
layers into oil layer receiving flasks; (3), rectifying and purifying hexenal crude products, carrying out normal-pressure rectification to obtain substances with low boiling points and then carrying out reduced pressure rectification to obtain the trans-2-hexenal. A
molar ratio of
butyraldehyde to vinyl ethyl
ether is 2:1-5:1, and the usage of the acidic
ionic liquid accounts for 0.1-5% of the total weight of the vinylethyl
ether; the acidic
ionic liquid is [(CH2)3SO3HMIM][HSO4] or [(CH2)3SO3HMIM][CF3SO3]. The oil
layers are the hexenal crude products; the
mass concentration of the dilute
sulfuric acid aqueous solution is 0.5-25%, and a weight ratio of the dilute
sulfuric acid aqueous solution to the intermediates A is 0.2:1-2:1. The method has the advantages of
environmental protection, low cost and high yield.