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.