Research Of Synthesizing Citral From Dehydrolinlool

Citral is an extremely important raw material, which is mainly used for the synthesis of high-grade fragrance such as ionone, irone products and vitamin A, vitamin E, β-carotenoids. At present, the domestic citral is mainly extracted from cubeba oil by vacuum distillation. With the expansion of the application of citral, the demand continues to increase. The preparation of citral through using plant resources has been unable to meet market demand. Therefore, organic chemical synthesis citral attracts more and more attention, especially, dehydrolinalool route for preparing citral. It is an atom economy rearrangement reaction and has most development prospect.The synthesization of citral through Meyer-Schuster rearrangement of dehyrolinalool was studied in this paper. The catalytic system including different Ti-catalyst, co-catalyst and organic acid was invesigated. Experimental results showed the catalytic activity sequence for titanium-based catalysts as follows:tetraisopropyl titanate (TPT)>titanyl acetylacetonate [TiO(acac)2]>tetrebutyl titanate (TBT). The tetraisopropyl titanate as a catalyst combinating with cuprous chloride and methyl benzoate exhibited excellent catalytic performance. Under optimal reaction conditions as follows: n(DHOL)/n(TPT)=60, n(CuCl)/n(TPT)=0.25, n(methyl benzoate)/n(TPT)=6, reaction at temperature 110℃ for 2h, the conversion of dehyrolinalool and the yield of citral reached to 99% and>85%, respectively. Using toluene as a solvent, m(dehyrolinalool)/m(toluene)=2, the conversion of 98% and the yield of 93% were obtained when reaction carried out at 110℃ for 5h. Separating the reaction mixture with TPT as the catalyst by steam distillation, the purity of citral could reach to 97% with the separation yield of 60%.