Synthesis Of Neohexene

Neohexene is an important intermediate of fine chemical. A novel synthesis route was proposed based on literatures and comprehensive comparison. There are altogether two steps from commercial tert-butyl bromide to 1-neohexyl bromide via the addition reaction of ethylene which was catalyzed by anhydrous aluminium chloride, then the intermediate obtained should be react with the solvent of 1-methyl-2-pyrrolidone, so we can get the final product neohexene.In the first step, Fridel-Crafts alkylation ethene with tert-butyl bromide is gas-liquid system, which was promoted by increasing the solubility of ethene in the liquid under pressures, and the second step the elimination of hydrobromide from 1-neohexyl bromide was also improved by using the reaction-distillation method, because of the boiling point for the product neohexene is much lower than that of reactants.Fridel-Crafts alkylation ethene with aluminium chloride through tert-butyl bromide, hexane as solvent, took place at 50 , the pressure is 0.7-0.8MPa, the reaction is lasted 2 hours. Purify the matter of reaction by distillation, yielding 80% 1-neohexyl bromide with the basis of tert-butyl bromide , the solvent distilled can be reused.Elimination of hydrobromide from 1-neohexyl bromide was taken under a reaction-distillation system. The intermediate, 1-neohexylbromide obtained in the first step, solvent 1 -methyl-2-pyrrolidone(NMP), potassium hydroxide and 0.5%(Wt) Phase-Transfer-Catalyst(PTC) were refluxed at 140~165 . The distillates less than 46 give 85% of neohexene according to 1-neohexyl bromide. The product with purity more than 98 % can be obtained by simple distillation.The reuse of bromine which is intermediate element in the synthesis was also studied. Potassium bromide produced in the elimination step was cleaned with steam treatment, then used to bromize tert-Butyl alcohol, producing tert-butyl bromide. It has been shown that 85% of bromine in the process can be reused without reducing the yield as well as the quality of the product. Make reuse of the bromine element in the reaction system is meaningful both economically and environmentally.