Study On The Synthesis Of L-menthol

Menthol is one of the most popular perfumes in the world, applied in various areas of the fine chemical industry, such as pharmaceutical, additives and perfumes. Natural menthol obtained from menthe arvensis or mentha piperita does not meet the need of industrialization, considering the advantage of productivity and price of man-made menthol, chemical synthesis has become more and more important. In consideration of abundant and cheap raw materials, rapid reaction, simple procedures, we determined to prepare menthol from achiral compound, thymol, through catalytic hydrogenation.Firstly, the categories and activation methods of catalysts were researched, operating conditions for hydrogenation and mechanism of side reactions were studied systematically. Results show that the SRNA-4amorphous raney nickel which was activated through Tl method was more effictive. At the temperature of160℃, under the pressure of6Mpa and in the neutral system, the conversion and the selectivity of the reation were relatively good as the percentage of menthol was59.8%and the yield of menthol was56.5%. The side reactions consist of menthol dehydration and the demethylation of menthol and thymol under200℃,3MPa, due to activated C-C bonds and C-O bonds by Ni catalyst. The main by-products were alkylated phenol, alkylated cyclohexanol and alkylated cyclohexane, and the possibility order of these side products is as follows:alkylated phenol> alkylated cyclohexanol> alkylated cyclohexane.Secondly, the retification process of menthol isomers was studied with Aspen Plus software. The main products-menthol, neomenthol and isomenthol can be separated through two rectifying columns in series. As it’s difficult to separate menthol from isomenthol with ordinary distillation, the simulation calculations of extractive distillation was also carried out for separation of these components in this dissertation.Lastly, the feasibility study on esterification and induced crystallization of d,l-menthol were conducted to obtain1-menthol benzoate. Menthyl benzoate was produced by using menthol and benzoyl chloride under optimum reaction conditions which were:triethylamine was acid binding agent and4-dimethylaminopyridine (DMAP) acted as catalyst, the mole ratio of triethylamine to menthol was1.2, the mole ratio of DMAP to menthol was0.2, and the mole ratio of benzoyl chloride to menthol was1.1, menthyl benzoate yield was91%. Crystallization solvent was petroleum ether of60-90℃and the solution concentration was120g/100ml, the induced crystallization temperature was controlled at about4℃, the optical rotation of1-menthyl benzoate was-86°, crystallization yield was6.2%。...