Study On The Application Of Ionic Liquid In The Synthesis

Citronellyl acetate is a kind of colourless liquid with odor of the lemon and an important part of the flavor and fragrance and is widely applied in food and cosmetics. The traditional production methods of citronellyl acetate generate some by-products to affect the quality of the product and cause environmental pollution. Ionic liquids have advantages such as stability, non-volatility, alkalinity or acidity and adjustability, and have the potential of acidic catalysts and green solvent. In view of the present problems of the production of citronellyl acetate, this article studied the application of ionic liquids as acidic catalyst and reaction medium in preparation of citronellyl acetate, including esterification and transesterification catalyzed by acidic ionic liquids, and lipase-catalyzed transesterification in ionic liquids.Transesterification of citronellol with vinyl acetate to citronellyl acetate catalyzed by acidic ionic liquids was investigated. The effect of acidic ionic liquids, the mole ratio of vinyl acetate to citronellol, temperature, catalyst dosage and agitation speed on the reaction process were studied. The experimental results showed that [BSO3HMIM]HSO4had best catalytic effect in the reaction among the ionic liquids purchased by laboratory. Keeping reaction temperature at60℃, the influence degree of various factors on the experimental results was determined by the orthogonal experiment, and exhibited from big to small as follows: reaction time, the mole ratio of vinyl acetate to citronellol, the mass ratio of ionic liquid to citronellol and agitation speed. At the same time, combined with single factor experiments, the final optimized experimental conditions was determined: mole ratio of9:1of vinyl acetate to citronellol, the mass ratio of7%of ionic liquid to citronellol, the agitation speed of150rpm, reaction temperature of60℃, the reaction time of5h. The yield of citronellyl acetate reached83.66%under these conditions. The catalytic effect was reduced by23.87%when the ionic liquid reused in the second time.Esterification of citronellol with acetic anhydride to citronellyl acetate catalyzed by acidic ionic liquids was studied. The effect of acidic ionic liquids, catalyst dosage, the mole ratio of acetic anhydride to citronellol, temperature and agitation speed on the reaction process were investigated. The experimental results showed that [BSO3HMIM]HSO4had best catalytic effect in the reaction among the ionic liquids purchased by laboratory. The impact of various factors on the experimental results determined by factorial experiments and exhibited from big to small as follows:temperature, reaction time, the mole ratio of acetic anhydride to citronellol, catalyst dosage and agitation speed. The factors of remarkable influence were temperature, reaction time, the mole ratio of acetic anhydride to citronellol. Response surface experiment had been done by using the factors of remarkable influence. Combined with the results of single factor experiments, final optimization experiment conditions were determined as follows: the molar ratio of1.5:1of acetic anhydride to citronellol, the mass ratio of0.3%of ionic liquid to citronellol, reaction temperature of60℃, the agitation speed of150rpm and the reaction time of60min. The yield of citronellyl acetate was97.58%under the optimization conditions. The catalytic effect of ionic liquid was reduced by38.78%after repeated use one time.The reaction is a catalytic esterification catalyzed by acidic ionic liquid, and is a homogeneous acid catalytic esterification, following the bimolecular reaction mechanism.The lipase-catalyzed transesterification of citronellol with vinyl acetate to citronellyl acetate was investigated in ionic liquid. After screening the laboratorial existing six kinds of ionic liquids and six different sources of lipases, the result show that the best catalyst is the lipase derived from Pseudomonas fluorescens and the best solvent is the ionic liquid [BMIMN]TF2. The effects of various parameters were studied and optimized. The optimal reation conditions is: a mole ratio of3:1of vinyl acetate to citronellol, Reaction temperature of40℃, enzyme load of10mg/mL, the agitation speed of200rpm. The yield of citronellyl acetate was99.46%under these conditions. Substrate inhibition was not found when the substrate concentration was below500mmol/L, but the study have showed that the product inhibition effect should be considered. The Reusability of the lipase were studied, results show that the lipase catalytic activity was reduced by20%after reused7times. The results from the reaction kinetics analysis showed that the reaction obeys the ping-pong bi-bi mechanism that is inhibited by citronellyl acetate. The reaction rate is:The experimental data was simulated and the parameters were as follows: Vm=0.50mmol/L/min, KA=2.09×103mmol/L, KB=9.90mmol/L, KAB=0.70, KQ=11.60mmol/L,KBQ=49.70, KIQ=3.84×102mmol/L.The experimental values could be satisfactorily fitted to the simulated values with a relative error of8.76%.