Trimethyl orthoacetate, also known as trimethoxyethane, is an important primary acid ester, the molecular formula (C5H12O3) is mainly used in medicine, pesticides, spices and other synthesis. The usual synthesis methods are acetonitrile process, which uses acetonitrile, anhydrous methanol and dry hydrogen chloride as raw materials. This process is simple and short, but the gas storage and transportation are inconvenient, and acetonitrile is too toxic to large-scale production. Another method is sodium metal process, which is prepared by sodium metal, anhydrous methanol, trichloroethane as raw materials. This method is suitable for industrial production with less equipment investment, but the metal sodium is expensive and dangerous when used, and the reaction stability of sodium methanol and trichloroethane is poor and the product yield is very low. In recent years, phase transfer catalytic synthesis has been widely used in organic synthesis because of its advantages of higher yield, lower consumption and less pollution. Phase transfer catalyst (PTC) was introduced in the experimental system of trimethyl orthoacetate synthesis from sodium hydroxide, trichloroethane and methanol. In the phase transfer catalysis, tetrabutylammonium bromide and tetrabutylammonium iodide were used as phase transfer catalysts due to the good oil solubility of the positive ions of quaternary ammonium salts.
1. Main reagents
Sodium hydroxide, trichloroethane, methanol, tetrabutylammonium bromide (TBAB), tetrabutylammonium iodide (TBAI), organic solvents, are all chemically pure reagents.
2. Synthesis steps
A 2000 mL three-mouth flask was filled with a prepared 40% sodium hydroxide solution. Then methanol and quantitative PTC were added, after full stirring, the temperature was raised to a certain temperature, and trichloroethane was added. The material quantity ratio of raw material was trichloroethane: methanol: sodium hydroxide =1.0:8.25:4.0; Reflux for 4h, after the reaction is completed, the products in the flask are divided into two layers, the upper organic phase is separated, the lower water phase is extracted with organic solvent, the organic phase is combined, the anhydrous calcium chloride is dried, the atmospheric pressure distillation, the collection of 107~109 ℃ fractions, that is, the finished product
3. Conclusion
By using PTC, the yield of the product was greatly improved, and the best reaction conditions were as follows: the ratio of the raw material was trichloroethane: methanol: sodium hydroxide =1.0:8 25:4.0; TBAB was used for PTC, and the amount of TBAB was 2.6% of the mass of trichloroethane. The temperature of drip adding trichloroethane is maintained at 40-50℃. Then reflux for 4h, the yield can reach 53%.
