Synthesis
The innovation of the present invention lies in the fact that the lactyl ester of the by-product menthyl lactylate is converted to menthyl lactylate by the addition of a buffer solution or a saturated solution of acidic salts during the reaction of lactic acid and menthol, while the hydrolysis of the conversion of menthyl lactylate to lactic acid and menthol proceeds to a lesser extent. Under this hydrolysis condition there is no need to control the pH of the system, and the target products are rarely converted to lactic acid and menthol, even with much excess of buffer solution or saturated solution of acid salts and long processing times.
Conventional methods for the preparation of menthyl lactate from lactic acid and menthol result in approximately 60% menthyl lactate (GC normalized) after the reaction is completed, compared to which the yield of menthyl lactate prepared by direct reaction can be significantly increased using the method described in the present invention. The lactyl ester of menthyl lactate is almost completely converted to menthyl lactate, and the content of menthyl lactate in the raw material, target product, and by-product can reach up to 94.5%, and the yield based on the addition of menthol can reach 92.4%. Ideally suited for industrial production.
