Preparation process of DL-2-hydroxy-3-butenoic acid ester

The invention discloses a preparation process of a DL-2-hydroxy-3-butenoic acid ester represented by a general formula (I). In the general formula (I), R represents methyl, ethyl or n-propyl. The preparation process includes that cheap acrolein and hydrocyanic acid are used as initial raw materials, alcohol ROH is used as a solvent, the mixture is catalyzed by inorganic ammonia salts or organic amine and then subjected to cyaniding reaction to obtain 2-hydroxy-3-butenenitrile, concentrated sulfuric acid is added into the obtained reaction fluid or hydrogen chloride is accessed to the obtained reaction fluid to adjust PH value of solution to 1-6, the solid-liquid separation is performed, under the catalysis of the concentrated sulfuric acid or the hydrogen chloride, the obtained fluid and the alcohol ROH are subjected to hydrolyzing and esterification to achieve one-step preparation of the DL-2-hydroxy-3-butenoic acid ester, and the obtained reactant is subjected to simple purification to obtain highly purified DL-2-hydroxy-3-butenoic acid ester products. The preparation process has the advantages of being short in synthetic route and simple and convenient to operate, and the products are easy to separate, high in purity and yield, low in producing cost and good in application prospect.