The invention discloses a preparation method for a
levetiracetam intermediate (S)-alpha-ethyl-2-oxo-1-
pyrrolidine acetic acid, which takes (RS)-alpha-ethyl-2-oxo-1-
pyrrolidine acetic acid as the starting material and takes (R)-alpha-methyl
benzylamine as resolving agent to get the product through resolving in resolving
solvent. The invention is characterized in that the resolving
solvent can be C1-C7 ketones, C1-C7 alcohols, C1-C4 esters or the mixture of the solvents. In addition, the by-product (R)-alpha-ethyl -2 - oxo -1 -
pyrrolidine acetic acid can be recovered through
racemization under the effect of alkali so as to regain the (RS)-alpha-ethyl -2-oxo-1- pyrrolidine acetic acid. Compared with the existing invention, the preparation method of the invention has the advantages that during resolving, the
solvent selected for the compound (RS)-alpha-ethyl -2-oxo -1 - pyrrolidine acetic acid has high resolving efficiency and small
toxicity; the resolving salt only needs to be refined once, so that the optical purity of (S)-alpha-ethyl -2-oxo -1 - pyrrolidine acetic acid can meet the requirement (alpha20D is equal to -25.0 plus or minus 1 degree (C is equal to 1,
acetone)). In addition, the racemic
recovery of the compound (R)-alpha-ethyl -2-oxo-1-pyrrolidine acetic acid can reduce environmental
pollution and decrease the cost of the product.