The invention discloses a preparation method of (R)-(+)-
lipoic acid and belongs to the field of organic and
medicinal chemistry. The preparation method comprises the following steps: (S)-ethyl 6,8-dichloro caprylate and
sulfur are fed into a reaction container equipped with a stirring device, the mixture is heated, an aqueous
sodium sulphide solution is added dropwise for a cyclization reaction, heat is preserved, then extraction and concentration are performed, and a cyclization liquid is obtained; the cyclization liquid is fed into the reaction container, an alkaline solution is added, a
hydrolysis reaction is performed, and a
hydrolysate is obtained through cooling; an
organic solvent is added to the
hydrolysate, pH is regulated with acid, extraction is performed, an
organic layer obtained through extraction is washed to be neutral, then an
organic solvent is removed through
pressure reduction, a primary product is obtained, a mixed
solvent is added to the primary product, the mixture is heated and dissolved, a filter aid is added, stirring and adsorption are performed, filtering is performed, a faint yellow liquid is obtained and cooled, crystals are precipitated, and a finished product is obtained. The steps are reduced, and the preparation efficiency is high;
raw material consumption is reduced, the
optical rotation of (R)-(+)-
lipoic acid reaches 117-118 degrees, the ee value is 99.0%-99.5%, the content is higher than 99%, and waste emission is reduced.