Process for the optical resolution of mixtures of D- and L-2-(6-methoxy-2-naphthyl)-propionic acids

A process for the resolution into the optically active isomers of a substantially racemic mixture of d- and l-2-(6-methoxy-2-naphthyl)-propionic acids which consists of:

• (a) preparing a solution of a molar equivalent of said mixture and about 0.5 molar equivalent of cinchonidine, in an organic solvent which is dimethylformamide or dimethylacetamide, at a temperature of about 75.degree.-80.degree. C.;
• (b) gradually cooling the obtained solution and, at a temperature between about 60.degree. and 66.degree. C., seeding with crystals of the cinchonidine salt of d-2-(6-methoxy-2-naphthyl)-propionic acid containing 9.5%-12% by weight of dimethylformamide or 10.5%-14% of dimethylacetamide, and continuing to cool to a temperature between about room temperature and about 0.degree. C., whereby the cinchonidine salt of d-2-(6-methoxy-2-naphthyl)-propionic acid containing from about 9.5% to about 14% by weight of dimethylformamide or dimethylacetamide precipitates;
• (c) treating the said product from step (b) with hydrochloric acid in the presence of ethyl acetate to obtain the free d-2-(6-methoxy-2-naphthyl)-propionic acid.

The cinchonidine salt of d-2-(6-methoxy-2-naphthyl)-propionic acid containing 10.6% by weight of dimethylformamide.

The cinchonidine salt of d-2-(6-methoxy-2-naphthyl)-propionic acid containing 11.2% by weight of dimethylacetamide.

A process for preparing the cinchonidine salt of d-2-(6-methoxy-2-naphthyl)-propionic acid containing from about 9.5%-12% by weight of dimethylformamide or 10.5%-14% of dimethylacetamide, which consists of dissolving a molar amount of d-2-(6-methoxy-2-naphthyl)-propionic acid and a molar equivalent of cinchonidine in dimethylformamide or dimethylacetamide at a temperature between about 55.degree. and about 65.degree. C., slowly cooling the resulting solution to about 20.degree. C., letting the product precipitate and filtering the product.