GB954207A - Process for preparing l-ª‡-aminolactam from a mixture of d-and l-ª‡-aminolactam - Google Patents

Abstract

Racemic a -aminolactams are resolved by forming a precipitate containing only or primarily either D-or L-a -aminolactam as the salt of the optically active pyrrolidone carboxylic acid with the same steric configuration, such precipitation being effected in a liquid medium in which the salt of both D-and L-a -aminolactam with the said acid are insoluble or substantially insoluble, using the pyrrolidine carboxylic acid as such or as ammonium pyrrolidonate and in such smaller amount than that which is equivalent to the total amount of a -aminolactam that all or most of one of the optical antipodes of the said mixture remains in the liquid phase. The optically-active a -aminolactams are subsequently separated from their salts with the pyrrolidone carboxylic acid. The liquid medium used for the resolution is preferably dioxane or a hydrocarbon. Both the a -aminolactam and the pyrrolidone carboxylic acid may be added to the liquid medium of the process as solutions in a polar solvent, such as water or an alcohol, and this polar solvent is preferably expelled from the liquid medium at the same rate as it is added, e.g. by means of azeotropic distillation. When L-pyrrolidone carboxylic acid or its ammonium salt is used for resolution, the preferred amount is not more than 1 mole for mole of L-a -aminolactam. The precipitate is then predominantly L, L-salt, and this may be taken up in a polar solvent and treated with an amount of L-a -aminolactam which is at least equivalent to the amount of D-a -aminolactam occurring as a L, D-salt contaminant in the L, L-salt. The solution of L, L-salt in a polar solvent is then added to a further amount of the liquid medium used in the process, and pure L, L-salt is precipitated by expelling the polar solvent. The L, L-salt may be passed as an aqueous solution over a cation exchanger in the ammonium form. L-pyrrolidone carboxylic acid passes through as the ammnoium salt and may be used again for the resolution step, while L-a -aminolactam may be recovered by subsequent elution with aqueous ammonia. The original mother liquor containing mainly D-a -aminolactam may be racemized for re-use by heating it with sodium or anhydrous caustic soda. When D-pyrrolidone carboxylic acid or its ammonium salt is used for resolution, the preferred amount is at least 1 mole per mole of D-a -aminolactam present. The precipitate is then predominantly D,D-salt, from which D-a -aminolactam may be recovered using an ion exchanger as before. The recovered D-a -aminolactam is then dissolved in fresh liquid medium and racemized for re-use by heating it with anhydrous caustic soda. The original mother liquor containing mainly L-a -aminolactam may be subsequently evaporated to yield the required product. The processes described above may be adapted for continuous working. Specified starting materials are racemic a -aminocaprolactam, a -aminovalerolactam and a -amino-oenantholactam. Specification 884,299 is referred to.