Process for the preparation of D-(-)-4-hydroxyphenylglycine and L-(+)-4-hydroxyphenylglycine, starting from D.L.-4-hydroxyphenylglycine

A process for the preparation of D-(-)-4-hydroxyphenylglycine and L-(+)-4-hydroxyphenylglycine starting from D.L.-4-hydroxyphenylglycine, comprised of dissolving D.L.-4-hydroxyphenylglycine in a suitable solvent or a mixture of solvents at an increased temperature of 40.degree. C. to 100.degree. C., which solvent mixture comprises an organic solvent, 0% to 30% water H.sub.2 SO.sub.4 in a molar ratio of 1:1 to the added D.L.-4-hydroxyphenylglycine, after which the solution obtained is cooled to 40.degree. C. to 0.degree. C. and to the cooled solution are added D-(-)-4-hydroxyphenylglycine sulphate inoculation crystals at a quantity of 2 weight percent or more of the dissolved D.L.-4-hydroxyphenylglycine for crystallizing the D-(-)-4-hydroxyphenylglycine sulphate, followed by filtering of the formed crystals, while for recovery of L-(+)-4-hydroxyphenylglycine sulphate remaining in the mother liquor, the mother liquor is heated until 40.degree. C. to 100.degree. C., followed by the addition of D.L.-4-hydroxyphenylglycine and H.sub.2 SO.sub.4 in water in a molar ratio of 1:0.5, after which the thus obtained solution is cooled down until 40.degree. C. to 0.degree. C. followed by addition of L-(+)-4-hydroxyphenylglycine sulphate inoculation crystals at a quantity of 2 weight percent or more of the dissolved D.L.-4-hydroxyphenylglycine, from which mixture after further cooling the L-(+)-4-hydroxyphenylglycine sulphate crystallizes;

• whereby one may also act reversely, that is first the L-(+)-4-hydroxyphenylglycine sulphate is crystallized and wherein said crystallized L-(+)-4-hydroxyphenylglycine sulphate the molar ratio of the L-(+)-4-hydroxyphenylglycine to sulphate is 2:1 and thereafter from the mother liquor the D-(-)-4-hydroxyphenylglycine sulphate and, if desired, from the formed sulphates the D-(-)-4-hydroxyphenylglycine and the L-(+)-4-hydroxyphenylglycine, respectively, may be recovered by hydrolysis making a solution of the sulphate in water at a concentration of 10% to 20% by a temperature of 20.degree. C. to 70.degree. C. and neutralizing the obtained solution using an aqueous solution of NaOH, KOH or NH.sub.4 OH in a molar ratio of 1 mol sulphate and 2 mol of alkali and recuperating during the neutralization crystallized D(-)-4-hydroxyphenylglycine or L(+)-4-hydroxyphenylglycine by filtration.