Process for the preparation of optically highly pure (R)- and
(S)-.alpha.-hydroxycarboxylic acids, in which either isolated, impure (R)-
and (S)-.alpha.-hydroxycarboxylic acids prepared by acidic hydrolysis of
the (R)- and (S)- cyanohydrins obtained by enzyme-catalyzed addition of a
cyanide group donor to the corresponding aldehydes or ketones are
recrystallized in an aromatic hydrocarbon, optionally in the presence of a
cosolvent, and optically highly pure (R)- and
(S)-.alpha.-hydroxycarboxylic acids having an optical purity of over 98%ee
are obtained or the hydrolysis solution obtained by acidic hydrolysis of
the (R)- and (S)-cyanohydrins is treated directly with an aromatic
hydrocarbon, optionally in combination with a cosolvent, and is then
extracted at hydrolysis temperature, whereupon after cooling of the
organic phase the corresponding chemically and optically highly pure (R)-
and (S)-.alpha.-hydroxycarboxylic acids having an optical purity of over
98%ee crystallize out.
