Non-Equimolar Discrete Phases Formed in the System of Malic Acid Enantiomers

X-Ray diffractometry was employed to investigate the possibility of formation of non-equimolar discrete compounds in the chiral system of malic acid S- and R-enantiomers. Samples studied were mixtures of single enantiomers or an enantiomer and the various polymorphs of the racemic compound. From samples prepared via recrystallization of the melt and grinding of initial reactants, it is demonstrated that the malic acid enantiomers can form stable stoichiometric compounds in S:R ratios of 3:1 and 1:3. Compared to the known racemic and pure enantiomer phases, the corresponding compounds S₃R/SR₃ are characterized by a proper powder diffraction pattern and melting point.