[FTIR studies of L-threonic acid and its metal compounds]

Highly pure solid compounds, such as L-threonic acid, calcium L-threonate, magnesium L-threonate, manganese L-threonate, cobalt L-threonate, nickel L-theronate, and zinc L-threonate, were prepared, wherein, L-threonic acid was obtained from calcium L-threonate by strong acid type ion exchange process, calcium L-threonate or zinc L-threonate was prepared by alcohol extracting the concentrated filter liquor of the reaction of Vc, H2O2 and CaCO3 or ZnCO3, the reminder of the compounds were synthesized using alcohol extracting the concentrated solution derived from the reaction of L-threonic acid solution, prepared by double decomposition reaction of calcium L-threonate with oxalic acid, and superfluous MgO, MnCO3, Co2(OH)2CO3 and Ni2(OH)2CO3. The compositions of the compounds were determined by chemical and elemental analysis, and these compounds have the formula M(C4H7O5)2.nH2O (M = Ca, Zn, n = 0; M = Mg, Mn, Co, n = 1; M = Ni, n = 2). The purity of the compounds was 99.60% by HPLC. The IR spectra of the complexes were similar with each other but different from that of L-threonic acid. The characteristic absorption peaks of water were not observed in those of calcium L-threonate or zinc L-threonate, which showed that the molecule of water was not involved in the complexes. Further analyses indicate that M2+ in the compounds coordinated to oxygen atom of the carboxy group, while the proton of the carboxyl group was dissociated and the proton belonging to hydroxyl was not M2+ coordinated to L-threonic acid through the sp3 hybrizated fashion. It was assumed that the coordination number of M2+ was 4.