Synthesis, structures, characterization and deterioration of potassium glycolate hemihydrate

Abstract

The process of glycolate crystallization is well documented; however, research on the formation of potassium chelates with glycolate and the characteristics of the resulting crystals remains limited. In this study, a potassium glycolate hemihydrate (PGH) crystal, ideally K(C2H3O3)ˑ0.5H2O, was obtained by freeze-drying, evaporation, and liquid phase diffusion. PGH was characterized by single-crystal X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, DFT calculation, thermogravimetric analysis, and powder X-ray diffraction refinement. A structurally similar compound, potassium glycolate glycolic acid [K(C2H3O3)(C2H4O3), PGGA], was synthesized for comparison. The results revealed that PGH is monoclinic with space group P 21/m and unit cell parameters a = 5.8982(1), b = 7.2515(1), c = 11.0270(1) Å, β = 102.253(1) ˚, V = 460.890(11) Å3. The infrared and Raman spectra of PGH and PGGA exhibit notable similarities and are highly consistent with the calculated infrared spectra. Thermogravimetric analysis indicated that PGH dehydrated at approximately 60 °C; however, further experiments showed that PGH gradually transformed into PGGA at 30 °C. This study provides new insights into the bonding behavior of glycolate and the stability of its crystalline forms.