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 chelate with glycolate and the characteristics of the resulting crystals remains limited. In this study, a potassium glycolate hemihydrate (PGH) crystal, ideally K(C₂H₃O₃)·0.5H₂O, 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 the space group P2₁/m and unit cell parameters a = 5.8982(1), b = 7.2515(1), c = 11.0270(1) Å, β = 102.253(1)°, and V = 460.890(11) ų. The infrared and Raman spectra of PGH and PGGA exhibit notable similarities and are highly consistent with the calculated infrared spectra calculated. 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.