Pantolactone as a Plastic Crystal

Abstract

D-Pantolactone crystals showed anomalous thermal behavior, that is, two endothermic peaks (62.0 and 91.6°C) were observed in the differential scanning calorimetry curves. The entropy change of the first transition was calculated as 44.4 JK^-1 mol^-1 and that of the second transition was 9.20 JK^-1 mol^-1. The powder X-ray diffraction patterns of D-pantolactone differed significantly before and after the transition (62.0°C) and only one sharp peak at 2θ=17.4° was observed at 75°C. At 75°C, carbon-13 nuclear magnetic resonance chemical shifts of D-pantolactone were clearly observed by the pulse Fourier-transform technique.It was concluded that D- and L-pantolactone showed a stable plastic crystal phase between 62.0 and 91.6°C, and that DL-pantolactone is in a plastic crystal phase at room temperature.