Etude thermoanalytique de substances psychotropes: VI. Butobarbital

Abstract The thermoanalytical study of butobarbital has enabled the existence of polymorphs and solvates to be shown. Thermal stability and vaporization kinetics of a commercial sample have been determined. The transition and melting temperatures have been determined using differential scanning calorimetry and thermomicroscopy. The commercial sample shows a solid-solid transition in the form I . After recrystallization, three polymorphs have been identified by thermoanalytical methods and X-ray diffraction: form I T f = 123.0±0.5°C, Δ H f = 17.30±0.40 kJ mol −1 ; form II T f = 121.0±0.5°C, Δ H f = 13.60±0.31 kJ mol −1 ; form III T f = 119.5±0.50°C, Δ H f = 14.70 ±0.32 kJ mol −1 . Many other polymorphs show transitions between 80 and 115°C into form I . Two solvates have been found on crystallization at −18° C; one of the form III and one of the form IV melting at 114.0±0.5°C (Δ H f = 11.67±0.20 kJ mol −1 ). Forms I and II , I and III , I and IV , II and IV , III and IV are monotropic.