Physicochemical Properties of Plant Protection Substances: I Polymorphism and Binary Systems of Triadimenol

 The fungicide triadimenol consists of a mixture of two diastereoisomers. Diastereoisomer A (1RS,2SR) could be obtained from the mixture by fractionated crystallization from ethanol/water and toluene, successively, whereas diastereoisomer B (1RS,2RS) could be separated by column chromatography on a silica gel column using ethylacetate as eluent. Four different crystal forms of diastereoisomer A could be derived. The modifications were characterized by means of thermal analysis (thermomicroscopy, DSC), FTIR-spectroscopy, FT-Raman-spectroscopy and powder X-ray diffraction, as well as pycnometry. The thermodynamic relationships are illustrated in a semischematic energy/temperature-diagram which provides information about the relative thermodynamic stabilities and physical properties of the four crystal forms. Mod. II (m.p. 132 °C, ΔH_f 33.1±0.2 kJ mol⁻¹, density 1.271±0.001 g cm⁻³) was obtained from toluene after the separation of diastereoisomer A and is enantiotropically related to mod. I (m.p. 138 °C, ΔH_f 32.0 ± 0.2 kJ mol⁻¹, density 1.243±0.001 g cm⁻³). The transition point of mod. II with mod. I was determined between 30 and 40 °C, which means that mod. II is thermodynamically stable at ambient conditions. Mod. III (m.p. 112 °C, ΔH_f 25.1±0.5 kJ mol⁻¹) and mod. IV were obtained from the melt. Furthermore, the phase diagrams of the binary systems of diastereoisomer B and the four modifications of diastereoisomer A were calculated by means of the experimentally obtained thermodynamical data. Received September 30, 1999. Revision July 30, 2000.