Solubility Behavior of the CL-20-MDNT Cocrystal System and Improved Sensitivity through Vacuum Evaporative Crystallization

2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and 1-Metyl-3,5-dinitrotriazole (MDNT) form a promising cocrystal, with predicted detonation velocities 200 m/s faster than HMX. To develop a scalable cocrystallization process, precise solubility data of the coformers and the cocrystal are essential. The solubility data of CL-20 and MDNT in three pure solvents were measured with the soil body method in the range of 283.1 K to 323.1 K. Additional measurements in three binary solvents at 293.1 K were performed to find the optimal solvent for a process working with a 1:1 molar ratio of the coformers. The experimental data were correlated by the Van’t Hoff equation and modified Apelblat equation for the pure solvents and with the CNIBS/R-K and Jouyban-Acree Model for the binary solvents. It was found that both could obtain correlation results according to relative average deviations, root-mean-square deviations, and correlation coefficients above 𝑅2 > 0.98. Combined with literature data, it was found that the coformers are molar equally soluble in ethyl acetate at 291.3 K and acetone at 249.9 K. With the vacuum evaporative crystallization in ethyl acetate at 291.3 K and pressures in the range of 130 to 200 mbar in a rotary evaporator, phase pure Cocrystal samples, with mean diameters between 20 to 260 µm, were obtained. Impact and friction sensitivity measurements show an improvement in crystal quality against known literature data of the Cocrystal from 4 J to 7.5 J in impact sensitivity and from 120 N to 216 N in Friction sensitivity. First evaluation suggests that the reduced mechanical sensitivity is related to the specific crystal shape, which was adjusted by tuning the evaporation rate and thus the supersaturation of the solvent.