Determination and Correlation of the Solubility of 2,4,6,8,10,12-Hexacyclobutyl-2,4,6,8,10,12-Hexaazaisowurtzitane in Twelve Pure Solvents from 273.15 to 313.15 K

Reliable solubility data are needed for solvent selection and process optimization in the synthesis, purification, and nitration of 2,4,6,8,10,12-hexacyclobutyl-2,4,6,8,10,12-hexaazaisowurtzitane (HCBIW), a key precursor of CL-20. In this work, the solid–liquid equilibrium solubility of HCBIW in 12 pure solvents was measured by the gravimetric method at 0.1 MPa from 273.15 to 313.15 K. The solubility increased with temperature in all solvents, with the highest value in chloroform and the lowest in acetonitrile. The data were correlated using the modified Apelblat equation, Yaws model, van’t Hoff equation, and a polynomial empirical equation, all giving satisfactory fits with R2 > 0.99. Hansen solubility parameter analysis indicated that HCBIW is a weakly polar, dispersion-dominated cage compound, with δd = 17.91 (MPa)0.5, δp = 4.59 (MPa)0.5, and δh = 8.38 (MPa)0.5. The HSP distances and Hansen distances rationalized its good compatibility with chloroform and dichloromethane and poor compatibility with acetonitrile and alcohols. KAT-LSER analysis showed that solvent hydrogen-bond basicity suppresses HCBIW dissolution, whereas hydrogen-bond acidity and cohesive energy density promote dissolution. These results support solvent screening and crystallization process design for HCBIW.