Energetics, Shock Sensitivity, and Thermal Hazards of Cubane and Bicyclo[1.1.1]pentane Derivatives

Strained polycyclic ring structures such as cubanes and bicyclo[1.1.1]pentanes (BCPs) are gaining popularity as isosteres in the pharmaceutical and agrochemical industries. It has been previously reported that these ring systems contain significant strain energy. Employing a combination of differential scanning calorimetry (DSC), adiabatic calorimetry, and impact sensitivity testing (BAM Fallhammer), 8 cubane and 25 BCP derivatives were characterized for energetic potential and thermal hazards. The DSC decomposition enthalpy of cubanes was found to be about 64% of the theoretical ring strain energy, and that of BCPs was found to be about 75% of the ring strain energy, where nonenergetic substituents bonded to the bicyclic ring structure generally had minimal impact on the molar decomposition enthalpy. The impact sensitivity of these compounds varies and is not readily predicted by the Yoshida correlation. Our DSC and impact-sensitivity results are compared with previous literature reports, and several cubane and BCP materials were found to be more shock-sensitive than previously reported. The ethynyl group bonded to one of these strained ring structures leads to a lower onset temperature compared with other functional groups. A thermokinetic analysis was conducted for 1,3-diiodobicyclo[1.1.1]pentane which was used to predict the decomposition kinetics for this compound at different temperatures.