An adiabatic calorimetric study of the phase situation in 2,2-dinitropropane

Specific heat measurements are made for 2,2-dinitropropane ((CH3)2C(NO2)2) in the temperature range of 100 to 347 K. Three anomalies on the specific heat curve are found: melting at a temperature of (324.5 ± 0.1) K and two phase transitions in the solid state – one at a temperature of (267.7 ± 0.1) K and another at a temperature of (259.67 ± 0.28) K. It is found that the hightemperature transition is additionally split. The entropy changes associated with these anomalies are as follows: for melting ΔS = (1.94 ± 0.09) cal/mol K for the high-temperature transition Δ = (10.07 ± 0.34) cal/mol K and for the low temperature transition ΔS = (1.72 ± 0.34) cal/mol K These values are interpreted in terms of a reorientation of the entire molecule and NO2 groups in the plastic phase.