ENTHALPIES OF COMBUSTION OF 4-DIMETHYLAMINONITROSOBENZENE AND 4-DIMETHYLAMINONITROBENZENE

The standard (po = 0.1 MPa) molar enthalpies of combustion at the temperature T = 298.15 K were measured by static-bomb calorimetry for crystalline 4-dimethylaminonitrosobenzene and 4-dimethylaminonitrobenzene. The standard molar enthalpies of sublimation of these compounds at T = 298.15 K were derived from vapour pressures as functions of T determined using Knudsen cells in a microcalorimeter. From the standrd molar enthalpies of formation of the gaseous compounds, the molar dissociation enthalpy of the (N-O) bond in 4-dimethylaminonitrobenzene was derived: D(N-O)/(kJ·mol-1) = (371.4 ± 3.5). These thermochemical results demonstrate additional stabilization energy in 4-dimethylaminonitrosobenzene providing an explanation of why this nitrosoderivative does not dimerize in the solid state. © 1994 Academic Press Ltd.