Heats of Combustion of Some Peroxides and the Heats of Formation of Acetate, Propionate, and Butyrate Radicals

Heats of combustion of acetyl, propionyl, and butyryl peroxide were measured using a bomb calorimeter. The heats of formation obtained are: ΔHf = — 127.9 for acetyl peroxide, — 148.2 for propionyl peroxide, and — 161.0 for butyryl peroxide (in kcal/mole for the liquid state at 25°C). The heats of formation of the acetate, propionate, and butyrate radicals have been computed and the relative stability of the acetate compared to the benzoate radical is discussed. The RC(O)O–H bond dissociation energies in the respective acids and the sums of electron affinities plus solvation energies of the respective ions are computed. These calculations seem to indicate that acidic properties of carboxylic acids are due to the high electron affinities+solvation energies of R·COO radicals, and not to the low R·CO·O–H bond dissociation energies, since the latter are comparatively high.