Experimental standard molar enthalpies of formation of crystalline 3,5-dimethylpyrazole, 3,5-dimethyl-4-nitrosopyrazole, 1,3,5-trimethyl-4-nitrosopyrazole, and 3,5-dimethyl-1-phenyl-4-nitrosopyrazole

The standard (p(o) = 0.1 MPa) molar enthalpies of combustion in oxygen, at T = 298.15 K, for crystalline 3,5-dimethylpyrazole (Me(2)Pyr), 3,5-dimethyl-4-nitrosopyrazole (Me(2)PyrNO), 1,3,5-trimethyl-4-nitrosopyrazole (Me(3)PyrNO), and 3,5-dimethyl-1-phenyl-4-nitrosopyrazole (Me(2)PhPyrNO) were measured by static-bomb calorimetry. These values were used to derive the standard molar enthalpies of formation of the crystalline compounds. The standard molar enthalpies of sublimation for these four compounds were measured by microcalorimetry. [GRAPHICS] The experimental results obtained allow us to derive the values of the standard molar enthalpies of formation, in the gaseous state, for the monomeric compounds involved in this work. These last values are discussed comparatively with results previously obtained for some aromatic nitroso derivatives. (C) 2001 Academic Press.