STANDARD MOLAR ENTHALPIES OF FORMATION OF SOME CRYSTALLINE AMINE N-OXIDES

Based on the fact that N-oxide groups are kinetically reduced by titanium solution, a general thermochemical reaction, 3LO(c) + KX(c) = KXO3(c) + 3L(l); DELTA(r)H(m)-degrees (LO = N-oxide compound, L = amine, X = Cl, Br), was employed to determine through solution-reaction calorimetry the standard molar enthalpies of formation of crystalline ortho-, meta- and para-methylpyridine N-oxides, as well as those of triethyl- and tri-n-butylamine N-oxides, giving 10.3 +/- 0.8, 8.8 +/- 0.7, 12.9 +/- 0.9, 9.0 +/- 0.8 and 16.0 +/- 1.1 kJ mol-1, respectively. The advantage of this method is that it avoids combustion calorimetry in which it is difficult for this kind of substance to achieve complete combustion.