Thermochemical studies of 1-hydroxyisoquinoline, 5-hydroxyisoquinoline and 1,5-dihydroxyisoquinoline

Abstract

The standard ( p ∘ = 0.1 MPa) molar enthalpies of formation, Δ f H m ∘ , for crystalline 1-hydroxyisoquinoline, 5-hydroxyisoquinoline and 1,5-diidroxyisoquinoline, were derived from the standard molar enthalpies of combustion, in oxygen, at the temperature 298.15 K, measured by static bomb-combustion calorimetry. The standard molar enthalpies of sublimation, Δ cr g H m ∘ , at T = 298.15 K, were determined by Calvet microcalorimetry. The results were as follows: - Δ c H m ∘ ( cr ) / kJ · mol - 1 Δ cr g H m ∘ / kJ · mol - 1 1-Hydroxyisoquinoline 4395.1 ± 1.5 113.6 ± 2.2 5-Hydroxyisoquinoline 4455.2 ± 1.9 109.6 ± 2.1 1,5-Dihydroxyisoquinoline 4194.1 ± 2.2 123.6 ± 2.2 The derived standard molar enthalpies of formation, in the gaseous state, are analysed in terms of enthalpic increments and interpreted in terms of molecular structure.