Search Results
Two compounds of sulphamide type:p-amino-benzene sulphonamide (I) and 3,4-dimethylisoxazol 5-sulphanylamide (II) were studied by combustion calorimetry and by differential scanning calorimetry (DSC).
Abstract
A micro-combustion calorimeter was developed. The small energy equivalent (ca. 68 JK–1) of this calorimeter makes it possible to measure combustion energies of very small samples. The energy equivalent was determined by burning 2 mg of benzoic acid. The standard deviation of the mean energy equivalent was reduced to 0.014% in 5 experiments. The standard massic energy of combustion of salicylic acid and the standard deviation of the mean were determined to be –21871±5 J g–1, which agrees well with the literature values. The standard molar enthalpy of formation of salicylic acid was derived as –591.2±1.7 kJ mol–1.
Summary The standard molar enthalpy of formation of methyl methylthiomethyl sulfoxide, CH3(CH3SCH2)SO, at T=298.15 K in the liquid state was determined to be -199.4±1.5 kJ mol-1 by means of oxygen rotating-bomb combustion calorimetry.
Anthrone, coumarin and phenazine were studied by combustion calorimetry of small amounts of substance, sublimation calorimetry, neat capacity measurements and differential thermal analysis.
Abstract
The standard (p 0=0.1 MPa) molar enthalpy of formation, Δf H 0 m, for crystalline N-phenylphthalimide was derived from its standard molar enthalpy of combustion, in oxygen, at the temperature 298.15 K, measured by static bomb-combustion calorimetry, as –206.03.4 kJ mol–1. The standard molar enthalpy of sublimation, Δg cr H 0 m , at T=298.15 K, was derived, from high temperature Calvet microcalorimetry, as 121.31.0 kJ mol–1. The derived standard molar enthalpy of formation, in the gaseous state, is analysed in terms of enthalpic increments and interpreted in terms of molecular structure.
Abstract
The energy of combustion of crystalline 3,4,5-trimethoxybenzoic acid in oxygen at T=298.15 K was determined to be -4795.91.3 kJ mol-1 using combustion calorimetry. The derived standard molar enthalpies of formation of 3,4,5-trimethoxybenzoic acid in crystalline and gaseous states at T=298.15 K, ΔfHm Θ (cr) and ΔfHm Θ (g), were -852.91.9 and -721.72.0 kJ mol-1, respectively. The reliability of the results obtained was commented upon and compared with literature values.
Abstract
The standard (p 0=0.1 MPa) molar enthalpy of formation of 1-cyanoacetylpiperidine, in the crystalline state, at T=298.15 K, has been derived from measurements of its standard massic energy of combustion, by static bomb combustion calorimetry, as Δf H m 0=−217.1±1.4 kJ mol−1. The standard molar enthalpy of sublimation was measured, at T=298.15 K, by the microcalorimetric sublimation technique as Δcr g H m 0=103.5±1.9 kJ mol−1.
Abstract
The standard (p 0=0.1 MPa) molar enthalpy of formation, Δf H m 0(l)=169.8±2.6 kJ mol−1, of the liquid 3-bromoquinoline was derived from its standard molar energy of combustion, in oxygen, to yield CO2(g), N2(g) and HBr·600H2O(l), at T=298.15 K, measured by rotating bomb combustion calorimetry. The Calvet high temperature vacuum sublimation technique was used to measure the enthalpy of vaporization of the compound, Δ1 g H m 0=70.7±2.3 kJ mol−1. These two thermodynamic parameters yielded the standard molar enthalpy of formation, in the gaseous phase, at T=298.15 K, Δf H m 0(g)=240.5±3.5 kJ mol−1.
Abstract
The thermal behaviour of salicylsalicylic acid (CAS number 552-94-3) was studied by differential scanning calorimetry (DSC). The endothermic melting peak and the fingerprint of the glass transition were characterised at a heating rate of 10C min-1. The melting peak showed an onset at T on = 144C (417 K) and a maximum intensity at T max = 152C (425 K), while the onset of the glass transition signal was at T on = 6C. The melting enthalpy was found to be ΔmH = 28.90.3 kJ mol-1, and the heat capacity jump at the glass transition was ΔC P = 108.10.1 J K-1mol-1. The study of the influence of the heating rate on the temperature location of the glass transition signal by DSC, allowed the determination of the activation energy at the glass transition temperature (245 kJ mol-1), and the calculation of the fragility index of salicyl salicylate (m = 45). Finally, the standard molar enthalpy of formation of crystalline monoclinic salicylsalicylic acid at T = 298.15 K, was determined as ΔfHm o(C14H10O5, cr) = - (837.63.3) kJ mol-1, by combustion calorimetry.
Thermochemical study of 2- and 3-alkyl substituted thiophenes
Energetic-structural correlations
Abstract
The standard (p 0=0.1 MPa) molar enthalpies of formation, in the condensed phase, of nine linear-alkyl substituted thiophenes, six in position 2- and three in position 3-, at T=298.15 K, were derived from the standard massic energies of combustion, in oxygen, to yield CO2(g) and H2SO4·115H2O(aq), measured by rotating-bomb combustion calorimetry. The standard molar enthalpies of vaporization of these compounds were measured by high temperature Calvet Microcalorimetry, so their standard molar enthalpies of formation, in the gaseous phase, were derived. The results are discussed in terms of structural contributions to the energetics of the alkyl-substituted thiophenes, and empirical correlations are suggested for the estimation of the standard molar enthalpies of formation, at T=298.15 K, for 2- and 3-alkyl-substituted thiophenes, both in the condensed and in the gaseous phases.
