Standard Enthalpies of Formation of 2,6-Di-tert-butyl4-methylphenol and 3,5-Di-tert-butylphenol and Their Phenoxy Radicals

The standard (p^o = 0.1 MPa) enthalpies of formation of 2,6-di-tert-butyl-4-methylphenol and 3,5-di-tert-butylphenol in the gaseous phase, –315.5 ± 4.4 kJ mol^–1 and –312.7 ± 4.6 kJ mol^–1, respectively, were derived from the standard enthalpies of combustion, in oxygen, at 298.15 K, measured by static bomb combustion calorimetry, and from the standard enthalpies of sublimation, at 298.15 K, measured by Calvet microcalorimetry. The O—H bond dissociation enthalpies in those compounds were determined in benzene by photoacoustic calorimetry, leading to the standard enthalpies of formation of the gaseous phenoxy radicals: –189 ± 8 kJ mol^–1 and –154 ± 6 kJ mol^–1, respectively. These results were used to calculate enthalpies of substituent redistribution reactions, which are proposed as a method to estimate new data for substituted phenols.     

The mean enthalpy of the lanthanide-oxygen bond in 2,2,6,6-tetramethyl-3,5-heptanedione chelates of praseodimium and holmium

The general thermochemical reaction LnCl₃·6H₂O(c)+3Hthd(1)+73.92H₂O(1) = Ln(thd)₃(c) +3HCl·26.64H₂O(aq); rHm (Ln = Pr, Ho and thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) was employed to determine through solution-reaction calorimetry at 298.15 K the standard molar enthalpies of formation of crystalline chelates, –2434.3±11.5 (Pr) and –2384.8±11.5 (Ho) kJ mol^–1. These values and the corresponding molar enthalpies of sublimation enabled the determination of the standard molar enthalpies of chelates in the gaseous phase. From these values the mean enthalpies of the lanthanide-oxygen bond, 265±10 (Pr) and 253±10 (Ho) kJ mol^–1 were calculated.     

A calorimetric and computational study of the thermochemistry of halogenated 1-phenylpyrrole derivatives

The standard molar enthalpies of formation, in the crystalline phase, of three halogenated 1-phenylpyrrole derivatives, namely 1-(4-fluorophenyl)pyrrole, 1-(4-chlorophenyl)pyrrole, and 1-(4-iodophenyl)pyrrole were derived from the respective enthalpies of combustion, measured by rotating-bomb combustion calorimetry. Their enthalpies of sublimation, at T = 298.15 K, were obtained from the Knudsen mass-loss effusion technique. From these two experimental parameters, the standard molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, of 1-(4-fluorophenyl)pyrrole, 1-(4-chlorophenyl)pyrrole, and 1-(4-iodophenyl)pyrrole were calculated, respectively, as (26.2 ± 2.4) kJ · mol⁻¹, (196.2 ± 2.5) kJ · mol⁻¹, and (311.5 ± 2.4) kJ · mol⁻¹.The gas-phase enthalpies of formation of both fluorine and chlorine compounds were estimated by G3(MP2)//B3LYP computations. For the iodine compound, the B3LYP/6-311G(d):ECP46MDF approach was employed. Additionally, the DFT calculations were extended to estimate the enthalpy of formation of the bromine derivative, 1-(4-bromophenyl)pyrrole, performed at the B3LYP/6-311G(d) level of theory.     

Experimental Enthalpies of Formation and Strain of the Methylated 1-Amino-2-phenylethanes

The standard molar enthalpies of formation H _f ^00B0; (liq) at the temperature t = 298.15 K were determined using combustion calorimetry for N-methyl-3-methyl-3-phenyl-2-butaneamine 1a, N,N-dimethyl-3-methyl-3-phenyl-2-butaneamine 1b N-methyl-2,3-dimethyl-3-phenyl-2-butaneamine 2a, and N,N-dimethyl-2,3-dimethyl-3-phenyl-2-butaneamine 2b. The standard molar enthalpies of vaporization H _vap ^00B0; of these compounds were obtained from the temperature variation of the vapor pressure measured in a flow system. The following standard molar enthalpies of formation in gaseous phase H _f ^00B0; (g) are obtained from these data: for 1a – 10.9 ± 1.9; 1b – 3.6 ± 1.8; 1c – 26.6 ± 1.4, and 1d – 23.0 ± 1.8 kJ mol^–1. From the standard molar enthalpies of formation for gaseous compounds which are available in the literature, improved values for the increments of the Benson group addivitiy scheme of amines were calculated. They are used to determine the strain enthalpies of the amines 1 and 2 from this investigation.     

Thermochemistry of Amines: Experimental Standard Molar Enthalpies of Formation of N-Alkylated Piperidines

The standard molar enthalpies of formation _f H _m ^° (l) at the temperature T = 298.15 K were determined using combustion calorimetry for N-methylpiperidine (A), N-ethylpiperidine (B), N-propylpiperidine (C), N-butylpiperidine (D), N-cyclopentylpiperidine (E), N-cyclohexylpiperidine (F), and N-phenylpiperidine (G). The standard molar enthalpies of vaporization _l ^g H ^{m °} of these compounds were obtained from the temperature variation of the vapor pressure measured in a flow system. From these data the following standard molar enthalpies of formation in gaseous phase _f H _m ^° (g) were derived for: A –(61.39 ± 0.88); B –(88.1 ± 1.3); C –(105.81 ± 0.66); D –(126.2 ± 1.3); E ( –88.21 ± 0.75); F –(135.21 ± 0.94); G (70.3 ± 1.4) kJ · mol^–1. They are used to determine the strain enthalpies of the cyclic amines A–G. The N-alkylated piperidine rings have been found to be about strainless.     

Thermochemical study of 2- and 3-alkyl substituted thiophenes

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.     

Standard molar enthalpies of formation of 2-, 3- and 4-cyanobenzoic acids

The standard (p = 0.1 MPa) molar enthalpies of formation of 2-, 3- and 4-cyanobenzoic acids were derived from their standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The Calvet high temperature vacuum sublimation technique was used to measure the enthalpies of sublimation of 2- and 3-cyanobenzoic acids. The standard molar enthalpies of formation of the three compounds, in the gaseous phase, at T = 298.15 K, have been derived from the corresponding standard molar enthalpies of formation in the condensed phase and standard molar enthalpies for phase transition. The results obtained are −(150.7 ± 2.0) kJ · mol⁻¹, −(153.6 ± 1.7) kJ · mol⁻¹ and −(157.1 ± 1.4) kJ · mol⁻¹ for 2-cyano, 3-cyano and 4-cyanobenzoic acids, respectively. Standard molar enthalpies of formation were also estimated by employing two different methodologies: one based on the Cox scheme and the other one based on several different computational approaches. The calculated values show a good agreement with the experimental values obtained in this work.     

Thermochemical properties of three piperidine derivatives

The standard (p ^o=0.1 MPa) molar energies of combustion for the crystalline 1-benzyl-4-piperidinol and 4-piperidine-piperidine, and for the liquid 4-benzylpiperidine, were measured by static bomb calorimetry, in oxygen, at T=298.15 K. The standard molar enthalpies of sublimation or vaporization, at T=298.15 K, of these three compounds were determined by Calvet microcalorimetry. Those values were used to derive the standard molar enthalpies of formation, at T=298.15 K, in their condensed and gaseous phase, respectively.     

Thermochemical study of 5-methyluracil, 6-methyluracil, and 5-nitrouracil

The standard (p° = 0.1 MPa) molar enthalpies of formation, in the crystalline phase, at T = 298.15 K, for 5-methyluracil, 6-methyluracil, and 5-nitrouracil were derived from the values of the standard massic energies of combustion measured by static bomb combustion calorimetry. The results obtained together with literature values of the enthalpies of sublimation yielded the standard molar enthalpies of formation, in gaseous phase, at T = 298.15 K. These values are discussed in the terms of structural enthalpic increments.     

Standard molar enthalpies of formation of 5- and 6-nitroindazole

The present work reports the experimental determination of the standard (p ^o = 0.1 MPa) molar enthalpies of formation in the condensed and gaseous phases, at T = 298.15 K, of 5- and 6-nitroindazole. These results were derived from the measurements of the standard molar energies of combustion, using a static bomb calorimeter and from the standard molar enthalpies of sublimation derived by the application of Clausius–Clapeyron to the temperature dependence of the vapour pressures measured by the Knudsen effusion technique. The results are interpreted in terms of the energetic contributions of the nitro groups in the different positions of the aromatic ring.     

Thermochemical studies for determination of the molar enthalpy of formation of aniline derivatives

The standard (p ^o=0.1 MPa) molar enthalpies of combustion atT=298.15 K were measured by static bomb combustion calorimetry for liquidN,N-diethylaniline,N,N-dimethyl-m-toluidine,N,N-dimethyl-p-toluidine, andN-ethyl-m-toluidine. Vaporization enthalpies forN,N-dimethyl-m-toluidine andN-ethyl-m-toluidine were determined by correlation gas chromatography. Derived standard molar values of _f H _m ^o (g) at 298.15 K forN,N-diethylaniline (62.1±7.6);N,N-dimethyl-m-toluidine (72.6±7.3),N,N-dimentyl-p-toluidine (68.9±7.4),N-ethyl-m-toluidine (30.5±3.8 kJ· mol^–1) were obtained.     

Standard molar enthalpies of combustion of five trans -dimethoxycinnamic acids

The standard (p^o =  0.1 MPa) molar enthalpies of formation for 2,3-, 2,4-, 2,5-, 3,4- and 3,5- trans -dimethoxycinnamic acids, in the gaseous phase, were derived from the standard molar enthalpies of combustion in oxygen, of the crystalline compounds, determined by static bomb combustion calorimetry at T =  298.15 K and from the literature values for the respective enthalpies of sublimation.     

Thermochemistry of Alcohols: Experimental Standard Molar Enthalpies of Formation and Strain of Some Alkyl and Phenyl Congested Alcohols

The standard molar enthalpies of formation _f H _m ^° (cr) at the temperature T = 298.15 K were determined using combustion calorimetry for di-tert-butyl-methanol (A), di-tert-butyl-iso-propyl-methanol (B), and di-phenyl-methyl-methanol (C). The standard molar enthalpies of sublimation _cr ⁸ H _m ^° of these compounds and of di-phenyl-methanol (D) were obtained from the temperature variation of the vapor pressure measured in a flow system. Molar enthalpies of fusion _cr ¹ H _m ^° of the compounds A–D and of tri-phenyl-methanol (E) were measured by differential scanning calorimeter (DSC). From these data and data available from the literature, the following standard molar enthalpies of formation in gaseous phase _f H _m ^° (g) for A, (–397.0 ± 1.2); B, (–418.1 ± 2.3); C, (–34.2 ± 1.3); and D, (0.9 ± 2.1) kJ · mol^–1 were derived, which correspond to strain enthalpies (H _S) of 46.1, 114.7, 8.1, and 5.0 kJ · mol^–1, respectively.     

Aqueous solubilities and enthalpies of solution of adenine and guanine

A generator column—liquid chromatographic technique was used to determine the aqueous solubility of adenine from 20 to 30°C, and of guanine from 15 to 40°C. The 95% confidence limits of the solubilities and molar enthalpies of solution at 25°C are: 8.7±0.1×10^–3M and 33.5±0.5 kJ-mol^–1 for adenine; 3.9±0.1×10^–5M and 49.2±0.6 kJ-mol^–1 for guanine. the adenine enthalpy value includes a small correction for association in the saturated solutions. The previously undetermined molar enthalpy of the second ionization step of guanine (to form the doubly-charged guanine anion) is estimated from our data combined with other measurements to equal 33.8±2.9 kJ-mol^–1.     

Standard molar enthalpies of formation of some methylfuran derivatives

The standard (p ^o = 0.1 MPa) molar enthalpies of formation \Updelta_\textf H_\textm^\texto ( \textl), {{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} ( {\text{l),}} of the liquid 2-methylfuran, 5-methyl-2-acetylfuran and 5-methyl-2-furaldehyde were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The Calvet high temperature vacuum sublimation technique was used to measure the enthalpies of vaporization of the three compounds. The standard (p ^o = 0.1 MPa) molar enthalpies of formation of the compounds, in the gaseous phase, at T = 298.15 K have been derived from the corresponding standard molar enthalpies of formation in the liquid phase and the standard molar enthalpies of vaporization. The results obtained were −(76.4 ± 1.2), −(253.9 ± 1.9), and −(196.8 ± 1.8) kJ mol⁻¹, for 2-methylfuran, 5-methyl-2-acetylfuran, and 5-methyl-2-furaldehyde, respectively.     

Preparation and Thermochemistry of Complexes of Zinc Nitrate with Threonine

The solubility property of Zn(NO₃)₂–Thr–H₂O system (Thr—threonine) at 25°C in the entire concentration range has been investigated by the phase equilibrium semimicromethod. The corresponding phase diagram and refractive index diagram were constructed. From the phase equilibrium results, the incongruently soluble compounds of Zn(Thr)(NO₃)₂ · 2H₂O, Zn(Thr)₂(NO₃)₂ · H₂O, and Zn(Thr)₃(NO₃)₂ · H₂O were synthesized and characterized by IR, XRD, TG–DTG, chemical and elemental analyses. The constant-volume combustion energies of the compounds, _c E, determined by precision rotating bomb calorimeter at 298.15 K, were –6266.88 ± 3.72, –9263.28 ± 2.23, and –11 423.11 ± 6.81 J/g, respectively. The standard enthalpies of combustion for these compounds, _c H _m ^° (complex, s., 298.15 K), were calculated as –2147.40 ± 1.28, –4120.83 ± 0.99, and –6444.68 ± 3.85 kJ/mol and the standard enthalpies of formation, _f H _m ^° (complex, s., 298.15 K), are –1632.82 ± 1.43, –1885.55 ± 1.50, and –2770.25 ± 4.21 kJ/mol. The enthalpies of dissolution of the complexes in a medium of simulated human gastric juice (37°C, pH 1, in the solution of hydrochloric acid), _dis H _m ^° (complex, s., 310 K), which were also measured by a microcalorimeter to be 13.36 ± 0.06, 15.53 ± 0.06, and 17.04 ± 0.05 kJ/mol, respectively.     

Thermochemical studies of phthalimide and two N-alkylsubstituted phthalimides (ALKYL=ETHYL AND n-PROPYL)

The standard (p⁰=0.1 MPa) molar enthalpies of formation, Δ_fH_m⁰, for crystalline phthalimides: phthalimide, N-ethylphthalimide and N-propylphthalimide were derived from the standard molar enthalpies of combustion, in oxygen, at the temperature 298.15 K, measured by static bomb-combustion calorimetry, as, respectively, – (318.0±1.7), – (350.1±2.7) and – (377.3±2.2) kJ mol^–1. The standard molar enthalpies of sublimation, Δ_cr^gH_m⁰, at T=298.15 K were derived by the Clausius-Clapeyron equation, from the temperature dependence of the vapour pressures for phthalimide, as (106.9±1.2) kJ mol^–1 and from high temperature Calvet microcalorimetry for phthalimide, N-ethylphthalimide and N-propylphthalimide as, respectively, (106.3±1.3), (91.0±1.2) and (98.2±1.4) kJ mol^–1. 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.     

Standard enthalpy of formation of 3,4,5-trimethoxybenzoic acid

The energy of combustion of crystalline 3,4,5-trimethoxybenzoic acid in oxygen at T=298.15 K was determined to be -4795.9±1.3 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, Δ_fH_m ^Θ (cr) and Δ_fH_m ^Θ (g), were -852.9±1.9 and -721.7±2.0 kJ mol^-1, respectively. The reliability of the results obtained was commented upon and compared with literature values. This revised version was published online in August 2006 with corrections to the Cover Date.     

Enthalpy of formation of triphenylphosphine sulfide

The first measurements of the enthalpies of combustion, sublimation, and fusion of an organo-phosphorus sulfide, triphenylphosphine sulfide, are reported: _c H _m ^o (C₁₈H₁₅PS, cr)=–(10752.58 ±2.90), _sub H _m ^o (C₁₈H₁₅PS, 403 K)=(136.80±6.09), and _fus H _m ^o (C₁₈H₁₅PS, T_m=435.92 K) =(30.53±0.21) kJ·mol^–1. Correction of the phase change enthalpies toT=298.15K and p^o =0.1 MPa results in the standard phase change enthalpy values of _sub H _m ^o (298.15 K)=(142.8 ±6.8) and _fus H _m ^o (298.15 K)=(19.28±0.21) kj·mol^–1. Accordingly, the enthalpies of formation of solid, liquid, and gaseous triphenylphosphine sulfide are derived: _f H _m ^o (C₁₈H₁₅PS, cr) =(63.20±2.56), _fH _m ^o (C₁₈H₁₅PS, l)=(82.48±2.57), and _fH _m ^o (C₁₈H₁₅PS, g)=(206.0±7.3) kJ·mol^–1. From these ancillary data, the P=S double-bond enthalpy is 394 kJ-mol^–1 and in good agreement with earlier reaction calorimetry results. These phosphorus sulfide values are compared with those for the arsenic sulfides. Plausibility arguments are given for our results.     

Combined experimental and computational thermochemistry of isomers of chloronitroanilines

The standard (p^° = 0.1 MPa) molar enthalpies of formation, at T = 298.15 K, of 4-chloro-3-nitroaniline and 5-chloro-2-nitroaniline, in the condensed phase, were derived from their standard molar energies of combustion, in oxygen, to yield CO₂(g), N₂(g), and HCl · 600H₂O(l), measured by rotating bomb combustion calorimetry. From the temperature dependence of the vapour pressures of these compounds, measured by the Knudsen effusion technique, their standard molar enthalpies of sublimation, at T = 298.15 K, were derived by means of the Clausius–Clapeyron equation. The Calvet microcalorimetry was also used to measure the standard molar enthalpies of sublimation of these compounds, at T = 298.15 K. The combination of the standard molar enthalpies of formation in the condensed phases and the standard molar enthalpies of sublimation yielded the standard molar enthalpies of formation in the gaseous phase at T = 298.15 K for each isomer. Further, the standard (p^° = 0.1 MPa) molar enthalpies, entropies and Gibbs free energies of sublimation, at T = 298.15 K, were also derived.The standard molar enthalpies of formation, in the gaseous phase of all the chloronitroaniline isomers were also estimated by the Cox scheme and by the use of computational thermochemistry and compared with the available experimental values.