Enthalpies of formation and substituent effects of ortho-, meta-, and para-aminotoluenes from thermochemical measurements and from ab initio calculations

The molar enthalpies of vaporization of 2-amino-, 3-amino-, and 4-aminotoluenes were obtained from the temperature dependence of the vapor pressure measured by the transpiration method. The molar enthalpy of sublimation of 4-aminotoluene was measured in the same way. The standard (p(o) = 0.1 MPa) molar enthalpy of formation delta fH(o)m(cr) at the temperature T = 298.15 K of crystalline 4-aminotoluene was measured using combustion calorimetry. The thermochemical investigations of aminotoluenes available in the literature were collected and combined with our own experimental results to obtain our own reliable standard molar enthalpies of formation at T = 298.15 K in the gaseous state. Ab initio calculations of aminotoluenes have been performed using the MP2Full/6-31G(d) and G3(MP2) basis sets, and the results from the bond separation method are in excellent agreement with the experiment. These new results help to resolve the uncertainty in the available thermochemical data on aminotoluenes. Weak mutual interactions of substituents in aminotoluenes have been realized using an isodesmic reaction procedure.     

Thermochemistry of ionic liquid-catalyzed reactions. experimental and theoretical study of chemical equilibria of isomerization and transalkylation of tert-butylbenzenes

The chemical equilibrium of mutual interconversions of tert-butylbenzenes was studied in the temperature range 286 to 423 K using chloroaluminate ionic liquids as a catalyst. Enthalpies of five reactions of isomerization and transalkylation of tert-butylbenzenes were obtained from temperature dependences of the corresponding equilibrium constants in the liquid phase. Molar enthalpies of vaporization of methyl-tert-butylbenzenes and 1,4-di tert-butylbenzene were obtained by the transpiration method and were used for a recalculation of enthalpies of reactions and equilibrium constants into the gaseous phase. Using these experimental results, ab initio methods (B3LYP and G3MP2) have been tested for prediction thermodynamic functions of the five reactions under study successfully. Thermochemical investigations of tert-butylbenzenes available in the literature combined with experimental results have helped to resolve contradictions in the available thermochemical data for tert-butylbenzene and to recommend consistent and reliable enthalpies of formation for this compound in the liquid and the gaseous state.     

Organic carbonates: experiment and ab initio calculations for prediction of thermochemical properties

This work has been undertaken in order to obtain data on thermodynamic properties of organic carbonates and to revise the group-additivity values necessary for predicting their standard enthalpies of formation and enthalpies of vaporization. The standard molar enthalpies of formation of dibenzyl carbonate, tert-butyl phenyl carbonate, and diphenyl carbonate were measured using combustion calorimetry. Molar enthalpies of vaporization of these compounds were obtained from the temperature dependence of the vapor pressure measured by the transpiration method. Molar enthalpy of sublimation of diphenyl carbonate was measured in the same way. Ab initio calculations of molar enthalpies of formation of organic carbonates have been performed using the G3MP2 method, and results are in excellent agreement with the available experiment. Then the group-contribution method has been developed to predict values of the enthalpies of formation and enthalpies of vaporization of organic carbonates.     

Thermodynamic properties of caffeine: Reconciliation of available experimental data

Molar enthalpies of sublimation of two crystal forms of caffeine were obtained from the temperature dependence of the vapour pressure measured by the transpiration method. A large number of primary experimental results on the temperature dependences of vapour pressure and phase transitions have been collected from the literature and have been treated in a uniform manner in order to derive sublimation enthalpies of caffeine at T = 298.15 K. This collection together with the new experimental results reported here has helped to resolve contradictions in the available sublimation enthalpies data and to recommend a consistent and reliable set of sublimation and formation enthalpies for both crystal forms under study. Ab initio calculations of the gaseous molar enthalpy of formation of caffeine have been performed using the G3MP2 method and the results are in excellent agreement with the selected experimental data.     

Thermochemistry of 2- and 3-thiopheneacetic acids: calorimetric and computational study

The enthalpies of formation in the condensed and gas states, Delta f H m degrees (cd) and Delta f H m degrees (g), of 2- and 3-thiopheneacetic acids were derived from their respective enthalpies of combustion in oxygen, measured by a rotating bomb calorimeter, and the variation of vapor pressure with temperature determined by the Knudsen effusion technique. Theoretical calculations at the G3 level were performed, and a study on molecular and electronic structure of the compounds has been carried out. Calculated Delta f H m degrees (g) values using atomization and isodesmic reactions are compared with the experimental data. Experimental and theoretical results show that the 3-thiopheneacetic acid is thermodynamically more stable than the 2-isomer.     

Combined experimental and computational study of the thermochemistry of the fluoroaniline isomers

The standard (p degrees = 0.1 MPa) molar enthalpies of formation in the condensed phase of all the fluoroanilines, with the exception of the 2,3,5-trifluoroaniline compound, were derived from the standard molar energies of combustion in oxygen at T = 298.15 K, measured by rotating bomb combustion calorimetry. Calvet high-temperature vacuum sublimation experiments were performed to measure their enthalpies of vaporization or sublimation. These experiments allowed the determination of the standard molar enthalpies of formation in the gaseous phase and at T = 298.15 K. These values are also compared with estimates based on G3MP2B3 and BP86/6-31+G(d) computations, which have been extended also to the fluoroaniline that was not studied experimentally. The results are in close agreement with a mean deviation of approximately 3 kJ.mol-1. The largest difference between experimental and G3MP2B3 values is found for the pentafluoroaniline (-7.0 kJ.mol-1). For the three monofluoroanilines, the composite approach has been used also to compute gas-phase acidities, electron and proton affinities, ionization enthalpies and N-H bond dissociation enthalpies. The computed values compare well with available experimental results supporting the new computed data.     

Iterative and regioselective cross-couplings of 2-chloro-3,4-diiodopyridine leading to 2,3,4-triheteroarylpyridines

A one-pot synthesis of 2-chloro-3,4-diiodopyridine from 2-chloropyridine is described via a Directed ortho Metallation (DoM)/Halogen Dance (HD) mechanism in 26-28% yields. By performing sequential, iterative Suzuki-Miyaura cross-couplings using a variety of functionalised heteroaryl and arylboronic acids, a series of novel 2,3,4-triheteroarylpyridine scaffolds have been accessed in synthetically viable yields, including sterically hindered derivatives. 2-Chloro-4-heteroaryl-3-iodopyridines and 2-chloro-3,4-diheteroarylpyridines are also reported. The synthesis of 5-[3,4-bis(2-phenylethynyl)pyridin-2-yl]-2-fluoropyridine via a two-step Sonogashira/Suzuki-Miyaura reaction sequence from 2-chloro-3,4-diiodopyridine, phenylacetylene and 6-fluoropyridin-3-yl-3-boronic acid has been achieved in 48% overall yield.     

Pairwise-substitution effects and intramolecular hydrogen bonds in nitrophenols and methylnitrophenols. Thermochemical measurements and ab initio calculations

The standard molar enthalpies of formation in the gaseous state of a series of nitrophenols, 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 5-methyl-2-nitrophenol, 2-methyl-5-nitrophenol, and 3-methyl-4-nitrophenol, have been obtained from combustion calorimetry and results from the temperature dependence of the vapor pressure measured by the transpiration method. To verify the experimental data, ab initio calculations of all compounds have been performed using MP, DFT, and G3 methods. Enthalpies of formation derived from the G3 methods are in a good agreement with the experimental results. The quantitative analysis of ortho, meta, and para pairwise-substituent effects in nitrophenols has been performed, and the strength of intramolecular hydrogen bonding in o-nitrophenol has been derived from thermochemical results and compared with those obtained from spectroscopic experiments and ab initio calculations. The new results help to resolve uncertainties in the available thermochemical data on extended series of nitrophenols.     

Calculation of the enthalpies of formation and proton affinities of some isoquinoline derivatives

Ab initio molecular orbital theory has been used to calculate enthalpies of formation of isoquinoline, 1-hydroxyisoquinoline, 5-hydroxyisoquinoline, and 1,5-dihydroxyisoquinoline as well as some pyridine and quinoline derivatives. The proton affinities of the four isoquinoline derivatives were also obtained. The high-level composite methods G3(MP2), G3(MP2)//B3LYP, G3//B3LYP, and CBS-QB3 have been used for this study, and the results have been compared with available experimental values. For six of the eight studied compounds, the theoretical enthalpies of formation were very close to the experimental values (to within 4.3 kJ · mol⁻¹); where comparison was possible, the theoretical and experimental proton affinities were also in excellent agreement with one another. However, there is an extraordinary discrepancy between theory and experiment for the enthalpies of formation of 1-hydroxyisoquinoline and 1,5-dihydroxyisoquinoline, suggesting that the experimental values for these two compounds should perhaps be re-examined. We also show that popular low cost computational methods such as B3LYP and MP2 show very large deviations from the benchmark values.     

Dissociation Constants of Protonated Amines in Water at Temperatures from 293.15 K to 343.15 K

The dissociation constants of protonated 2-amino-1-ethanol (MEA), diethanol amine (DEA), triethanol amine (TEA), methyldiethanol amine (MDEA), 2-amino-2-methyl-1-propanol (AMP), 3-dimethylamino-1-propanol (DMAP), tris(hydromethyl)aminomethane (THAM), 2-[2-(dimethylamino)ethoxy]ethanol (DMAEOE) and, 1,2-bis(2-aminoethoxy)ethane (DiAEOE) were determined in the temperature range 293.15 to 343.15 K using a potentiometric titration method. The experimental technique was first validated using as reference the available literature data of MDEA. The dissociation enthalpies of amines were derived from their dissociation constants using the Van’t Hoff equation. Experimental dissociation constants and dissociation enthalpies were discussed in term of amine structure and compared with literature values when available.     

Characterization of fluvalinate residues in honey by gas chromatography–atomic emission detection and gas chromatography–mass spectrometry

Two hyphenated techniques, gas chromatography–mass spectrometry and gas chromatography–atomic emission detection, have been used to identify the degradation products of the acaricide fluvalinate in a methanol solution of the commercially available formulation Mavrick, as well as in honey from beehives treated with this product. The major degradation products were 2-chloro-4-trifluoromethylaniline (I), methyl 2-[2-chloro-4-trifluoromethylaniline]-3-methylbutanoate (II), N-(2-chloro-4-trifluoromethyl-phenyl)valine (III), and 3-phenoxybenzaldehyde (IV). Fluvalinate in honey is gradually degraded, 3-phenoxybenzaldehyde being the most abundant residue.     

Thermochemistry of 2- and 3-acetylthiophenes: calorimetric and computational study

The relative stabilities of 2- and 3-acetylthiophenes have been evaluated by experimental thermochemistry and the results compared to high-level ab initio calculations. The enthalpies of combustion, vaporization, and sublimation were measured by rotating-bomb combustion calorimetry, Calvet microcalorimetry, correlation gas chromatography, and Knudsen effusion techniques and the gas-phase enthalpies of formation, at T = 298.15 K, were determined. Standard ab initio molecular orbital calculations at the G2 and G3 levels were performed, and a theoretical study on the molecular and electronic structures of the compounds studied has been conducted. Calculated enthalpies of formation using atomization and isodesmic reactions are compared with the experimental data. Experimental and theoretical results show that 2-acetylthiophene is thermodynamically more stable than the 3-isomer. A comparison of the substituent effect of the acetyl group in benzene and thiophene rings has been carried out.     

Synthesis of isothiocoumarin derivatives

A method was developed for the synthesis of 1-oxo-1H-isothiochromenes from 2-benzofuran-1(3H)-one (phthalide). 3-Bromo-6-chloro- and 3,6-dibromo-2-benzofuran-1(3H)-ones were prepared by the bromination of 6-chloro- and 6-bromo-2-benzofuran-1(3H)-ones and were converted by hydrolysis into 5-chloro- or 5-bromo-2-formylbenzoic acids. The condensation of these acids with rhodanine followed by recyclization gave 7-chloro- and 7-bromo-1-oxo-1H-isothiochromene-3-carboxylic acids.     

Synthetic and structural studies of some chloro-substituted methyl 2,1-benzisoxazole-3-carboxylates and related compounds

Methyl 5-chloro- and 5,7-dichloro-2,1-benzisoxazole-3-carboxylates have been synthesized by treatment of o-nitromandelic and 5-chloro-2-nitroamandelic methyl esters, respectively, with thionyl chloride under appropriate reaction conditions. The structural assignments of both heterocyclic products were based on elemental and spectral analyses, and their conversion to the corresponding 5-chloro- and 5,7-dichloro substituted 2,1-benzisoxazole-3-carboxylic acids and isatins. Methyl α-chloro-o-nitrophenylacetate and o-nitrophenylcarbomethoxymethinyl sulfite were also obtained from reactions of methyl o-nitromandelate and thionyl chloride. A possible reaction mechanism involving two consecutive nucleophilic substitutions of methyl o-nitromandelate with thionyl chloride was proposed to account for the formation of methyl 5-chloro-2,1-benzisoxazole-3-carboxylate.     

Gaussian-3 study of the thermochemistry of the germane and its fluoro chloro derivatives

The thermochemistry of all fluoro and chloro substituted germane molecules have been theoretically studied. Computed G3//B3LYP standard enthalpies of formation at 298 K obtained from isodesmic reaction schemes were compared with values derived via total atomization energies. Bond dissociation energies and energy barriers for the lowest dissociation pathways were estimated at 0 K. From these data, the most probable dissociation products at 0 K were predicted for the thermal decomposition reactions of the gaseous species. Calculated results are compared with experimental determinations as well as other theoretical data when available. The following isodesmic enthalpies of formation in kcal x mol(-1) were calculated for 10 new germane species simultaneously substituted with fluoro and chloro atoms, for which no previously available computations were found in the literature: GeHFCl2, -125.8; GeCl2F, -104.3; GeHFCl, -67.5; GeF2Cl2, -186.3; GeF3Cl, -242.9; GeH2FCl, -89.7; GeCl3F, -159.6; GeHClF2, -168.0; GeF2Cl, -144.3; GeFCl, -81.1.     

Interactions of Some Amino Acids with Aqueous Osmoprotectant Proline at 298.15 K: Volumetric and Calorimetric Studies

Apparent molar volumes of a homologous series of amino acids in aqueous proline solutions have been obtained from densities at 298.15 K, measured with a vibrating-tube digital densimeter. These data have been used to deduce the partial molar volumes of transfer from water to aqueous proline solutions; these partial molar volumes of transfer are found to be positive for glycine, alanine, α-amino-n-butyric acid and valine, whereas they are negative for leucine. The number of water molecules hydrated to the amino acids was estimated from the partial molar volume data. In order to supplement this information, enthalpies of transfer of aqueous amino acids from water to 0.1, 2.25 and 1 mol⋅dm⁻³ aqueous proline have been determined at 298.15 K using a VP-ITC titration calorimeter. The data on the partial molar volumes and enthalpies of transfer are discussed in terms of various interactions operating in the ternary mixtures of amino acids, water and proline.     

水溶液中氨基酸与甲脲的焓相互作用

用LKB-2277精密微热量计测定了298.15 K时甘氨酸、L-丙氨酸、L-丝氨酸、L-缬 氨酸、L-苏氨酸和L-脯氨酸六种α-氨基酸分别与甲脲分子在水溶液中的混合过程焓变及 这些溶质分子在水溶液中的稀释焓.实验数据根据McMillan-Mayer理论进行回归分析,得到 各级交叉焓相互作用系数.讨论了不同氨基酸与甲脲分子的相互作用机制.结果表明,氨基酸 的两性离子部分、α-碳上的非极性脂肪侧基、极性的羟基侧基和五元吡咯环结构对交叉焓 对作用系数hxy具有不同贡献.与尿素相比,甲脲分子中-CH3基团的引入明显增强了分子的 疏水性.     

Di-hydroxybenzenes: Catechol, resorcinol, and hydroquinone: Enthalpies of phase transitions revisited

Molar enthalpies of sublimation of 1,2-di-hydroxybenzene, 1,3-di-hydroxybenzene, and 1,4-di-hydroxybenzene were obtained from the temperature dependence of the vapor pressure measured by the transpiration method. The molar enthalpies of fusion of 1,2- and 1,4-isomers were measured by differential scanning calorimetry (DSC). A large number of the primary experimental results on the temperature dependences of vapor pressure and phase transitions have been collected from the literature and have been treated in a uniform manner in order to derive sublimation, vaporization and fusion enthalpies of di-hydroxybenzenes at the reference temperature 298.15 K. The data sets on phase transitions were checked for internal consistency. This collection together with the new experimental results reported here has helped to resolve contradictions in the available thermochemical data and to recommend consistent and reliable sublimation, vaporization and fusion enthalpies for all three isomers under study.     

Determination of vapor pressures and enthalpies of vaporization of 1,2-alkanediols

Molar enthalpies of vaporization of 1,2-ethanediol, 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, and 1,2-octanediol were obtained from the temperature dependence of the vapor pressure measured by the transpiration method. The measured data sets were successfully checked for internal consistency. A large number of the primary experimental results on temperature dependences of vapor pressures have been collected from the literature and have been treated uniform in order to derive vaporization enthalpies at the reference temperature 298.15 K. This collection together with the experimental results reported here has helped to resolve some contradictions which have been met in the available literature.     

Energetic polymer salts from 1‐vinyl‐1,2,4‐triazole derivatives

Energetic polymers salts from 1‐vinyl‐1,2,4‐triazole derivatives have been synthesized via free radical polymerization of 1‐vinyl‐1,2,4‐triazolium monomer salts or by protonation of poly(1‐vinyl‐1,2,4‐triazole) with inorganic or organic acids. Standard enthalpies of formation of the new monomer salts were calculated using the computationally feasible DFT(B3LYP) and MP2 methods in conjunction with an empirical approach based on densities of salts. Compared with the monomer salts, the polymer salts have good thermal properties with high densities > 1.5 g cm^?3. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2414–2421, 2008