Enthalpy characteristics of dilute solutions of amides in acetonitrile

The enthalpy of mixing of formamide,N-methylformamide,N,N-dimethylformamide, and hexamethylphosphoric triamide with MeCN was measured in the 283–328 K range. The enthalpic coefficients of the binary and ternary interactions between the amide molecules are calculated within the framework of the McMillan-Mayer theory. The contributions to the enthalpy of dissolution due to cavity formation in the solvent (Δ_cav H ⁰) and due to solute-solvent interaction (Δ_int H ⁰) were determined. The enthalpies of specific and nonspecific solvation of amides in MeCN were calculated. The main contribution to the enthalpy of solvation of formamide andN-methylformamide is from specific interactions, while forN,N-dimethylformamide and hexamethylphosphoric triamide it is from nonspecific interactions. The values obtained are compared with those for solutions of the amides mentioned in water and methanol. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1730–1735, October, 1993.     

Enthalpy characteristics of dilute solutions of acetonitrile

The enthalpies of mixing of acetonitrile with formamide,N-methylformamide,N,N-dimethylformamide, and hexamethylphosphoric triamide were measured in the temperature interval from 283.15 to 328.15 K. The enthalpy coefficients of binary and ternary interactions were calculated by the methods of the McMillan-Mayer theory. The contributions to the enthalpy of solution due to the formation of a cavity in the solvent, Δ_cav H°, and those due to the interaction of the solute with the solvent, Δ_int H°, were determined. The enthalpies of the specific and non-specific solvation of acetonitrile in the corresponding amides were calculated. Specific interactions were found to contribute the most to the solvation enthalpy of acetonitrile. The obtained values were compared with analogous values for solutions of acetonitrile in water and alcohols. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 289–293, February, 1997.     

Thermodynamische Untersuchungen ann-Alkan/n-Alkin-Systemen

Heats of mixing (H ^E)ofn-octane with 1,2,3,4-isomers ofn-octyne,n-heptane withn-1-heptyne andn-nonane withn-1-nonyne at temperatures from 298.15 to 318.15 K were measured with aCalvet-type microcalorimeter. The results are presented in tables and correlated with theRedlich-Kister equation.

     

Topological and thermodynamic investigations of molecular interactions of aniline and o-toluidine with chloroform

Molar excess volumes, V^E, molar excess enthalpies, H^E, and speeds of sound data, u, of chloroform (i) + aniline or o-toluidine (j) binary mixtures have been measured as a function of composition at 308.15 K. Isentropic compressibility changes of mixing, have been determined by employing speed of sound data. Topological investigations of V^E data reveals that aniline, chloroform and o-toluidine are associated entities and these (i + j) mixtures contain a 1:1 molecular complex. The IR studies lend further support to the nature and extent of interaction for the proposed molecular entity in the mixtures. H^E and values have also been calculated by employing Moelwyn-Huggins concept [Polymer 12 (1971) 387] taking topology of the constituents of the mixtures. It has been observed that calculated H^E and values compare well with their corresponding experimental values. The observed V^E, H^E and data have also been analyzed in terms of Flory theory.     

Synthesis and structure of azomethines based onN-vinyl derivatives of 2-amino- and 2-formylimidazoles

New Schiff's bases of theN-vinylimidazole andN-vinylbenzimidazole series were synthesized.¹H NMR data suggest that the azomethines exist in theE-form with respect to the CH=N bond and that the vinyl groups havetrans-orientation relative to each other. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 1857–1859, October, 1997.     

Prediction of vapor-liquid equilibrium from excess enthalpy data for binary ether +n-alkane or cyclohexane mixtures

Vapor liquid equilibrium (VLE) is successfully predicted from excess enthalpy H^E data for binary ether + n-alkane or cyclohexane mixtures. Parameters for the continuous linear association model (CLAM) and for the UNIQUAC Model for the excess Gibbs energy G^E were determined from H^E data measured at a low temperature (ambient temperature). These parameters are used to predict VLE data at low and high temperatures. The dependence of the accuracy of predictions on the set of H^E data chosen to evaluate the parameters and on the model for G^E are discussed.     

N-substituted amides of 2-cyanopenta-2E,4-dienoic acid

N-Substituted amides of 2-cyanopenta-2E,4-dienoic acid were synthesized by condensation ofN-substituted cyanoacetamides with acrolein in a dioxane-DMSO solution in the presence of Zn(OAc)₂·2H₂O as a condensing agent. X-ray diffraction study of 3-methylanilide of 2-cyanopenta-2E,4-dienoic acid (2d) demonstrated that the crystal structure of this compound is similar to that of 2-cyanopenta-2E,4-dienoic acid studied previously. However, the presence of themeta-tolyl substituent in molecule2d apparently results in the fact that the β-structure, which is typical of 2-cyanopenta-2E,4-dienoic acid, does not exist in the crystalline phase of2d. Henkel Kommanditgesellschaft auf aktien, Deutschland, D-40191 Dusseldorf, Henkelstrasse, 67. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 933–937, May, 1999.     

Dependence of the solution and transfer enthalpies of DL-α-alanyl-DL-α-asparagine on the composition of water-amide binary solvents at 298.15 K

Solution enthalpies of DL-α-alanyl-DL-α-asparagine (AlaAsn) in water-formamide, water-N-methylformamide, water-N,N-dimethylformamide, and water-N,N-dimethylacetamide mixtures were measured in the range of amide mole fractions x ₂ = 0–0.3. The standard enthalpies of solution (Δ_sol H°) and transfer (Δ_tr H°) of AlaAsn from water to the binary solvent and enthalpy coefficients of pair-wise interactions (h _xy ) of AlaAsn with amide molecules were calculated. The influence of the composition of the water-organic mixture on the enthalpy characteristics of AlaAsn is discussed. It is shown that the enthalpy characteristics of solution and transfer of AlaAsn are related to the structure of amides.     

Topological and thermodynamic investigations of binary mixtures: Molar excess volumes, molar excess enthalpies and isentropic compressibility changes of mixing

Molar excess volumes, V^E, molar excess enthalpies, H^E, and speeds of sound, u, of o-toluidine (i) + cyclohexane or n-hexane or n-heptane (j) binary mixtures have been determined over entire range of composition at 308.15 K. Speeds of sound data have been utilized to predict isentropic compressibility changes of mixing, of (i + j) mixtures. The observed V^E, H^E and data have been analyzed in terms of Graph theory. The analysis of V^E data by Graph theory reveals that o-toluidine exists as an associated molecular entity and (i + j) mixtures contain 1:1 molecular complex. It has been observed that V^E, H^E and values calculated by Graph theory compare well with their corresponding experimental values. The observed data have also been analyzed in term of Flory theory.     

Prediction of free excess enthalpy and excess enthalpy of nonelectrolyte mixtures with the modified TASQUAC model

Summary Using the known models for liquid mixtures (NRTL, UNIQUAC,...), the excess free enthalpy and the heats of mixing cannot be calculated simultaneously in good agreement with experimental data using only two parameters (or three for NRTL) per temperature and binary system. The excess enthalpy can be estimated only qualitatively but not quantitatively. There is also much doubt about the sign of the predictedH ^E data if the absolute value ofH ^E is small [1]. In this work, we examined the possibilities of modified TASQUAC in simultaneous prediction ofVLE andH ^E data and the thermodynamic consistency of experimental data.

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Vorhersage von freier Exzessenthalpie und Exzessenthalpie von Nichtelektrolytmischungen mit Hilfe des modifizierten TASQUAC-Modells

Zusammenfassung Mit Hilfe der bekannten Modelle für flüssige Mischungen (NRTL, UNIQUAC,...) können die freie Exzeßenthalpie und die Mischungswärme nicht gleichzeitig in guter Übereinstimmung mit experimentellen Daten berechnet werden. Die Exzeßenthalpie kann, ausgehend von Parametern, die ausVLE-Daten erhalten wurden, nur qualitativ, nicht quantitativ beschrieben werden. Weiterhin ist das berechnete Vorzeichen der Mischungswärme bei betraglich kleinen Werten der Exzeßenthalpie unsicher [1]. In dieser Arbeit werden die Möglichkeiten des modifizierten TASQUAC-Modells zur simultanen Beschreibung vonVLE- undH ^E-Daten untersucht sowie die thermodynamische Konsistenz der verwendeten Daten überprüft.

     

Enthalpies of transfer of ubiquinone-0 from water to aqueous surfactant solutions at various temperatures

Mixing and dilution enthalpies of aqueous solutions of 2,3-dimethoxy-5-methyl-1,4-benzoquinone (UQ₀) and of N,N-dimethyl-dodecylamine-N-oxide (DDAO) were measured and used to calculate the enthalpies of transfer δH(W →W +S) of UQ₀ from water to DDAO aqueous solutions at 20‡, 25‡, 30‡, and 35‡C. From the dependence of δH(W →W +S) on surfactant concentration, the distribution constant between aqueous and micellar phases and the standard transfer enthalpy of UQ₀ from water to DDAO micelles were evaluated along with the standard transfer free energy and entropy. The approach used required knowledge of the CMC and micellization enthalpy at each temperature. Thus, the thermodynamics of micellization of DDAO was studied by means of dilution enthalpy measurements at the several temperatures.     

Solvation of amides of carboxylic acids in aqueous solutions of ethylene glycol

Enthalpies of solution of amides of formic, acetic, and propionic acids with different degrees of N-substitution in aqueous solutions of ethylene glycol were measured at 298.15 K. The concentration of ethylene glycol did not exceed 4 mol kg^–1. The reasons for increasing endothermic values of the enthalpies characterizing the amide transfer from water to a mixed aqueous-organic solvent on going from primary to tertiary amides and from formamides to the corresponding acetamides are discussed. The enthalpic coefficients of pair interactions between amides and ethylene glycol in water were calculated. The endothermicity of the interaction of the alkyl groups of the amide molecules with ethylene glycol results in positive values of the coefficients. The coefficient values increase with the enhancement of the hydrophobic properties of hydrophilic non-electrolytes (urea, formamide, ethylene glycol) due to an increase in the contribution of the hydrophobic component and a decrease in the contribution from the interaction of the polar groups of amides to the total interaction.     

Topological investigations of the molecular species and molecular interactions that characterize pyrrolidin-2-one + lower alkanol mixtures

Molar excess volumes, V^E, molar excess enthalpies, H^E, and speeds of sound data, u, of pyrrolidin-2-one (i) + ethanol or propan-1-ol or propan-2-ol or butan-1-ol (j) binary mixtures have been determined over entire composition range at 308.15 K. The observed speeds of sound data have been utilized to predict excess isentropic compressibilities, of the investigated binary mixtures. The observed excess thermodynamic properties V^E, H^E and have been analyzed in terms of Graph theory. The analysis of V^E data by the Graph theory suggests that pyrrolidin-2-one exists mainly as a mixture of cyclic and open dimer; ethanol as a mixture of dimer and trimer; butan-1-ol and propan-2-ol as mixture of monomer and dimer and propan-1-ol as a dimer in the pure state, and their mixtures contain 1:1 molecular complex. The IR studies lend additional credence to the nature and extent of interactions for the proposed molecular entities in the mixtures. Also, it has been observed that V^E, H^E and values predicted by the Graph theory compare well to with their corresponding experimental values.     

The effect of pressure on order destruction and order creation in linear or branched alkane mixtures

The pressure dependence of the excess enthalpy H ^E , dH ^E /dP, has been calculated from experimental excess volumes V ^E and dV ^E /dT using dH ^E /dP=V ^E –TdV ^E /dT. dH ^E /dP at zero pressure are reported at 25°C and equimolar concentration for the mixtures: cyclohexane with the series of normal alkanes (n-C _n , where n=6,8,10,12,14 and 16) and with the series of highly branched alkanes (br-C _n , where n=6,8,12 and 16), benzene, toluene and p-xylene +n-C _n and 1-chloronaphthalene +n-C _n and br-C _n . Experimental and Flory theory dH ^E /dP values are in good agreement for the whole cyclohexane +br-C _n series. For the n-C _n series, dH ^E /dP becomes increasingly positive deviating from the Flory predictions. This discrepancy is due to the presence of short-range orientational order in the higher n-C _n pure liquids which makes dH/dP more negative and which, upon mixing, is destroyed producing a positive contribution to dH ^E /dP not accounted for by the theory. The discrepancy between theoretical and experimental dH ^E /dP is large for benzene, but progressively smaller for toluene, p-xylene and 1-chloronaphthalene. These results are consistent with creation of order between the aromatic plate-like molecule and the long n-C _n in solution. For 1-chloronaphthalene +n-C _n , this order creation process produces a negative contribution to dH ^E /dP which balances the positive order-destruction contribution originated by the rupture, upon mixing, of short-range orientational order in pure n-C _n .     

Standard molar enthalpies of formation and sublimation of <Emphasis Type="Italic">N</Emphasis>-phenylphthalimide

The standard (p ⁰=0.1 MPa) molar enthalpy of formation, Δ_f 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 –206.0±3.4 kJ mol^–1. The standard molar enthalpy of sublimation, Δ^g _cr H ⁰ _m , at T=298.15 K, was derived, from high temperature Calvet microcalorimetry, as 121.3±1.0 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.     

Thermodynamic study of poly(N-vinyl caprolactam) hydration at temperatures close to lower critical solution temperature

The lower critical solution temperature of aqueous solutions of poly(N-vinyl caprolactam) falls in the 305–307 K range and depends on the molecular weight of the polymer. The thermodynamic functions of mixing at 298 K have been calculated from measurements of vapor pressures and heats of dissolution and dilution. Partial Gibbs energy, partial enthalpy, and partial entropy of mixing were negative over the entire range of composition. Increasing temperature resulted in a decrease in the exothermal character of mixing. Excessive heat capacity values, calculated from the dependencies of enthalpy of mixing on temperature, were positive over the entire composition range. Heat capacity of dilute solutions was measured at 298 K and partial heat capacity of poly(N-vinyl caprolactam) at infinite dilution was shown to be positive. The data obtained point out the hydrophilic and hydrophobic hydration of poly(N-vinyl caprolactam) in aqueous solutions. Hydrophobic hydration dominates at temperatures close to binodal curve. As a result, the mutual mixing of the polymer with water is decreased and phase separation takes place.     

Excess molar enthalpies of the ternary system <Emphasis Type="Italic">p</Emphasis>-xylene+decane+diethyl carbonate

Excess molar enthalpies of the ternary system {x ₁ p-xylene+x ₂decane+(1–x ₁–x ₂)diethyl carbonate} and the involved binary mixtures {p-xylene+(1–x)decane}, {xp-xylene+(1–x)diethyl carbonate} and {xdecane+(1–x)diethyl carbonate} have been determined at the temperature of 298.15 K and atmospheric pressure, over the whole composition range, using a Calvet microcalorimeter. The experimental excess molar enthalpies H _m ^E are positive for all the binary systems studied over the whole composition range. Excess molar enthalpy for the ternary system is positive as well, showing maximum values at x ₁=0, x ₂=0.4920, x ₃=0.5080, H _m,123 ^E=1524 J mol^–1.     

Nitrogen bridgehead compounds. Part 50 . Vilsmeier-haack acylation of 6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidin-4-ones,Part 5

6-Methyl-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidin-4-ones 1-5 were subjected to Vilsmeier-Haack acylation with complexes of phosphoryl chloride and different amides. Acylation at position 9 of the pyridopyrim-idines was successful with the iminium salt formed in situ from N-formylpiperidine, N-methylformanilide or N,N-diethylbenzamide, but unsuccessful with the iminium salt formed from N,N-diethylacetamide or N,N-di-ethylisobutyramide, respectively. The iminium salt formed from formanilide, N-methylpyrrolidinone or formamide reacted only with those tetrahydropyridopyrimidinones which contain a strongly electronegative substituent (e.g. CN or CO₂Et) in position 3. With the latter derivatives, the 9-phenylaminomethylene group could be introduced using N,N-diphenylformamide or in a “one-pot” procedure with aniline and triethyl orthoformate. Ethanolysis of 9-N-methyl-N-phenylaminomethylene derivatives 15 and 19 afforded 9-ethoxy-methylene compounds 26 and 27 in the presence of hydrogen chloride. The structures of the 9-substituted 6-methyltetrahydropyridopyrimidin-4-ones 14-25 were elucidated by means of uv, ¹H and ¹³C nmr spectroscopy. 9-Piperidinomethylene 14 , 9-(N-methyl-N-phenylaminomethylene 15-19 and 9-(N-methyl-2-pyrrolidinylidene) 21 derivatives exist as E geometric isomers. 9-Phenylaminomethylene-6-methyl-4-oxo-6,7,8,9-tetra-hydro-4H-pyrido[1,2-a]pyrimidine-3-carbonitrile 20 displays a solvent-dependent E-Z isomerism. The bis-compound 25 contains both E and Z geometric exo C ? CH double bonds. 9-Benzoyl derivatives 23 and 24 exist predominantly as the 1,6,7,8-tetrahydropyridopyrimidin-4-one tautomer.     

Excess volumes of the binary mixtures 1,2-dichloroethane ? n -alkanols [C2?C6]

Volume changes on mixing of binary systems formed by 1,2-dichloroethane andn-alcohols, namely, ethanol,n-propanol,n-butanol,n-pentanol andn-hexanol were measured as a function of composition at 30, 35, 40 and 45 °C. At all compositions theV ^E values are all positive for all systems. The molar excess volumes of mixing for equimolar mixtures increase as the length of carbon chain increases.V ^E becomes more positive on increasing temperature. The positive value of the excess volume has been attributed to breaking of hydrogen bonds of associated species of alcohol by dilution with 1,2-dichloroethane.     

Hydrolysis of ureas. Kinetics and mechanism of the basic hydrolysis of indole-1-carboxamides and (5H-dibenz[b,f]azepine)-5-carboxamide

The hydroxide ion catalyzed hydrolysis of indole-1-carboxamide and indole-1-(N,N-dimethyl)carboxamide has been studied in water at 60.0° and [OH⁻] concentration between 0.3--2.4N. The rate constants of formation of the tetrahedral intermediate are strongly increased by N-substitution with a heteroaromatic ring in comparison with simple amides. Carbamazepine, (5H-dibenz[b,f]azepine)-5-carboxamide, a potent anticonvulsant drug, is particularly stable under these conditions.