Solvent effects on the dissociation of weak acids of three charge types in water/N-methylacetamide media

In order to elecidate the role of charge type on the change of dissociation constant with increasing polarity of the solvent medium, the pK values and associated thermodynamic quantities for an uncharged acid (acetic acid), a cationic acid (protonated tris(hydroxymethyl)aminomethane), and two ampholytes (MOPS and Tricine) were determined in mixtures of water andN-methylacetamide (NMA). Electromotive-force measurements of cells without liquid junction containing hydrogen electrodes and silver-silver bromide electrodes were used to determine the pK at nine temperatures from 5 to 45°C. The solvent compositions varied from pure water to a mixture containing a mole fraction of NMA of 0.25 (57.5 mass % NMA). The solvent effects are compared with similar data for water/methanol solvents of decreasing polarity. They reflect both the reduction in interionic energy accompanying the elevation in dielectric constant and also the greater protophilic character of NMA as compared with methanol.     

Thermodynamic properties of LiCl solutions in <Emphasis Type="Italic">N</Emphasis>-methylacetamide at 308.15–328.15 K

Enthalpies of dissolution of crystalline LiCl and enthalpies of dilution of LiCl solutions in N-methylacetamide (NMA) with electrolyte concentrations no greater than 0.32m are measured on an isoperibolic calorimeter at 308.15, 318.15, and 328.5 K. Standard enthalpies of the dissolution of LiCl in NMA are calculated at different temperatures. The thermodynamic properties of the solution and its components are calculated and analyzed in the investigated range of concentrations and temperatures.     

Densities and Excess Molar Volumes of Alkane (Heptane, Octane, Nonane, or Decane) + Thiophene from T=293.15 to 313.15 K

Densities of four binary systems composed of an alkane (heptane, octane, nonane, or decane) and thiophene were measured at temperatures from 293.15 to 313.15?K at atmospheric pressure (0.7?atm). Measurements were made covering the full range of compositions for all systems studied and for the pure compounds by using a vibrating-tube densimeter (VTD). Excess molar volumes have been obtained from these experimental results and were fitted to a Redlich?CKister type expansion. The excess molar volumes exhibit positive deviations from ideal behavior for all of the binary systems studied here.     

Viscosities,densities and speeds of sound of the binary systems: 2-propanol with octane,or decane,or dodecane at T=(293.15, 298.15, and 303.15) K

Viscosities, densities and speed of sound have been measured over the whole composition range for (2-propanol with octane, or decane, or dodecane) at T=(293.15, 298.15, and 303.15) K and atmospheric pressure along with the properties of the pure components. Excess molar volumes, isentropic compressibility, deviations in isentropic compressibility and viscosity deviations for the binary systems at the above-mentioned temperatures were calculated and fitted to Redlich–Kister equation to determine the fitting parameters and the root-mean-square deviations. Prediction of the dynamic viscosities of this binary mixture from UNIFAC-VISCO and ASOG-VISCO methods has been determined.     

Rate constants for the gas-phase reactions of OH radicals with a series of bi- and tricycloalkanes at 299 ± 2 K: Effects of ring strain

Relative rate constants for the gas-phase reactions of OH radicals with a series of bi- and tricyclic alkanes have been determined at 299 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with cyclohexane of 7.57 × 10^?12 cm³/molec·s, the rate constants obtained are (× 10¹² cm³/molec·s): bicyclo[2.2.1]heptane, 5.53 ± 0.15; bicyclo[2.2.2]octane, 14.8 ± 1.0; bicyclo[3.3.0]octane, 11.1 ± 0.6; cis-bicyclo[4.3.0]nonane, 17.3 ± 1.3; trans-bicyclo[4.3.0]nonane, 17.8 ± 1.3; cis-bicyclo[4.4.0]decane, 20.1 ± 1.4; trans-bicyclo[4.4.0]decane, 20.6 ± 1.2; tricyclo[5.2.1.0^2,6]decane, 11.4 ± 0.4; and tricyclo[3.3.1.1^3,7]decane, 23.2 ± 2.1. These data show that overall ring strain energies of ?4–5 kcal mol^?1 have no significant effect on the rate constants, but that larger ring strain results in the rate constants being decreased, relative to those expected for the strain-free molecules, by ratios which increase approximately exponentially with the overall ring strain.     

Study of hydrogen bonds in N-methylacetamide by DFT calculations of oxygen, nitrogen, and hydrogen solid-state NMR parameters

Solid-state nuclear magnetic resonance (NMR) parameters of ¹⁷O, ¹⁴N/¹⁵N, and ²H/¹H nuclei were evaluated in two available neutron crystalline structures of N-methylacetamide (NMA) at 250 and 276 K, NMA-I and NMA-II, respectively. Density functional theory calculations were performed by B3LYP method and 6-311++G** and IGLO-II type basis sets to calculate the electric field gradient (EFG) and chemical shielding (CS) tensors at the sites of mentioned nuclei. In order to investigate hydrogen bonds (HBs) effects on NMR tensors, calculations were performed on four-model systems of NMA: an optimized isolated gas-phase, crystalline monomers, crystalline dimers, and crystalline trimers. Comparing the calculated results reveal the influence of N–H···O=C and C–H···O=C HB types on the NMR tensors which are observable by the evaluated parameters including quadrupole coupling constant, C _Q, and isotropic CS, σ _iso. Furthermore, the results demonstrate more influence of HB on the EFG and CS tensors of NMA at 276 K rather than that of 250 K.     

Volumetric and transport properties of binary liquid mixtures of N-methylacetamide with lactones at temperatures (303.15 to 318.15) K

The values of density (ρ), viscosity (η) and speed of sound (u) have been measured for binary liquid mixtures of γ-butyrolactone (GBL), δ-valerolactone (DVL), and ε-caprolactone (ECL) with N-methylacetamide (NMA) over the whole composition range at T = (303.15 to 318.15) K and atmospheric pressure. From these data, excess molar volume (V^E), deviation in viscosity (Δη), and deviation in isentropic compressibility (Δκ_s), are calculated. The results are fitted to a Redlich–Kister type polynomial equation to derive binary coefficients and standard deviations.     

Solvation Properties of Aliphatic Alcohol–Water and Fluorinated Alcohol–Water Solutions for Amide Molecules Studied by IR and NMR Techniques

Solvation properties of aliphatic alcohol–water and fluorinated alcohol–water solutions were probed by amide molecules as solutes using infrared (IR) and ¹H and ¹³C NMR techniques. These include four alcohols: ethanol (EtOH), 2-propanol (2-PrOH), 2,2,2-trifluoroethanol (TFE), and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and three amides: N-methylformamide (NMF), N-methylacetamide (NMA) and N-methylpropionamide (NMP). The hydrogen bonds of the amide carbonyl oxygen with water are gradually weakened as the alcohol content increases. This decreases in the order of HFIP > TFE ≈ 2-PrOH > EtOH. In TFE– and HFIP–water solutions, the hydrogen bond between the amide amino hydrogen and water is also gradually broken with increasing x _A. This trend is more notable in the order of NMP > NMA > NMF. The hydrophobic moieties of the amide methyl and ethyl groups are solvated by the fluoroalkyl groups of fluorinated alcohols due to the hydrophobic interaction among them. Thus, the steric hindrance generated by the solvated alkyl group of amides promotes the breaking of the hydrogen bonds between amide and water.     

Chlorination of N-Methylacetamide: A kinetic study

In the pH range 4.3–13, the reaction between N-methylacetamide (NMA) and sodium hypochlorite in dilute aqueous solution to give N-chloro-N-methylacetamide (CINMA) was found to be far slower than analogous reactions affording N-chloramines or N-chloroamino acids. The rate expression for chlorination was first-order each in [NMA] and [Cl_tot] (the total concentration of chlorinating species). A rate constant calculated for chlorination by each chlorinating species indicated that the order of increasing reactivity was HClO < ClO^? < Cl₂ < CH₃COOCl (formed in the presence of acetic/acetate buffer). At pH > 7 the reaction rate was unaffected by variations in [Cl^?] or pH, but under acidic conditions the rate increased with [Cl^?] and decreasing pH. Regardless of pH, the reaction rate was not affected by changes in ionic strength. The influence of temperature on the reaction rate was also studied which allowed calculation of thermodynamic activation parameters for the N-chlorination reaction. © 1995 John Wiley & Sons, Inc.     

Synthesis of isatin-N-mannich bases

The synthesis of a series of isatin-N-Mannich bases derived from isatin, 5-methyl and 5-bromoisatins as the active hydrogen component and dimethylamine, diethylamine, morpholine, piperidine, N-ethylcyclohexylamine, 3-azabicyclo[3.2.2]nonane and 3-aza-bicyclo[3.2.1]octane as the secondary amine moiety is described. These compounds are to be screened for their pharmacological properties.     

Electron transfer from highly strained polycyclic molecules

The details of electron transfer from strained, saturated hydrocarbons in electrochemical oxidations on platinum have been studied. Among the systems investigated were tetracyclo[3.2.0.0^2,7.0^4,6]heptane, tricyclo [4.1.0.0^2,7]heptane, pentacyclo[4.3.0.0^2,4.0^5,7]nonane, pentacyclo[4.4.0.0^2,5.0^3.8.0^4,7] decane, pentacyclo[4.2.0.0^2,5.0^3,8.0^4,7]octane, pentacyclo[4.3.0.0^2,5.0^3,8.0^4,7]nonane, bicyclo[2.1.0]pentane, and a variety of bicyclo[1.1.0]butane derivatives. The oxidation of 1,2,3-trimethylbicyclo [1.1.0]butane is discussed in detail.     

Anomalous volumetric behavior of water-hexane and water-decane mixtures in the vicinity of the critical region as studied by infrared spectroscopy

Infrared spectra of binary mixtures of water with hexane and decane were measured at temperatures and pressures in the 473-648 K and 70-350 bar ranges, respectively. Volumetric concentrations of water and the hydrocarbons in the mixtures were obtained from absorption intensities of the fundamental OH stretching band of HDO and combination transitions of the hydrocarbons. Using both the concentrations, densities of the aqueous mixtures were estimated and compared with densities before mixing, which were calculated using literature densities of the neat liquids. It is found that anomalously large volume expansion on mixing occurs in the vicinity of the critical region of the mixtures.     

Phase behavior of binary mixtures of water,carbon dioxide and decane predicted with a lattice-gas model

The Kleintjens—Koningsveld lattice-gas model is used to predict the phase behavior of pure CO₂, water and decane, and of binary mixtures of CO₂ with water and decane. The model, with parameters fitted to experimental data, predicts very accurate vapor pressures and liquid—vapor coexistence densities for the pure fluids. For the binary mixtures, the model correctly predicts the qualitative patterns of phase behavior using two temperature-dependent mixture parameters fitted to simple polynomials over a small range of temperature. For quantitative predictions over wide temperature ranges, however, the temperature dependence of the mixture parameters must be fitted carefully over the same ranges of temperatures. The performance of the Kleintjens—Koningsveld model is compared to that of the Peng—Robinson model.     

Synthesis of 1‐azabicyclic systems by double cyclization

5‐Cyano‐1‐azabicyclo[3.3.0]octane ( 1 ) was prepared in one step from 1,7‐dichloro‐4‐heptanone ( 4 ) under mild conditions. The application of this method for the preparation of 5‐cyano‐4,6‐dimethyl‐1‐azabicy‐clo[3.3.0]octane ( 11 ) gave two diastereomers in equilibrium. The NMR measurements of 11 and its reduced compound 15 showed that the major isomer is the cis‐exo form, and the minor isomer is the trans form. Molecular orbital calculations indicated that the cis‐exo form is more stable than the trans form, in agreement with the experimental results. Furthermore, 6‐cyano‐1‐azabicyclo[4.3.0]nonane ( 17 ) and 1‐azabicy‐clo[4.4.0]decane ( 19 ), both including a six‐membered ring, were prepared from appropriate haloketones by using this double cyclization method.     

Measurement and correlation of liquid-liquid equilibria of methanol+alkane+ether ternary systems

Liquid-liquid equilibrium (LLE) data at 25°C are reported for eight ternary systems consisting of methanol, alkane (heptane, octane, nonane or decane), and ether (diethyl ether or dibutyl ether). The UNIFAC group contribution method was used to predict or correlate the ternary LLE data obtained. The predicted results shows the discrepancy from the experiments. Therefore, the UNIFAC group interaction parameters were adjusted to give better correlation performance.     

Synthèse de spirohydantoines dérivées du diphényl-2,4-aza-3-bicyclo-[3.3.1]nonane et du diphényl-7,9-aza-8-bicyclo[4.3.1]decane par réaction de Bucherer dans la N,N-diméthylformamide: Influence de la température et cours stéréochimique. Communication préliminaire

Synthesis of Spyrohydantoines Derivatives of 2,4-Diphenyl-3-azabicyclo[3.3.1]nonane and 7,9-Diphenyl-8-azabicyclo[4.3.1]decane via Bucherer Reaction in N,N-Dimethylformamide: Influence of the Temperature and Stereochemical Path The unreactives ketones related to 2,4-diphenyl-3-azabicyclo [3.3.1]nonan-9-one to the Bucherer reaction in usuals conditions show excellent reactivity in DMF. as unique solvant. The stereochemical paths of these reactions and the synthetic utility of the temperature modification are described.     

Solvation of decane and benzene in mixtures of 1-octanol and <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylformamide

The heats of dissolution of decane and benzene in a model system of octanol-1 (OctOH) and N,N-dimethylformamide (DMF) at 308 K are measured using a variable temperature calorimeter equipped with an isothermal shell. Standard enthalpies are determined and standard heat capacities of dissolution in the temperature range of 298–318 K are calculated using data obtained in [1, 2]. The state of hydrocarbon molecules in a binary mixture is studied in terms of the enhanced coordination model (ECM). Benzene is shown to be preferentially solvated by DMF over the range of physiological temperatures. The solvation shell of decane is found to be strongly enriched with 1-octanol. It is obvious that although both hydrocarbons are nonpolar, the presence of the aromatic π-system in benzene leads to drastic differences in their solvation in a lipid–protein medium.     

Volume expansion behavior of water–hydrocarbon mixtures at high temperatures and pressures as studied by infrared spectroscopy

Infrared spectra of binary mixtures of water with toluene and ethylbenzene have been measured at temperatures and pressures in the 473–623 K and 100–350 bar ranges, respectively. Concentrations of water and hydrocarbons in the hydrocarbon-rich phase have been estimated from the integrated band intensities, and using these results, densities of the hydrocarbon-rich phase have been obtained as a function of temperature and pressure. In order to characterize the density of the hydrocarbon-rich phase, the experimental densities have been compared with the average densities before mixing, which were calculated from the literature densities of pure water and pure hydrocarbon with the experimental concentrations. All the experimental densities of the mixtures are lower than the average densities before mixing at the same condition. Relative volume change for mixing has been estimated and an anomalously large increase in volume has been found in the vicinity of the critical region of the water–hydrocarbon mixtures. This volumetric behavior is very similar to that previously found for water–benzene mixtures, and may be characteristic of the critical behavior of fluid mixtures of water and hydrocarbons.     

Determination of absolute photoionization cross‐sections of alkanes and cyclo‐alkanes

Absolute photoionization and dissociative photoionization cross‐sections of eleven n‐alkanes (n‐pentane, n‐hexane, n‐heptane, n‐nonane, n‐decane, n‐undecane, n‐dodecane, n‐tridecane, n‐tetradecane, n‐pentadecane and n‐hexadecane), three cyclo‐alkanes (cyclopentane, methylcyclohexane and trans‐decahydronaphthalene) and iso‐octane were measured for photon energies from the ionization thresholds to 11.5 eV. The measurements were performed with the binary‐liquid‐mixture method utilizing the photoionization cross‐sections of benzene as a calibration standard. The ionization energies of n‐alkanes and cyclo‐alkanes were also calculated at the B3P86/6‐31 + +G(d,p) level and by the G3B3 method. Copyright © 2010 John Wiley & Sons, Ltd.     

DMA水溶液的1H NMR研究

测量了N,N-二甲基乙酰胺(DMA)水溶液体系不同温度下全浓度范围的¹H NMR数据, 对体系中的缔合情况进行了讨论, 应用化学缔合模型求得了各缔合平衡常数K和缔合平衡的ΔH. 结合N,N-二甲基甲酰胺(DMF)和N-甲基乙酰胺(NMA)水溶液的研究结果, 发现酰胺自身结构和酰胺浓度是影响酰胺水溶液性质的主要因素.