Infrared spectrometric study of the interaction between 2-dimethylamino-3,3-dimethyl-1 azirine and some phenol derivatives

The H-bonded complexes between 2-dimethylamino-3,3-dimethyl-1-azirine (TMAAZ) and some phenol derivatives have been studied by IR spectrometry in carbon tetrachloride. The equilibrium constants at 300, 315 and 328 K and the ? ΔH°, ? Δν_OH and Δν_CN values have been determined. The comparison with previously studied OH … N complexes shows that TMAAZ forms stronger complexes than would be expected from the pK_a value. These facts are discussed in terms of steric, hybridization, solvation and charge transfer effects. From a pK_a of 8, the IR spectrum shows the appearance of ion pairs N⁺-H …^?O. A predominance of protonated species can be calculated for a pK_a of 6. This can explain why 1,2-ring cleavage whose first step is probably the formation of an azirinium cation, occurs for acids characterized by pK_a values lower than 5 but not for enolizable ketones having pK_a values higher than 9.     

Thermodynamics of the second-stage dissociation of n-(2-acetamido)iminodiacetic acid in water from 5 to 55°c

The thermodynamic second dissociation constants of the protonated form of N-(2-acetamido)iminodiacetic acid were determined at 12 temperatures from 5–55°C by measurement of the electromotive force using a cell without liquid junction, with hydrogen and silver—silver bromide electrodes. At 25°C, pK₂is 6.844. The standard changes in Gibbs energy, enthalpy, entropy and heat capacity were derived from the change of the pK₂ values with temperature. At 25°C, ΔG° = 9335 cal mol^-1, ΔH° = 2928 cal mol^-1, ΔS^o = -21.5 cal K^-1 mol^-1, and ΔC°_p = -34 cal K^-1 mol^-1. The results are interpreted and compared with those of structurally related compounds.     

Steric and Inductive Effects on Ionic Association in Aqueous Solutions Using an ion Selective Electrode Technique. II. Magnesium Salts

The stoichiometric association constants, K, the thermodynamic association constants, K_A, and the thermodynamic parameters ΔS°, ΔH°, ΔG° for the association between Mg(II) ion with o-, m and p-toluates,o-,m, and p-chlorobenzoates, and o-, m- and p-bromobenzoates have been determined at 15°C, 25°C, 35°C and 45°C in aqueous media. Ion selective electrodes were used to measure the Mg^{2 +} activities. The trends in the association behavior of Mg(II) salts of aromatic acids connot be explained on the basis of steric effects but can be explained according to the trend of the pKa of the parent organic acids, and the Hammett function, σ, of the salts themselves relative to the corresponding benzoate salt.     

Elastic properties of a nematic in a tetrapalladium organyl-pentadecane system

The temperature dependences of birefringence Δn, anisotropy of permittivity ?_a, and elastic constants K ₁₁ and K ₃₃ in the nematic phase of a tetrapalladium organyl-pentadecane system with a pentadecane content of 55 wt % have been investigated experimentally. It has been shown that, as temperature is elevated, ?_a, K ₁₁, and K ₃₃ values decrease and Δn remains unchanged. Elastic constants K ₁₁ and K ₃₃ have been established to vary from 3.4 × 10^?7 to 5.6 × 10^?6 dyn and from 1.3 × 10^?6 to 27.4 × 10^?5 dyn, respectively. The value of ?_a has been revealed to vary over the range 0.2–0.5. It has been found that, at temperatures above the N₂ → Cr phase transition by 6°C, an imposed electric field induces the growth of tetrapalladium organyl crystals.     

Thermodynamics of cycloalkane-1,1-dicarboxylic acids in aqueous solution

The proton ionization in (Na, H)ClO₄ 0.1 M aqueous solution of cycloalkane- 1,1-dicarboxylic acids at 25°C was studied by means of potentiometric and calorimetric measurements. The thermodynamic functions pK, ΔG, ΔH and ΔS were obtained. The ΔS values were discussed in terms of solute-solvent interaction changes related to the conformational features of the acids.     

Thermodynamics of the complexing of uranyl ions with 1-phenyl-3-methyl-4-benzoylpyrazolone-5 in aqueous dioxane

The thermodynamics of the complexing between hexavalent U and 1-phenyl-3-methyl-4-benzoylpyrazolone-5 (PMBP) have been studied in 70 vol% aqueous—dioxane medium at 25 and 35±0.1°C following the Bjerrum—Calvin pH titration technique, as applied by Van Uitert and Haas. The ligand is mono-protonic. The refinement of results of formation constants has been accomplished by the method of least squares treatment after an algebraic transformation. The formation of 1:1, 1:2 and 1:3 complexes has been observed, the order of stability being log K₁ > log K₂ > log K₃. The stability invariably increases with an increase in temperature both in aqueous as well as aqueous dioxane media. The changes in ΔG⁰, ΔH⁰ and ΔS⁰ at 25 and 35°C for the overall equilibrium constants have also been evaluated. Uranyl complexes of PMBP are entropy stabilized, the values of enthalpy changes being positive. Other factors which affect chelate stability are briefly discussed.     

A theoretical study of the limits of the acidity of carbon acids in phase transfer catalysis in water and in liquid ammonia

The acidities of a large number of carbon acids have been theoretically calculated for the gas-phase and for DMSO solution. The gas-phase values, both ΔH and ΔG, are very well correlated with the available experimental data. From the calculated ΔG values in DMSO and the pKas in the same solvent, a homogeneous set of pK _a (DMSO) values was devised that was used to generate pK _a (water). These last pK _as were used to establish the limits of the acidity of carbon acids for reactions under PTC conditions both alkylations and H/D exchange. A step further led to the pK _as in liquid ammonia and from them to the virtual use of PTC using liquid ammonia instead of water.      

The acid—base equilibria of dimethylphenols in the ground and the first excited singlet states

Measurements of the acidity constants in the ground (pK_a(S₀)) and the lowest excited singlet (pK_a(S₁)) states for 2,3-, 2,4-, 2,5-, 2,6-, 3,4- and 3,5-dimethylphenols in aqueous solution have been carried out spectrophotometrically at 25°C. The pK_a values in S₀ have been derived from the absorption spectra and the pK_a values in S₁ were estimated by means of the Forster cycle. It is found that the hydroxy group is more acidic in the first excited singlet than in the ground state.     

Hydrogen bonding and the protonation site in 3-methyl-4-pyrimidone

The interaction between 3-methyl-4-pyrimidone and phenol derivatives or HBr has been studied by IR spectrometry in solution and in the solid state. For pK_a values ranging from 10.3 to 4.5, normal OH··· OC hydrogen bonds are formed. With stronger acids (PK_a = 0.4 to ?6) protonation occurs at the N(1) nitrogen atom of the ring. For phenols of intermediate pK_a values (3.5), there is no preferred site of interaction, both OH···OC and NH⁺···O^? bonds being formed in solution.     

Effect of temperature on O⊘ reactions and equilibria: A pulse radiolysis study

The pK_a of the hydroxyl radical was measured over the 20–80°C temperature range. At 20°C, the pK_a was 11.84 and fell to 10.81 at 80°C. The dissociation constant for the ozonide anion (O⊘₃⇌O₂+O⊘) was found to be 5.5 × 10^-7 mol dm^-3 at 20°C and 46.2 × 10^-7 mol dm^-3 at 70°C. The rate constants and activation energies for the reaction of O⊘ and OH with 2-propanol, methanol and 3-hexene-1,6-dicarboxylate ions have also been measured.     

Analytical properties of the amidooxime group. V. Thermometric study of 3,3′-oxy-, 3,3′-thio- and 3,3′-iminodipropioamidooxime

The thermometric behaviour of three amidooximes (3,3′-oxy-, 3,3′-thio- and 3,3′-iminodipropioamidooxime) is studied in order to evaluate the errors in their thermometric titration with HCl and the corresponding neutralization enthalpies from the analysis of the enthalpograms. The dissociation parameters (ΔG_i, ΔH_i and ΔS_i) of the three compounds at 25°C are evaluated from the pK_a values and neutralization enthalpies.     

Complex formation of halogenated alcohols with various electron donors

The results are reported of a study, by the near i.r. spectroscopic method, of the hydrogen bonding between 2-bromoethanol, 2-chloroethanol and 2-fluoroethanol, and hexamethylphosphortriamide, dimethyl sulfoxide, dibenzyl sulfoxide, di-p-tolyl sulfoxide and diphenyl sulfoxide in carbon tetrachloride at 288.15, 298.15, 308.15 and 318.15 K.The K₁₁, ΔH°, ΔG° and ΔS° values for the complex formation show that the complex formation ability of the 2-halogen substituted ethanols is weak towards the selected electron donors and much weaker than found earlier for the corresponding 2,2,2-trihalogen substituted ethanols. The basicity order of the electron donors decreases in the order hexamethylphosphortriamide ⪢ dimethyl sulfoxide ⪢ dibenzyl sulfoxide ⪢ di-p-tolyl sulfoxide ⪢ diphenyl sulfoxide, while the proton donating ability of the halogenated alcohols is in the order 2-bromoethanol ⪢ 2-chloroethanol ⪢ 2-fluoroethanol. The pK_a values of the alcohols determined in water are in the same order. Therefore the order of the complex formation ability is opposite to the acidity order in water.     

Thermodynamics of metal cyanide coordination : Part IX. Log K, ΔH, and ΔS values for the Ni-, Zn-, Cd-, and Hg- CN systems at 10, 25, and 40 °C

Log K, ΔH⁰, and ΔS⁰ values valid at zero ionic strength are reported or summarized from previous studies for cyanide ion interaction with bivalent nickel, zinc, cadmium, and mercury at 10, 25, and 40 °C. From the values of ΔH⁰ as a function of temperature, average ΔC_p⁰ values are calculated.     

Buffer Standards for the Physiological pH of the Zwitterionic Compound, HEPPSO from 5 to 55 °C

The values of the thermodynamic second dissociation constant, pK ₂, and related thermodynamic quantities of N-(2-hydroxyethyl)piperazine-N′-2-hydroxypropanesulfonic acid (HEPPSO) have already been reported from 5 to 55?°C, including 37?°C, by the emf method. This paper reports the results for the pH of one chloride-free buffer solution containing the composition: (a) HEPPSO (0.08 mol?kg^?1)+NaHEPPSO (0.04 mol?kg^?1). The remaining seventeen buffer solutions contain a saline medium of ionic strength I=0.16 mol?kg^?1, matching closely that of physiological fluids. Conventional pH values, denoted as pa _H, for all eighteen buffer solutions from 5 to 55?°C have been calculated. The operational pH values, designated as pH, with residual liquid-junction corrections for five buffer solutions, one without NaCl, and four with buffer solutions in saline media of I=0.16 mol?kg^?1 are recommended as pH standards in the range of physiological application. These are based on the NBS/NIST standard scale for pH measurements.     

Elektrometrische Untersuchung der Zusammensetzung und Stabilität von Thiomilchsäurekomplexen mit Zn2+ und UO 2 2+

The complexation of thiolactic acid with Zn²⁺ and UO₂ ²⁺ has been investigated by potentiometric and conductometric titration techniques. Both the metals form 1∶1 and 1∶2 complexes in different pH ranges. Their logK _stab values have been determined byCalvin andMelchior's extension ofBjerrum's method and were further refined by alternative methods at temperatures 20, 30, and 40°C. The values of overall changes in ΔG, ΔH and ΔS for complexation have also been reported.     

Thermodynamic dissociation constants of risedronate using spectrophotometric and potentiometric pH-titration

Risedronate inhibits bone resorption in diseases like osteoporosis, Paget’s disease, tumor bone diseases or the malfunction of phosphocalcium metabolism. The acid-base properties of risedronate in an aqueous solution have been studied in a pH range from 2 to 12 and can be described in terms of four dissociation steps: pK _a,2, pK _a,4, pK _a,5 (related to the dissociation of POH groups) and pK _a,3 related to the dissociation of protonated amino group NH₃ ⁺. The mixed dissociation constants were determined at different ionic strengths I = 0.02 to 0.20 mol dm⁻³ KCl and of 25°C and 37°C using pH-spectrophotometric and pH-potentiometric titration methods. Determination of group parameters L ₀, H _T might lead to false estimates of common parameters p K _a;therefore, the computational strategy employed is important. A comparison between the two programs ESAB and HYPERQUAD demonstrated that the ESAB program provides a better fit of potentiometric titration curve. The thermodynamic dissociation constants pK _a^T were estimated by a nonlinear regression of (pK _a, I) data and a Debye-Hückel equation at 25°C and 37°C, pK _a,2^T = 2.37(1) and 2.44(1), pK _a,3^T = 6.29(3) and 6.26(1), pK _a,4^T = 7.48(1) and 7.46(2) and pK _a,5^T = 9.31(7) and 8.70(3) at 25°C and 37°C using pH-spectroscopic data and pK _a,2^T = 2.48(3) and 2.43(1), pK _a,3^T= 6.12(2) and 6.10(2), pK _a,4^T = 7.25(2) and 7.23(1) and pK _a,5^T = 12.04(5) and 11.81(2) at 25°C and 37°C. The ascertained estimates of three dissociation constants pK _a,3, pK _a,4, pK _a,5 are in agreement with the predicted values obtained using PALLAS      

Thermodynamic studies of hydrogen iodide in dioxane-water mixtures from electromotive force measurements

The standard potentials of the silver-silver iodide electrode were measured in 10,20,30 and 40% (w/w) dioxane-water mixtures at 15,25,35 and 45°C. These values have been used to determine the thermodynamic quantities ΔG_t°, ΔS_t°, ΔH_t° for the transfer of H⁺I^? from water to various dioxane-water mixtures. The ionic ΔG_t° values for H⁺, Cl^?, Br^? and I^? are determined using Feakins method. The chemical and electrical contributions of ΔG_t° are also calculated using the method proposed by Roy and co-workers. The significance of these thermodynamic functions is discussed in relation to the acid—base character of the solvents.     

Buffer Standards for the Physiological pH of the Zwitterionic Compound, ACES, from 5 to 55 °C

The values of the second dissociation constant, pK ₂, and related thermodynamic quantities of [N-(2-acetamido)-2-aminoethanesulfonic acid] (ACES) have already been reported over the temperature range 5 to 55 °C including 37 °C. This paper reports the pa _H values of four chloride ion free buffer solutions and eight buffer solutions with I=0.16 mol⋅kg⁻¹, matching closely that of the physiological sample. Conventional pa _H values for all twelve buffer solutions from 5 to 55 °C are reported. The residual liquid-junction potential correction for two widely used temperatures, 25 and 37 °C, has been made. The flowing-junction calomel cell method has been utilized to measure E _j , the liquid-junction potential. The operational pH values for four buffer solutions at 25 and 37 °C are calculated using the physiological phosphate buffer standard based on the NBS/NIST convention. These solutions are recommended as pH standards in the pH range of 6.8 to 7.2 for physiological fluids.     

A study of helix formation in polydimethysiloxane by Raman scattering

Depolarization ratios ρ of the Raman bands due to CH₃ stretching at 2907 cm^?1 and the Si? O skeletal mode at 491 cm^?1 have been measured in polydimethylsiloxane gum as a function of temperature from 100°C to ?45°C. Below 0°C the changes in p have been interpreted in terms of the formation of helical regions in the gum. The enthalpy of helix formation ΔH has been determined as 3200 ± 600 cal/mole. An upper limit on the entropy change, ΔS, of 16 ± 3 e.u./mole and minimum values of helix content at different temperatures have been found. The Raman spectrum of crystalline polydimethylsiloxane is presented.     

Molecular structure and conformation of gaseous chloroacetyl chloride as determined by electron diffraction

Chloroacetyl chloride is studied by gas-phase electron diffraction at nozzle-tip tempera- tures of 18, 110 and 215°C. The molecules exist as a mixture of anti and gauche confor- mers with the anti form the more stable. The composition (mole fraction) of the vapor with uncertainties estimated at 2σ is found to be 0.770 (0.070), 0.673 (0.086) and 0.572 (0.086) at 18, 110 and 215°C, respectively. These values correspond to an energy difference with estimated standard deviation ΔE^o = E^o_g -E^o_a = 1.3 ± 0.4 kcal mol^?1 and an entropy difference ΔS^o = S^o_g -S^o_a = 0.7 ± 1.1 cal mol^?1 K^?1. Certain of the diffraction results permit the evaluation of an approximate torsional potential function of the form 2V = V₁(1 - cos φ) + V₂(1 - cos 2φ) + V₃(1 - cos 3φ); the results are V₁ = 1.19 ± 0.33, V₂ = 0.56 ± 0.20 and V₃ = 0.94 ± 0.12, all in kcal mol^?1. The results for the distance (r_a), angle (_∠α) and r.m.s. amplitude parameters obtained at the three temperatures are entirely consistent. At 18°C the more important parameters are, with estimated uncertainties of 2σ, r(C-H) = 1.062(0.030) Å, r(CO) = 1.182(0.004) Å, r(C-C) = 1.521(0.009) Å. r(CO-Cl) = 1.772(0.016) Å, r(CH₂-Cl) = 1.782(0.018) Å, ∠C-C-0 = 126.9(0.9)°, ∠CH₂-CO-C1 = 110.0(0.7)°,∠CO-CH₂-C1 = 112.9(1–7)°, ∠H-C-H = 109.5° (assumed), ∠φ (gauche torsion angle relative to 0° for the anti form) = 116.4(7.7)°, δ (r.m.s. amplitude of torsional vibration in the anti conformer) == 17.5(4.2)°.