Thermodynamic properties of N,N-dimethylformamide + water

The excess viscosities, η^E, and excess energy of activation (ΔΕ_η)^Ε of dynamic viscosity have been investigated by using dynamic viscosity measurements for N,N-dimethylformamide + water (DMFW) mixtures over the entire range of mole fractions at five different temperatures. The results were also fitted with the Redlich–Kister equation. This system exhibited very large positive values of η^E and (ΔΕ_η)^Ε due to the increased dipole–dipole interactions and correlation length between unlike molecules. The activation parameters ΔΗ_σ and ΔS_σ have been also calculated, and they show that the critical region has an important effect on the dynamic viscosity properties. The results obtained are discussed from the viewpoint of the existence of interactions between the components.     

Effect of sodium caproate on the volumetric and viscometric properties of glycine,dl-α-alanine,and dl-α-amino-n-butyric acid in aqueous solutions

The apparent molar volumes (V_m,2) and relative viscosities (η_r) at T=(298.15 and 308.15) K have been obtained for glycine, dl-α-alanine, and dl-α-amino-butyric acid in aqueous sodium caproate solutions from measurements of density and the flow time. The standard partial molar volumes (V^∘_m,2), standard volumes of transfer (Δ_tV^∘), the viscosity B-coefficients, and the activation thermodynamic quantities (Δμ₂^∘≠ and ΔS₂^∘≠) of viscous flow have been calculated for the amino acids. It is shown that the standard partial molar volumes, viscosity B-coefficients, and activation free energies for viscous flow increase with increasing number of carbon atoms in the alkyl chain of the amino acids. An increase in V^∘_m,2 and Δ_tV^∘ with increasing electrolyte concentrations have been explained due to the interactions of sodium caproate with the charged center of zwitterions for the amino acids. A comparison of the V^∘_m,2 values for glycine, dl-α-alanine, and dl-α-aminon-n-butyric acid in different aqueous salts solutions showed that carboxylate ions have stronger interactions with amino acid than chloride, thiocyanate, and nitrate ions. Results of viscosity are discussed in terms of changes in solvent structure.     

Effect of sodium acetate on the rheological behaviour of some mono-, di-, and tri-saccharides in aqueous solutions over the temperature range (288.15 to 318.15) K

The Jones–Dole viscosity B-coefficients for various mono-, di-, and tri-saccharides in water and in (0.5, 1.0, 2.0, and 3.0) mol · kg^?1 aqueous solutions of sodium acetate have been determined at different temperatures, T = (288.15, 298.15, 308.15, and 318.15) K from viscosity data. Densities used to determine viscosities have been reported earlier. The viscosity B-coefficients of transfer, Δ_tB, has been estimated for the transfer of saccharides from water to aqueous sodium acetate solutions. The positive Δ_tB values were obtained in all cases and their magnitudes increase with the increase in concentration of sodium acetate. Pair, η_AB and higher order, η_ABB viscometric interaction coefficients (using McMillan–Mayer theory), and dB/dT coefficients have also been determined. Activation Gibbs free energies and other related thermodynamic activation parameters of viscous flow have been determined using Feakin’s transition-state theory. These parameters have been discussed in terms of solute–solute and solute–solvent interactions occurring in these solutions.     

Molecular structure of a water-polyethylene glycol-KOH system, according to densitometry and viscometry data

The dynamic viscosity and density of a water-polyethylene glycol-KOH system are measured at temperatures of 293.15 to 323.15 K in concentrations ranging from 0.00001 and 0.001 (mole fractions). The activation parameters of viscous flow (ΔG _η ^≠ , ΔH _η ^≠ , and ΔS _η ^≠ ), structural temperature (T ₀), the partial molar volume of polyethylene glycol (PEG) in solution $\left( {\tilde V} \right)$ , intrinsic viscosity([η]), and the Huggins constant (K _H), are calculated. It is found that PEG has a structuring effect on water in water-PEG and water-PEG-KOH systems, with the PEG structuring effect in the latter being somewhat attenuated by the destructuring influence of KOH.     

Viscosities and Refractive Indices of Binary Mixtures of Dimethylsulphoxide with Some Aromatic Hydrocarbons at Different Temperatures: An Experimental and Theoretical Study

The viscosities, η, and refractive indices, n, of pure dimethylsulphoxide (DMSO), benzene, toluene, o‐xylene, m‐xylene, p‐xylene and mesitylene, and those of their 54 binary mixtures, with DMSO as common component, covering the whole composition range have been measured at 298.15, 303.15, 308.15, 313.15, and 318.15 K. From the experimental data, the deviations in viscosity, Δη and deviations in molar refraction, ΔR_m have been calculated. The variation of these parameters with composition and temperature of the mixtures have been discussed in terms of molecular interaction in these mixtures. The effect of the number and position of the methyl groups in these aromatic hydrocarbons on molecular interactions in these mixtures has also been discussed. The free energies, ΔG^*, enthalpies, ΔH^* and entropies, ΔS^* of activation of viscous flow have also been obtained by using Eyring viscosity equation. The ΔH^* values were found independent of temperature. The dependence of these thermodynamic parameters on composition of the mixtures has been discussed. Further, the viscosities and refractive indices of these binary mixtures were calculated theoretically from pure component data by using various empirical and semi‐empirical relations and the results were compared with the experimental findings.     

KINETICS AND MECHANISM FOR INTRAMOLECULAR ISOMERIZATION OF HRu3 (μ3-η3-EtSCCMeCMe)(CO)9 TO Ru3(μ-SEt) (μ3-η3-CCMeCHMe)(CO)9

Abstract

The kinetics for isomerization of HRu₃ (μ₃-η³-EtSCCMeCMe)(CO)₉ TO Ru₃(μ-SEt) (μ₃-η³-CCMeCHMe)(CO)₉, were determined. The overall process involves C[sbnd]H elimination, C[sbnd]S and Ru[sbnd]Ru bond cleavage and Ru₂(μ-S) bond formation. Activation parameters were determined from the temperature dependence (ΔH^? = 127(3) kJ/mol, ΔS^?= 56(11) J/mol-K) and from the pressure dependence (0[sbnd]207 MPa, ΔV^? ₀ +12.7(1.1) cm³/mol, Δβ^? = +0.037(0.012) cm³/(mol-MPa)) of the rate constant. The data are consistent with an intramolecular reaction involving significant metal-metal or carbon-sulfur bond cleavage in the transition state. The activation volume is too large to be accommodated by C[sbnd]H elimination alone and CO dissociation is not involved.     

Volumetric,acoustic, and viscometric studies of molecular interactions in binary mixtures of diethylene glycol monomethyl ether with 1-alkanols at temperatures from (293.15 to 308.15) K

In this work, densities ρ, speeds of sound u, and viscosities η, have been measured over the whole composition range for the binary mixtures of diethylene glycol monomethyl ether (DEGMME), CH₃(OCH₂CH₂)₂OH with 1-hexanol, CH₃(CH₂)₅OH, 1-octanol, CH₃(CH₂)₇OH, and 1-decanol, CH₃(CH₂)₉OH at T = (293.15, 298.15, 303.15, and 308.15) K along with the properties of the pure components. By using the experimental values of ρ, u, and η, excess molar volume, $V_m^E$, deviations in viscosity, Δη, isentropic compressibility κ_S, deviations in isentropic compressibility Δκ_S, deviations of the speed of sound Δu, have been calculated. The viscosity results have also been analysed in terms of some semi-empirical equations.     

Measurement and Calculation the Excess Molar Properties of Binary Mixtures Containing Isobutanol, 1-Amino-2-Propanol,and 1-Propanol at Temperatures of (293.15 to 333.15) K

Densities, ρ, and viscosities, η, of pure isobutanol, 1-amino-2-propanol, and 1-propanol, along with their binary mixtures of {x ₁isobutanol + x ₂1-propanol}, {x ₁1-amino-2-propanol + x ₂1-propanol}, and {x ₁1-amino-2-propanol + x ₂isobutanol} were measured over the entire composition range and at temperatures (293.15–333.15) K at ambient pressure (81.5 kPa). Excess molar properties such as the excess molar volume, V _m ^E , partial molar volumes, \( \bar{V}_{1} \) and \( \bar{V}_{2} \), excess partial molar volumes, \( \bar{V}_{1}^{\text{E}} \) and \( \bar{V}_{2}^{\text{E}} \), thermal expansion coefficient, α, excess thermal expansion coefficient, α ^E, viscosity deviation, Δη, and the excess Gibbs energy of activation, ?G ^E*, for the binary mixtures were calculated from the experimental values of densities and viscosities. The excess values of the binary mixtures are negative in the entire composition range and at all temperatures, and increase with increasing temperature. Viscosity deviations, Δη, are negative over the entire composition range and decrease with increasing temperature. The viscosities of the mixtures were correlated by the models of McAllister, Heric, Hind, Katti, and Nissan. The obtained data were correlated by Redlich–Kister equation and the fitting parameters and standard deviations were determined.     

Rheological behaviour of some saccharides in aqueous potassium chloride solutions over temperature range (288.15 to 318.15) K

The viscosities, η of mono-, di-, tri-saccharides and methylglycosides, viz., d(+)-xylose (XYL), d(?)-arabinose (ARA), d(?)-ribose (RIB), d(?)-fructose (FRU), d(+)-galactose (GAL), d(+)-mannose (MAN), d(+)-glucose (GLU), d(+)-melibiose (MEL), d(+)-cellobiose (CEL), d(+)-lactose monohydrate (LAC), d(+)-maltose monohydrate (MAL), d(+)-trehalose dihydrate (TRE), sucrose (SUC), d(+)-raffinose pentahydrate (RAF), α-methyl-d(+)-glucoside (α-Me-GLU), methyl-α-d-xylopyranoside (Me-α-XYL), and methyl-β-d-xylopyranoside (Me-β-XYL) in water and in (0.5, 1.0, 2.0, and 3.0) mol · kg^?1 aqueous solutions of potassium chloride (KCl) have been determined at T = (288.15, 298.15, 308.15, and 318.15) K from efflux time measurements by using a capillary viscometer. Densities used to determine viscosities have been reported earlier. The viscosity data have been utilized to determine the viscosity B-coefficients employing the Jones–Dole equation at different temperatures. From these data, the viscosity B-coefficients of transfer, Δ_tB have been estimated for the transfer of various saccharides/methylglycosides from water to aqueous potassium chloride solutions. The Δ_tB values have been found to be positive, whose magnitude increases with the increase in concentration of potassium chloride in all cases. The dB/dT coefficients, pair, η_AB and triplet, η_ABB viscometric interaction coefficients have also been determined. Gibbs free energies of activation and related thermodynamic parameters of activation of viscous flow have been determined employing Feakin’s transition-state theory. The signs and magnitudes of various parameters have been discussed in terms of solute–solute and solute–solvent interactions occurring in these solutions. The effect of substitution of –OH by methoxy group, –OCH₃ has also been discussed.     

Thermal studies and spectral characterization of the chelate of bis-(η5-cyclopentadienyl titanium(IV) with salicylidene-4-methylaniline

A new chelate (η⁵-C₅H₅)₂Ti(SB)₂, whereSB=O, N donor Schiff base salicylidene-4-methylaniline, was synthesized. The course of thermal degradation of the chelate was studied by thermogravimetric (TG) and differential thermal analysis (DTA) under dynamic conditions of temperature. The order of the thermal decomposition reaction and energy of activation was calculated from TG curve while from DTA curve the change in enthalpy was calculated. Evaluation of the kinetic parameters was performed by Coats-Redfern as well as Piloyan-Novikova methods which gaven=1, ΔH=1.114 kJ·mol^?1, ΔE=27.01 kJ·mol^?1, ΔS=?340.12 kJ·mol^?1·K^?1 andn=1, ΔH=1.114 kJ·mol^?1, ΔE=20.01 kJ·mol^?1, ΔS=?342.60 kJ·mol^?1·K^?1, respectively. The chelate was also characterized on the basis of different spectral studies viz. conductance, molecular weight, IR, UV-visible and¹H NMR, which enabled to propose an octahedral structure to the chelate.     

Determination of composition of ethylene–propylene copolymers by intrinsic viscosity

Intrinsic viscosities have been measured at 25° on five ethylene–propylene copolymer samples ranging in composition from 33 to 75 mole-% ethylene. The solvents used were n-C₈ and n-C₁₆ linear alkanes and two branched alkanes, 2,2,4-trimethylpentane and 2,2,4,4,6,8,8-heptamethylnonane (br-C₁₆). This choice was based on the supposition that the branched solvent would prefer the propylene segments and the linear solvent the ethylene segments, due to similarity in shape and possibly in orientational order. It was found that [η]_n ? [η]_br ≡ Δ[η] is indeed negative for propylene-rich copolymers, zero for a 56% ethylene copolymer, and positive for ethylene-rich copolymers. The Stockmayer–Fixman relation was used to obtain from Δ[η] a molecular-weight independent function of composition. The quantities (Δ[η]/[η])(1 + aM^?1/2) and Δ[η]/M are linear with the mole percent ethylene in the range investigated with 200 ≤ a ≤ 2000. The possibility of using these results for composition determination in ethylene–propylene copolymers is discussed. Intrinsic viscosities in the same solvents are reported for two samples of a terpolymer with ethylidene norbornene.     

Thermodynamic and transport properties of binary liquid mixtures of cyclohexanol with isomeric chlorotoluenes

Densities (ρ) at different temperatures from 303.15 to 318.15 K, speeds of sound (u) and viscosities (η) at 303.15 K were measured for the binary mixtures of cyclohexanol with 2-chlorotoluene, 3-chlorotoluene and 4-chlorotoluene over the entire range of composition. The excess volumes (V^E) for the mixtures have been computed from the experimental density data. Further, the deviation in isentropic compressibilities (Δκ_s) and deviation in viscosities (Δη) for the binary mixtures have been calculated from the speed of sound and viscosity data, respectively. The V^E values and Δκ_s values were positive and Δη data were negative for all the mixtures over the whole range of composition at the measured temperatures. The calculated excess functions V^E, Δκ_s and Δη were fitted to Redlich–Kister equation. The excess functions have been discussed in terms of molecular interactions between component molecules of the binary mixtures.     

Oscillating frequency of piezoelectric quartz crystal in solutions

Oscillating frequencies of a piezoelectric crystal were measured in various solutions. One side of the crystal surface was coated with a silicon sealant. This coating was useful for measuring the oscillation of crystals in solutions for a wide range of products of density (?) and viscosity (η) and in electrolyte solutions. For measurement in solutions, the frequency change depended on the circuit used, whereas for measurements in air the circuit did not influence the frequency change. All experimental data showed that the frequency change from pure water, ΔF_w, followed ΔF_w = ? K(√?η ? √?_wη_w) except for electrolyte and polymer solutions, where K is a proportionality constant, η_w the density of pure water and η_w the viscosity of water.     

Mechanistic investigation of the thermal decomposition of Biphen(OPi-Pr)PtEt2: An entrance into C-C single bond activation?

Biphen(OPi-Pr) and (COD)PtCl₂ give Biphen(OPi-Pr)PtCl₂ which upon treating with ethyl Grignard forms Biphen(OPi-Pr)PtEt₂. The thermal decomposition of Biphen(OPi-Pr)PtEt₂ was investigated in the temperature range of 353-383 K. The clean and quantitative formation of the Pt(Ethene) adduct was observed. X-ray structures of a molecule in the solid state of all three reaction products and two further related complexes with phenyl fingers instead of i-Pr have been determined. For the complexes with i-Pr fingers a decisive deviation from a square plane is observed in contrast to the complexes with phenyl fingers. The P-Pt-P angle increases from about 95° in Biphen(OPi-Pr)PtCl₂ to about 120° in Biphen(OPi-Pr)Pt(Ethene), forcing the bridging C-C single bond of the biphenyl fragment as near as 4.17 Å to the Pt center. No through-space coupling between the bridging C atoms and the Pt center could be observed in ¹³C NMR spectroscopy. No bond lengthening of the bridging C-C single bond in the biphenyl fragment was observed in Biphen(OPi-Pr)Pt(Ethene) in comparison to the precursor complexes. The thermal decomposition of Biphen(OPi-Pr)PtEt₂ can be described by a first-order kinetic and the activation parameters were determined (temperature range: 353-383 K; ΔH^‡ = 173.8 ± 16.2 kJ/mol and ΔS^‡ = 104.7 ± 44.1 J/(mol K)). The reaction kinetics were also measured for perdeuterated ethyl groups yielding in a kinetic isotopic effect of 1.56 ± 0.14 which was almost temperature-independent. Selective deuteration at α and β position of the ethyl group, respectively, showed that β-H elimination takes place fast in comparison to the complete thermolysis. In the temperature range of 333-353 K only a scrambling of the deuterium atoms was found without further decomposition (temperature range: 333-353 K; Δ_scramH^‡ = 76.1 ± 15.2 kJ/mol, Δ_scramS^‡ = −80.7 ± 45.5 J/(mol K) for Biphen(OPi-Pr)PtEt₂-d⁶). The ethene is not lost during the scrambling process. The scrambling process is connected with a primary KIE decisively larger than 1.56. Biphen(OPi-Pr)Pt(Ethene) exchanges the coordinated ethene with ethene in solution as proven by labeling experiments. Both a dissociative and an associative mechanism could be shown to take place as ethene exchange reaction by means of VT¹H NMR spectroscopy via line shape analysis (temperature range: 333-373 K; Δ_assH^‡ = 26.9 ± 29.6 kJ/mol, Δ_assS^‡ = −148.0 ± 87.5 J/(mol K), Δ_dissH^‡ = 86.0 ± 6.5 kJ/mol, Δ_dissS^‡ = 5.4 ± 17.8 J/(mol K)). The Pt(0) complex formed during the dissociative loss of ethene activates several substrates among them: O₂, H₂, H₂SiPh₂ via Si-H activation, MeI presumably via forming a cationic methyl adduct and ethane via C-H activation but it was proven that the bridging C-C single bond of the biphenyl fragment is not even temporarily broken. The materials were characterized by means of ¹H NMR, ¹³C NMR, ³¹P NMR, ¹⁹⁵Pt NMR, EA, MS, IR, X-ray analysis and polarimetric measurement where necessary.     

Conformational behaviour of poly(2,6-dimethyl-1,4-phenylene oxide) in solution—I: Intrinsic viscosity as a function of temperature

Intrinsic viscosities [η] of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) solutions have been measured as a function of temperature between 60 and 25°C. The solvents were toluene and trichloroethene. In both solvents, the [η]-T curve exhibited a point of inflection in the range 45-35°. This phenomenon is explained as a conformational transition, which is possibly involved in the nucleation process of the solution crystallization of PPO. Assuming constancy of the coil expansion factor α_η and the solvent draining over the whole temperature interval, a slight increase of characteristic parameter C_α, with decreasing temperature has been calculated.     

Viscosities and Surface Tensions of Phenetole with <Emphasis Type="Italic">N</Emphasis>-Methyl-2-pyrrolidone, <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Dimethylformamide and Tetrahydrofuran Binary Systems at Three Temperatures

Viscosities, η, and surface tensions, σ, of binary systems of phenetole (ethoxy benzene or ethyl phenyl ether) with N-methyl-2-pyrrolidone, N,N-dimethylformamide or with tetrahydrofuran were measured over the entire mole fraction range and at (298, 303 and 308) K. The experimental data was used to compute the deviations in viscosity, Δη, and surface tension, Δσ. Values of the excess Gibbs energy of activation G*^E, surface entropy S _σ and surface enthalpy H _σ were calculated. Viscosity data of the binary systems were calculated using the Grunberg and Nissan and the three-body and four-body McAllister correlations. The Redlich–Kister method was used for evaluation of coefficients and standard deviations for Δη, Δσ and G*^E. The results were interpreted in terms of the probable effect of molecular interactions between components as well as polarity.     

Effect of G/M ratio on the radiation-induced degradation of sodium alginate

Radiation-induced degradation of sodium alginate (NaAlg) having different G/M ratios was investigated. NaAlg samples were irradiated with gamma rays in air at ambient temperature in the solid state at low dose rate. Change in their molecular weights was followed by size exclusion chromatography (SEC). Changes in their rheological properties and viscosity values as a function of temperature, shear rate and irradiation dose were also determined. Chain scission yields, G(S), and degradation rates were calculated. It was observed that G/M ratio was an important factor controlling the G(S) and degradation rate of sodium alginate.     

Physicochemical properties of {1-methyl piperazine (1) + water (2)} system at T = (298.15 to 343.15) K and atmospheric pressure

Densities (ρ) and viscosities (η) of aqueous 1-methylpiperazine (1-MPZ) solutions are reported at T = (298.15 to 343.15) K. Refractive indices (n_D) are reported at T = (293.15 to 333.15) K, and surface tensions (γ) are reported at T = (298.15 to 333.15) K. Derived excess properties, except excess viscosities (Δη), are found to be negative over the entire composition range. The addition of 1-MPZ reduces drastically the surface tension of water. The temperature dependence of surface tensions is explained in terms of surface entropy (S^S) and enthalpy (H^S). The measured and derived properties are used to probe the microscopic liquid structure of the bulk and surface of the aqueous amine solutions.     

Evaluation of single-point equations to determine intrinsic viscosity of sodium alginate and chitosan with high deacetylation degree

A viscometric study of two polyelectrolytes, chitosan (CH, with 94% deacetylation degree, in a solute-mixture of acetic acid (0.1 mol L⁻¹) and sodium chloride (0.2 mol L⁻¹) and sodium alginate (SA, with 62% M-units, in sodium chloride (0.1 mol L⁻¹), was performed at 25 °C. Five different equations were applied to calculate intrinsic viscosity [η]: Huggins, Kraemer and Schulz-Blaschke (SB) by graphical extrapolation; Solomon-Ciuta, Deb-Chanterjee and again SB, by faster single-point determination. Viscometric constants were calculated employing graphical extrapolation equations. Average molar mass (‾M_v) values were determined by applying the Mark-Houwink-Sakurada equation. For the samples analyzed, Huggins equation was the most suitable to calculate [η] and‾M_v by graphical extrapolation for chitosan, while Schulz-Blaschke and Solomon-Ciuta were adequate for single-point determinations of sodium alginate. Viscometric constants indicated that the aqueous mixture of acetic acid and sodium chloride is a poor solvent for chitosan, while sodium alginate is well solvated by aqueous sodium chloride.     

Modelling of proton and metal exchange in the alginate biopolymer

Acid–base behaviour of a commercial sodium alginate extracted from brown seaweed (Macrocystis pyrifera) has been investigated at different ionic strengths (0.1≤I/mol l^?1≤1.0) and in different supporting electrolytes (Et₄NI, NaCl, KCl, LiCl, NaCl+MgCl₂), with the aim of examining the influence of ionic medium on the proton-binding capacity and of quantifying the strength of interaction with light metal ions in the perspective of speciation studies in natural aqueous systems. Potentiometric ([H⁺]-glass electrode) and titration calorimetric data were expressed as a function of the dissociation degree (α) using different models (Henderson–Hasselbalch modified, Högfeldt three parameters and linear equations). The dependence on ionic strength of the protonation constants was taken into account by a modified specific interaction theory model. Differences among different media were explained in terms of the interaction between polyanion and metal cations of the supporting electrolytes. Quantitative information on the proton-binding capacity, together with the stabilities of different species formed, is reported. Protonation thermodynamic parameters, at α=0.5, are log K ^H=3.686±0.005, ΔG ⁰=?21.04±0.03 kJ mol^?1, ΔH ⁰=4.8±0.2 kJ mol^?1 and TΔS ⁰=35.7±0.3 kJ mol^?1, at infinite dilution. Protonation enthalpies indicate that the main contribution to proton binding arises from the entropy term. A strict correlation between ΔG and TΔS was found, TΔS=?9.5–1.73 ΔG. Results are reported in light of building up a chemical complexation model of general validity to explain the binding ability of naturally occurring polycarboxylate polymers and biopolymers. Speciation profiles of alginate in the presence of sodium and magnesium ions, naturally occurring cations in natural waters, are also reported.