Mixture Of Isobutyric Acid Research Articles

A test of the universality principle: The solubility of metal salts and oxides in isobutyric acid + water near its consolute point

A mixture of isobutyric acid + water has a critical point of solution at a composition of 38.8 mass % isobutyric acid and a temperature near 300 K. Under these conditions, the pH = 2, which makes the mixture a ready solvent for metal salts and basic/amphoteric oxides. Measurements of the temperature dependence of the solubility of a solid in the critical region of such a mixture can be used as a test of the Principle of Critical Point Universality. This inductive generalization, which is thought to govern all critical phenomena, predicts that there will be a critical effect in the solubility of a solid when at constant temperature and pressure the position of equilibrium is specified by no more than three fixed variables. We report herein a determination of the temperature dependence of the solubility of gallium (III) oxide in a mixture of isobutyric acid + water, and in a separate experiment the determination of the temperature dependence of the solubility of titanium dioxide in this solvent. In a third experiment, we report the effects of the critical point of this mixture on the simultaneous dissolution of calcium sulfate and barium sulfate. In each of these experiments, there are three fixed variables. We carry out a fourth experiment involving the solubility of solid lead (II) iodide in isobutyric acid + water doped with completely dissolved sodium sulfate. In this case, four variables are fixed. Independent of the chemical details, and consistent with the universality principle, we find a critical solubility effect in each of the first three experiments but none in the fourth.

Gel Volume Near the Critical Point of Binary Mixture Isobutyric Acid-Water.

The volume of a cylindrical polyacrylamide gel was measured when immersed in a binary mixture of isobutyric acid–water at different temperatures and weight fractions of isobutyric acid. Near the upper critical solution temperature of the binary mixture, the curve for gel volume vs. isobutyric acid weight fraction has a shoulder or a peak near the critical weight fraction. On the other hand, in a region away from the critical temperature, the gel volume decreased monotonically with increasing isobutyric acid weight fraction. The cloud point temperature of the binary mixture inside the gel was lower than that outside the gel. Thermodynamic description for the gel in the critical mixture is derived on the basis of the Ising model. By the description, the experimental results are explained consistently. The theoretical analysis shows that the shoulder and the peak appearing in the swelling behavior of the gel are respectively induced by the criticalities of the binary mixture outside and inside the gel. It also shows that the cloud point temperature lowering of the binary mixture inside the gel is attributed to the effective enhancement of the temperature of the binary mixture inside the gel induced by the presence of the gel polymer.

Ion exchange at the critical point of solution

A mixture of isobutyric acid (IBA)+water has an upper critical point of solution at 26.7°C and an IBA concentration of 4.40M. We have determined the Langmuir isotherms for the hydroxide form of Amberlite IRN-78 resin in contact with mixtures of IBA+water at temperatures, 27.0, 29.0, 31.0 and 38.0°C, respectively. The Langmuir plot at 38.0°C forms a straight line. At the three lower temperatures, however, a peak in the Langmuir plot is observed for IBA concentrations in the vicinity of 4.40M. We regard this peak to be a critical effect not only because it is located close to 4.40M, but also because its height becomes more pronounced as the temperature of the isotherm approaches the critical temperature. For concentrations in the vicinity of the peak, the data indicate that the larger isobutyrate ion is rejected by the resin in favor of the smaller hydroxide ion. This reversal of the expected ion exchange reaction might be used to separate ions according to size. Using the Donnan theory of ion exchange equilibrium, we link the swelling pressure to the osmotic pressure. We show that the peak in the Langmuir plot is associated with a maximum in the “osmotic” energy. This maximum has its origin in the concentration derivative of the osmotic pressure, which goes to zero as the critical point is approached.

A chemical test of critical point isomorphism: reactive dissolution of ionic solids in isobutyric acid + water near the consolute point.

Binary liquid mixtures having a consolute point can be used as solvents for chemical reactions. When excess cerium(IV) oxide is brought into equilibrium with a mixture of isobutyric acid + water, and the concentration of cerium in the liquid phase is plotted in van't Hoff form, a straight line results for temperatures sufficiently in excess of the critical solution temperature. Within 1 K of the critical temperature, however, the concentration becomes substantially suppressed, and the van't Hoff slope diverges toward negative infinity. According to the phase rule, one mole fraction can be fixed. Given this restriction, the temperature behavior of the data is in exact agreement with the predictions of both the principle of critical point isomorphism and the Gibbs-Helmholtz equation. In addition, we have determined the concentration of lead in the liquid phase when crystalline lead(II) sulfate reacts with potassium iodide in isobutyric acid + water. When plotted in van't Hoff form, the data lie on a straight line for all temperatures including the critical region. The phase rule indicates that two mole fractions can be fixed. With this restriction, the data are in exact agreement with the principle of critical point isomorphism.

Critical-point universality in adsorption: The effect of charcoal on a mixture of isobutyric acid and water near the consolute point

The mixture of isobutyric acid and water has a consolute point at a temperature of 25.75 °C and mole fraction 0.1148 isobutyric acid. When charcoal is added to this mixture, the concentration of isobutyric acid is reduced by adsorption. We have measured the action of charcoal on solutions of isobutyric acid and water as a function of isobutyric acid mole fraction at temperatures of 25.85 and 32.50 °C. At the higher temperature, the specific adsorption density (y(2)(α)/m) satisfies the Freundlich equation (y(2)(α)/m)=KX(2)(1/n), where y(2)(α) is the mass of isobutyric acid adsorbed, m is the mass of charcoal, X(2) is the equilibrium mole fraction of isobutyric acid, n is the Freundlich index, and K=K(T) is an amplitude that depends upon the temperature T. At 25.85 °C, a critical endpoint is located at an isobutyric acid mole fraction X(2)(ce)=0.09. When compared with the Freundlich equation at this temperature, a plot of the specific adsorption density as a function of X(2) in the vicinity of the critical-endpoint composition assumes a shape which is reminiscent of the derivative of a Dirac delta function. Using critical-point scaling theory, we show that this divergent pattern is consistent with the principle of critical point universality.

A chemical test of the principle of critical point universality: The solubility of nickel (II) oxide in isobutyric acid + water near the consolute point

A mixture of isobutyric acid + water has an upper consolute point at 38.8 mass % isobutyric acid and temperature near 26 °C. Nickel (II) oxide dissolves in this mixture by reacting with the acid to produce water and nickel isobutyrate. The solubility of nickel (II) oxide in isobutyric acid + water has been measured as a function of temperature at compositions, 25, 38.8, and 60 mass % isobutyric acid. For values of the temperature, T, which were at least 2 K in excess of the liquid-liquid phase transition temperature, the measured values of the solubility, s, lie on a straight line when plotted in van't Hoff form with ln s versus 1∕T. The slope, (∂ln s∕∂(1∕T)), of the line is negative indicating that the dissolution reaction is endothermic. When the temperature was within 2 K of the phase transition temperature, however, (∂ln s∕∂(1∕T)) diverged toward negative infinity. The principle of critical point universality predicts that when excess solid nickel (II) oxide is in dissolution equilibrium with liquid isobutyric acid + water, (∂ln s∕∂(1∕T)) should diverge upon approaching the consolute point along the critical isopleth at 38.8 mass % isobutyric acid. As determined by the sign of the enthalpy of solution, the sign of this divergence is expected to be negative. Not only do our experiments confirm these predictions, but they also show that identical behavior can be observed at both 25 and 60 mass % isobustyric acid, compositions which lie substantially to either side of the critical composition.

Density, viscosity and electrical conductivity of isobutyric acid–water with added ions in the critical regions

Density, viscosity and electrical conductivity of the six concentrated binary ionic mixtures of isobutyric acid–water with X M [KCl] at the critical concentrations were measured as functions of temperature (ΔT = T − T c ≤ 2 K) and at various compositions, X, in the critical regions. The molar volumes have been calculated from their densities. The molar volume data dependence of viscosity and conductivity has been fitted to an equation similar to the Vogel–Tammann–Fulcher (VTF) based on the free volume model. The concentration of ions (K+, Cl−), dependence of the Vogel temperature, the intrinsic volume and the transport properties are primarily governed by the existence of intermolecular interactions.

Evidence of Vogel–Tamman–Fulcher behavior in ionic binary fluids

The electrical conductivity σ of the six concentrated binary ionic mixtures of isobutyric acid–water with XM [KCl] at the critical concentrations was measured over an extended temperature range above the critical consolute point. Far from the critical temperature T c, the electrical conductivity is accurately described by the Vogel–Fulcher–Tammann (VFT) law. However, in a temperature range ΔT = T − T c ≤ 2 K, the electrical conductivity exhibits a monotonous deviation from the VFT behavior. This anomaly is finite at T c. The asymptotic behavior of the electrical conductivity anomaly is described by a power law (t)(1− α ), with t = (T − T c)/T c, the reduced temperature, and α the critical exponent of the specific heat anomaly at constant pressure. This critical anomaly is similar to the one observed in other different concentrated critical electrolytes. The degree of dissociation αdiss of the salt for the critical mixture is estimated from the value of the Walden product computed at T c. When the salt is added, the degree of dissociation αdiss shows dependence on the (K+, Cl−) concentrations: 0.15 < αdiss < 0.68.

A rapid, small-scale procedure for the structural characterization of lipid A applied to Citrobacter and Bordetella strains: discovery of a new structural element

Endotoxins [lipopolysaccharides (LPSs)] are part of the outer cell membrane of Gram-negative bacteria. Their biological activities are associated mainly with the lipid component (lipid A) and even more specifically with discrete aspects of their fine structure. The need for a rapid and small-scale analysis of lipid A motivated us to develop a procedure that combines direct isolation of lipids A from bacterial cells with sequential release of their ester-linked fatty acids by a mild alkali treatment followed by MALDI-MS analysis. This method avoids the multiple-step LPS extraction procedure and lipid A isolation. The whole process can be performed in a working day and applied to lyophilized bacterial samples as small as 1 mg. We illustrate the method by applying it to the analysis of lipids A of three species of Citrobacter that were found to be identical. On the other hand, when applied to two batches of Bordetella bronchiseptica strain 4650, it highlighted the presence, in one of them, of hitherto unreported hexosamine residues substituting the lipid A phosphate groups, possibly a new camouflage opportunity to escape a host defense system.

Coexistence curves of electrical conductivity in critical solution: isobutyric acid–water with added ions

Comprehensive results of temperature (T) studies of electrical conductivity (σ) in the one-and-two phase regions of the binary fluid mixture of isobutyric acid–water (IBAW) with X M[KCl] at various critical concentrations are presented. A strong asymmetry of the coexistence curves as determined causes a strong violation of the law of rectilinear diameter. The obtained critical anomalies in the homogeneous phase σcrit (T) or the diameter of the σd (T) are associated with the same critical exponent θ = 1 − α ≈ 0.88, where α is the specific heat critical exponent. For the mixture with critical composition, the two phase regions show a concentration behavior with σl − σu ≈ |−t|β. The phase transition region shifts as a function of the salt concentration. The effective critical exponent β* = (0.264–0.296) is neither compatible with the Ising value β = 0.325 nor with the Fisher renormalized value ∼0.365.

Reaction Kinetics and Critical Phenomena: Rates of Some First Order Gas Evolution Reactions in Binary Solvents with a Consolute Point

We have measured the rate of carbon dioxide evolution in the aniline catalyzed decomposition of acetone dicarboxylic acid in a mixture of isobutyric acid + water near its consolute point. Within a temperature interval of 1 degrees C, which included the critical solution temperature, the first-order rate constant oscillated in magnitude by about 10% as it passed through three complete cycles of slowing down followed by speeding up. Whereas we can find no ready explanation for the speeding up, we suggest that, because the mixture contained no inert components, the slowing down should belong to the Griffiths-Wheeler class of strong critical effects [Phys. Rev. A 1970, 2, 1047]. As a check on this conclusion, we have measured the rate of the SN1 decomposition of benzene diazonium tetrafluoroborate in 2-butoxyethanol + water near the lower critical solution temperature and also the rate of the acid-catalyzed decomposition of ethyl diazoacetate in isobutyric acid + water near the upper critical solution temperature. Both of these reactions evolve nitrogen. In the first reaction, 2-butoxyethanol is inert, whereas in the second, isobutyric acid is inert. In both cases, because there was one inert component, we regarded the response of the rate constant to temperature in the critical region to be representative of the Griffiths-Wheeler class of weak critical effects. Within our accuracy of measurement of about 2% in the rate constant and about 1 mK in the temperature, we could detect no effect of the critical point on the rates of either of these reactions, suggesting that a weak effect may be too small to be seen with our experimental apparatus. The successful observation of a critical effect in the rate of decomposition of acetone dicarboxylic acid proves, however, that kinetic critical phenomena are observable in heterogeneous reactions.

Domain growth in the presence of quenched disorder

We describe the results of experiments investigating the growth dynamics of domains which form spontaneously in a portion of the one-phase region of a binary fluid mixture in the presence of quenched disorder. Dilute silica gels imbibed with mixtures of isobutyric acid and water were pressure quenched from an equilibrium one-phase state to a region of the phase diagram lying within the coexistence curve of the pure, or gel-free, system, but outside the coexistence curve of the gel-mixture system. Small-angle light-scattering measurements revealed a ring of scattered light which appeared at large scattering wave vectors and evolved to smaller scattering wave vectors in a manner consistent with ${t}^{1/3}$ domain growth; no evidence of domain pinning was observed during the first 1000 s following a quench. Furthermore, most measurements were consistent with dynamic scaling behavior. An unexpected feature of this system was the rapid growth of long-wavelength fluctuations immediately following the quench.

Phase equilibrium and conformation of a polymer in a binary solvent

The phase equilibrium behavior of a dilute high molecular weight polymer (poly-ethylene oxide PEO, molecular weight 9 × 10 5, concentration 0.001 g/cc) solution in a two-component liquid mixture (isobutyric acid + water, IBAW) is studied experimentally. Far above the critical temperature T c of IBAW, we found that although PEO dissolved in pure isobutyric acid (IBA) and pure water, mixtures of IBA and water with 0.1% PEO became cloudy within a certain composition range. Far below T c , when the binary mixture phase separates in two coexisting phases, the presence of PEO which dissolved in both phases did not affect the coexistence curve of the binary mixture. Around T c , three phases in coexistence were obsrrved in a narrow composition range near the critical composition of IBAW. At high temperature (≈ 24°C above T c ) the size of PEO in IBAW was measured by light scattering method at different IBAW compositions. We observed expansion of PEO molecules in the mixed solvent, which can be explained using the single liquid approximation by Scott. Such an expansion caused the macromolecules to overlap and separate from the solvent.

Ionic structure in a binary fluid

The tracer diffusion coefficient D3+ of the trivalent lanthanide cation 153Gd3+ is studied in mixtures of isobutyric acid, water and 5*10-4 M Gd(NO3)3 using an open-ended capillary tube. These data are given over the complete composition range at T-Tc=0.171 K. The coefficients D3+ are combined with the shear viscosity eta of the electrolyte. The results are discussed in terms of the Einstein-Stokes law; our analysis suggests three different behaviours of the diffusing entity in the mixtures and it is based on the preferential solvation phenomenon.

Kinetics of nucleation and growth in a near-critical binary liquid mixture at rest and under a shear flow.

Nucleation and growth in a mixture of isobutyric acid and water are studied by small-angle light scattering under a shear flow. The study is restricted to off-critical quenches, just below the coexistence curve, where nucleation is essentially heterogeneous. When no shear is applied, the distribution of the droplet radii is peaked around its mean value, which behaves as R(t)=R 0 t a , with a=0.6±0.1. A continuous shear flow is shown to accelerate the growth. An advection-diffusion process is proposed, which allows the data to be expressed in a scaled form, over a wide range of shear rates.

Viscosity of a phase-separating critical mixture

Onuki has predicted the existence of a significant enhancement of the viscosity of a liquid mixture in the course of spinodal decomposition. We discuss a method to measure this effect in a critical mixture of isobutyric acid and water in which spinodal decomposition is induced by a pressure-quench technique. In addition, by varying the static pressure in the homogeneous phase, experimental information about the dynamic critical exponent for the viscosity is obtained.

Electric field effect in a conducting binary critical mixture

Abstract We investigate the change in the concentration-concentration correlation function to lowest order in an electric field, when the electric field is applied to a conducting binary critical mixture so that power is dissipated. We obtain an estimate of the size of the electric field, as a function of temperature, which must be applied in order that an appreciable effect is obtained. We briefly apply our results to a critical mixture of isobutyric acid and water.