Electrochemical behavior of copper electrode in different solutions of adrenalin chydrogentatrate and catechol

Galvanic anodic polarization of copper electrode at different current densities in electrolytes of different pH values containing adrenaline hydrogen tartarte [AHT] and catechol [Cat.] have been studied. The effect of complex formation on the underlying anodic reactions and inhibition effect of these complexes on copper electrode is also studied. The cathodic deposition of copper in the prepared complexes on the surface of the cathode is involved to check their stability at different pH values and the effect of this stability on cathodic behavior of copper electrode

Molecular association in binary mixtures of polyethylene glycol and some aldehydes

Dipole-dipole association in mixtures of polyethylene glycol [400] with both propionaldehyde and benzaldehyde, as representative aliphatic and aromatic aldehydes, has been studied. Decreases in molar volume were calculated from density measurements at different temperatures using the intercept method. The results indicated the formation of the associated aggregates in the ratio [2 propionaldehyde: 1 polyethylene glycol] and [1 benzaldehyde: 1 polyethylene glycol], which mean that the association between the aliphatic aldehyde and polyethylene glycol is greater than that for the aromatic aldehyde. This result is in an agreement with the thermodynamic parameters of dielectric relaxation and viscous flow; namely, the apparent activation energy of dielectric relaxation delta H epsilon and the enthalpy of activation of viscous flow delta Hv calculated from dielectric and viscosity measurements for the two systems

Reaction kinetics of bromine and aminophenols

The kinetics of reactions of bromine and aminophenols has been studied at different temperatures. The overall order of the reactions determined from the half-life times was found to be 2.1, 2.12 and 2.4 for, 0-, m- and p-aminophenol, respectively. The thermodynamic parameters of activations were calculated and discussed. The final products of the reactions were investigated by elemental analysis, IR and mass spectra. Proposed schemes for these reactions were presented

Electrochemical behaviour of stainless steel in acidic water-ethylene glycol mixture

The corrosion behavior of stainless steel type 304 in acidic solutions of water-ethylene glycol mixtures have been studied by both potentiostatic polarization and weight loss methods at 25. The active passive transition depends strongly on the acid concentration and water content of the medium. The results are interpreted in terms of the dependence of corrosion rate of the metal on the properties of the medium such as viscosity, dielectric constant, solvation and Hammett acidity function

Natural convection mass transfer in presence of small amounts of alcohols

The effect of methanol, ethanol, n-propanol and isopropanol on the rate of cathodic deposition of copper from acidified copper sulfate solution was studied. These alcohols caused a decrease in the limiting current by an amount ranging from 5.95 to 35.55%, depending on the type of alcohol and concentration. Langmuir adsorption isotherm was applied. The values of heat absorption and free energy of adsorption were calculated

Physico-chemical studies of alcohol-water binary systems at different temperatures

Density and viscosity measurements carried out in aqueous binary mixtures of n-propanol, and iso-propanol at different temperatures. The volume contraction either [Delta] or [Delta V] for these systems revealed occurrence of a minimum at X [alc approximately 0.31 indicates the probability of the existence of [1 alcohol: 2 water] molecular complex. Calculation of the deviation of the molar viscosity [Delta neta [M12]] for both mixtures at different compositions gives negative values with a minimum at the same mole fraction of alcohol which supports the existence of the suggested molecular complex. The Eyring's equation for the temperature dependence of viscosity is used to predict enthalpy [Delta H degree] and entropy [Delta S degree] of activation for the flow process. The conclusion is that the behaviour of each alcohol when mixed with water is dependent mainly on its structure

effect of solvent structure on the dissociation constant of p-nitroanilinium ion in mixed solvents

The dissociation constant pka of p-nitroanilinium ion was determined spectrophotometrically at 25 in various acidified n-propanol-water, and isopropanol-water mixtures. The range of solvent composition varied from 0 to 100 wt.% alcohol. The dissociation constant was found to decrease, with the addition of alcohol, passed through a minimum, and then rose again at high alcohol concentrations. This indicated that the basicity of the medium was increased by the addition of organic solvent, then decreased again. The Gibbs energy of ionic solutes clearly changed with altered solvent composition. The relation between delta pka and the dielectric constant of the medium indicated that the total medium effect can be explained by the superposition of electrostatic and nonelectrostatic effects

Kinetics of the reaction of N-2, 6-tri-chlorobenzoquinonimine with sodium thiosulphate in methanol-water mixtures

The kinetics of the reaction of N-2,6-trichlorobenzoquinonimine with sodium thiosulfate has been studied in methanol-water mixtures over the temperature range 25-40C. The rates were found to increase with increasing dielectric constant. The reaction was found to obey the Arrhenius equation. The energy of activation and the thermodynamic parameters of activation were calculated and discussed as evidence of solvation effects

Kinetics of addition of aromatic amines on trans-3- [P-Substituted phenyl] -1- Phenyl-Prop-2-En-1-Ones

The reactions of a series of trans-3-[p-substituted phenyl]-1-phenyl- prop-2-en-1-ones Ia-e with p-anisidine and p-nitroaniline IIa,b were studied in methanol, and their reaction rates were measured. The reaction followed a second order kinetics. In addition, the activation parameters delta H* and delta S* for the reactions of both amines were calculated and led to the conclusion of a cyclic multistep mechanism for that amine. Michael addition reaction involving one molecule from each of olefin and amine used. The nucleophilic attack of the aromatic amines IIa,b on olefines Ia-e obeyed Hamett equation

New aspect of epoxide ring opening

The rates of reactions of some trans-P-substituted epoxy benzalacetophenones with morpholine in acetonitrile have been measured at different temperatures. The reactions are second order and proceeds via SN2 like mechanism to give the corresponding alpha- hydroxy-beta-morpholino-beta-[P-substituted phenyl propiophenones. Effect of substituents has been analyzed in terms of Hammett linear free energy relationship

use of Hammett acidity function for the characterization of the corrosion behavior of stainless steel in aqueous and mixed methanol-water media containing acid

The electrochemical behavior of stainless steel [304 and 316] has been investigated in aqueous solutions of hydrochloric acid and in acidic mixed methanol-water solvents. The comparison of the results obtained in different concentrations would be questionable if the main physicochemical properties of the solutions were not vigorously defined. In the case of acidity which is one of the most important parameters for comparison of the corrosion mechanism, the use of the Hammett acidity function, Ho, is more suitable than scale in the organic mixed solvents. This study pointed out that Hammett acidity function, may be a correct measurement of the acid strength of the proton, is the main factor governing the corrosion phenomenon

Kinetics of aminolysis of some antibacterial vinylic ketones II Effect of solvents on aminolysis of trans -3- [p-substituted phenyl] -1- phenyl- prop -2-en -1-one

The reactions of a series of trans-3-[p-substituted phenyl]-1-phenyl- prop-2-en-1-ones Ia-e with p-toluidine and p-nitroaniline IIa, b have been studied in benzene, and their reaction rates were measured. In addition, activation parameters delta H* and delta S* were evaluated, and good Hammett correlation with positive P values of 1.2-1.9, were obtained which suggest the anionic character of the transition state

Physico-chemical studies on acidity functions in mixed solvents II Studies on the pH of potassium hydroxide solutions in ethanol-, n-propanol-, Iso-propanol- and ethylene glycol water mixtures

The slope factors of the lines relating the electromotive force E of the pH-meter cell with the pH reading R agree consistently with the theoretical values for all test solutions at 25 degree. This may be considered as an indication of the proper function of the glass electrode as a standard hydrogen electrode. A discussion is made of the factor governing the glass electrode function such as chemical composition, water content, alkali and acid errors. The validity of Dole 's theory is examined by plotting the voltage deviation E against-log H2O of the solvent mixtures and determining the number of water molecules associated with proton in its migration from the solution into the surface of the electrode glass membrane. Deviation of the experimental points from the fitted least squares -lines proves that the theory is not valid, particularly for solutions of potassium hydroxide in ethylene glycol-water mixtures. Although the availability of the transferable protons is considerably affected by changes of the activity of water, it seems unlikely that the transfer of water through the surface of the galss membrane plays any part in the electrochemical process responsible for the development of the pH response. Calculated values of the operational pHx and liquid-junction potentials Ej are obtained for the different test solutions. Variation of the pHx with solvent composition is explained in terms of solvent-solvent and ion-solvent interactions

Physio-chemical studies on acidity functions in mixed solvents III Studies on the optical absorption characteristics of p-nitroaniline, phenol and thioacetamide in solutions of potassium hydroxide

The ultraviolet absorption properties of the four above indicators in solutions of potassium hydroxide of different concentrations in ethanol water mixture are studied. The absorption spectra so obtained disclose absorption peaks of situation dependent on alkali concentration and alcohol content of the medium. The peaks are slightly shifted towards higher wave lengths with rise in alkali concentrations. The results substantiate that the different indicators with the OH-ions present in the solution by proton loss rather than by hydroxide addition. Calculations are made of the molar extinction coefficients epsilon, epsilon A. and epsilon HA. of, respectively, the partially ionised, completely ionised, and unionized forms of each indicator. The values of these coefficients are then used for the computation of the indicator ratios I of the different indicators in the various solutions. In additions, the pka values of the indicators in questions are obtained by plotting [log I -log COH-] against COH[-] and extrapolating to zero concentration. These values of T and pKA are of importance in the evaluation of the acidity function H- of the different solutions

Physico-chemical studies on acidity functions in mixed solvents IV Studies on the optical absorption characteristics of p-nitroaniline

The ultraviolet absorption spectra of p-nitroaniline in the 1 different alkaline solutions support the idea that the indicator reacts with the OH- ions existing in solution by proton loss rather than by hydroxide ion addition. Straight lines are obtained by plotting the molar extinction coefficients epsilon of the partially ionized form of the indicator against the reciprocals of the molar concentrations of the alkali in every solvent, with intercepts equal to the values of the molar extinction coefficient epsilon A- of the completely ionized form of the indicator. The values of the ratio R of the intercept to the slope of each line as well as of the equilibrium constant K['] are derived. The observed variations in K['] may be attributed to changes in the ratio fOR-/ fOH- or the ratio fA-/ fOR. FAH, or in both ratios. Also, a procedure is developed for the determination of the equilibrium constants K'm for the indicator in solutions of Li OH, KOH and NaOH in pure methanol, with the assumption that this constant is a true thermodynamic constant independent of solvent composition. The same procedure is followed for the estimation of the values of the equilibrium constants K' and K'm for the same indicator in solutions of potassium hydroxide in ethanol-water mixtures. The attempt is also made to calculate the equilibrium constant K degree of p nitroaniline in solutions of LiOH, KOH, and NaOH in methanol-water mixtures containing from 10-70 percent by weight of methanol. The calculated values of the constant K degree are subsequently used for the evaluation of the fraction OH-/Cb of the base present as OH- ions

Physico-chemical studies on acidity functions in mixed solvents V Studies on the acidity function H of solutions of LioH, NaOH and KOH in methanol-water mixtures using p-nitroaniline as indicator

The limited range of the operational pH[x] from 0 14 is a drawback of this acidity function. The validity of Hammett function H0 in solutions of strong acids in alcohol -water mixtures stands behind the desire to construct a scale of acidity in solutions of strong alkalies in these mixtures which are frequently used. For this purpose, calculations are made to calculate the values of H- from the spectrophoto-metrically determined molar extinction coefficients epsilon,, epsilon A- and epsilon HA of p-nitroaniline in solutions of LiOH, NaOH and KOH in methanol-water mixtures. By plotting log. H- against the reciprocal of the stoichiometric molar concentration C of every alkali solution, straight lines are obtained whose intercepts and slopes are computed by use of the least-squares method. These values facilitate the derivation of the value of H- for any of the solutions studied by interpolation. On the other hand, the plots relating H. with medium composition disclose several maxima and minima the location of which does depend on alkali concentration and identity. This reflects the medium effect on the trend of variation of H- in the different solutions. The basic strength in water and pure methano1 increases according to the order KOH>NaOH> LiOH, whereas in methanol-water mixtures is a composite function of alkali concentrations and medium composition. These findings are explained in terms of variations in s Ivation and medium effect with addition of alcohol to aqueous solution. Hence, the solvation factor[r-p-I]and medium effect of log f[mlH] are estimated for the I M solution of the three alkalies. Besides, the values of the O H- ion concentration in solution, the autoprtolysis constant pK[m] and the parameter Beta are given and the validity of H- is emphasized by plotting the logarithm of the indicator ratio I against H- where linear plots are obtained with unit slope

Physico-chemical studies on acidity functions in mixed solvents VI Studies on the acidity function H of solutions of KOH in ethanol water mixtures

The values of H[-] are computed for solutions of different concentrations of KOH in ethanol-water mixtures, from the spectrophotometric measurements of ultraviolet absorption of p-nitroaniline, o-nitroaniline, phenol and thioacetamide which arc structurally different indicators. The mean values H[-] and their standard deviations are given together with these deviations expressed in percent. The values of S mean fall between +/- 0.12 percent and +/- 2.05 percent, depending on alkali hydroxide concentration and solvent composition. These reasonable values of S mean denote that H[-] is more or less independent of the indicator used, which may be taken as an evidence in support of the validity of HEI as a measure of acidity in the investigated solutions. Such a validity is also emphasized by the linear plots of unit slope, relating the logarithm of the indicator ratio I and H[-] for the four indicators in solutions of different concentrations of KOH in ethanol water mixtures. The parameters of the linear relationship between H[-] and the reciprocal of the KOH concentrations are also computed by the use of the least-squares method. These parameters facilitate the calculation of the value of H[-] for any other concentration of KOH in the same mixtures. The plots of H[-] against alcohol content in mole percent disclose several peaks and minima the location of which depend on the base concentration and indicator used for the determination of H[-]. This is explained in terms of solvent-solvent and solute-solvent interactions. The values which are computed for K['],K degree, [OH[-]], [r-p-I], and log f[f/m] reflect the effects of these interactions in defining the basicity of the different solutions examined

Physico-chemical studies on acidity functions in mixed solvents VII Studies on the acidity function H of solution of KOH in propanol-, Iso-P ropanol-, and ethylene glycol-water mixtures

Values of the acidity function H[-] arc determined, using p-nitroaniline as indicator, for the 1.0 M solutions of KOH in n-propanol-and iso-propanol-water matures, as well as for solutions of different concentrations of the same alkali hydroxide in ethylene glycol-water mixtures. The plots of H[-] against" alcohol content exhibit several maxima and minima, denoting that the function is affected by several factors and interactions taking part in the whole system. For one and the same KOH concentration, the variation of H[-] with the length and branching of the alcohol chain, as well as with the presence of two OH groups instead of one in ethylene glycol, do not follow a definite order. The validity of the function is emphasized by plotting the logarithm of the indicator ratio I against H[-] where linear plots are obtained. The change; in H[-] with medium completion are explained in terms of the chemical and physical properties of the mixtures in question, as well as changes in solvation, activity coefficient, medium effect log. F[m/H] and autoprotolysis constant pK[m] as a result of addition of alcohol or glycol to the purely aqueous solutions of the alkali hydroxide

Physico-chemical studies on activity functions in some mixed solvents I Studies on lithium sodium and potassium hydroxide solutions in methanol water mixtures

The function of glass electrode, as a measure of acidity in terms of pH value, was studied for LiOH, NaOH and KOH solutions in methanol-water mixtures of different composition. The slopes of linear plots relating e.m.f. and pH values at different temperatures agreed well with those calculated theoritically. This indicated that the glass electrode behaved strictly as H2 electrode in all test solutions. The validity of Dole's theory of acid error delta E for the glass electrode indifferent alkali solutions was investigated. The number of water molecules associated with .the proton, in its migration from the solution into the glass surface, was determined and found to be unity. An attempt was also made to calculate the deviation delta of the pH-meter readings R[x] from the operational pH[j] values and the corresponding liquid junction potentials E[j] as well. delta and E[j] were found to be complex functions of alkali content, solvent composition and temperature probably due to changes in solvation and acidity coefficients of the ions in solution and also to the dielectric constant and basicity with additions of methanol to the purely aqueous solutions