New redox titrants in non-aqueous or partially aqueous media-V Potentiometric titrations with iodosobenzene diacetate in acetic acid medium

A stable new redox titrant, viz., iodosobenzene diacetate in anhydrous acetic acid medium, is proposed for the potentiometric determination of a number of reductants such as As(III), I(-), Fe(II), N(2)H(4), [Fe(CN)(6)](4-), Tl(I), Sb(III), hydroquinone, ascorbic acid, phenol, aniline and oxine.     

Dichloramine-B as redox titrant in non-aqueous or partially aqueous media

Dichloramine-B is proposed as a redox titrant in glacial acetic acid medium. The general conditions for its use and the procedures for estimating hydrazine, ascorbic acid, ferrocyanide, hydroquinone, oxine, antimony(III) and thallium(I) potentiometrically and allyl, crotyl and cinnamyl alcohols by a back-titration procedure are described.     

Dibromamine-B as a new redox titrant in non-aqueous or partially aqueous media

A new redox titrant, dibromamine-B (N,N'-dibromobenzene sulphonamide) is introduced for use in acetic acid medium. Direct potentiometric determinations of hydrazine, ascorbic acid, aniline, thiourea and its metal complexes and oxine and its metal complexes have been described.     

Mechanism of oxidations in partially aqueous media: Kinetics of oxidation of thiosemicarbazide and thiosemicarbazone by chloramine-T and dichloramine-T in aqueous methanol

Kinetics of oxidation of thiosemicarbazide (TSC) and its hydrazone (Benzaldehyde thiosemicarbazone) by chloramine-T (CAT) and dichloramine-T (DCT) in aqueous methanol medium in the presence of perchloric acid has been studied. Oxidation of TSC by both the oxidants showed first order dependences in [oxidant], fractional order in [TSC] and nearly inverse first order in [H⁺]. The conversion of TSC into its benzaldehyde hydrazone changed the rate dependence in [CAT] from first to second order, while the dependence in [DCT] remained unchanged. The dependence in [TSC] changes from fractional order to zero order in both CAT and DCT oxidations. The rate followed inverse fractional order kinetics in [H⁺] in both the cases. Increase in ionic strength of the medium slightly decreased the rate, while the decrease in dielectric constant of the medium increased the rates of oxidations for both the oxidants. But the addition of reaction products, p-toluenesulphonamide and chloride had no effect on the rate. Oxidation of TSC with both the oxidants has been shown to follow Michaelis-Menten type mechanism. In hydrazone oxidations oxidants have been shown to disproportionate in slow steps to HOCl, which in turn attacks the substrate in fast steps to give the final products. [TSC] was varied at different temperatures and the constants of rate limiting steps were calculated at each temperature. Using the latter constants the activation parameters have been computed from the Arrhenius plots. The rate constants have been predicted from the rate law for the variation of [H⁺] at constant [TSC] and [oxidant]. The predicted values are in reasonable agreement with the experimental rate constants, providing additional support to the suggested mechanisms.     

Dichloramine-T as a new oxidimetric titrant in non-aqueous and partially aqueous media

A new oxidimetric titrant, dichloramine-T, is proposed for redox titrations in glacial acetic acid medium. The general analytical conditions for using this oxidant and the procedures for potentiometric determination of ascorbic acid, iodide, arsenic(III) and iron(II) are described.     

A comparison of redox processes for polypyrrole/dodecylsulfate films in aqueous and non-aqueous media

Polypyrrole/dodecylsulfate (PPy/DDS) films were synthesized in aqueous and ethanolic solutions and investigated in aqueous, ethanolic, methanolic and acetonitrile solutions by cyclic voltammetry (CV). The amounts of anions and cations in the films before and after electrochemical treatment were determined by electron probe microanalysis (EPMA); the film morphology was studied by scanning electron microscopy (SEM). The results prove that the mobility of bulky DDS^– ions in PPy increases in the order: water<acetonitrile<ethanol<methanol. It was found that dopant DDS^– ions can be easily removed from PPy matrix swollen in alcohols or acetonitrile by electrochemical reduction or by soaking in electrolyte solutions of these solvents. The influence of electrochemical treatment on the change of doping level in aqueous solution is essentially less and depends on the cations in the test solution. Although the electroneutrality of PPy/DDS films during redox cycling is realized mainly by movement of the cations in aqueous solution and by movement of the anions in organic solvents, nevertheless the participation of anions in aqueous and cations in organic solvents is also established. The redox properties of PPy/DDS are more dependent on the solvent of the test solutions than of the synthesis solutions. Electronic Publication     

Thermometric titration of some monoprotic and diprotic acids in aqueous and non-aqueous media

Some mono- and diprotic acids have been titrated thermometrically with strong alkalis in aqueous and non-aqueous media. Thermograms with sharp arrest points were obtained, from which heats of neutralization were measured. Heats of neutralization in the media used were compared and an effect attributable to hydrogen bonding was found.     

Determination of some steroidal bases in non-aqueous media by potentiometric titrations at a small constant current

In this work the volumetric and coulometric titrations of some newly synthesized androstene steroidal compounds with pyridine ring are carried out. The titrations were followed potentiometrically at a small constant current using pairs of identical platinum or glassy carbon electrodes, both in presence of quinhydrone. As the titration reagent, in volumetric titrations served 0.01 mol dm^?3 perchloric acid, and in coulometric titrations hydrogen ions were anodically generated in situ from quinhydrone at the platinum electrode. Sodium perchlorate served as the supporting electrolyte.Amounts of 1.18-5.35 mg of the investigated steroidal compounds were determined with a relative standard deviation less than 1.4% at volumetric and 1.2% at coulometric determinations. A negative influence of the supporting electrolyte on magnitude of the signal change in potentiometric determinations was observed. Glassy carbon electrodes are more advantageous over platinum ones.The achieved results are in good agreement with those of catalytic thermometric titrations.     

Conductometric and potentiometric titrations of nitrogen bases in non-aqueous solvents

This paper describes an experimental study of the conductometric and potentiometric titrations of nitrogen bases in non-aqeous media. It is shown that for bivalent bases the factors governing the shape of the titration curve are the same as those previously found for dibasic acids, viz. solvent, acid anion, temperature, and distance between basic groups. With the aid of this knowledge a new indifferent solvent system for potentiometric titrations has been developed, which is very attractive for the analysis of mixtures of bases.     

Separation of phenothiazines in aqueous and non-aqueous capillary electrophoresis

Summary Four phenothiazines, promethazine, dioxypromethazine, chlorpromazine, and trifluoperazine have been separated by capillary electrophoresis using N,N,-dimethylformamide (DMF) as separation medium with UV absorbance detection. High voltage and concentrated buffer were used with small current and low electroosmosis. Good resolution and high column efficiency were obtained. Separation selectivity in DMF was different from that in water because of the different solvation interactions. The influence of buffer composition on separation selectivities and electroosmosis were also studied.     

The conductometric titration of carboxylic and phenolic acids in non-aqueous solutions: The resolution of acid mixtures and some practical applications

A detailed study has been made of non-aqueous conductometric titrations suitable for the resolution of acid mixtures. The optimum conditions for the various determinations with respect to base and solvent are extensively discussed. The applications include determinations of diphen-ylolpropane, naphthenic acids, perchloric acid and mixtures containing sulphuric acid.     

(o-Hydroxyphenyl)methylphosphonic acids: Synthesis and potentiometric determinations of their pKa Values

(o-Hydroxyphenyl)methylphosphonic acids are readily obtained from o-(bromomethyl)- or o-(hydroxymethyl)phenols and trialkyl phosphites. Subsequent hydrolysis leads to the corresponding phosphonic acids. For a series of such compounds, the pK_a values have been determined by potentiometry. Their dependence on additional substituents in the aromatic ring is discussed in terms of electronic and steric effects.     

Thermodynamic parameters of some partially fluorinated and hydrogenated amphiphilic enantiomers and their racemates in aqueous solution

Micellization properties of aqueous solutions of four enantiomeric/racemic pairs obtained from partially fluorinated octylesters (PFOEs) and hydrogenated dodecylesters (DDEs) of alanine and serine were investigated by electrical conductivity, surface tension and density measurements over the temperature range of (15 to 35) °C. The Krafft temperatures (T_Ks) of most of the esters were found to be below or near zero temperature. The critical micelle concentrations (cmcs) of the PFOEs were found to be larger than those of the DDEs from which it was calculated that a CF₂ group in the partially fluorinated chain is approximately equivalent to 1.8 CH₂ group in the hydrogenated dodecyl chain and there were no noteworthy differences in the cmcs of the L- and DL-forms of the studied amphiphiles. The thermodynamic quantities of micellization (ΔG_mic, ΔH_mic, ΔS_mic) and adsorption (ΔG_ad), and the adsorption parameters at the air/water interface, the surface excess concentration (Γ_max), the minimum area per head group of a molecule (A_min) and the efficiency in the surface tension reduction (pC₂₀), were also calculated. It was found that the micellization for DDE of alanine and the adsorption for PFOE of serine were more favoured than the other L-and DL-forms where the latter was in part as dimer at the air/water interface. Furthermore, except for the ΔH_mic values, there were no significant differences in these quantities for the L-and DL-forms of the studied systems. The mass density measurements showed that the apparent molal volumes ($V_{\phi }^{\text{cmc}}\text{,}{V}_{\phi }^{\text{mic}}$) of the hydrogenated esters were strikingly larger than those of the partially fluorinated ones, whereas the change of the apparent molal volume upon micellization ($\mathrm{\Delta }{V}_{\phi }^{\text{mic}}$) exhibited reverse behaviour, from which it was concluded that the micelles of the partially fluorinated esters were larger than those of the hydrogenated ones.     

Determination of oxytetracycline and some impurities in plasma by non-aqueous capillary electrophoresis using solid-phase extraction

Summary The potential of a non-aqueous, capillary electrophoresis (NACE) system for separating oxytetracycline from three of its impurities—tetracycline, 4-epioxytetracycline and 4-epitetracycline—using UV detection has been studied. The running buffer was: 25 mM sodium acetate, 1 mM EDTA, methanesulfonic acid, pH 4, dissolved in MeOH-ACN (50∶50,v/v). The method was also used to determine these compounds in pig plasma. A solid-phase extraction (SPE) procedure as a clean-up step has also developed. For this we tested Sep Pak C₁₈, LiChrolut EN and OASIS cartridges. OASIS cartridges were best. Recoveries were 90–100% for all compounds except EOTC which had a recovery of 74%.     

FIA titrations of phenothiazine derivatives in aqueous micellar and non-aqueous media

New methods of flow injection analysis (FIA) neutralization titrations of phenothiazine derivatives in aqueous micellar medium of a cationic surfactant using potentiometric and spectrophotometric detection were proposed; titrations with a mixing gradient chamber and high-speed titrations were compared. The FIA titration method in non-aqueous media based on an official method of determination (titration with perchloric acid in anhydrous acetic acid) was also developed. Under optimized reaction conditions and flow-through parameters, the calibration range and equations, the sensitivity, and the repeatability of all methods were found and discussed. All titrations were assayed for medicinal forms.     

Vibrational spectroscopic studies of uranyl complexes in aqueous and non-aqueous solutions

Vibrational spectra have been obtained for aqueous solution of uranyl-perchlorates, -fluorides, -chlorides, -acetates and -sulphates over a range of solution composition with added anions. We have prepared [Buⁿ₄N][UO₂Cl₄], [Me₄N][UO₂Cl₄], [Prⁿ₄N][[UO₂(NO₃)₃], [Buⁿ₄N][UO₂(NO₃)₃], with the expectation that the large cation would give a better approximation to vibrational frequencies of the free anion and would allow measurements in non-coordinating solvents. As the perchlorate is not coordinated to [UO₂]²⁺ in aqueous solution the expected structure is a solvated cation [UO₂(OH₂)₅]²⁺ with characteristic infrared 962.5, 253 and 160 cm⁻¹ and Raman 874 and 198 cm⁻¹ bands. The formation of weak, solvated [UO₂X]⁺ complexes (X=F, Cl) has been established with frequencies at 908, 827, 254, 380 cm⁻¹ and 956, 871, 254 and 222 cm⁻¹ for [UO₂F]⁺ and [UO₂Cl]⁺, respectively. Bidentate NO₃ coordination has been established for solid and dissolved (in CH₂Cl₂) [R₄N][UO₂(NO₃)₃] (R=Prⁿ, Buⁿ). Aqueous solutions of UO₂(NO₃)₂ and Cs[UO₂(NO₃)₃] show no clear evidence that bidentate or monodentate nitrate is present. Both unidentate and bidentate linkage of acetate-uranyl were established for acetate complexes in aqueous solutions. For the uranyl sulphate system, monodentate sulphate coordination is the major mode at low SO₄:U ratios, and even at a ratio of 3:1 there is very little free sulphate.     

A deuterium-palladium electrode as a new sensor in non-aqueous solutions: potentiometric titration of weak acids in acetonitrile and benzonitrile

A deuterium-palladium electrode was employed as a new indicator electrode for the titration of weak acids in acetonitrile and benzonitrile. The investigated electrode showed a linear dynamic response for p-toluenesulfonic acid in the concentration range from 0.001 M to 0.1 M with a Nernstian slope of 48 mV in acetonitrile. Sodium methylate, potassium hydroxide and tetrabutylammonium hydroxide proved to be very suitable titrating agents for these titrations. The response time was less than 10-11 s and the lifetime of the electrode was limitless. Advantages of the electrode are: long-term stability, fast response, reproducibility, easy preparation and low cost.     

Determination of gold(III) alone or in some mixtures and alloys by potentiometric titration of iodide

The present work is an application of iodide to the reduction of gold(III), in an attempt to develop new method for gold(III) based on potentiometric back-titration of the excess of iodide with mercury(II). Although it was proved by calculation that the reduction of tetrachloroaurate to the metal should proceed quantitatively to completion, yet our experiments showed that the reduction under ordinary conditions, gave Au(I) in the form of a white precipitate of AuI. We succeeded to push the reduction with iodide to the metal by an excess of ethanol-ether catalyzed iodide at somewhat elevated temperature.With the experimental conditions established a reliable procedure have been developed involving a potentiometric finish which enabled accurate determination of gold(III), either alone or in some of its alloys.     

Electron free energy levels in oxidic solutions: relating oxidation potentials in aqueous and non-aqueous systems

We provide background to the problem of describing the state of redox couples in different types of solvent media ranging from acidic aqueous solutions to high temperature molten silicates, pointing out the essential similarity between these solvent media in Lewis acid–base terms. We review the adaptation of the Gurney proton energy level diagram approach to the case of electron transfer processes. Using data from various spectroscopic and analytical chemistry sources, we review the construction of electron free energy level diagrams for redox couples in aqueous and non-aqueous systems using, as a common reference, the potential of the oxygen gas (1 atm)/oxide ion couple in the solution of interest. We emphasize the anomalous effect of “oxide ion activity” (mean ionic activity of alkali oxide) on the state of equilibrium and interpret this in terms of oxide ion transfers that accompany electron transfers. After showing the essential agreement between recent direct electrochemical assessments of the energy levels and those deduced in our original analysis of oxidic melts of different glass formers, we provide an interpretation of the apparent “oxide ion transfer” in terms of the differential medium polarization by the two redox species involved in the equilibrium. We anticipate the extension of these ideas to redox chemistry in the currently burgeoning field of “ionic liquids” in its recent ambient temperature liquid incarnation. Dedicated to the 85th birthday of John O’M. Bockris.

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