The enhancement of acidity in non-aqueous solvents

Summary The acid strength of short-chain carboxylic acids in acetonitrile and acrylonitrile can, by addition of anhydrous alkaline earth perchlorates, be enhanced sufficiently to permit titration of the acid with a tertiary amine in the presence of acid anhydride. This salt effect has been studied by means of potentiometric and automatic thermometric titrations and two distinct mechanisms are thought to be involved: a metathetical reaction at low salt concentrations and a proton desolvation effect at high salt concentrations. High-resolution infra-red spectroscopy has been used to assess the extent of sol vent-cation interaction in acetonitrile. Several equations are used to describe the probable interactions taking place in such salt enhancement phenomena.

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Steigerung der Acidität in nichtwärigen Lösungsmitteln

Zusammenfassung Der Säuregrad von kurzkettigen Carbonsäuren in Acetonitril und Acrylnitril kann durch Hinzufügen von wasserfreien Perchloraten der Erdalkalien genügend gesteigert werden, um bei Vorhandensein von Säureanhydrid eine Titration der. Säure mit einem tertiären Amin zu ermöglichen. Dieser Salzeffekt wurde mit Hilfe von potentiometrischen und automatischen thermometrischen Titrationen untersucht, und es wird angenommen, daß dabei zwei verschiedene Vorgänge eine Rolle spielen: eine Austauschreaktion bei schwachen und ein Desolvatationseffekt bei hohen Salzkonzentrationen. Zur Beurteilung des Ausmaßes der Wechselwirkung zwischen Lösung und Kation in Acetonitril wurde die Infrarot-Spektroskopie mit hoher Auflösung benutzt. Die wahrscheinlich stattfindenden Reaktionsvorgänge werden anhand verschiedener Gleichungen beschrieben.

Lecture presented at Euroanalysis I Conference, 28.8.–1. 9. 1972 in Heidelberg, Germany.     

Photosensitized oxidation of acetylenes

The sensitized (electron transfer) photo-oxidation of acetylenes to yield benzils is described and the mechanism is discussed.     

Cadmium colloids from non-aqueous solvents

Cadmium colloids have been prepared by Chemical Liquid Deposition (CLD). The metal is evaporated to yield atoms which are solvated at liquid nitrogen temperature, and upon warming, stable liquid colloids are formed with particle size ranging between 25–100 Å. Zeta potentials were calculated according to the conversion of Hunter and the Hückel equation, for ethanol and dimethyl sulphoxide. UV/VIS measurement of most of the black colloids showed absorption band around 280 nm. For comparison, we prepared CdS colloid with size 400–625 Å. The colloids are stable to oxidation in air and/or oxygen bubbling. The synthesis of colloids and films from Cd with acetone, 2-butanone, ethanol, 2-propanol, 2-methoxyethanol, DMF and DMSO is reported. Transmission Electron Microscopy (TEM) allows us to determine particle size.     

Coulometric titration of acids in non-aqueous solvents

Coulometric titrations of mineral acids, sulphonic acids, carboxylic acids, enols, imides and phenols have been carried out in t-butanol or in acetone with electrically generated tetrabutylammonium hydroxide. Either a potentiometric titration or a visual indicator end-point may be used. The amount of acid titrated ranges from 10 to 60 muequiv, and the precision and accuracy of the method are excellent.     

Titration of thiol groups in non-aqueous solvents

Thiols are titrated in acetone or dimethylformamide with sodium methoxide, employing visual end-point detection with Thymol Blue, Victoria Blue, p-hydroxyazobenzene or Azo Violet. Aromatic thiols are titrated in the presence of aliphatic thiols in acetone, with Thymol Blue as indicator.     

Kinetic-catalytic determination of vanadium in non-aqueous solvents

Determination of trace vanadium in organic solvents is studied by use of the oxidation of o-dianisdine with t-butyl hydroperoxide. The sensitivity of the catalyzed reaction is optimized by application of a modified simplex method. Under optimum conditions the detection limit is 0.7 ng V ml^?1 in acetonitrile and the relative standard deviation is 0.048. The effect of other metal ions and of co-solvents is discussed. The method is used for trace determinations of vanadium in organic solvents of high purity.     

Rearrangement oftrans-stilbene into diphenylacetaldehyde acetals induced by direct anodic oxidation

Direct anodic oxidation oftrans-stilbene in lower alcohols and in some other solvents in the presence of KF or Bu₄NBF₄ is accompanied by its electrooxidatve rearrangement into diphenylacetaldehyde acetals; a competing reaction yields 1,2-dialkoxy-1,2-diphenylethanes. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2202–2205, December, 1997.     

Polarographic reduction of hydrogen ion in non-aqueous solvents

The polarographic reduction of hydrogen ion, furnished by dissociation of a Brønsted acid or present in the undissociated Brønsted acid, is reviewed for the situation where a solvent other than water is involved.     

Electrocatalytic oxidation of cyclohexane by molecular oxygen in the presence of tertiary alkylammonium salts in non-aqueous solvents

A new electrocatalytic system (acetonitrile, quaternary ammonium salt, graphite cathode) for oxidizing cyclohexane to cyclohexanol by molecular oxygen at room temperature has been discovered.

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Alkaline errors of glass electrodes in non-aqueous solvents

Alkaline errors of glass electrodes in isopropanol were obtained from a comparison with the hydrogen electrode. Electrode glasses which show low alkaline errors in water are also more ideal in isopropanol. Univalent metal ions cause larger deviations than bivalent. Hysteresis effects were found in going from alkaline to acid solutions but not for the reverse direction.     

Electrochemical studies of complex fluorides in non-aqueous solvents

Electrochemical studies on hydrolytically unstable complex fluorides have been shown to be possible in highly purified acetonitrile. The techniques of study will be described briefly. A survey of the results obtained to date wille given.MoF₆ is a stronger oxidising agent than WF₆ by 1.06 volts. Neither |MoF₆|^? nor |WF₆|^? can be reduced below |MF₆|^? in acetonitrile. |UF₆|^? can be reduced to the transient species |UF₆|^2? which is unstable in solution. |OsF₆|^? undergoes successive reduction to |OsF₆|^2? and |OsF₆|^3?.|MF₆L|^? undergoes complex electrochemical behaviour involving reduction to |MF₆L|^2? with subsequent dissociation to |MF₆|^? and L^?. Reoxidation is in the presence of L^? and hence none of the redox steps are fu]ly reversible. The relation between the electrode potentials and the ligand L will be discussed.We thank NATO for a grant in support of this work.     

The effect of water on the anodic dissolution of aluminum in non-aqueous electrolytes

The influence of water concentration on the electrochemical behavior of Al anodes in Al/active-non-aqueous electrolytes is investigated. Normally passive, Al exhibits facile electrochemical oxidation in both AlCl₃/γ-butyrolactone (AlCl₃/BLA) and (C₂H₅)₄NCl acetonitrile (TEAC/ACN) electrolytes. However, in these two electrolytes, the influence of water on Al oxidation shows opposite effects. Incremental increase from 0 to 1.5 M H₂O (0 to 3% water by volume) hinders Al oxidation in 1 M AlCl₃/BLA, increasing polarization loss from 100 to 400 mV cm² mA⁻¹. Yet in 0.3 M TEAC/ACN, Al is passive in the absence of water, exhibiting currents only in the μA cm⁻² domain, equivalent to oxidative polarization losses of over 1000 mV cm² mA⁻¹. This polarization loss is alleviated by water addition, and decreases from 20 to 7 mV cm² mA⁻¹ as water is increased from 0.3 to 1.5 M. FT-IR spectroscopy, linear voltammetry, galvanostatic reduction, surface microscopy and electrolytic conductivity measurements were conducted to probe competing water activation or water passivation effects on organic-phase Al electrochemistry.     

Electrocatalytic oxidation of cyclohexane by molecular oxygen in non-aqueous solvents in the presence of perchloric acid and perchlorates

Several new electrocatalytic systems are described for the oxidation of cyclohexane by molecular oxygen at room temperature. The solvent is acetonitrile. Perchloric acid and perchlorates are used as supporting electrolytes. The maximum electrochemical yield amounts to 9.6% and is observed in the presence of perchloric acid.

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Artifacts in amine analysis from anodic oxidation of organic solvents upon electrospray ionization for mass spectrometry

Different phenylenediamines were used to explore anodic oxidation in solution during electrospray ionization (ESI) mass spectrometry analysis. In our experiments, a series of unknown ionic species was detected in the phenylenediamine solutions. Our results propose that reactions of phenylenediamines with species formed by anodic oxidation of typical ESI solvents during the electrospray ionization process such as formaldehyde are producing these peaks. Identification of these compounds inter alia suggests formal alkylation, a reaction not reported so far as a result of electrolytic oxidation in the prospective organic solvents.