Coulometric generation of acetylions by oxidation of mercury in acetic anhydride and in acetic acid/acetic anhydride mixture

Coulometric generation of acetyl (CH₃CO⁺) ions by oxidation of mercury in acetic anhydride and in acetic acid/acetic anhydride (5:95, v/v) is described. Current/potential curves for solvents, titrated bases, indicator and mercury showed that in both these solvents mercury is oxidized at potentials which are much more negative than those for the titrated bases and other components present in the solution. Quinoline, triethanolamine, triethylamine, pyridine and quinolin-8-ol in acetic anhydride, as well as triethylamine, 2,2′-bipyridine, 2,4,6-collidine, pyridine and sodium acetate in acetic acid/acetic anhydride were titrated with acetyl ions generated by the oxidation of mercury. In this way, it was established that the oxidation of mercury to mercury (I) ions proceeds quantitatively with 100% current efficiency.     

Behaviour of membrane graphite electrodes in potentiometric titrations of reducing substances with bromine in acetic acid

A platinum electrode, a Radelkis OP-C-7111D graphite electrode and a laboratory-prepared silicone-rubber-based membrane graphite electrode were used in potentiometric titrations of reducing substances with bromine in acetic acid. In determinations of hydroquinone, 2-methylhydroquinone, 2-chlorohydroquinone and ascorbic acid, the Radelkis electrode showed the greatest sensitivity. The advantage of the laboratory-prepared membrane graphite electrode lay in its rapid attainment of stable potential values. Titrations were improved by addition of potassium acetate to the solutions analysed. The effects of water and acetic anhydride on the results were also investigated.     

Quantitative anodic generation of cerium(IV) in acetic acid

Conditions for the electrochemical generation of cerium(IV) in acetic acid with high current efficiency are described. Coulometric titrations for determining hydroquinone, 2-methylhydroquinone, 2-chlorohydroquinone and ascorbic acid biamperometric or potentiometric end-points are reported; benzidine is viable for visual end-points. Current efficiency depends on the composition and concentration of the supporting electrolyte and the amount of water and acetic anhydride in the anolyte. The formal redox potential of the Ce(IV)/Ce(III) system decreases as concentration of potassium acetate in the solution increases.     

Coulometric redox titrations of some biologically active thiols with iodine in methanol and bromine in acetic acid

The possibility of coulometric titrations of cysteine, 2-thio-uracil, 6-mercaptopurine, and 6-thioguanine with iodine and bromine in methanol and with bromine in acetic acid has been investigated. Conditions have been found for the direct titration of the test substances with iodine in methanol based on their 1-electron oxidation to the corresponding disulphides and for their direct and indirect determination with bromine in acetic acid based on their 6-electron oxidation to the corresponding sulphonic acids.On leave from Department of Analytical Chemistry, Charles University, Prague, Czechoslovakia     

Coulometric titrations of arsenic(III) and antimony(III) with electrically generated bromine in acetic acid

Conditions for the coulometric titrations were investigated. Arsenic(III) could be titrated by continuous or discontinuous generation of bromine, and antimony(III) by discontinuous generation or back-titration. The accuracy and reproducibility depend on the pretreatment of the platinum electrodes.     

Electrochemical generation of manganese (III) at glassy carbon electrode in acetic acid

Conditions were established for the electrochemical generation of manganese(III) at glassy carbon in acetic acid. In the oxidation of manganese-(II) in potassium acetate supporting electrolyte high current efficiencies were achieved in a wide range of current densities at the working electrode, whereas in the presence of sodium perchlorate a successful generation of manganese(III) could be performed only at low current densities. With increasing content of water in the anolyte the amount of generated manganese (III) was abruptly decreased and its stability in the solution was diminished. Procedures are given for a successful coulometric titration of reducing substances with anodically generated manganese (III); biamperometric, potentiometric and bipotentiometric methods for the location of the end-point were employed. The error of the determinations did not exceed ± 2%.     

Microdetermination of ascorbic acid using bromine monochloride in water-acetic acid medium

A micromethod for the determination of ascorbic acid has been developed. A 2–10 mg sample dissolved in glacial acetic acid is reacted with a known excess of bromine monochloride at ice-bath temperature, and the excess reagent is back-titrated iodometrically. The maximum deviation in the results is ± 1.5%.     

Oxidation of pseudocumene in acetic acid

The oxidation of pseudocumene in the benzene nucleus can be effected in HOAc solution by using inorganic oxidizing agents containing oxygen, such as NaNO₃, hetero-polyacids, O₂, Na₂S₂O₈ and H₂O₂, with Pd(OAc)₂ as catalyst. Na₂S₂O₈ and H₂O₂ are the most effective, being also active in the absence of Pd(II).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2069–2073, September, 1989.The authors thank V. I. Zheivot, V. A. Bushmelev and K. F. Obzherinoi for their assistance in the investigation.     

The kinetics and mechanism of the oxidation of formic acid by bromine in acid aqueous media

The reaction between formic acid and bromine in strongly acid aqueous media at 298 K was studied by absorption spectrophotometry (λ = 447 nm). Reaction rates, expressed as R = -d[Br₂]/dt, depend on the concentrations of HCOOH (0.3–2.4M), Br₂[(2.7–13.6) × 10^?3M], H⁺ (0.03–2.0M), and Br^? (up to 0.6M). The mechanism with k₁ = 20.2 ± 1.2 M^?1 sec^?1, pK₂ = 3.76, pK₃ = ?1.20, accounts for all experimental observations. Br₃^? and HCOOH can be considered unreactive within experimental error. Apparent deviations from the basic mechanism at higher acidities can be quantitatively ascribed to the nonideality of ionic species.     

The pH-dependent energetic uncoupling ofZymomonas by acetic acid

Applied Biochemistry and Biotechnology - pH-dependent energetic uncoupling ofZymomonas by acetic acid occurs by virtue of the permeability of the plasma membrane to the undissociated form of acetic...     

The electrochemical generation of small amounts of hydrogen cyanide

Hydrogen cyanide was generated by constant-current oxidation of an aqueous solution of potassium thiocyanate at a platinum wire anode. In a solution of 0.1M potassium thiocyanate and 0.01M potassium sulphate at a nitrogen flow-rate of 3.5-5.0 ml sec , the rate of production of HCN was a linear function of the generation current I from 10 to 200 microA. The relative standard deviation for an HCN production rate of 6.07 ng sec (I = 130 microA) was 1.8% and that for 0.92 ng sec (I = 20 microA) was 5.9%. The time required to establish steady-state production after a change in the generation current was 10 min.