Single Anodic Wave Research Articles

Molecular wires built from binuclear cyclometalated complexes.

Binuclear complexes with cyclometalated ends of the [Ru(bpy)(2)(ppH)](+) type (bpy = 2,2'-bipyridine, ppH = 2-phenylpyridine), linked by various spacers, have been prepared. These spacers are made of one or two triple bonds, or bis-ethynyl aryl groups, with aryl = benzene, thiophene, or anthracene. The complexes with bis-ethynyl aryl spacers are obtained by Sonogashira couplings with suitable bis-alkynes, starting from the [Ru(bpy)(2)(ppBr)](+) synthon. Complexes with one or two triple bonds are obtained from the true alkyne [Ru(bpy)(2)(pp-CCH)](+) cyclometalated precursor, using respectively a Sonogashira coupling with the iodo derivative [Ru(bpy)(2)(ppI)](+), or an oxidative homocoupling. Some complexes with tert-butyl-substituted bipyridine ancillary ligands have also been obtained. Oxidation of the binuclear complexes occurs near 0.5 V, i.e., more easily than with [Ru(bpy)(3)](2+)-based complexes. A single anodic wave is observed, with almost no detectable splitting, corresponding to two closely spaced one-electron processes. Differential pulse voltammetry allows the determination of the corresponding comproportionation constants involving the mixed valence Ru(II)[bond]Ru(III) forms. Controlled potential electrolysis yields the mixed valence forms in comproportionation equilibrium with homovalent forms. Analysis of the intervalence transitions allows the calculation of the electronic coupling element V(ab). This series of complexes exhibit relatively large couplings when comparing with complexes of similar metal-metal distances, with a special mention for the anthracene-containing spacer, which appears particularly efficient for mediating the metal-metal interaction. The results can be rationalized by theoretical calculations at the extended Hückel level.

Electrochemical Oxidation of Probucol in Anhydrous Acetonitrile

Electrochemical oxidation of probucol in anhydrous acetonitrile was studied as a model of the metabolic oxidation of the substance. The study was performed by DC voltammetry, potentiostatic coulometry, cyclic voltammetry and preparative electrolysis. Probucol gives a single anodic wave E1/2 = 0.92 V. Cyclic voltammetry showes that its electrooxidation proceeds by formation of probucol radical. 2,6-Di-tert-butyl-4-(isopropylsulfanyl)phenol, 2,6-di-tert-butyl-4-sulfanylphenol, 2,6-di-tert-butyl-4-methylphenol and 2,6-di-tert-butylphenol were isolated as products of electrochemical oxidation.

Why the reduction of Hg(cyclam) 2+ exhibits a single voltammetric peak while the oxidation of Hg in the presence of cyclam produces two voltammetric peaks

The cyclic voltammetric response of Hg(cyclam) 2+ at mercury electrodes consists of a single cathodic and a single anodic wave. By contrast, two anodic and two cathodic peaks appear in cyclic voltammograms for the free cyclam ligand (1,4,8,11-tetraazacyclotetradecane) in unbuffered solutions at mercury electrodes. An explanation for the differences in the voltammetric responses is provided. It is based on the acid—base chemistry of cyclam and the unequal diffusion coefficients of protonated cyclam and the hydroxide ion.

Polarographic studies on the interaction between macrocyclic compounds and cations or acids in acetonitrile

At the DME, 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (Me 4[14]aneN 4, TMC) in acetonitrile containing 0.1 mol dm −3 Et 4NClO 4 as the supporting electrolyte gave a single anodic (mercury dissolution) wave at −0.41 V vs. Ag/0.1 mol dm −3 AgClO 4+MeCN electrode. The reversible anodic wave is attributed to the reaction: Hg+TMC ⇌; [Hg(tmc)] 2+ + 2 e −. The formation of the [Na(tmc)] + complex has been clarified, and the formation constant of the complex obtained not only by the shift in E 1 2 of the anodic wave from TMC but also by that of the cathodic wave of [Hg(tmc)] 2+ (produced by the addition of Hg(ClO 4) 2 to TMC) in the presence of a large excess of Na +. By the addition of a large excess of benzoic acid (HA) to the TMC solution, the TMC(H +) 2(A −(HA) 2) 2 species was formed. 1,4,8,11-Tetrathiacyclotetradecane ([14]aneS 4, TTCT) and [16]aneS 4-3,11-diol also gave single anodic waves at more positive potentials to form mercuric complexes. Oxygen-substituted compounds, 18-crown-5 and 12-crown-4, gave incomplete anodic waves.

Polarographic Behavior of 1,4,8,11-Tetraazacyclo-tetradecane in Acetonitrile

1, 4, 8, 11-tetraazacyclotetradecane(cyclam) gave two anodic waves (1:1) (E1/2=-0.35 and -0.52V) in acetonitrile containing 0.1mol dm-3 R4NClO4 (R=Et or Bu) or 0.05mol dm-3Me4NClO4 as the supporting electrolyte at 25°C. With 0.1mol dm-3 NaClO4, the potential difference between two waves became small (E1/2=-0.325 and -0.465V), and finally, with 0.1mol dm-3 LiClO4, the two waves were combined into a single anodic wave at E1/2=-0.225V. The anodic waves of cyclam (L) with R4NClO4 were based on successive mercury dissolution reactions: L+Hg_??_[HgL]+_??_[HgL]2+. The process was reversible: the [HgL]2+ complex gave two cathodic waves on the DME at the same potential as the anodic waves from cyclam. The single anodic wave from cyclam in the presence of Li+ ions was attributed to the reaction: [LiL]++Hg_??_[HgL]2++Li+. The formation constant of [LiL]+ was evaluated (Li++L_??_[LiL]+, log K=ca. 6.0) indirectly by the shift of the cathodic half-wave potential of [HgL]2+ to a positive direction with increasing concentration of Li+. Other voltammetric techniques, such as cyclic voltammetry or differential pulse polarography and coulometry, were also employed to elucidate the electrochemical process.

Direct current and differential pulse polarographic behaviour of benzylpenicilloic acid

The differential pulse and direct current polarographic behaviour of benzylpenicilloic acid (BPA) is discussed. In pH 9.2 borate buffer, the single anodic wave ( E 1 2 = -0.25 V) obtained is diffusion-controlled at concentrations less than 2 × 10 -5 M but adsorptioncontrolled in 10 -4 M solution. Cyclic voltammetry at a hanging mercury drop electrode shows that the electrode reaction is reversible at pH 9.2. The differential pulse peak current is linearly related to concentration in the range 10 -6—2 × 10 -5 M. Penicillamine yields an anodic peak well separated from the BPA peak. Both substances may be determined in each other's presence. Intact penicillin decreases the BPA peak but the linearity between i p and BPA concentration is maintained.

ChemInform Abstract: ANODIC OXIDATION OF SULFONAMIDES. II. ANODIC OXIDATION OF 4′‐SUBSTITUTED BENZENESULFONANILIDES IN ACETONITRILE

AbstractVerschiedene Sulfonamide wie (I) oder (IV) werden der anodischen Oxidation unterworfen und die erhaltenen Reaktionsprodukte charakterisiert.

Anodic oxidation of sulfonamides. II. Anodic oxidation of 4'-substituted benzenesulfonanilides in acetonitrile.

Anodic oxidation of benzenesulfon-p-anisidide (I), benzenesulfon-p-toluidide (II), and N-methylbenzenesulfon-p-anisidide (III) were investigated by cyclic voltammetry and controlled potential electrolysis at a glassy-carbon anode in acetonitrile. I showed a single anodic wave in the absence of pyridine, and three anodic waves in the presence of pyridine. On electrolysis of I in the absence of pyridine, p-benzoquinone and benzenesulfonamide were formed. On electrolysis of I in the presence of pyridine, N, N'-dibenzenesulfonyl-N-(4'-methoxyphenyl)-5-methoxy-o-phenylenediamine (IV) and 1-(2-benzenesulfonamido-5-methoxyphenyl) pyridinium perchlorate (V) were obtained. Anodic oxidation of II in acetonitrile containing excess of pyridine gave N, N'-dibenzenesulfonyl-N-(p-tolyl)-5-methyl-o-phenylenediamine (VI) and N, N'-dibenzenesulfonyl-5, 5'-dimethyl-2, 2'-biphenyldiamine (VII). The formation of VI and VII was interpreted in terms of one-electron transfer followed by dimerizations of the free radical of II. On electrolysis of III in the presence of pyridine, 1-(N-methyl-3-benzenesulfonamido-6-methoxyphenyl) pyridinium perchlorate (VIII) was formed as the main product. The position of pyridination, which was ortho to the methoxy-group, was explained on the basis of steric factors.

Cyclic voltammetry and controlled potential electrolysis of benzenesulfon-p-anisidide.

Anodic oxidation of benzenesulfon-p-anisidide (I) was investigated by cyclic voltammetry and controlled potential electrolysis at a glassy-carbon electrode in aqueous acetonitrile solution. I showed a single anodic wave below pH 7, and two anodic waves above pH 7.5. Electrolysis of I at pH 3.9 gave a coulometric n-value of two, and p-benzoquinone and benzenesulfonamide were obtained. Electrolysis of I at pH 10.5 and the potential of the first wave gave an n-value of about one, and N, N'-dibenzenesulfonyl-N-(4'-methoxy-phenyl)-5-methoxy-o-phenylenediamine (IV) was obtained. The formation of IV was interpreted in terms of a head-to-tail coupling of the free radical of I.

Anodic oxidation of chlorides, bromides and iodides on a platinum microelectrode with periodical renewal of the diffusion layer

The redox process, Cl 2+2 e→ 2 Cl −, occurs reversibly on a platinized-platinum microelectrode with periodical renewal of the diffusion layer. the processes, Br 2+2e → 2 Br − and I 2+2e→2I − occur reversibly in 1 N HCIO 4 either on a smooth or platinized electrode. In 1 N Nano 3 the first of these reactions occurs only on a smooth electrode. the voltammetric curves obtained with a 5.10 −4 M Iodide solution in Hcl at a concentration between 1 and 10 −3 N (the ionic strength being kept constant by the addition Of HCIO 4) show two anodic waves of about the same height. the first wave is due to the oxidation of iodide ion to iodine, the second to the reaction 1 2+4 Cl −→ 2 ICl − 2 +2 e or I 2+2 Cl −→ ICl − +2 e, according to the activity of the chloride ion in the solution. the voltammetric curves obtained with 5.10 −4 M iodide ion in HBr at a concentration between 1 and 0.28 N show a single anodic wave corresponding to the oxidation, I − +2 Br − → IBr 2 − + 2 e. Decreasing the bromide ion concentration below 0.28 N causes a distortion of the wave and finally a splitting : the two waves thus obtained correspond to the oxidation reactions of iodide ion to iodine and of this iodine to IBr 2 − or to IBr. the reversibility of the various oxidation-reduction systems and also the E 1 2 -values of the corresponding waves as functions of the concentrations of halide ions, have been verified. a strict relation between the e 1 2 -potentials and the electrode characteristics has been established. The results are in very good agreement with the values calculated on the basis of the equation valid for spherical diffusion.

Voltammetry of tetra-alkyl ammonium salts at platinum in sulphur dioxide solution: Oxidation of the halides

The polarographic or voltammetric behaviour of a selected group of tetra-alkyl ammonium halides and related compounds in liquid sulphur dioxide was investigated, using a stationary disk platinum indicating micro-electrode and a silver/silver-bromide reference electrode with compensation for the IR drop of the solution. The electrochemical oxidation-reduction patterns are characteristic of the natures of the cation and anion composing the compound.Generally, good reproducible polarograms are obtained. The anodic patterns indicate that the oxidation of each halogen ion can occur in multiple stages, although the bromides generally show only a single anodic wave. The order of ease of electrolytic oxidation in sulphur dioxide is iodide (easiest), bromide and chloride.Sulphur dioxide solutions of the tetra-alkyl ammonium salts show a characteristic cathodic discharge potential in the range of −0·3 to −0·6 V vs Ag/AgBr. If the sulphur dioxide is insufficiently purified, two cathodic waves appear, which are apparently due to a non-condensable gas other than oxygen, sulphur trioxide or water.