Anodic oxidation of 5,10-dihydro-5,10-dimethylphenazine

Summary The compound 5,10-dihydro-5,10-dimethylphenazine (DMPZ) exhibits two succesive reversible, 1-electron oxidation-reduction steps in acetonitrile and propylene carbonate as solvents. This system has been tested by most of the known diagnostic criteria of electrochemical reversibility and found to adhere to all of them unambiguously. This model system provides a reference for comparison of other multi-stage electrochemical processes.When DMPZ is oxidized in solvents or additives which are strong nucleophiles demethylation accompanies the second stage of oxidation. Since this chemical follow-up reaction occurs in aqueous media it is of significance in the biological redox reactions of N-alkylated phenazines.

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Zusammenfassung Die Verbindung 5,10-Dihydro-5,10-dimethylphenazin (DMPZ) weist in Acetonitril und Propylencarbonat als Lösungsmittel zwei aufeinanderfolgende reversible einelektronige Oxydations-Reduktions-Stufen auf. Dieses System wurde mit Hilfe der meisten Kriterien für elektrochemische Reversibilität untersucht und in allen Fällen ein eindeutiges Verhalten festgestellt. Das System kann als Bezug zum Vergleich anderer vielstufiger elektrochemischer Prozesse dienen. Wird DMPZ in Lösungsmitteln oder in Gegenwart von Zusätzen, die stark nucleophil sind, oxydiert, so begleitet eine Demethylierung die zweite Stufe der Oxydation. Da diese Reaktion in wäßrigem Medium verläuft, ist sie von Bedeutung bei biologischen Redoxreaktionen von N-alkylierten Phenazinen.

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Dedicated to Prof. Dr. M. von Stackelberg on his 70th birthday.     

Anodic oxidation of sodium-O-cyclohexylphosphonite

The research data on the anodic oxidation of sodium salt of cyclohexyl ester of hypophosphorous acid on a Pt electrode are shown. The molecule of this salt has two electroactive centers: phosphoryl (PONa) and phosphine (P-H).     

Polarographic oxidation of some 5,10-dihydrophenazine derivatives

The polarographic anode oxidation of 5-substituted dihydrophenazines in an aprotic medium and an aqueous acetone solution has one-electron or two-electron character. It was shown by means of the electronic and ESR spectra that the intermediates in the anode oxidation of dihydrophenazine and 5-methyldihydrophenazine are cation radicals and that the products of one-electron oxidation of 1,3-dinitro-5-aryl-substituted dihydrophenazines are phenazyl radicals. The final products of anode oxidation are phenazinium salts.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 548–551, April, 1976.     

Anodic oxidation potentials of aromatic cyanoesters

Using cyclic voltammetry, the anodic oxidation potentials for a series of 15 substituted aromatic cyanoesters have been measured and analyzed. Irreversible anodic oxidations were observed, in addition to a cathodic reduction wave. The different aromatic species exhibited different potential values, in accordance with the type of the substituent and nature of the aromatic nucleus.

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Anodische Oxidationspotentiale aromatischer Cyanoester (Kurze Mitteilung)

Zusammenfassung Unter Verwendung von cyclischer Voltametrie wurden die anodischen Oxidationspotentiale einer Serie von 15 substituierten aromatischen Cyanoestern gemessen und analysiert. Zusätzlich zu einer kathodischen Reduktionswelle wurden irreversible anodische Oxidationen beobachtet. Dabei zeigten die verschiedenen Verbindungen je nach dem Substitutionstyp und der Natur des aromatischen Kerns unterschiedliche Potentialwerte.

     

Anodic oxidation of ring A-aromatic steroids. Regioselective benzylic oxidation

A new method for benzylic alkoxylation and hydroxylation of 3-methoxy-estra-1,3,5(10)-trienes (I) is described. 9α- and 9β-methoxy- and 9α- and 9β-hydroxy-3-methoxy-estra-1,3,5(10)-trienes (II and III) were prepared by electrochemical oxidation in a methanolic or aqueous solvent supporting electrolyte (SSE).     

Anodic oxidation of 1-naphthylamine in acetonitrile

The anodic oxidation of 1-naphthylamine (ArNH₂) has been studied at the platinum electrode in acetonitrile by controlled potential electrolysis, chronopotentiometry, cyclic voltammetry, cyclic voltammetry and spectrometric methods. From the electrochemical data a complex ECE type of mechanism is inferred with an overall efficiency of one electron per molecule of ArNH₂. The electrochemical steps are reversible and the chemical process seems to follow second order kinetics and is extremely fast. The cation radical produced in the first charge transfer step suffers fast decomposition to give dimers which are easier to oxidize than ArNH₂. The dimeric products were identified by comparison with authentic samples. Further complications arise due to slow reactions of the oxidized dimers. Electrochemical studies in basic media (pyridine and 2,6-lutidine) and acid media (anhydrous trifluoroacetic acid) were also performed.     

Anodic oxidation of dialkyl and diaryl dithioacetals

The mechanism of the anodic oxidation of dithioacetals is discussed, taking into account new results concerning both mixed electrolyses and oxidations in super-dried solvents. In the case of the oxidation of aryldithioacetals, the formation of the -S-S- linkage is involved with a bond cleavage followed by a dimerisation. On the other hand, in the case of aliphatic starting materials the mechanism looks more consistent with the existence of a dicationic intermediate which is scavenged by nucleophiles.     

Anodic oxidation of selenadiazoloquinolones in alkaline media

Newly synthesized derivatives of 6-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4-h]quinoline variously substituted at position 7 (R = H, COOH, COCH(3), CN, COOC(2)H(5) and COOCH(3)) are established in strongly alkaline aqueous solutions (0.1 M NaOH; pH ～ 13) as N(9)-deprotonated structures, but in less alkaline solutions (0.001 M NaOH; pH ～ 11) the N(9)-protonated oxo tautomeric forms dominate. Upon their anodic oxidation in alkaline solutions, the selenadiazole ring is replaced, forming instead the paramagnetic species analogous to the ortho semiquinone radical anions as monitored by in situ EPR spectroscopy. The quantum chemical calculations for two representative selenadiazoloquinolones (R = H and COOH) and their anodic oxidation products presented are in agreement with experiments.     

Anodic oxidation of gallium in alkaline solution

The anodic oxidation of Ga in basic solutions is studied using data of potentiostatic and galvanostatic methods, observation of two types of light emission, and measurement of gas evolution. Oxide layers are formed on Ga and dissolve in the electrolyte. The rate of dissolution and nature of the layers depends on the pH.     

One-Pot Synthesis of 2-Amino-5,10-dihydro-5,10-dioxo-4-phenyl-4H-benzo[g]chromene Derivatives Catalyzed by ZnCl2

An efficient one-pot synthesis of 2-amino-5,10-dihydro-5,10-dioxo-4-phenyl-4H-benzo[g]chromene derivatives has been achieved by the reaction of 2-hydroxynaphthalene-1,4-dione, cyanothioacetamide, and aromaticaldehyde in EtOH at room temperature catalyzed by ZnCl₂. The structures of the products were characterized by infrared, ¹H NMR, mass, and elemental analysis.

Anodic oxidation of mono- and disubstituted 1,4-dimethoxybenzenes

The electrochemical oxidation of mono- and disubstituted 1,4-dimethoxybenzene derivatives with zero, one, and two benzylic CH(2)X groups (X = OAc, Cl, OH) (5a-c and 6a-c) has been carried out by using both constant-current and controlled-potential techniques in methanol and in the presence of different electrolytes and working electrodes. Constant-current electrolysis in KOH-methanol solutions yielded mostly the corresponding 1,4-quinone derivatives from 5a-c and 6b, whereas the disubstituted 1,4-dimethoxybenzenes 6a,c underwent side-chain oxidation to form 2,5-dimethoxyterephthalaldehydes. Upon alteration of the medium from the commonly used basic KOH-methanol to neutral LiClO(4)-methanol, a new spectrum of products was achieved in most cases, involving novel coupling products from monosubstituted substrates and quinone derivatives from disubstituted ones. Controlled-potential oxidation at the glassy carbon anodes and in a neutral LiClO(4)-methanol medium led to more complex mixtures of products, namely, polymers and new coupling products from monosubstituted substrates and quinones and side-chain oxidation (or substitution) products from the disubstituted ones. Three new coupling products were isolated and characterized by X-ray measurements.     

Anodic oxidation of sulfide ions from chloride brines

The anodic oxidation of sulfide ions from chloride brines at graphite electrodes is shown to produce elemental sulfur, that was identified using XPS and EDS measurements. The process is controlled by charge transfer at the interface and diffusion of the sulfide ions in the electrolyte. Potentiostatic current transients reveal exponential decay of the current with time accompanied by gradual increase of the polarization resistance of the interface, at a rate which increases with increase of the potential in the noble direction. This behavior is attributed to passivation of the electrode by the elemental sulfur which deposits on its surface.     

Anodic oxidation of manganous ion in liquid ammonia

In acidic solutions of liquid ammonia, manganous ions can be oxidised anodically at a vitreous carbon electrode, probably yielding Mn³⁺ species. By means of non-steady state measurements of the re-reduction of the oxidation product, the apparent rate constant and standard potential have been determined. The Mn³⁺ species is unstable in the medium and decomposes by oxidation of the solvent.     

Crystal Structure of 2-Amino-5,10-dioxo-4-aryl-5,10-dihydro-4H-naphtho [2,3-b]pyran-3-carboxylic Acid Ethyl Ester

The title compounds have been synthesized via a three-component reaction and their structures were characterized by IR, ^1H NMR, ^13C NMR and X-ray single-crystal diffraction. The crystal of compound 4a belongs to monoclinic, space group P121/c1 with a = 8.575（3）, b = 9.590（3）, c = 21.431（6）A, β = 91.172（3）°, V = 1762.1（9）A^3, Mr = 393.36, Z = 4, Dc= 1.483 g/cm^3, μ（MoKα） = 0.113 mm^-1, F（000） = 816, the final R = 0.0366 and wR = 0.0941. The crystal of compound 4b is of triclinic, space group P-1 with a = 8.6420（17）, b = 9.761（2）, c = 11.132（2） A, α = 97.51（3）, β = 97.86（3）, γ = 92.85（3）°, V = 920.1（3） A^3, Mr = 393.36, Z = 2, Dc = 1.420 g/cm^3, μ（MoKα） = 0.108 mm^-1, F（000） = 408, the final R = 0.0612 and wR = 0.1781. In each molecular structure, the naphthalene rings and pyran rings are almost coplanar with the latter in an envelope conformation. The rings formed by the N-H…O intramolecular hydrogen bonds are almost planar in these compounds. Their crystal packing is stabilized by intermolecular hydrogen bonds together with C-H…π and π-π stacking interactions.