Jaromír Hlavatý

Electrochemical behaviour of 2,2′-dinitrodiphenylsulphide and its cyclization reactions initiated by an electrode reduction

Abstract In supporting electrolytes containing 50% ethanol, 2,2′-dinitrodiphenylsulphide(I) is reduced at mercury electrodes to 2,2′-di(hydroxylamino)diphenylsulphide(III) and after protonation to 2,2′-diaminodiphenylsulphide. In a chemical follow-up reaction III undergoes an intramolecular disproportionation and yields finally the thiadiazepine(IV). This product, however, can be easily reduced at the given potential to the dihydrothiadiazepine(V). This mechanism has been confirmed by dc polarography, cyclic voltammetry, controlled-potential coulometry and controlled-pontential preparative electrolysis. The yield in the electropreparation of IV is better than in a chemical procedure. This holds true in particular for slightly acidic, neutral and slightly alkaline solutions with 50% ethanol or for a 0.5 M LiCl solution in anhydrous ethanol. At pH 4.6 III is very stable and can be obtained in a high yield as a valuable intermediate for further chemical reactions.

Electrochemically initiated intramolecular cyclization of 2-nitro-2′-isothiocyanatobiphenyl

Abstract 2-Nitro-2′-isothiocyanatobiphenyl was prepared as a new substance, suitable for the investigation of an electrochemically initiated intramolecular cyclization. If it is reduced at a mercury cathode in acidic media an acid catalysed intramolecular follow-up reaction occurs which leads to the formation of 6-mercaptodibenzo ( d, f )-(1,3)-diazepin-5-oxide. The rate of the follow-up reaction decreases in neutral or alkaline media and the reduction of the isothiocyanato group also takes place. The main product is here 5,6-dihydrobenzo( c )cinnoline.

The influence of H+ ions liberated by electropolymerization on the decomposition of propylene carbonate

Abstract The effect of H + ions, liberated in the course of pyrrole electropolymerization, on the chemical decomposition of propylene carbonate (PC) containing LiClO 4 as an electrolyte was investigated. GC analyses of model solutions (0.05–0.5 M HClO 4 /PC) revealed CO 2 and allyl alcohol as primary products. Allyl alcohol is converted, probably by reaction with residual water, to 1,2-propanediol. The concentration of both allyl alcohol and 1,2-propanediol increases with time up to about 0.1 M. An excess of pyrrole inhibits the PC decomposition whereas the presence of polypyrrole does not.

Electrochemical reduction of 2,2′-dinitrobiphenyl-X type substances in nonaqueous and aprotic solvents

The oxidation-reduction behaviour of 2,2′-dinitrobiphenyl-X type compounds (X = O, S, NH, CH2, CO) and of 2,2′-dinitrobiphenyl in non-aqueos acetonitrile and dimethylformamide and their mixtures with water was investigated by polarography and cyclic voltammetry at mercury drop electrodes. In combination with ESR-spectroscopy the reversible formation of a radical anion has been found in the primary one-electron step which is followed by a second one-electron uptake leading to a di-anion. According to the group X, to the water content and to the supporting electrolyte the second reduction step is or is not reversible. The ease of reduction decreases in the following sequence with changing X : CO > NH > S > O> - >CH2(ie E12 becomes more negative). According to the composition of the solution further 2 or 6 electrons are consumed at more negative potentials, giving to the 2-hydroxylamine-2′-nitro derivative or to the 2,2′-di-hydroxylamine compound, respectively. In solutions with more than approx 5–10% (by vol.) of water the reduction of the two nitro groups proceeds either in a single 8-electron step or in two 4-electron waves. In 90–94% acetonitrile solutions with alkali metal cation salts as supporting electrolytes a dip appears on the limiting current of the overall 8-electron reduction wave with the dme. The inhibition of the reduction process has been interpreted in terms of formation at the electrode of an insoluble precipitate of tri-ions resulting from the interaction between the di-anion and the alkali metal cations.

Anodic oxidation of o-toluenesulphonamide to saccharine on a NiO(OH)-coated nickel anode

Abstracto-Toluenesulphonamide has been electrolytically oxidized at low current density to saccharine in aqueous solutions of alkali carbonates on anodes coated with NiO(OH). This electrolytic oxidation led to a 40% yield of saccharine. The application of carbon and glassy-carbon counter electrodes or of various supports for the working electrodes did not result in improved saccharine yield. Moreover, the choice of a different potential and a different current density or the use of organic co-solvents did not substantially affect the course of the electrolytic oxidation.In the electrolytic oxidation ofo-toluenesulphonamide a parasitic evolution of oxygen occurred which caused a partial degradation of the starting material. In strongly alkaline media, i.e. in aqueous solutions of alkali hydroxides, a fission of the NH2 group with formation ofo-toluenesulphonate occurred during the electrolysis.

Anodic alkoxylation of N-phenylsulfonylpyrrole

Abstract The anodic alkoxylation of N -phenylsulfonylpyrrole (1) yielded products of nucleophilic addition on a cation radical or cation resulting from the primary electrochemical step. 2,5-Dimethoxy-1-phenylsulfonyl-3-pyrroline (3) was isolated in 46% yield and 2,5-diethoxy-1-phenylsulfonyl-3-pyrroline (5) in 38% yield. The dimethoxypyrroline derivative 3 splits off methanol when heated, giving 2-methoxy-1-phenylsulfonylpyrrole (7).

Electrolytical reduction of maleinamide and fumaramide of 2-nitrobiphenyl-2′-amine at mercury electrodes

Abstract The role played by geometric isomerism in the intramolecular cyclization reaction initiated by the electrode reduction of maleinamide and fumaramide of 2-nitrobiphenyl-2′-amine was studied at mercury electrodes. The cyclization reaction leading to the formation of benzo( c )cinnoline occurs with the former substance whereas only a reduction of the nitro group and of the CC double bond could be observed with the latter.