Georges Le Guillanton

A new preparation of alpha-oxo-thioesters by electro-oxidation of diaryl disulfides in the presence of alkynes

A mechanism for the electrochemical oxidation of diaryl disulfides in organic solvents is proposed. A difference is observed according to the nature of the solvent. In dichloromethane and in neutral conditions it is a two-electron process leading to the postulated cation Ar-S + . By reactions in situ with terminal alkynes in the presence of nucleophiles, α-oxothioesters of the type R-CO-CO-S-Ar were obtained.

The conductive sulfur/carbon mixture cathode. An efficient synthesis of thiophenes and related compounds from acetylenes

Abstract The electroreduction of Michael acceptors such as acetylenic derivatives at a compact sulfur- carbon electrode in aprotic media affords thioorganic compounds, mainly thiophenes, in fairly high yields. Their formation is discussed as a function of the electronic effect of the substituents on the acetylenic triple bond.

Determination of Mixtures of Polysulfides by Cyclic Voltammetry

A new method is described for determining the composition of a mixture of disulfides, trisulfides, and tetrasulfides by cyclic voltammetry. Oxidation potentials of the three species are generally well separated and become more positive when the sulfur chain increases in length. Results are compared with those obtained by high-performance liquid chromatography and nuclear magnetic resonance.

Reduction electrochimique de propene nitriles substitues—III alkyl(aryl)oxy-3 phenyl-3 propene nitriles Z et E

The preparation and the separation of E- and Z-isomers of 3-alkyl(aryl)oxy-3-phenylpropenenitriles are described. Configurations are assigned by nmr. n nIn aqueous-organic media Z-isomers are more easily reduced than E-isomers. In anhydrous acetonitrile differences between E12 of E- and Z-isomers are smaller or null. n nPolarography, cyclic voltammetry and macro-scale reductions with identification of products permit us to propose a reduction mechanism. If Tafts constant σ* of R group is negative the Cue5fbC double bond is reduced with formation of 3-alkyl(aryl)oxy-3-phenylpropanenitriles. If σ* is positive the intermediate radical-anion loses RO− ion; cinnamonitrile is formed but immediately reduced, either to in 3-phenylpropanenitrile, or to in 3,4-diphenylhexane dinitrile. n nIt is possible to get hydrodimers while conserving OR group.

The reversible anodic coupling of anions of polysulphones in basic media

Abstract The electrochemical oxidation of acidic sulphones (1 ,3-disulphones, 1,3,5,-trisulphones and trisulphonyl methanes) was conducted in organic medium in the presence of a base. In certain cases dimers may be obtained: these are not thermically stable and, upon heating cleave in radicals detectable by e.s.r, spectroscopy.

Anodic behaviour of unsaturated systems—I. Oxidation of some enol ethers: alkyl (aryl) oxy-3 propenonitriles

Abstract Enol ethers corresponding to the title compounds are oxidized at a platinum or glassy carbon anode in acetonitrile. In poorly nucleophilic media, the electrochemical reaction principally leads to dimers and oligomers due to the electrophilic attack of transient cations on the aromatic substituents of the ethylenic double bond. On the other hand, in the presence of efficient nucleophiles, the anodic reaction may appear to be more selective (at least in certain cases) and the product distribution demonstrates the formation of an intermediate epoxonium ion after the transfer of two electrons. In all media, reactions are furthermore discussed according to the nature of the substituents of the enol ether double bond.

Anodic oxidation of di-tert-butyl disulfide: a facile method for the preparation of N-tert-butylamides

The electrochemical oxidation of di-tert-butyl disulfide is shown to correspond to a one electron process; at 1.3 V, one carbon–sulfur bond is cleaved yielding two intermediate special : the tret-butyl cation and the radical ButS–S˙; a Ritter reaction occurs with the cation when the sovent is a nitrile and the cation dimerizes in to a tetrasulfide; at a more positive potential (1.9V) the two carbon–sulfur bonds are cleaved giving But+ and sulfur.

Anodic Activation of Sulfur in Organic Solvents

The electro-oxidation of sulfur in polar organic media is reported at room temperature, the first such report under these conditions. Electroanalytical techniques such as current-potential curves, coulometry, and mirage effect demonstrated the formation of an electrophilic species S 2+ (consumption of sixteen moles of electrons per mole of S g ). At room temperature S 2+ appears sufficiently stable in solution to be used as a reagent to prepare thio-organic compounds in the presence of nucleophiles

Electrogenerated electrophilic reagents from sulphur: a new access to bis-methoxyaryl sulphides

The oxidation of a sulphur/carbon anode may produce electrophilic species derived from sulphur, and addition of aromatic ethers to the solution allows the two-stage formation of the corresponding diaryl sulphides.

New cathodic cyclodimerisations of 4-pyrones

Under certain conditions, the electrolysis of pyrones leads to complex ‘double dimers’ with a degree of selectivity.