Andre Thiebault

Electrochemically induced aromatic nucleophilic substitution in liquid ammonia. Competition with electron transfer

Electrochemical inducement of aromatic nucleophilic substitution of ArX compounds is investigated for a number of substrate and nucleophile systems in liquid ammonia. Electron transfer to the Armradical resulting from the initial reductive cleavage is essentially the only reaction competing with substitution. The competition occurs under two different regimes in- volving either homogeneous or heterogeneous electron transfer leading to different kinds of kinetic control. Cyclic voltammetry is used both for a rapid estimate of the nucleophile reactivity and for a quantitative determination of the rate constants of the nucleophile addition on Are. The method is also applied to the determination of the kinetic stabilities of the substrate anion rad- icals which is not possible through the standard application of electrochemical techniques. The agreement of the predicted ki- netics with the experimental data both under homogeneous and heterogeneous electron transfer conditions provides further support for the SRNI mechanism.

Electrosynthesis of unsymmetrical biaryls using a SRN1 type reaction

Abstract A new synthetic route to unsymmetrical biaryls is described involving an electrochemically induced chain reaction of the S RN 1 type.

Hydrogen atom transfer oxidation of primary and secondary alcoholates into aldehydes and ketones by aromatic halides in liquid ammonia. A new electrochemically induceable reaction

It is possible to induce the oxidation of alcoholates into the corresponding carbonyl compounds by electrochemical reduction of aromatic halides in liquid ammonia, Le., to electrochemically trigger the reaction ArX + >CH-OArH + >C=O + X-. H-Atom transfer from the alcoholate to the aryl radical formed upon reduction of the aryl halide appears as the key step of the oxidation process. The ketyl anion radical thus formed can be oxidized into the parent carbonyl compound, remain electrochemically stable, or be reduced into the dianion depending upon the location of the two corresponding standard potentials toward the reduction potential of the aryl halide. Electricity consumption thus tends toward 0, 1, and 2 F/mol for the three cases, respectively. The reactions competing with H-atom transfer, thus lowering the efficiency of the electrochemical inducement of the oxidation process, are electron transfers to the aryl radical which occur at the electrode surface and/or in the solution. These will play the role of termination steps for the corresponding chain systems involving homogeneous initiation of the reaction. The kinetic analysis of the competition between H-atom transfer and homogeneous or heterogeneous electron transfer allows a detailed investigation of the reaction mechanism by electrochemical techniques such as cyclic voltammetry. This also leads to the determination of the rate constant of H-atom transfer of the alcoholate-aryl radical couple. Electrochemical inducement of a chemical reactionza is based upon the reactivity of the system being larger at a higher or a lower oxidation level than at the original one. A few examples of such processes have been described in organic or coordination chemistry? This reaction that has been the most extensively studied in this respect is SRNl aromatic nucleophilic s~bs t i t u t ion ,~ the electrochemical inducement”Sk of which is based on the following reaction sequence: ArX + l e 9 ArX-. ArX-. Ar. + XAr. + NuArNu-.

Surface modification of halogenated polymers: 1. Polytetrafluoroethylene

Solutions of solvated electrons in the presence of magnesium offer many advantages for the surface treatment of PTFE when compared to the classical solutions of solvated electrons in the presence of alkalis: the polymer remains white instead of black, its surface is not destroyed and presents a controlled hydrophilic character.

Hyperpolarization properties of pyridinium and quinolinium salts determined by hyper-Rayleigh scattering

Abstract The quadratic hyperpolarizabilities of a series of pyridinium and quinolinium salts are measured by hyper-Rayleigh scattering in solution. These salts present high hyperpolarizabilities combined with good transparencies in the visible region of the spectrum. The higher efficiency of the teraryl over the biaryl for the conjugation path between the donor and the acceptor groups is clearly evidenced.

Electrosynthesis of unsymmetrical donor-acceptor polyaryls

Abstract Unsymmetrical Donor-Acceptor Polyaryls are synthesized by an electrochemically induced S RN 1 reaction using 2,6-ditertbutyl phenoxide as nucleophile and acceptor substituted polyarylbromides The latter are synthesized by a cross coupling reaction of aromatic organometallic reagents and aromatic halides catalyzed by palladium complexes.

Surface modification of halogenated polymers 3. Influence of additives such as alkali cations or nucleophiles on the magnesium reductive treatment of polytetrafluoroethylene

The presence of a small amount of an alkali cation in a magnesium solution dramatically increases the rate of defluorination of PTFE and enhances oxygenation. Evidence of this effect is observed for concentrations down to 1 mM and treatment durations of only 10 s. The presence of the alkali cation also makes the polymer porous. The rate of defluorination and the depth of attack increase both with the alkali cation concentration and with the duration of the treatment. Sodium is more reactive than potassium which is itself more reactive than lithium. The phenomenon is not limited to alkali cations and is also evident with the tetrabutylammonium cation. When nucleophiles such as diethylphosphite, thiophenoxide or the anions of 2-mercaptopyridine and thiourea are present in a solution of magnesium containing a moderate amount of solvated electrons ( < 50 mM), the grafting of the nucleophile to the polymer occurs but leads to poor yields

Electrochemically induced SRN1 aromatic nucleophilic substitution: monoanions of β-dicarbonyl and β-cyanocarbonyl compounds as nucleophiles

Abstract Monoanions deriving from β-dicarbonyl or β-cyanocarbonyl compounds can be used as nucleophiles in electrochemically induced SRN1 aromatic nucleophilic substitution with different substrates including cyano or benzoyl substituted aromatic halides and 2-chloroquinoline.

Addition of aryl radicals generated from electrochemical reduction of aryl halides on carbon-carbon double bonds.

Abstract Aryl radicals generated by electrochemical reduction of aryl halides in aprotic medium react with styrene and its derivatives to give arylated addition compounds.

Electrochemical reduction in liquid ammonia: electrolytic birch reactions and chemical bond fissions

Abstract A procedure of electrochemical reduction in liquid ammonia using a single-compartment cell equiped with a soluble anode is described and illustrated in the case of aromatic compounds and esters.