Gino Bontempelli

Anodic oxidation of triphenylphosphine at a platinum electrode in acetonitrile medium

Summary The electrochemical oxidation of Ph 3 P at a platinum electrode in CH 3 CN solvent has been studied using cyclic voltammetry and controlled potential electrolysis. In the anodic reaction, the triphenylphosphinium cation radical initially produced reacts both with Ph 3 P to form a phosphonium cation and with the trace of water present in the solvent to give triphenylphosphine oxide in a ratio depending on water content. When Ph 3 P is oxidized in presence of benzene tetraphenylphosphonium ion is found. The yield of Ph 4 P + in the electrolytic preparation is not very high because a Ph 3 P portion reacts to give Ph 3 PH + and Ph 3 PO.

An electroactive nickel containing polymeric film obtained by electrochemical reduction of an aryl-nickel derivative

Abstract The electrochemical reduction of [Ni(PPh 3 ) 2 ( p -C 6 H 4 Br)Br] in acetonitrile results in a polymeric coating of a nickel-containing poly- p -phenylene, formulated as [-Ni( p -C 6 H 4 ) n -] ( n =6−7) on the basis of elemental analysis, IR, UV, MS and ESCA measurements. This coating is found to undergo a two-electron reversible reduction and a one-electron reversible oxidation with a large potential window (3.6 V), without the polymeric film being destroyed. Moreover, the polymer obtained is shown to be electroactive towards dissolved reactants via permeation or mediated electron transfer, depending on the molecular size of the electroactive species employed.

On the reaction kinetics of electrogenerated superoxide ion with aryl benzoates

Abstract The reactions between electrogenerated superoxide ion O 2 ⨪ and two benzoate esters in N, N-dimethylformamide containing tetrabutylammonium perchlorate have been investigated. By using cyclic voltammetric techniques an e.c.e. type mechanism was found to be operative; this was confirmed by controlled potential electrolysis experiments. Secondorder rate constants for nucleophilic displacement by O 2 ⨪ on p -chlorophenyl benzoate and phenyl benzoate were estimated to be 25.0±5 and 3.0±0.3 M −1 s −1 respectively by fitting potential step reduction data to i k / i d vs. log kt working curves.

Electrochemical behaviour of the bromide ion at a platinum electrode in acetonitrile solvent

Summary The voltammetric behaviour of the bromide ion at a platinum electrode in acetonitrile solvent has been investigated. The occurrence of three subsequent anodic processes has been established. Experimental evidence of the electrochemical formation of the Br + species is gained and suggestions about the reaction mechanism are advanced.

Electrochemical behaviour of diphenyl sulfide in aceto-nitrile medium at a platinum electrode

Summary The electrochemical behaviour of PhSPh at a platinum electrode in CH 3 CN solvent has been studied. PhSPh undergoes three irreversible consecutive oxidation steps. The anodic products have been identified as sulfonium salts. Suggestions are advanced for the mechanisms of the anodic reactions.

Anodic and cathodic deposition of electroactive polyfluorene films: A comparison bewteen the two methods

Abstract Electroactive polyfluorene films were electrodeposited on platinum and glassy carbon electrodes both by anodic coupling from fluorene and by nickel-catalyzed reduction of 2,7-dibromofluorene in acetonitrile. The broad voltammetric peaks exhibited in the former case are substituted for spike-shaped peaks in the latter, in which a higher stereospecificity was found by IR spectroscopy. The properties of polyfluorene films are compared with those of analogously prepared polyaromatic deposits and the advantages of the cathodic method emphasized.

Electrochemical oxidation of phenyldisulfide in acetonitrile medium

Summary The electrochemical oxidation of phenyldisulfide at a platinum electrode has been studied in acetonitrile with NaClO 4 and fluoroborate salts as supporting electrolytes. The cations initially generated are shown to react in different ways depending on the nature of the supporting electrolyte. With NaClO 4 , evidence of ClO 2 , Cl − and PhSO 3 Na was obtained. With fluoroborate salts it is suggested that cations electrochemically generated are involved in chemical reactions with themselves and the solvent.

Redox properties of the nickel(II),(I),(0)-triphenylphosphine system in acetonitrile

The cathodic behaviour of electrochemically generated nickel(II) has been investigated in acetonitrile in the presence of triphenylphosphine at a platinum electrode. An appropriate combination of voltammetric, spectrophotometric and NMR findings has allowed us to establish that Ni(II) is present in solution as [Ni(PPh3)2 (CH3CN)42+.]. For the reduction of this species an EECE mechanism is proposed which is consistent with the data. It undergoes an irreversible two-electron reduction giging the Ni(0) complex [Ni(PPh3)4] which reacts quickly with the depolarizer. In this last homogeneous redox reaction the not previously reported Ni(I) complex [Ni(PPh3)4+] is obtained. The degree of reversibility of the redox processes involved has been discussed taking into account the structure, the coordination number and the nature of the ligands in both the redox partners.

Acid-base equilibria in organic solvents : Part 1. Evaluation of solvent basicity by cyclic voltammetry

Abstract Cyclic voltammetry is applied to evaluate the relative basicity of some organic polar solvents of electroanalytical interest (nitromethane, acetonitrile, tetrahydrofuran, 1,2-dimethoxyethane, dimethylformamide, dimethyl sulphoxide and pyridine). For this purpose, anhydrous perchloric acid is electrogenerated in these solvents and the half-wave potentials of the redox couple H + /H 2 are recorded by referring them to a reference system independent of the nature of the solvent. The proton-basicity scale so obtained is compared with previous basicity series and the observed analogies and differences are discussed. The same procedure is also applied to evaluate, in the solvents mentioned, the relative strengths of some bases which can be used as titrants in nonaqueous media.

Electrochemical synthesis of tris(tri-o-tolylphosphite)nickel(0)

Abstract An electrochemical procedure for the preparation of tris(tri-o-tolylphosphite)nickel(0) in acetonitrile solution is suggested. This procedure includes two steps: 1) the preliminary preparation of an extremely pure nickel(II) solution by anodic oxidation of metallic nickel and 2) the cathodic reduction of this solution on mercury in the presence of an excess of tri-o-tolylphosphite, this excess being necessary to prevent the formation of metallic nickel. The electrochemical behaviours of a nickel electrode and of tris(tri-o-tolylphosphite)nickel(0) in acetonitrile are also reported.