M. Lipsztajn

Ion pair formation effects in the reversible electroreduction of nitrobenzene in N,N-dimethylformamide

Summary From polarographic measurements p K ass values of ion pairs formed by the nitrobenzene radical anion N − and cations M + have been estimated. Application of the function (R+δ) −1 distinctly improved the empirical relation between E 1/2 ipf and ionic potentials verifying the assumption of the considerable influence of solvation effects on ion pair formation. This is also supported by a thermocycle treatment of solvation and association of ions and ion pairs.

Polarographic investigation of the interactions between nitrobenzene radical anions, water and univalent cations in dimethylformamide/water mixtures

Summary Dependences of the half-wave potential of the first reduction wave of nitrobenzene in 0.1 M Li+, Na+, K+ and Et4N+ perchlorates in DMF on varied amounts of water were studied polarographically. At fixed concentrations of water (cf. Table 1) plots of E1/2 against the logarithm of the Na+ concentration have been made and respective composition of associate species were determined. Extension of the Peover-Davies method of evaluating the equilibrium constants of ion-pair formation from polarographic measurements has been given. From the analysis of polarographic data equilibrium constants have been determined for associates like (NB⨪, H2O), and partial equilibrium constants for the system (NB⨪, Na+)/(NB⨪, 2Na+). The dependence of activity coefficients of H2O in DMF on the composition of the mixture is given.

Electrochemical investigations of intermediates in electroreduction of aromatic nitro and nitroso compounds in DMF: Part I. Electrochemical behaviour of azoxybenzene

Summary The overall mechanism of electroreduction of azoxybenzene in DMF is presented. The process is found to proceed in several steps. The absorption spectrum of the azoxybenzene radical anion obtained in the first, one electron, step of reduction is presented. The identity of the final step of reduction of azoxybenzene and azobenzene is also evident. Considerable dependence of the mechanism of reduction of azoxybenzene on the nature and concentration of cation of the supporting electrolyte is shown.

Electrochemical investigations of intermediates in electroreduction of aromatic nitro- and nitroso-compounds in DMF: Part III. Electrochemical characteristics of additional (red-ox) systems formed during the electroreduction of nitroso-, azoxy- and azobenzene

Abstract In cyclic voltammetric measurements of DMF solutions of nitroso-, azoxy- and azobenzene using HMDE it was found that besides the usual peaks of red-ox processes an additional, new system of peaks was observed. Its properties were nearly identical for all three depolarizers. Taking into account various possible interpretations, based on experimental facts observed, the most probable is to attribute this additional system of peaks to electrode reaction of the material of electrode (i.e. Hg) in the presence of adsorbed azobenzene dianion.

The mechanism of electroreduction of nitrobenzene and 3-nitropyridine in DMF in the presence of divalent cations

Abstract The differences in electrochemical behaviour of nitrobenzene and 3-nitropyridine connected with a change of supporting electrolyte are discussed. It is shown that in the presence of alkaline earch metal cations a deposit of composition (NB−. Me2+) is formed at the electrode surface. The cations: Ba2+, Ca2+ and Mg2+ cause the instability of the nitrobenzene radical anion formed in the first electroreduction step. It was found that in the presence of Ba2+ and Ca2+ the NOB/NO−. couple is stabilized.

Quantum-chemical approach to the ion pair formation (IPF) equilibrium constants of nitrobenzene radical anions with univalent cations and water molecul

Abstract The simple HMO method extended to problems of ionic association of cations with organic radical anions by McClelland [1] and Goldberg and Bolton [2] was successfully used not only in the case of ion pair formation between nitrobenzene radical anion and univalent cations (eqn. (1)) but also when interactions are between this radical and water molecule (eqn. (2)). p]Inspection of a plot of log K ass against E HMO ass for eqns. (1) and (2) leads to the conclusion that the treatment considered here, although very empirical, can be applied advantageously to prediction of association constants for equilibria like (1) and (2). The simplicity of this treatment suggests wide applications for more complex systems.