Issue 6, 1986

Protonation of the dianion of tetraphenylethylene by alcohols and water in acetonitrile. Case of mixed first-order and second-order kinetics in the proton donor

Abstract

The electrochemical reduction of tetraphenylethylene has been studied in dipolar aprotic solvents containing tetraethylammonium perchlorate. While in hexamethylphosphoramide and N,N-dimethylformamide the radical anion is more stable than the dianion, in acetonitrile the dianion is directly produced at the electrode in a reversible two-electron step. Voltammetric measurements in acetonitrile indicate that the disproportionation equilibrium constant of radical anions is large (>3 × 102), suggesting that ion-pair interactions play a leading role in the overall reduction.

The protonation of the dianion by alcohols and water (ROH proton donors) has been studied. Kinetic measurements have led to a rate law in which the pseudo-first-order rate constant can be expressed as the sum of two terms, i.e. kobs=a[ROH]+b[ROH]2. The reactivity sequence of ROH proton donors is MeOH > EtOH > H2O > PriOH > ButOH and MeOH > EtOH, H2O > PriOH > ButOH for the first- and second-order contributions, respectively. Analysis of kinetic data and solute–solute–solvent interactions has led to a protonation mechanism based on the existence of a hydrogen-bonded complex between the ion-paired dianion and the ROH proton donors. The role of a second ROH species in the actual proton transfer is discussed.

Article information

Article type
Paper

J. Chem. Soc., Faraday Trans. 1, 1986,82, 1885-1892

Protonation of the dianion of tetraphenylethylene by alcohols and water in acetonitrile. Case of mixed first-order and second-order kinetics in the proton donor

G. Farnia, F. Maran and G. Sandonà, J. Chem. Soc., Faraday Trans. 1, 1986, 82, 1885 DOI: 10.1039/F19868201885

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