Ana Paula Bettencourt

Biomass conversion: attempted electrooxidation of lignin for vanillin production

Electrochemical oxidative degradation of Kraft lignin was investigated in batch and flow cells on Pt, Au, Ni, Cu, DSA–O2 and PbO2 anodes. Production of vanillin was evaluated by means of formal kinetic analyses. Conversion and chemical yields were found to be dependent mainly on the applied current density, that is on the partial pressure of oxygen at the interface, while the nature of the electrode influenced the reaction rates.

Kinetics of proton transfer from phosphonium ions to electrogenerated bases: polar, steric and structural influences on kinetic acidity and basicity

Derivative cyclic voltammetry (DCV) and linear sweep voltammetry (LSV) have been used to measure rates of proton transfer in DMSO solution between different types of electrogenerated base (EGB) and a series of phosphonium ions of relevance to ylide formation for synthetic reactions. Although the electrochemical methods are convenient for the measurement of rates of proton transfer in these systems a major conclusion of the study is that considerable care must be exercised in the application of the methods and in drawing general conclusions from the results. In particular, comparison of kinetic acidity with thermodynamic pK values in DMSO shows that a single Bronsted relationship does not hold for the series of phosphonium ions. The kinetic acidities are profoundly affected by: whether the EGB is a carbon or nitrogen base; the propensity of some of the phosphonium ions to enolise; and steric factors. Other measures of electron-demand at the acidic methylene groups (13C and 1H chemical shifts, reduction potentials) are consistent with the pK(DMSO) values. The kinetic results confirm that the Ph3P+ group is, for non-enolisable phosphonium salts, more activating than Bu3P+.

Investigation of the Wittig reaction with electrogenerated bases: Influence of experimental conditions on the yield and stereochemistry

Abstract The influence of experimental parameters on the yields and stereochemistry of the Wittig reaction was studied using the synthesis of stilbene initiated by different electrogenerated bases as a model reaction. Electrolyses were carried out in batch cells under different conditions, including constant potential or constant current with different electrode materials and using solvents of different polarity. It is shown that proper selection of experimental conditions in Wittig reactions allows a choice of stereoselectivity in the reactions and the optimization of yields.