Efficient Preparation of the Esters of Biomass-Derived Isohexides by Base-Catalyzed Transesterification under Solvent-Free Conditions

The monoesters and diesters of glucose-derived isosorbide (IS) have potential applications as sustainable dispersants, surfactants, emulsifiers, monomer units for polymers, and plasticizers. This work reports a solvent-free, high-yielding, and scalable pathway for producing the monoesters and diesters of IS by a transesterification reaction using K2CO3 as an efficient, inexpensive, and recyclable base catalyst. In the case of monoesters, the selectivity toward the exo-monoester of IS was found higher than that toward the endo-monoester. The methodology was successfully extended to synthesize the monoesters and diesters of isomannide and isoidide. The gram-scale preparation of alkyl, vinyl, and aryl esters of isohexides was optimized on the reaction temperature, duration, equivalence of the ester reagent, and catalyst loading. Under optimized conditions (50 mol % K2CO3, 180 °C, 6 h), various aryl and alkyl esters of the isohexides were isolated in satisfactory yields. The unsymmetrical diesters of the isohexides were conveniently synthesized by stepwise transesterification

Electrocatalysis by crown-type polyoxometalates multi-substituted by transition metal ions; comparative study

The difference in electrochemical properties of three crown-type polyoxometalates multi-substituted by Fe3+, Ni2+ or Co2+ ions and their precursor has been rationalized with respect to their electrocatalytic performances studied in solution and in the immobilized state within the layer-by-layer film formed with a positively charged pentaerythritol-based Ru(II)-metallodendrimer. The film assembly was monitored with electrochemical methods and characterized by surface analysis techniques. An influence of the terminal layer on the electrode reaction and on film porosity has been observed. The electrocatalytic performance of the compounds on nitrite reduction was assessed in solution and in the immobilized state. (C) 2015 Elsevier Ltd. All rights reserved

Redox, surface and electrocatalytic properties of layer-by-layer films based upon Fe(III)-substituted crown polyoxometalate [P8W48O184Fe16(OH)28(H2O)4]20-

The electrocatalytic ability of the iron-substituted crown-type polyoxometalate (POM)Li4K16[P8W48O184Fe16(OH)28(H2O)4]·66H2O·2KCl (P8W48Fe16) towards the reduction of both nitriteand hydrogen peroxide reduction has been studied in both the solution and immobilized states for thePOM. P8W48Fe16was surface immobilised onto carbon electrode surfaces through employment of thelayer-by-layer technique (LBL) using pentaerythritol-based Ru(II)-metallodendrimer [RuD](PF6)8as thecationic layer within the resulting films. The constructed multilayer films have been extensively studiedby various electrochemical techniques and surface based techniques. Cyclic voltammetry and impedancespectroscopy have been utilized to monitor the construction of the LBL film after the deposition of eachmonolayer. The electrochemical behaviour of both a cationic and anionicredox probes at the LBL films has been undertaken to give indications as to the film’s porosity. The ele-mental composition and the surface morphology of the LBL films was conifmrde through the employmentof AFM, XPS and SEM