Sodium borohydride (BH, NaBH 4 ) has wide application as a reducing agent in organic and inorganic synthesis. Herein, sodium benzylborohydride (BBH, NaC 7 H 7 BH 3 ), sodium phenylborohydride (PBH, NaC 6 H 5 BH 3 ) and sodium 4-chlorophenylborohydride (CPBH, NaC 6 H 4 BH 3 Cl) are synthesized with high purity, as confirmed by NMR and FTIR. A direct relationship between the organic substituents and the reducing power of the borohydride center is investigated by electrochemical methods. Gold (Au) and platinum (Pt) disk electrodes are used to study the electrooxidation of these organoborohydride (OGB) compounds in dimethyl sulfoxide. Linear scan voltammetry and chronoamperometry measurements are carried out in 0.001-0.01 M solutions of each OGB at temperatures ranging from 25 to 65 • C. The results are directly compared to those obtained with BH solutions in the same conditions. A Pt microelectrode is used to perform diffusion coefficient measurements, whose values range from 9.10 × 10 −8 cm 2 s −1 for CPBH to 2.87 × 10 −7 cm 2 s −1 for BH. The number of exchanged electrons range between 1.6 for CPBH to 6.6 to BH and charge transfer coefficients are ca. 0.9-1.0. First order reactions are evaluated for the electrooxidation of the four studied borohydride compounds and the corresponding apparent activation energies range between 15 and 33 kJ mol −1 .
Sodium borohydride (NaBH4) has wide application as a reducing agent in organic and inorganic synthesis. In this work, sodium benzylborohydride (C7H7BH3Na) and sodium phenylborohydride (C6H5BH3Na) are synthesized and a direct relationship between the organic substituents and the reducing power of the borohydride center is investigated. Platinum and gold disk macroelectrodes and microelectrodes are used to study the electrooxidation of these organoborohydride compounds. Chronoamperometry and cyclic voltammetry measurements are carried out in dimethyl sulfoxide (DMSO) solution using 0.001 M of each compound at temperatures ranging from 25 to 65 ºC. The results are directly compared to those obtained with NaBH4 solutions in the same experimental conditions. The main electrochemical parameters are evaluated, including number of exchanged electrons, charge transfer coefficients, reaction orders and diffusion coefficients. Moreover, the activation energy for the borohydride oxidation reaction is calculated assuming Arrhenius behavior for the selected range of temperatures.
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