Phenols electrocatalytic reduction

Inert metal ion aqua complexes such as [Cr(NH3)5(OH2)] can accelerate the hydrolysis of phosphate esters. These species are believed to act as a general base catalyst. On the other hand, CrOj inhibits the enzyme action of phosphatase and sulfatase and the inhibitary action is enhanced by the addition of phenol. Certain Cr(III) complexes can also act as catalysts in the electrocatalytic reduction of CO2 to MeOH, but they are not as efficient as iron complexes. 

Porphyrins are often employed in sensors on account of their ability to act as cation hosts and, with a suitable metal ion coordinated, as redox catalysts. Electropolymerised poly(metalloporphyrin)s have been used as potentiometric anion-selective electrodes [131] and as amperometric electrocatalytic sensors for many species including phenols [132], nitrous oxide [133] and oxygen [134]. Panasyuk et al. [135] have electropolymerised [nickel-(protoporphyrin IX)dimethylester] (Fig. 18.10) on glassy carbon in the presence of nitrobenzene in an attempt to prepare a nitrobenzene-selective amperometric sensor. Following extraction of the nitrobenzene the electrode was exposed to different species and cyclic voltammetric measurements made. A response was observed at the reduction potential of nitrobenzene (the polyporphyrin film acts only to accumulate the analyte and not in a catalytic fashion). Selectivity for nitrobenzene compared with w-nitroaniline and o-nitroto-luene was enhanced compared with an untreated electrode, while a glassy carbon-... 

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