Phenomenology related to the kinetics of Kolbe electrosynthesis

Abstract

The Kolbe electrosynthesis on polycrystalline platinum in 1 M acetic acid/l M potassium acetate electrolyte at 30 o C was studied by using potentiostatic, low-frequency potentiodynamic and impedance techniques. Reaction products and their distribution as a function of potential were determined. There is a good correspondence in the potential ranges where changes in both stationary and non-stationary kinetic data, electrode resistance, electrode capacitance and reaction products were found. Results confirm the existence of different electrochemical reactions and correspondingly different reaction intermediates in the various Tafel regions.

Surface electrochemistry of the oxidation of glycine at Pt

“…It is of interest that a more normal vaue of @ is actually observed for the acetate Kolbe reaction in completely anhydrous solution (18). Recently, the results of several studies of the Kolbe electrosynthesis under a variety of conditions have been attributed to the surface adsorption of radicals (37)(38)(39).…”

The Dilemma of Supporting Electrolytes for Electroorganic Synthesis: A Case Study on Kolbe Electrolysis

“…[3,30] The reason provided for why alkaline pH should be avoided is the increased competition of reactant anionsa nd hydroxide ions for binding sites at the electrode, [37] leadingt od ecreased reactantc onversion efficiency and promotion of oxygen evolution. [27,30,[39][40][41] Independent of the possible inhibition of oxygen evolution at more alkaline pH, as hift towardsn on-Kolbe products would still be expected, owing to an increased number of hydroxide, carbonate, and biocarbonate ions that increaset he spatial spacingo ft he formed alkyl-radicals at the electrode surface, rendering dimerizationl ess likely than further oxidation to carbocations. [27,30,[39][40][41] Independent of the possible inhibition of oxygen evolution at more alkaline pH, as hift towardsn on-Kolbe products would still be expected, owing to an increased number of hydroxide, carbonate, and biocarbonate ions that increaset he spatial spacingo ft he formed alkyl-radicals at the electrode surface, rendering dimerizationl ess likely than further oxidation to carbocations.…”

“…[38] On the other hand, it is stated that anodic oxygen evolution during Kolbe electrolysis is mostly inhibited, despite being energeticallyf avored, [39] either by the formation of an oxide layer or ahydrophobic layer composed of organic products on the platinum electrode surface that inhibits electrode-water contact (i.e.,o xygen evolution would not be apredominant side reaction). [27,30,[39][40][41] Independent of the possible inhibition of oxygen evolution at more alkaline pH, as hift towardsn on-Kolbe products would still be expected, owing to an increased number of hydroxide, carbonate, and biocarbonate ions that increaset he spatial spacingo ft he formed alkyl-radicals at the electrode surface, rendering dimerizationl ess likely than further oxidation to carbocations. The latter are stabilized by the anions in their proximity,a ltogether shiftingt he product composition towards non-Kolbe products.H owever,t his was not found in our study; ChemSusChem 2016, 9,[50][51][52][53][54][55][56][57][58][59][60] www.chemsuschem.org the reason forw hich we can only speculate.…”

“…Surprisingly,s tartingf rom air in the headspace(% 20 %o xygen)t he oxygen concentration decreasedd uring electrolysis for all batch experiments, irrespective of pH (FigureS1) and T,i ndicating no or very little oxygen evolution taking place, as discussed in literature. [27,30,[39][40][41] On the other hand, it is possible that the produced oxygen was immediately consumed at the counter electrode of the undivided electrochemical cell, and thus not detected. In that case, cathodic hydrogen evolutionw ould be diminished, whichw as not the case.…”

Creation of Hybrid Photoactive Inorganic/Organic Interface Assemblies of Cadmium Oxide mixtures (CdO2/CdO)/Poly-2,2-Bithiophene; Optical and Photoelectrochemical Investigations

“…In the presence of acetate electrolyte, the photooxidation of acetate results in a Kolb-type reaction. In the presence of RCOO -such as acetate, the following reaction takes place (Cervino R. M. et al 1984) as illustrated in equation 4.…”