Platinum glyoxal oxidation

An interesting study examined the anodic oxidation of EDTA at alkaline pH on a smooth platinum electrode (Pakalapati et al. 1996). Degradation was initiated by removal of the acetate side chains as formaldehyde, followed by deamination of the ethylenediamine that formed glyoxal and oxalate. Oxalate and formaldehyde are oxidized to CO2, and adsoption was an integral part of the oxidation. 

The chemoselectivity can be strongly changed by the anode material. The oxidation of glycolaldehyde at a platinum anode affords mainly glyoxal while the conversion with a platinum anode modified by antimony or bismuth ad-atoms provides mainly glycolic acid (Fig. 29) [147]. 

In acidic medium, the electrocatalytic oxidation of glyoxal on platinum in the potential range 1 to 1.5 V/RHE leads mainly to formic acid (60%) and CO (40%). With lead adatoms, it becomes possible to oxidize glyoxal between 0.4 and 1.0 V/RHE leading mainly to CO2 formation (46%), while the selectivity towards, glyoxylic acid is sensibly increased (28%). At pH=7 and 1,9 V/RHE, the main oxidation product is formic acid (99%). Otherwise, in acidic medium the oxidation is more selective towards glyoxylic acid (70%), when the applied potential is in the range of 1.80 to 2.13 V/RHE. 

On the other hand, according to the study of Horanyi et al.[ °] on the oxidation of glyoxal and glyoxylic acid at platinum electrodes, the C-C bond breaking may play a significant role during the adsorption process. 

Fig. 1. Evolution of the voltammograms of a platinum electrode recorded during the prolonged electrolysis of glyoxal at a potential plateau Ep=1.18 V/RHE. The main oxidation peaks are labelled A, B and C. The potential programme is shown in the insert. Time of electrolysis (—) 0 hr, (.) 25 hrs, (---) 50 hrs.

Electrocatalytic oxidation of glyoxal on a platinum electrode modified by lead adatoms. 

Electrocatalytic oxidation of glyoxal on platinum in a buffer phosphate medium (pH=7). 

Glyoxylic acid (CHOCOOH), used in the preparation of fine chemicals (e. g., vanillin and penicillin), is prepared industrially by oxidation of glyoxal with nitric acid. An attempt was made to replace this stoichiometric process by oxidation of glyoxal with air on platinum catalysts [57-59]. In a first series of experiments, catalysts containing different platinum metals (Pt, Ir, Pd, Rh, Ru) prepared on the same active carbon and with the same particle size (1-2 nm) were compared. The initial rate of reaction increased in the sequence 0 = Ru < Rh < Pd < Ir < Pt, which is similar to that of the redox potentials of these elements. 

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