Peroxide hydrogen, electrochemical production

P.C. Foller and R.T. Bombard, Processes for the production of mixtures of caustic soda and hydrogen peroxide via the reduction of oxygen, J. Appl. Electrochem., 1995, 25, 613-627 M. Sudoh, H. Kitaguchi and K. Koide, Electrochemical production of hydrogen peroxide by reduction of oxygen, J. Chem. Eng. Jpn., 1985,18, 409-414. 

The goal of the present review is an analysis of the electrochemical sensor approaches used for the detection of hydrogen peroxide. Due to similarity of the subjects the present review discusses both, the development of the biosensors where hydrogen peroxide is a product/substrate of enzynutic reaction and also the development of chemical sensors/biosensors specifically designed for the detection of this analyte. Several rechnical aspects of the development of sensors for hydrogen peroxide are reviewed in the following chapters the choice of physical transducer, the choice of enzyme and immobilisation method, and the performance of sensors with respect to response time, sensitivity, linear range, detection limit and operational stability. 

The classical electrochemical production of hydrogen peroxide uses the electrolytic production of persulfate from sulfuric acid and hydrolyzes the persulfate in a second step into hydrogen peroxide and sulfuric acid. Hydrogen peroxide is always a by-product for the anodic production of oxidants in dilute solutions (Fig. 22.3). 

Typical electrochemically detectable (co-) substrates and products include oxygen, hydrogen peroxide, hydrogen ion, ammonia, carbon dioxide, reduced or oxidized cofactors, and redox-active (oxidized or reduced) prosthetic groups in oxi-doreductases, all of which can easily be converted into electrical signals by suitable transducers (e.g., amperometric or potentiometric electrodes or conductometric sensors. Table 19). 

Persulfuric acid is widely used as an oxidant in many applications. In wastewater treatment, it is used for cyanide removal from effluents. Other applications concern dye oxidation, fiber whitening, radical polymerization, and measurement of total organic compounds. Persulfuric acid is an important intermediate in the electrochemical production of hydrogen peroxide. 

Satisfactory 40% peracetic acid is obtainable from Buffalo Electrochemical Corporation, Food Machinery and Chemical Corporation, Buffalo, New York. The specifications given by the manufacturer for its composition are peracetic acid, 40% hydrogen peroxide, 5% acetic acid, 39% sulfuric acid, 1% water, 15%. Its density is 1.15 g./ml. The peracetic acid concentration should be determined by titration. A method for the analysis of peracid solutions is based on the use of ceric sulfate as a titrant for the hydrogen peroxide present, followed by an iodometric determination of the peracid present.3 The checkers found that peracetic acid of a lower concentration (27.5%) may also be used without a decrease in yield. The product was found to be sufficiently pure, after only one recrystallization from 60 ml. of petroleum ether (b.p. 40-60°) and cooling overnight to —18°, to be used in the next step. 

Great promise exists in the use of graphitic carbons in the electrochemical synthesis of hydrogen peroxide [reaction (15.21)] and in the electrochemical reduction of carbon dioxide to various organic products. Considering the diversity in structures and surface forms of carbonaceous materials, it is difficult to formulate generalizations as to the influence of their chemical and electron structure on the kinetics and mechanism of electrochemical reactions occurring at carbon electrodes. 

A wide variety of enzymes have been used in conjunction with electrochemical techniques. The only requirement is that an electroactive product is formed during the reaction, either from the substrate or as a cofactor (i.e. NADH). In most cases, the electroactive products detected have been oxygen, hydrogen peroxide, NADH, or ferri/ferrocyanide. Some workers have used the dye intermediates used in classical colorimetric methods because these dyes are typically also electroactive. Although an electroactive product must be formed, it does not necessarily have to arise directly from the enzyme reaction of interest. Several cases of coupling enzyme reactions to produce an electroactive product have been described. The ability to use several coupled enzyme reactions extends the possible use of electrochemical techniques to essentially any enzyme system. 

A homogeneous electrochemical enzyme immunoassay for 2,4-dinitrophenol-aminocaproic acid (DNP-ACA), has been developed based on antibody inhibition of enzyme conversion from the apo- to the holo- form Apoglucose oxidase was used as the enzyme label. This enzyme is inactive until binding of flavin adenine dinucleotide (FAD) to form the holoenzyme which is active. Hydrogen peroxide is the enzymatic product which is detected electrochemically. Because antibody bound apoenzyme cannot bind FAD, the production of HjOj is a measure of the concentration of free DNP-ACA in the sample. 

Another application of carbon and carbon hybrids is their use as electrode material in proton exchange membrane (PEM) electrochemical flow reactor for the production of hydrogen peroxide (H202). 

Oxidation indices, 656-72 peroxide determination, 762-3 peroxide value, 656, 657-64 colorimetry, 658-61 definition, 657 direct titration, 657 electrochemical methods, 663-4 IR spectrophotometry, 661-3 NIR spectrophotometry, 663 UV-visible spectrophotometry, 658-61 secondary oxidation products, 656, 665-72 tests for stability on storage, 664-5, 672 thermal analysis, 672 Oxidative amperometiy, hydroperoxide determination, 686 Oxidative cleavage alkenes, 1094-5 double bonds, 525-7 Oxidative couphng, hydrogen peroxide determination, 630, 635 Oxidative damage... 

The product of the one-electron reduction of O2, the superoxide ion, Oi, is highly unstable in acidic-aqueous solutions where its protonated form, the peroxyl radical H02(pA = 4.8), decomposes to ozone, oxygen, and hydrogen peroxide experiments have shown that the two latter compounds are produced almost quantitatively, when only traces of ozone are found. In alkaline solutions, the superoxide ion is more stable even if it decomposes spontaneously to O2 and H02 (AG-6-=—51.13 kj mol ), it has been studied by polarography in NaOH solutions, in the presence of compounds that adsorb at the surface of the electrode and slow down the protonation of 02 . From these electrochemical experiments... 

The production of industrially important perfluoroalkane sulfonic acids is generally accomplished by electrochemical fluorination. This method of preparation remains expensive and proceeds in good yields only for short hydrocarbon chains.30 Recently however, Wakselman and Tordeux have described a chemical method for the preparation of trifluoromethane sulfonic acid.31 The procedure involves reaction of a metal selected from zinc, cadmium, manganese, and aluminum with sulfur dioxide in DMF, followed by the introduction of trifluoromethyl bromide under slight pressure. The intermediate sulfinate is subsequently oxidized by hydrogen peroxide, and then hydrolyzed which leads to formation of the trifluoromethane sulfonic acid. Successful extension of the sulfination process to the modification of PCTFE should result in the formation of a sulfinated polymer which can ultimately be oxidized to give a sulfonic-acid modified polymer. 

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