Acidity electrochemical oxidation

The second important class of reducing agents is generated by means of oxidative decarboxylation of carboxylic acids. Electrochemical oxidation of oxalate ion C2042 produces, in aqueous as well as in acetonitrile solutions containing Ru... 

Nickelocene, a 20-electron compound, has two electrons in the antibonding e g orbitals. The monocation Cp Ni can be generated chemically with halogens or with dilute nitric acid. Electrochemical oxidation occurs in two steps to Cp Ni through Cp Ni. Reduction to Cp Ni has also been achieved. 

Polyaniline (PANI) can be formed by electrochemical oxidation of aniline in aqueous acid, or by polymerization of aniline using an aqueous solution of ammonium thiosulfate and hydrochloric acid. This polymer is finding increasing use as a "transparent electrode" in semiconducting devices. To improve processibiHty, a large number of substituted polyanilines have been prepared. The sulfonated form of PANI is water soluble, and can be prepared by treatment of PANI with fuming sulfuric acid (31). A variety of other soluble substituted AJ-alkylsulfonic acid self-doped derivatives have been synthesized that possess moderate conductivity and allow facile preparation of spincoated thin films (32). 

The purple permanganate ion [14333-13-2], MnOu can be obtained from lower valent manganese compounds by a wide variety of reactions, eg, from manganese metal by anodic oxidation from Mn(II) solution by oxidants such as o2one, periodate, bismuthate, and persulfate (using Ag" as catalyst), lead peroxide in acid, or chlorine in base or from MnO by disproportionation, or chemical or electrochemical oxidation. 

HCIO4, one of the strongest of the mineral acids. The perchlorates are more stable than the other chlorine oxyanions, ie, chlorates, CIO chlorites, CIO or hypochlorites, OCf (3) (see Chlorine oxygen acids and salts). Essentially, all of the commercial perchlorate compounds are prepared either direcdy or indirectly by electrochemical oxidation of chlorine compounds (4—8) (see Alkali and chlorine products Electrochemical processing). 

Highly pure perchloric acid can also be produced by a patented electrochemical process ia which 22% by weight hypochlorous acid is oxidized to chloric acid ia a membrane-separated electrolyzer, and then additionally oxidized to perchloric acid (8,84). The desired electrochemical oxidation takes place ia two stages ... 

Perchlorates. Historically, perchlorates have been produced by a three-step process (/) electrochemical production of sodium chlorate (2) electrochemical oxidation of sodium chlorate to sodium perchlorate and (4) metathesis of sodium perchlorate to other metal perchlorates. The advent of commercially produced pure perchloric acid directly from hypochlorous acid means that several metal perchlorates can be prepared by the reaction of perchloric acid and a corresponding metal oxide, hydroxide, or carbonate. 

Petoxycatboxyhc acids have been obtained from the hydrolysis of stable o2onides with catboxyhc acids, pethydtolysis of acyhinida2ohdes, reaction of ketenes with hydrogen peroxide, electrochemical oxidation of alcohols and catboxyhc acids, and oxidation of catboxyhc acids with oxygen in the presence of o2one (181). 

Treatment of halomycin B (55) using nitrous acid yields rifamycin S (24) and the pyrroHdine (57) as shown in Figure 6. The halomycin B stmcture was confirmed by heating rifamycin O (23) and (57) in tetrahydrofiiran to yield halomycin B (20) which can also be converted to rifamycin S by electrochemical oxidation (213). Upon treatment with nitrous acid, halomycin A (54) yields rifamycin S along with the pyrroHdine (58). The stmcture for halomycin C (56) was deterrnined to be 20-hydroxy halomycin B based on mass spectral data (212). 

Chromatographic methods, notably hplc, are available for the simultaneous deterrnination of ascorbic acid as weU as dehydroascorbic acid. Some of these methods result in the separation of ascorbic acid from its isomers, eg, erythorbic acid and oxidation products such as diketogulonic acid. Detection has been by fluorescence, uv absorption, or electrochemical methods (83—85). Polarographic methods have been used because of their accuracy and their ease of operation. Ion exclusion (86) and ion suppression (87) chromatography methods have recently been reported. Other methods for ascorbic acid deterrnination include enzymatic, spectroscopic, paper, thin layer, and gas chromatographic methods. ExceUent reviews of these methods have been pubHshed (73,88,89). 

Sodium chlorite is used to produce chlorine dioxide by chemical oxidation, electrochemical oxidation methods, or by acidification with acids. Most of the commercial methods employ chlorine or sodium hypochlorite. 

Hi) Electrochemical reactions and reactions with free electrons Electrochemical oxidation of 3-methyl-l-phenylpyrazole gave the 3-carboxylic acid whereas electrochemical reduction (Section 4.04.2.1.6(i)) of l,5-diphenyl-3-styrylpyrazole produced the A -pyrazoline (B-76MI40402) with concomitant reduction of the exocyclic double bond (343). 

Pentafluorophenol is oxidized to different products depending on oxidation agents and reaction condibons The mtermediate is usually pentafluorophenoxy radical, which attacks the aromabc nng to give dimenc and tnmenc products Electrochemical oxidation of pentafluorophenol m hydrogen fluonde solvent and in the presence of a strong Lewis base or acid leads to a different rabo of products [61] (equation 55)... 

Electrochemical oxidation of a mbiture of carboxylic acids can also give acceptable yields of one product. For example. l,l,l-tnfluoroethane-d3 and pen-tafluoropropane-d3 are prepared in good yields in this way [77] (equation 68). 

Electrochemical oxidation of oi-hydrogenperfluoro- and perfluorocarboxyhc acids in fluorosulfonic acid gives fluoroalkylfiuorosulfates [i] (equation 71). 

The dehydrogenation of 2,3-dihydro- and 2,5-dihydro-l//-l-benzazepines to 3//-l-benz-azepincs with heterocyclic enamines in the presence of boron trifluoride diethyl ether complex has been achieved in moderate yields (30-35%).241 In contrast, electrochemical oxidation of 2,5-dihydro-1 H- -benzazepines in buffered acetic acid solution furnishes initially 5//-l-benz-azepines in 35-45% yield.242... 

Komori and Nonaka132,133 electrochemically oxidized methyl, isopropyl, n-butyl, isobutyl, r-butyl and cyclohexyl phenyl sulfides (108) and cyclohexyl p-tolyl sulfide (109) to their sulfoxides using a variety of polyamino acid-coated electrodes to obtain the range of e.e. values shown in parentheses. The highest enantiomeric purities were obtained using an electrode doubly coated with polypyrrole and poly(L-valine), an electrode which also proved the most durable of those prepared. 

Electrochemical oxidation of 4-aryl-substituted thiane in aqueous organic solvents containing various halide salts as electrolytes gave selectively the trans-sulfoxide (lOe). Under acidic conditions a preferential formation of the cis-sulfoxide was attained328. The stereoselective potential of this method for the oxidation of cyclic sulfides139,329 is apparent (equation 123). 

Several alkyl aryl sulfides were electrochemically oxidized into the corresponding chiral sulfoxides using poly(amino acid)-coated electrodes448. Although the levels of enan-tioselection were quite variable, the best result involved t-butyl phenyl sulfoxide which was formed in 93% e.e. on a platinum electrode doubly coated with polypyrrole and poly(L-valine). Cyclodextrin-mediated m-chloroperbenzoic acid oxidation of sulfides proceeds with modest enantioselectivity44b. 

Most 2,5-unsubstituted pyrroles and thiophenes, and most anilines can be polymerized by electrochemical oxidation. For pyrroles, acetonitrile,54 or aqueous55 electrolyte solutions are normally used, while the polymerization of thiophenes is performed almost exclusively in nonaqueous solvents such as acetonitrile, propylene carbonate, and benzonitrile. 0 Polyanilines are generally prepared from a solution of aniline in aqueous acid.21 Platinum or carbon electrodes have been used in most work, although indium-tin oxide is routinely used for spectroelectrochemical experiments, and many other electrode materials have also been employed.20,21... 

Due to its electronic conductivity, polypyrrole can be grown to considerable thickness. It also constitutes, by itself, as a film on platinum or gold, a new type of electrode surface that exhibits catalytic activity in the electrochemical oxidation of ascorbic acid and dopamine in the reversible redox reactions of hydroquinones and the reduction of molecular oxygen iV-substituted pyrroles are excellent... 

The different classes of Ru-based catalysts, including crystalline Chevrel-phase chalcogenides, nanostructured Ru, and Ru-Se clusters, and also Ru-N chelate compounds (RuNj), have been reviewed recently by Lee and Popov [29] in terms of the activity and selectivity toward the four-electron oxygen reduction to water. The conclusion was drawn that selenium is a critical element controlling the catalytic properties of Ru clusters as it directly modifies the electronic structure of the catalytic reaction center and increases the resistance to electrochemical oxidation of interfacial Ru atoms in acidic environments. 

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