Indirect anodic oxidation

Recently, Germain et al. have also shown that the indirect anodic oxidation in fluorosulfuric add of fluorocarbon derivatives of the type RfCF2X (X — H, COOH, S03H, CH2OH, Br), which are not directly oxidizable, leads to fluorosulfates of the type FSG3CF3Rf (Eqs. 18 and 19) [37, 38], in these reactions, the peroxide (FS03)2, partially dissociated in its free radicals, is the in-situ electrochemically produced reactive intermediate as shown in Scheme 5.1. 

Alkenes, as other organic substrates, can be converted by indirect anodic oxidation. 

Oxidation of substituted toluenes to substituted benzaldehydes or their acetals is a reaction that is of high technical interest. It is performed by direct as well as indirect anodic oxidation. A number of direct oxidations is shown in Table 14, Nr. 4 to 6. 

Both direct and indirect anodic oxidation have a variety of advantages over chemical oxidation methods. 

The indirect anodic oxidation of ketones 42 in ammonia - containing methanol using iodide as a mediator afforded 2,5-dihydro-IH-imidazols 44 via oxidation of the intermediate ketimine 43 to AT-iodo imine followed by elimination of HI to afford the nitrenium ion, which subsequently reacts with ketimine 43 to give the product 44 [73] (Scheme 23). 

Steckhan and coworkers found that the indirect anodic oxidation of N-pro-tected dipeptide esters 56, in which the C-terminal amino acid is a-branched, can afford methyl imidazolidin-4-one-2-carboxylate 57 in 45-84% yields [86], This reaction can be performed at a Pt-anode by using Et4NCl as an electrolyte in the presence of 5% methanol in an undivided cell (Scheme 30). 

Indirect anodic oxidation of a-phenylthiomethylsilane in an alcohol using Ni2+/Ni3+-cyclam mediator also provides a-alkoxylated sulfides, although the turnover of the mediator is low (equation 24)29. 

On the other hand, indirect anodic oxidation of cyclic silyl enol ethers in the presence of iodide ions gives a-iodocyclic ketones (equation 39)43. 

Since our last effort a number of other reviews have appeared. Most notably among them is a thorough examination by Becker3 of topics discussed in the first review of this series, expanded to include a broader range of direct and indirect anodic oxidations not covered in the original review. 

Aldoximes may be transformed into nitriles via nitrile oxides, obtained by indirect anodic oxidation of the aldoxime in methanol, followed by cathodic reduction of the nitrile oxide [92]. 

Anodic oxidation of glucose gives mainly the glucono-(5-lactone (XCI) or gluconic acid (XCII) [Eq. (55)] [133-135]. Formation of aldonic acids from aldoses is the most commonly observed process in other cases [126]. Additional work has been done in the area of indirect anodic oxidation of partially protected carbohydrates at a nickel hydroxide anode [136]. 

On the anodic side, four cases of undivided cells and two cases of divided cells have been chosen. Two processes are direct and four are indirect anodic oxidations. The sebacic acid process, as described by Asahi Chemical [74], is the industrial realization of the oldest and most thoroughly studied electrochemical reaction, the Kolbe reaction. 

In contrast to this fluoride ion mediator effect, it has been established that bromosulfonium ions derived from sulfides and anodically generated bromonium ions can be used as so-called mediators for indirect anodic oxidations of alcohol. Therefore, it is interesting that the fluorosulfonium ions (G) also noticeably promote the anodic methoxylation. 

Similar indirect anodic oxidations of various fluoropropylamines and diphenyl disulfide in two-phase systems such as CH2Cl2-water provide useful fluorinated sulfenimines as shown in Eq. 66. ... 

Direct anodic oxidation of iodobenzene and /Mira-methyliodoben-zene did not give the corresponding hypervalent difluorides. Therefore, indirect anodic oxidation was attempted using a chloride ion mediator. In this case, the desired difluoro products are not formed but instead a novel hypervalent iodobenzene derivative, such as 73, having I-F and I-Cl bonds is produced. It was found that difluorina-tion occurs by the reaction of dithioacetals with iodobenzene chlo-rofluorides. Indirect anodic oxidation of dithioacetals by using a catalytic amount of para-methoxyiodobenzene was attempted as shown in Scheme 55 and it was found that desulfurizative difluorina-... 

III. Regioselective Oxidation of the Hydroxyl Group in Polyhydroxylated Triterpene by Indirect Anodic Oxidation Method... 

Table 4. Indirect Anodic Oxidation of Soyasapogenol B (51) with Different Electrolytes...

This review will deal with the direct and indirect anodic oxidation of unactivated CH bonds in alkanes, and of remote CH bonds in substrates with various functional groups. The conversion of CH bonds activated by vinyl, aryl, amino or alkoxy groups will not be dealt with in this chapter. However, the catalytic oxidation of alkanes in fuel cells and the oxidation of alkanes with molecular oxygen and iron catalysts are included. 

The oxidation of pentitols and hexitols by bromine in the presence of calcium carbonate to yield alduloses, and the indirect anodic oxidation of D-glucitol and D-mannitol are detailed in Chapter 17. 

Aldoses and ketohexoses were the primary products of indirect anodic oxidation of D-glucitol and of D-mannitol in aqueous calcium... 

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