Anodic oxides yield

The 7c-excessive character of furan facilitates single-electron oxidation however, the cation-radicals produced from simple furans are not, in general, persistent. The mediation of 2,5-dimetliylfuran cation-radical (1) has been proposed in anodic oxidations yielding methoxylated, cyanomethoxylated, and acyloxylated products.Although not specifically implicated, cation-radicals may be involved in very similar oxidative reactions. ... 

Oxadiazoles.—1,2,3-Oxadiazoles. 3-Phenylsydnone (594 R = H) is anodically chlorinated at position 4, while anodic oxidation yields mainly phenol and benzaldehyde. The foregoing sydnone reacts with tetracyanoethylene to give the ene-hydrazone (596), presumably via the cyclo-adduct (595), by loss of carbon dioxide and cleavage of the strained carbon-carbon single bond. Irradiation of diphenylsydnone (594 R = Ph) in the presence of methyl pro-piolate affords the pyrazole (597) by way of the nitrile imine PhC=N—NPh with benzonitrile, a mixture of the 1,2,3- and 1,2,4-triazoles (598) and (599), together with the 1,3,4-oxadiazolinone (600) and 7s/ -benzoyl-iV -phenylhydrazine, is formed. ATV -Dibenzoylphenylhydrazine is produced by photo-oxygenation of diphenylsydnone. 

At low temperatures, oxidation with chromic acid gives propynal [624-67-9] C2H2O (14), or propynoic acid [471-25-0] C2H2O2 (15), which can also be prepared in high yields by anodic oxidation (16). 

The anodic oxidation of hydroquiaone ethers to quiaone ketals yields synthetically useful iatermediates that can be hydroly2ed to quiaones at the desired stage of a sequence (76). The yields of iatermediate diacetal are 83% for chlorine and 75% for bromine. 

Anodic oxidation of 1-methylpyrazole in the presence of cyanide ions yielded 33% (344) and 6% (345) no 3-cyano derivative was formed (78RTC35). 

The anodic oxidation of the carboxylate anion 1 of a carboxylate salt to yield an alkane 3 is known as the Kolbe electrolytic synthesis By decarboxylation alkyl radicals 2 are formed, which subsequently can dimerize to an alkane. The initial step is the transfer of an electron from the carboxylate anion 1 to the anode. The carboxyl radical species 4 thus formed decomposes by loss of carbon dioxide. The resulting alkyl radical 2 dimerizes to give the alkane 3 " ... 

Anode processes yield gaseous chlorine, fluorine, carbon chloride or fluoride. In the case of melts containing dissolved tantalum oxide, carbon oxides (mostly carbon dioxide) are formed on the graphite anode [28,37]. 

For this class of reactions, only a few examples which proceed with reasonable diastereoselectivity are known. Allylation of a-methoxycarbamate 1, easily obtained as a 1 1 mixture of isomers by anodic oxidation of protected threonine, produces an 83 17 mixture of enantiomers on treatment with trimethyl(2-propcnyl)silanel03. Cyanation with trimcthylsilyl cyanide proceeds less stereoselectively (67 33 93 % yield). 

N 24.12% brick red solid mp, decomps when heated over 300°. Insol in w and the usual organic solvents as well as weak acids and alkalies. Comm prepn (Ref 3) is from thiocyanic acid and/or thiocyanates either by anodic oxidation or by interaction with hydrogen peroxide or halogens. The yield is impure because it contains both H and O. The S content varies between 45 and 55%. Lab prepn of the pure polymer is by reacting the Na salt of 5-chlor-3-mercapto 1,2,4-thiodiazols with either acet, ethanol or w (Refs 1 2)... 

Many anodic oxidations involve an ECE pathway. For example, the neurotransmitter epinephrine can be oxidized to its quinone, which proceeds via cyclization to leukoadrenochrome. The latter can rapidly undergo electron transfer to form adrenochrome (5). The electrochemical oxidation of aniline is another classical example of an ECE pathway (6). The cation radical thus formed rapidly undergoes a dimerization reaction to yield an easily oxidized p-aminodiphenylamine product. Another example (of industrial relevance) is the reductive coupling of activated olefins to yield a radical anion, which reacts with the parent olefin to give a reducible dimer (7). If the chemical step is very fast (in comparison to the electron-transfer process), the system will behave as an EE mechanism (of two successive charge-transfer steps). Table 2-1 summarizes common electrochemical mechanisms involving coupled chemical reactions. Powerful cyclic voltammetric computational simulators, exploring the behavior of virtually any user-specific mechanism, have... 

A further difficulty arises during preparative electrolyses in aprotic solvents because of the bulk pH change which commonly occurs. Thus cathodic reductions often require proton abstraction from the solvent in order to yield stable products, while many anodic oxidations, mcluding those of aromatic and aliphatic hydrocarbons, give rise to a quantitative yield of proton and the consequent changes in the pH. of the electrolysis media would be expected to lead to a variation in the products with the duration of the electrolysis. Unfortunately, the pH can be a very difficult parameter to control in aprotic solvents and most work reported in the literature has been carried out in unbuffered conditions. In the case of oxidations, organic bases, e.g. pyridine, have... 

Carboxylic acids can be converted by anodic oxidation into radicals and/or carbo-cations. The procedure is simple, an undivided beaker-type cell to perform the reaction, current control, and usually methanol as solvent is sufficient. A scale up is fairly easy and the yields are generally good. The pathway towards either radicals or carbocations can be efficiently controlled by the reaction conditions (electrode material, solvent, additives) and the structure of the carboxylic acids. A broad variety of starting compounds is easily and inexpensively available from natural and petrochemical sources, or by highly developed procedures for the synthesis of carboxylic acids. 

Romakhin et al. [49] showed that anodically generated phosphoniumyl radicals can add onto alkenes to yield phosphonylated alkenes through an anodic oxi-dation/addition/anodic oxidation/elimination/nucleophilic attack sequence (Scheme 17). 

GP 2] [R 3a] A nearly constant selectivity of up of about 60% at conversions ranging from 20 to 70% was determined for sputtered silver on anodically oxidized (porous) aluminum alloy (AlMg3) with two different ethylene loads (4 or 20 vol.-% ethylene, 80 or 96 vol.-% oxygen 0.3 MPa 230 °C) [44]. The highest yield... 

The set of all intermediate steps is called the reaction pathway. A given reaction (involving the same reactants and products) may occur by a single pathway or by several parallel pathways. In the case of invertible reactions, the pathway followed in the reverse direction (e.g., the cathodic) may or may not coincide with that of the forward direction (in this example, the anodic). For instance, the relatively simple anodic oxidation of divalent manganese ions which in acidic solutions yields tetrava-lent manganese ions Mn +— Mn -l-2e , can follow these two pathways ... 

It had been shown in the preceding sections that the initial step in a number of cathodic and anodic reactions yields organic radicals, which then undergo further oxidation, reduction, or dimerization. In some cases reactions of another type are possible reaction of the radical with the electrode metal, yielding organometallic compounds which are then taken up by the solution. Such reactions can be used in the synthesis of these compounds. 

The anodic oxidation reaction of sulphoxides was not much studied, and just a few reports are available so far. The conversion into the corresponding sulphones of some phenyl alkyl and diaryl sulphoxides (oxidation potential for 86 + 2.07 V vs. SCE in acetonitrile/NaC104 electrolyte, Pt anode) has been reported. Similarly, diphenyl suiphoxide was long known to be transformed in a quantitative yield into the sulphone (Pt anode, solvent glacial acetic acid). Additional examples of the oxidation of a suiphoxide function attached to aryl groups are available . 

In the concentration step the anodic oxidation must yield between the electrode material (generally Hg) and the analyte anion an insoluble compound... 

Et or Bu) and the phosphonation of iodoaromatics with dialkyl phosphonates, although in this case with poorer yields (better results of the dialkyl arylphosphonates are obtained by photostimulation). Chemical oxidation (using AgNO -peroxodi-sulphate) and anodic oxidation of aromatics in the presence of trialkyl phosphites produces dialkyl arylphosphonates in good yields. The Cul-catalysed arylation of dialkyl (cyanomethyl)-phosphonates affords dialkyl (a-cyanobenzyl)phosphonates. ... 

The metal is anodically oxidized to ions that react with the components of the solution to yield an insoluble compound forming a surface film on the electrode. 

Mechanism 3 involves NiOH in at least three reactions, and Ni(OH)2 as the active Ni reactant in solution. Since increasing the concentration of the complex-ant(s) in solution will reduce the concentration of both unhydrolyzed and hydrolyzed metal ions, arguments of complexation cannot be readily employed to either support or discount this mechanism. However, it has been this author s experience in formulating electroless Co-P solutions with various complexants for Co2+ that improper complexation which results in even a faint precipitate of hydrolyzed cobalt ions yields an inactive electroless Co-P solution. Furthermore, anodic oxidation of hypo-phosphite at Ni anodes does not proceed at a significant rate under conditions where the surface is most probably covered with a passive film of nickel oxide [48], e.g. NiO.H20, which would be expected to oxidize the reducing agent via a cyclic redox mechanism. 

---