Electrooxidation conditions

On the other hand, Af-alkoxyamines were more stable than styrenes under electrooxidation conditions. As a result, the electrooxidative intramolecular cychzed acetoxyamination product was obtained in good yields (equation 12fK... 

Fig. 15.6 Influence of temperature on phenol electrooxidation. Condition 150 mL of 19 mM phenol with 2 wt% NaCl, 2 Ah and 3 MPa air initially charged...

Mono- and difluorination of alkyl aryl thioethers under electrooxidative conditions also proceed when the phenyl ring is substituted by strongly electron-withdrawing groups, such as NO2, CN, SO Me, and S02Ph [116] (see Chapter 26). 

Fig. 1.1. Electronic states at the interface between a metal electrode and a redox couple A/B in solution at equal concentrations of the electroactive species. The applied potential corresponds to (a) equilibrium, (b) cathodic (electroreduction) and (c) anodic (electrooxidation) conditions.

It is known that tropylium may be prepared from tropylidene via hydride abstraction by PhgC or MegC carbonium ions therefore, it is very likely that here too the dehydrogenation is a hydride transfer from the 1,5-dione to an acceptor. A similar dehydrogenation of chromanones to chromones, with triphenylmethyl perchlorate was reported. A study of the electrooxidation of 1,5-diones on a rotating platinum electrode showed that 1,5-diaryl-substituted diones afford pyrylium salts in these conditions and that the half-wave potentials correlate with yields in chemical dehydrogenations. 

HydrophiIic versus hydrophobic coadsorption. The contrast between the hydrophilic and hydrophobic coadsorption seen on Rh(111) and Pt(lll), if confirmed under normal electrochemical conditions, might be of electrocatalytic importance. On Rh(lll), where net attractive CO-HgO interactions produce a mixed phase in which CO is displaced to a three-fold binding site which is not occupied in the absence of water, CO and water appear to occupy adjacent binding sites. Such thorough mixing of the oxygen source (water) and the intermediate [or poison] (CO) should improve electrooxidation rates for C 0 H fuels (11). On Pt(lll), where net repulsions cause condensation of CO and water into separate patches, reaction between the adsorbed species could occur only at the boundaries between patches, and one would expect slower kinetics. 

We have recently performed a variety of these and related SPAIRS-voltammetric measurements on platinum and palladium <5c. 12b ), and have concluded that the adsorbed CO formed in most cases acts predominantly as a poison for organic electrooxidation. Interestingly, the potential at which the CO undergoes electrooxidation, and hence where the electrocatalysis commences, can be strongly dependent on the structure of the solution species involved. Thus for acetaldehyde, for example, this process occurs at about 0.3 V lower overpotentials than for benzaldehyde under comparable conditions (5c). 

Heteroatom Oxidation, Dehydrogenation Electrooxidative kinetic resolution of rac alcohols mediated with a catalytic amount of an optically active A-oxyl was performed in an undivided cell at constant current conditions. A high enantiomeric purity for the recovered alcohol was found, which could be increased by electrolysis at lower temperatures. The optically active A-oxyl was recovered and used repeatedly without change in efficiency and selectivity [368]. Cyclovoltammetry with the A-oxyl (GR, 7S, 10/f)-4-oxo-2,2,7-trimethyl-10-isopropyl-l-azaspiro[5.5]undecane-A-oxyl as catalyst showed for rac-1-phenylethanol a highly enhanced catalytic... 

As a typical example of indirect electrooxidation of alkylbenzenes, the oxidation conditions and results on p-methoxytoluene (147) with CAN in acetic acid or methanol are shown in Scheme 59 [219]. The treatment of (147) with CAN in methanol at room temperature affords the aldehyde (148), exclusively. However, the oxidation of (147) with CAN in either aqueous 50% acetic acid... 

We have also investigated the electrooxidation of phenylethanoate, a system where there is no proton-loss pathway from the intermediate carbocation. Tab. 6.14 shows relative product ratios for phenylacetate in similiar conditions to those used for cyclohexane carboxylate, but employing 100 mA cm current density [59,60]. 

Column III shows the effect of ultrasound upon the product ratio with methanol as solvent. As can be seen there is now 53 % bibenzyl, 32 % of methyl ether and 6% of methyl ester (with a total of 5 % of other products) suggesting a slight shift towards the two-electron products, but with an overall diminuition of solvent discharge (approx. 6% ester) and side-reactions (approx. 6%). This result confirms the fact the phenyl acetate electrooxidation favours the one-electron route (to bibenzyl) in a wide range of conditions [61], and is much less sensitive to mechanistic switches by manipulation of parameters (e. g. ultrasound) than is cyclohexane carboxylate electrooxidation [54]. 

The EC technique is a general and versatile synthesis method for the preparation of high-quality single crystals involving molecular ions (Batail et al, 1998). The method requires electroactive species, neutral or charged, leading their electrooxidation (or reduction) to stable radicals. If soluble, the generated radical species may diffuse into solution, but under suitable conditions of concentration, solvent, temperature and current density, they will crystallize on the electrode. The choice... 

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