Iodide electrooxidation

The Ritter reaction [6] proceeds by the electrooxidation of alkyl iodides (56) in an MeCN-(Pt) system to form Ai-alkyl acetamides (58) (Scheme 21). Attack of carbenium ion intermediate - from dissociation of the initially formed alkyl cation radical - to acetonitrile would give the iminium cation (57). However, a different mechanism is proposed, whereby the alkyl iodide reacts with the electrogenerated iodo cation [I]" " [73]. 

Formation of the P—N bond has been observed when the cross-coupling of dialkylphosphites (59) with amines (60) proceeds by an iodo cation [I]+-promoted electrooxidation, affording N-substituted dialkylphosphor-amidates (61) (Scheme 22) [76]. Lack of alkali iodide in the electrolysis media results in the formation of only a trace of (61), indicating that the iodide plays an important role in the P—N bond-forming reaction. In contrast, usage of sodium bromide or sodium chloride brings about inferior results since the current drops to zero before the crosscoupling reaction is completed. 

We have also recently examined the electrooxidation of iodide at gold using the combined SERS-RDV approach.(22)The system was chosen as a simple example of a multistep process where the reaction products (iodine and/or triodide) as well as the reactant and any intermediates should be strongly adsorbed. This reaction has been studied extensively using conventional electrochemical techniques, yet the reaction mechanism remains in doubt.(23) At potentials well negative of the I /I2 formal potential, iodide yields a pair of SERS bands at gold at 124 and 158 cm-1, associated with adsorbed I -surface vibrations. 

The Effect of Hyamlne on the Electrooxidation of Iodide In Aqueous 2N Sodium Hydroxide (49)... 

Oxidation carried out in the presence of iodide and bromide ions have been extensively developed during the last two decades. They may often be used with advantage within a potential range in which other kinds of catalyst are not numerous (e.g., organic mediators) or need to be used ex-cell. Moreover, oxidized species obtained from I and Br are of a very broad applicability and are very active, even in water, toward substrates that are more difficult to oxidize than the halides. In most cases it has been demonstrated that such electrooxidized species often play a specific role at the anode (or close to it), whereas the same halogens in bulk solution are much less efficient. Only reactions offering that advantage are reviewed here. 

The iodide ion is adsorbed at the open circuit on palladium from 1 mM KI, pH 10 for 180 s. In this process, iodide is oxidized, forming a chemisorbed monolayer of zero-valence iodine atoms, while H+ or water molecules are reduced to produce molecular hydrogen. It can be observed from the potentiodynamic profile of palladium that the H-atom adsorption region is totally inhibited and the onset potential for the oxide formation is shifted toward more positive values. Besides, a large anodic peak current is developed as a result of the iodine electrooxidation to iodate. Complete iodine desorption can be accomplished by the application of negative potentials at pH 10. Thus, after 5 min of potential holding at —1.0 V in pH 10 and several cycles within the potential limits of water stability, the repetitive current potential profile of iodine-free palladium can be obtained. 

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