Hydrocarbons voltammetric studies

During the last decade, the concept of the oligomeric approach has been developed, which includes electrochemical studies of a great number of monodisperse chainlike hydrocarbons. Voltammetric... 

Indirect oxidation mechanisms have been proposed in some cases, such as for the oxidation of aliphatic hydrocarbons [25], for which voltammetric studies do not give unambiguous information about the nature of the electroactive species. Often, they are assumed to involve the oxidation of the anion of the supporting electrolyte to form an inorganic radical [Eq. (16)], which subsequently either attacks a C-H bond in the organic substrate [Eq. (17)] or oxidizes the substrate in an electron transfer process [Eq. (18)] ... 

The major voltammetric methods employed for studies of the anodic oxidation of aromatic hydrocarbons are linear sweep voltammetry (LSV), cyclic voltammetry (CV), and derivative cyclic voltammetry (DCV). Second harmonic ac (SHAC) voltammetry and... 

In liquid SO2 and CsAsFg as supporting electrolyte the oxidation of saturated hydrocarbons could be studied up to potentials of 6.0 V vs see by using platinum ultramicroelectrodes. Irreversible voltammetric waves were found for the compounds methane to n-octane that were studied The anodic peak currents suggest n-values around 2 a bulk electrolysis consumed 2 faradays per mole of alkane. The primary products in dilute solutions (1-10 mM) were shorter chain hydrocarbons. Electrolysis of more concentrated solutions led, via reaction of the oxidation products with starting material, to longer-chain hydrocarbons. 

The decreased iR drop in voltammetric experiments at ultramicroelectrodes has been exploited to perform electrochemistry under conditions in which no or only a small concentration of supporting electrolyte is added and allows measurements in low-polarity solvents (e.g. hydrocarbons), without the presence of excess ions, or even in the gas phase [51]. This topic is discussed further in Chapter 2.5 (Sect. 2.5.5.6). In these cases, the transport of charge in the electrolyte is realized by small amounts of impurities [48], by ions of the substrate material itself [52], or those generated in the electrode reaction [39]. Thus, migration has to be considered as an additional mode of transport, in particular for multiply charged species [52]. A recent modeling study [53] has provided evidence that LSV should be best suited to deal with situations of high uncompensated resistance as compared to chronopotentiometry and chronoamperometry. 

The oxidation of an aromatic hydrocarbon in the presence of acetate ions leads to the formation of aryl acetates. Detailed studies of the electrode reaction using polarographic and cyclic voltammetric techniques have established that direct oxidation of the aromatic molecule is the initial reaction. Certainly the facile decarboxylation of acetoxy radicals appears Jo preclude their involvement in this reaction. It has also been shown that the electrooxidation strongly resembles an electrophilic substitution reaction, particularly with respect to the distribution of ortho-, meta-, and para-substituted products. ... 

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