Toluene, anodic processes

Later, Saito et al. [58] studied anodes with a layered structure consisting of Li/ protective film/additive/protective film/Li/ protective film/additive/ -. They made the anode by dropping the additive on a lithium sheet, folding the lithium sheet, and then compressing the folded lithium with an oil press. They repeated this process more than ten times. The FOM in LiAsF6-EC/2MeTHF electrolyte was 7.41, 13.5, and 37.0 for a lithium anode without additives, a lithium anode with toluene in the electrolyte, and a layered-structure lithium anode containing toluene, respectively. 

One synthesis approach that does not rely on CNT formation from the gas phase is molten salt synthesis. The reactor consists of a vertically oriented quartz tube that contains two graphite electrodes (i.e. anode is also the crucible) and is filled with ionic salts (e.g. LiCl or LiBr). An external furnace keeps the temperature at around 600 °C, which leads to the melting of the salt. Upon applying an electric field the ions penetrate and exfoliate the graphite cathode, producing graphene-type sheets that wrap up into CNTs on the cathode surface. Subsequently, the reactor is allowed to cool down, washed with water, and nanocarbon materials are extracted with toluene [83]. This process typically yields 20-30 % MWCNTs of low purity. 

Kirk Mid Brandt [25] nitrated toluene with a mixture of nitric and sulphuric acids both by the usual method and by the simultaneous use of the electrolytic method Mid found that with the latter technique higher yields could be obtained. AtMiasiu Mid Belcot [26,27] treated aromatic hydrocarbons with a much dilute nitric acid (at a concentration insufficient for nitration) and, due to the electrolysis, which they carried out simultaneously, they succeeded in obtaining nitration in the anode area, hi studying the reaction they observed particularly vigorous oxidation processes. 

For some examples, the outcome of direct anodic methoxylations of activated carbons (benzylic, allylic, etc.) at BDD anodes is similar to graphite anodes (Putter et al. 2003). Further investigation of the reaction mechanism in the case of the methoxylation of /Me/y-butyl toluene (1) - a process of industrial relevance (Bosma et al. 1999) - showed that BDD electrodes favour the occurrence of bibenzylic intermediates 4 which were not observed at graphite electrodes. This difference has been attributed to a mechanism based on the non-catalytic character of BDD electrodes and to the presence of active functionalities on graphite electrodes (Zollinger et al. 2004a). 

Generation of substituted aryl radical cations in the presence of nucleophiles can lead to products of side-chain substitution (processes such as anodic benzylic substitution of toluenes, which are dealt with in a separate chapter) or to products of addition to the aromatic ring itself. Nuclear addition products in /j /m-substituted systems have been proposed to form in essentially one of two ways, depending on substitution pattern and reaction conditions. Radical cations formed by electrochemical reaction (E) may be trapped by chemical reaction (C) with a nucleophile (or its anion). Repeating this sequence leads to nuclear addition products (LXV), formed by what is referred to as the ECEC mechanism [Eq. (31)] [74]. An analogous pattern may be inferred for or / (9-substituted systems. 

Some of these processes have been developed for technical conversions and have heen summarized in Ref. [228, 229]. The anodic technical production of t-hutylhenzaldehyde has been coupled with the cathodic reduction of phthahc anhydride to phthalide in a paired electrosynthesis in a capillary gap cell [230]. Indirect oxidations with Mn +/Mn + or Ce " /Ce " as mediators are reported in [231-234]. With tris(2,4-dibromophenyljamine as mediator, different substituted toluenes are converted... 

A range of aromatic oxidations involve direct SET from an organic substrate to the oxidant (catalyst, anode), leading to a radical cation [35]. Radical cations are much stronger acids than the parent hydrocarbon molecules [35a, b]. For example, the of toluene drops from 41 to ca. -13 with the removal of one electron, which makes deprotonation the predominant process in the transformation of the radical cation. Benzyl radicals formed in this way dimerize and participate in the side-chain oxidation (Scheme 14.5). On the other hand, radical cation can undergo attack by nucleophiles (H O, AcOH, etc.) followed by the second FT leading to the ring oxidation products [36]. 

DTlia, LF., Rincon, L, and Ortiz, R. (2004) Evaluation of titanium dioxide and cerium oxide as anodes for the electrooxidation of toluene a theoretical approach of the electrode process. Electrochim. Acta, 49 (24), 4197-4203. 

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