Benzonitrile electrochemical oxidation

Most 2,5-unsubstituted pyrroles and thiophenes, and most anilines can be polymerized by electrochemical oxidation. For pyrroles, acetonitrile,54 or aqueous55 electrolyte solutions are normally used, while the polymerization of thiophenes is performed almost exclusively in nonaqueous solvents such as acetonitrile, propylene carbonate, and benzonitrile. 0 Polyanilines are generally prepared from a solution of aniline in aqueous acid.21 Platinum or carbon electrodes have been used in most work, although indium-tin oxide is routinely used for spectroelectrochemical experiments, and many other electrode materials have also been employed.20,21... 

Although Ceo is easily reduced, it is very difficult to oxidize [46, 53, 54, 72], The only definitive electrochemical oxidation of Cgo occurs at a potential of -F 1.76 V vs SCE in benzonitrile, and is irreversible [54]. The radical cation was reported to be produced by y-irradiation at 77 K in a glass, and to absorb near 980 nm [65, 66]. Attempts to generate the radical cation (Ceo) by electron transfer to singlet excited dicyanoanthracene, which has a reduction potential near + 2.0 V [73] were unsuccessful. This method has been used to generate, for example, trans-stilbene radical cation [73, 74]. The ion pair probably does not... 

Electrochemical oxidation of substituted hydrazones of benzaldehyde may result in cleavage of the nitrogen-nitrogen bond and formation of a benzonitrile [234] and oxidation products from the amine. 

Black, shiny single crystals with distorted-hexagon-shape (3 x 2 x 0.05 mm ) of k-(BEDT-TTF)2Cu(NCS)2 were prepared by the electrochemical oxidation of BEDT-TTF (prepared from CS2 by conventional methods) in 1,1,2-trichloroethane (TCE), benzonitrile or THF in the presence of (1) CuSCN, KSCN and 18-crown-6 ether, (2) K(18-crown-6 ether) Cu(NCS)2 or (3) CuSCN and TBA-SCN. For electrolytes (1) or (3), undissolved materials remained on the bottom of the cell during the course of electrocrystallization, but the precipitation did not affect the crystal growth. Crystals were grown in H cells (total volume ca. 20 mL) or modified H cells, where one cell compartment is an Erlenmeyer flask (total volume ca. 100 mL). The anode and cathode were separated by a medium-porosity frit. 

An example of reversible intramolecular electron transfer has now been reported though not for a metal-metal system. It had previously been shown that the complexes [Ni (TPP)] (TPP =tetraphenylporphinate) when electrochemically oxidized in benzonitrile solution yield first the brown-coloured nickel(m) complex, which then decays at a measurable rate by a process of ligand-to-metal electron transfer [reaction (7), forward step (TPP )"=radical-ion] ... 

The existing data on the electrochemical oxidation of the fullerenes suggest that the solvent plays a crucial role in determining the stability of the fullerene radical cations. This is best seen for which was studied under a variety of conditions [17,24,30,46,58] (see above). One could estimate that the Ceo lifetime differs by at least three orders of magnitude in different media. The reversible voltammograms recorded by Xie et al. [45] suggest that the lifetime of C60 in TCE at ambient temperatures is longer than around 0.3 s, while a lifetime shorter than 0.5 ms at — 15°C in benzonitrile can be estimated from the data of Dubois et al. [30]. An... 

By media variables we mean the solvent, electrolyte, and electrodes employed in electrochemical generation of excited states. The roles which these play in the emissive process have not been sufficiently investigated. The combination of A vV-dimethylformamide, or acetonitrile, tetra-n-butylammonium perchlorate and platinum have been most commonly reported because they have been found empirically to function well. Despite various inadequacies of these systems, however, relatively little has been done to find and develop improved conditions under which emission could be seen and studied. Electrochemiluminescence emission has also been observed in dimethyl sulfite, propylene carbonate, 1,2-dimethoxyethane, trimethylacetonitrile, and benzonitrile.17 Recently the last of these has proven very useful for stabilizing the rubrene cation radical.65,66 Other electrolytes that have been tried are tetraethylam-monium bromide and perchlorate1 and tetra-n-butylammonium bromide and iodide.5 Emission has also been observed with gold,4 mercury,5 and transparent tin oxide electrodes,9 but few studies have yet been made1 as to the effects of electrode construction and orientation on the emission character. 

From electrochemical studies it is known that an irreversible oxidation of C6o occurs at +1.76 V vs SCE in benzonitrile [165]. One of the first methods to generate the radical cation by radiation was performed by "/-irradiation of C6o in glass matrix at 77 K [166], A new absorption in the near IR at 980 nm was assigned to the C 6o (Fig. 19) [19]. Despite the sufficiently high reduction potential of +2.0 V of dicyanoanthracene, first attempts to generate the radical cation by photoinduced electron transfer were unsuccessful [Eq. (5)] [19]. One reason may be a fast back-electron transfer that competes with ionic dissociation in benzonitrile [19]. 

Electrochemical studies have shown that Ceo is easily reduced (E1/2 = —0.21 and 0.33 V vs Ag/AgCl in tetrahydrofuran and benzonitrile, respectively [52] and —0.42 V vs SCE in benzonitrile [53, 54]). Up to six electrons can be added reversibly [55]. Several authors have shown that the fullerenes form charge-transfer complexes with amines [33, 56-59]. Wudl et al. have shown that Cgo reacts chemically with amines, giving various substitution products [60, 61]. Since the reduction potential of Ceo should be higher than that of the ground state by the amount of the triplet energy [62,63], its first reduction potential should be near 1.14 V vs SCE in benzonitrile [64]. The triplet should therefore be easily reduced by electron transfer from electron donors of lower oxidation potential. 

Electrochemistry can also be used to induce aromatic nucleophilic substitutions by setting up the electrode potential at the level, which is appropriate to reduce an aromatic substrate. When this electrochemical process is carried out in the presence of a nucleophilic reagent, the or reactions take place. Indeed, halogenated derivatives of benzophenone, benzonitrile, and naphthalene undergo nucleophilic displacement reactions with thiolates, which are able to occur catalytically [76, 77]. The reaction mechanism involves the formation of the anion radical at the electrode and its further decomposition into a neutral radical, which reacts with a nucleophile, thus yielding the anion-radical of the substitution product. In case of the catalytic reaction, oxidation of the anion-radical species may occur by electron transfer with the substrate and/or the electrode (Scheme 17). 

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