Benzene electropolymerization

With benzene and biphenyl the nucleophilicity of the solvent was particularly critical, due to the high reactivity of the radical-cation. By testing different solvents such as DCM, NBACN or NM (considered as acidic, according to the Lewis concept), PC (neutral), MeOH, THF, DMSO and DMF (basic) it was found that the electropolymerization of benzene and biphenyl only occurred with strongly anhydrous ((H2O) < 5.10 M) solvents having a donor number (DN) less than 15 or a pKbh+ of less than —10 [113]. Addition of a strong acid to the solvent was also favourable, and it was found that the addition of triflic acid in NM increased the current efficiency of benzene electropolymerization considerably [107]. 

Lacaze and co-workers974 have prepared poly(pr ra-phenylene) films by electropolymerization of benzene in strong acidic media including triflic acid and... 

The reported semi-permeable membrane consists of an electropolymerized di-amino-benzene in phosphate buffer (pH 7). Polymerization is achieved by cycling the potential between 200 mV and + 800 mV for a certain period. In principle such an electrode modification hinders fouling in an excellent way [77]. 

As vehicles for the electropolymerization of benzene to form the conducting polymer poly (p-phenylene).47 Ionic liquids are said to be good alternatives to liquid sulfur dioxide. 

Endres et al. [82] have demonstrated the suitability of an air- and water-stable ionic liquid for the electropolymerization of benzene. This synthesis is normally restricted to media such as concentrated sulfuric acid, liquid SO2 or liquid HF as the solution must be completely anhydrous. The ionic liquid used, l-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate, can be dried to below 3 ppm water, and this ionic liquid is also exceptionally stable, particularly in the anodic regime. Using this ionic liquid, poly(para-phenylene) was successfully deposited onto platinum as a coherent, electroactive film. Electrochemical quartz crystal microbalance techniques were also used to study the deposition and redox behavior of the polymer from this ionic liquid (Section 7.4.1) [83]. 

Fig. 9.11 (a) Cyclic voltammogram of 0.2 M benzene in [HMIMJFAP on platinum. The numbers refer to the respective cycle. Scan rate lOmVs-. (b) SEM micrograph of the electropolymerized film on the platinum electrode after synthesis in [HMIMJFAP. 

Figure 72 Proposed mechanism for electropolymerization of benzene involving the stepwise coupling of cation-radical species. (From Ref. 313.)...

A mechanism involving the coupling of cation radicals has also been considered for the electropolymerization of benzene compounds [306,313]. This mechanism occurs by a sequence of events similar to those proposed for the electropolymerization of pyrroles. The first step is the oxidation of benzene to a cation radical (471). Two of these cation radicals combine to form a dication dimer (478). The neutral aromatic dimer (479) is formed upon loss of two protons. This dimer is then reoxidized to a cation radical (480). Chain growth is accomplished by the coupling reaction of this cation radical with other cation radicals followed by deprotonation to form aromatic structures. Polymer growth continues by this sequence of steps until precipitation from solution occurs (Fig. 72). 

Several benzo[c]thiophenes with substituents on the benzene ring have been electropolymerized recently <94CC825>. 

Lere-Porte, J. R, Radi, M., Chorro, C., Petrissans, )., Sauvajol, J. L., Gonbeau, D., Pfister-Guillouzo, G., Louarn, G., and Lefrant, S. (1993). Characterization from XPS, FT-IR and Raman spectroscopies of films of poly(p-phenylene) prepared by electropolymerization of benzene dissolved in ketyl pyridinium chloride-AICl3 melting salt. Synth. Met, 59, pp. 141-149. 

Although both of the previously mentioned methods yield high-quality polyparaphenylene films, polyparaphenylene can also be formed electrochemically from biphenyl (Fig. 21c) dissolved in acetonitrile under similar mild anodic conditions [367]. The electropolymerization of biphenyl may be advantageous in that the toxicity of biphenyl is lower than that of benzene. Furthermore, the resulting films are reported to have longer chain lengths and less cross-linking than the films synthesized directly from benzene [368]. 

AbedinSZE,BorissenkoN,EndresF (2004) Electropolymerization of benzene in a room tianperature ionic liquid. Electrochem Commun 6 422-426... 

Benzene dissolved and electropolymerized at 1.1 V versus Ag/AgCl in a superacid solution of SbFs in HE The polymer formed on the anode (Au, Pt or GC) was a brown, conducting material which was identified as poly(/ -phenylene) [105]. 

Traces of water ((H2O) 10 M) in DCM or NM could inhibit the electropolymerization of benzene and biphenyl. This effect was partially attributed to the nucleophilicity of water which reacts with the radical-cation as soon as it is formed. When a small amount of a dehydrating agent (P2O5 or CuC ) was added to the medium, the electropolymerization process could occur again [113]. 

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