Anions electropolymerization

Meanwhile, the R-R coupling (see Sect. 2.2) has evidently found general acceptance as the main reaction path for the electropolymerization of conducting polymers The ionic character of the coupling species explains why polar additives such as anions or solvents with high permittivity accelerate the rate of polymerization and function as catalysts. Thus, electropolymerization of pyrrole is catalyzed in CHjCN by bromide ions or in aqueous solution by 4,5-dihydro-1,3-benzenedisulfonic acid The electrocatalytic influence of water has been known since the work... 

The ideal electropolymerization scheme (Eq. (5.5.39)) is further complicated by the fact that lower oligomers can react with nucleophilic substances (impurities, electrolyte anions, and solvent) and are thus deactivated for subsequent polymerization. The rate of these undesired side reactions apparently increases with increasing oxidation potential of the monomer, for example, in the series ... 

The Teixidor team further improved upon this chemistry by covalently linking units of 109 to the polypyrrole monomer prior to electropolymerization.139 A [3,3 -Co(C2B<)H11)2] anion was covalently bound to a pyrrole via a spacer through one of its boron atoms by the reaction of the species [3,3 -Co(8-C4H802-l,2-C2B9H10)(r,2 -(C2B9H11)2] with potassium pyrrole, as functionalization through... 

Electrolytic polymerization or electrolytically initiated polymerization, or shortly electro-initiated polymerization or electropolymerization, generally means initiation by the electron transfer processes which occur at the electrodes of an electrolytic cell containing monomer and electrolyte, in that by controlling the electrolysis current it is possible to control the generation of initiating species. Under appropriate conditions it may proceed by a free radical, anionic or cationic mechanism. In addition to the electrolytic addition polymerization, production of polymers through condensation reaction by electrolytic means should also be covered. Examples of each of these propagation mechanisms have now been reported in the literature. 

A nitrate-selective potentiometric MIP chemosensor has been devised [197, 198]. For preparation of this chemosensor, a polypyrrole film was deposited by pyrrole electropolymerization on a glassy carbon electrode (GCE) in aqueous solution of the nitrate template. Potentiostatic conditions of electropolymerization used were optimized for enhanced affinity of the resulting MIP film towards this template. In effect, selectivity of the chemosensor towards nitrate was much higher than that to the interfering perchlorate ( o3 cio4 = 5.7 x 10-2) or iodide ( N03, r = x 10 2) anion. Moreover, with the use of this MIP chemosensor the selectivity of the nitrate detection has been improved, as compared to those of commercial ISEs, by four orders of magnitude at the linear concentration range of 50 pM to 0.5 M and LOD for nitrate of (20 10) pM [197]. 

Anion-Selective Electrodes Based on Electropolymerized Porphyrin Filins... 

Figure 8. Selectivity pattern of an ISE based on an electropolymerized cobalt porphyrin film. The electrode was exposed to the following anions thiocyanate (1), perchlorate (2), iodide (3), nitrite (4), salicylate (5), bromide (6), chloride (7), bicarbonate (8), phosphate (9). The baseline potential was 364 mV. (Adapted from ref. 26.)...

In summary, it has been demonstrated that ISEs can be designed by employing molecular recognition principles. In particular, the feasibility of using hydrophobic vitamin B12 derivatives and electropolymerized porphyrin films in the development of polymer membrane anion-selective electrodes has been demonstrated. The studies indicated that the changes in the selectivity of these ISEs can be explained by the difference in structure of the ionophores. In addition, it was shown that by electropolymerization of a cobalt porphyrin, anion-selective electrodes can be prepared that have extended lifetimes compared with PVC-based ISEs, which use a similar compound as the ionophore. 

In oxidative electropolymerization, monomers such as pyrrole, thiophene, alkylth-iophenes or aniline are dissolved in an appropriate solvent containing an electrolyte that can act as a source for the anions needed to neutralize the cations formed during the oxidation process [33,34]. The nature of this electrolyte is of great importance to the structural features obtained for the electropolymerized layer since the dopants become an intrinsic part of the polymer layer structure. A general outline of a mechanism describing the electropolymerization process is shown in Figure 4.21. 

Fig. 12.15. Examples of scanning tunnelling micrographs, (a) Copper electrode-posited from Cu(N03)2 solution on highly ordered pyrrolytic graphite and imaged at -0.5 V vs. Ag AgCl (tip bias potential +0.6 V) (from Ref. 51 with permission) (b) Electropolymerized polypyrrole with poly(4-styrenesulphonate) anion on graphite substrate (from Ref. 52 with permission).

A transformation of some synthetic versatility is the oxidation of methyl groups in a methylcobaltocenium salt by Mn04 to give the respective carboxylic acid. In this way, mono- and dicarboxylatocobaltocenium salts have been prepared. These acids can be further functionalized and used as receptors for the selective recognition of anion guest species. A pyrrole-fimctionalized cobaltocenium salt has also been electropolymerized on an electrode surface this system displays anion sensing in solution and when immobilized. ... 

It has been mentioned already that polypyrrole (25) and polythiophene (26) play an important role as electrical conductors and polymeric anodes in battery cells [2,47,226]. Since the charging and discharging of the conjugated polymer is accompanied by the incorporation and removal of counterions it is clear that the material can also act as a carrier of chemically different anions which influence the physical, chemical and physiological properties of the material [292]. With regard to the full structural elucidation of the polymers it must be added, however, that the electropolymerization process of pyrrole and thiophene does not provide a clean coupling of the heterocycles in the 2,5-positions. Instead, the 3- and 4-position can also be involved giving rise to further fusion processes under formation of complex polycyclic structures [47]. 

While all these proposals refer to a D/A battery, with a stoichiometric conversion of the electrolyte, some authors construct a D/D battery (cf. No. 14 in Table 10), were large anions, such as poly(styrene sulfonate) [503] or dodecylbenzene sulfonate are irreversibly inserted in the course of the electropolymerization [504], and the Li ion is reversibly cycled. 

Intramolecular asymmetric induction has also been used in electrochemistry as in the reduction of optically active alcohol esters or amides of a-keto [469,470] and unsaturated [471] acids and oximes [472] and in the oxidation of olefins [473]. A maximum asymmetric yield of 81% was obtained in the reduction of (5 )-4-isopropyl-2-oxazolidinone phenyl-glyoxylate [470]. Nonaka and coworkers [474,475] found that amino acid A-carboxy anhydrides were polymerized with various electrogenerated bases as catalyst to give the poly(amino acids) with high chirality in high yields. Conductive chiral poly(thiophenes) prepared by electropolymerization can be used for chiral anion recognition [476]. 

PPy films modified by platinum catalyst particles were also considered for electrocatalytic reactions (oxygen reduction and methanol oxidation) by Hepel et al. [41], The incorporation of a PtCl anion was performed during the electropolymerization of pyrrole and monitored by the electrochemical quartz crystal microbalance (EQCM) technique, allowing us to evaluate the amount of platinum obtained after reduction of the PPy/PtCl film. 

Electropolymerization Based on 4-Vinylpyrldlne and Related Ligands. The third technique for preparing electrode/film interfaces is in many ways the most interesting both in terms of the chemistry involved and the results so far obtained. The strategy is to induce polymerization directly at the electrode surface by oxidation or reduction and our emphasis has been on the reduction of coordinated 4-vinylpyridine and related compounds. It is known that 4-vinylpyridine is susceptible to anionic polymerization (38). 

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