Pyrroles polymerization

Indeed, it is often difficult to control electrophilic attack so that monosubstitution occurs. A further problem is that pyrrole polymerizes in the presence of strong acids and Lewis acids, so that... 

Other electrochemical processes of organic compounds on Pb electrodes or electrodes with UPD Pb have been studied - formaldehyde [323], oxalic acid [386], trichloro- and trifluoroethane [387], 1-phenylethylamine [388], 3-hydroxychi-nuclidine [388], dichlorodifluoromethane [389], polychlorobenzenes [390], 1-propa-nol [391], pyrrole polymerization [392], and inorganic compounds - phosphine [388] and sulfate(IV) ions [393]. Simultaneous catalytic or inhibiting influence of organic solvents - acetonitrile, dimethyl-sulfoxide, and Pb + presence on electrooxidation of small organic molecules on Pt electrodes has been studied using on-line mass spectroscopy [394],... 

Pyrrole polymerized at the interface of non-polymerizable 3-octadecanoyl pyrrole and transferred to substrates to form LB films FTIR and conductivity measurements Lateral d.c. conductivities as high as 0.1 S cm 1 were obtained 769, 770, 771... 

The effect of intrazeolite protons on pyrrole polymerization in faujasite with ferric ions was examined, in order to distinguish the relative influence of acidity and the one-electron oxidant. If water was co-adsorbed with pyrrole, the authors could prepare materials with conductivities vaiying over a wide range. It is not clear to what extent the conductivity is due to surface-adsorbed polypyrrole, because similar simthetic methods also produced pol)mier coatings on amorphous aluminosilicates. 

Pyrrole polymerizations have a significant advantage in terms of flexibility over polyaniline syntheses, described later in Chapter 4, in that they may be carried out in neutral aqueous solution (i.e., no acid is required). A range of organic solvents may also be employed, the limitation being the requirement to dissolve both the pyrrole monomer and the oxidant. 

Pyrrole, furan, and thiophene are aromatic compounds that undergo electrophilic aromatic substitution reactions preferendally at C-2. These compounds are more reactive than benzene toward electrophiles. When pyrrole is protonated, its aromahcity is destroyed. Pyrrole polymerizes in strongly acidic solutions. Indole, benzofuran, and benzothiophene are aromatic compounds that contain a five-membered aromatic ring fused to a benzene ring. 

The PPy formation mechanism has been addressed in many studies. The radical cation-neutral pyrrole (PyH) coupling followed by a further oxidation and de-protonation in the early stage of the pyrrole polymerization was first proposed by Genies et al. [60] and Fletcher et al [22]. Fletcher et al. concluded that the adsorption of a neutral FyH molecule takes place prior to its electro-oxidation resulting in the generation of the radical cation, which subsequencly polymerized as a consequence of instantaneous nucleation with three-dimensional growth. This conclusion was later supported by Marcos et al. [61]. 

In a mixture of water and methanol, a rapidly mixed reaction still produces mainly broken capsulelike structures. In isopropanol, both the monomer and the oxidant are soluble, therefore, no capsule-like structures are observed but rod-like nanostructures start to appear with large amounts of amorphous materials. Rapidly mixed reactions of pyrrole polymerization were carried out in water, methanol, and isopropanol. Large polypyrrole particles (micron size) were obtained in water, while smaller particles ( -150 nm) were obtained in methanol. In isopropanol, the product disperses very well and glomerates of tiny fibril structures (<30 nm) were found in the product This indicates that further tuning of the solvent-polypyrrole-dopant interactions, reveal well-defined nanoscale morpholr cal units for polypyrrole. 

The resulting CNTPE can also be modified by immersion, drop coating, or electrodeposition of different molecules, polymers, biomolecules, or metals. Some examples include 3,4-dihydroxybenzaldehyde [153] and polyOs-GDH-Dl-NAD" for the detection of glucose in alcoholic beverages [154] or pyrrole polymerized at CNTPE with a DNA probe for the detection of the hybridization event [155]. 

Haddad, R., Cosnier, S., Maaref, A., and Holzinger, M. (2009) Non-covalent biofunctionalization of single-walled carbon nanotubes via biotin attachment by 3t-stacking intercations and pyrrole polymerization. Analyst, 134 (12), 2412 - 2418. 

Example 18 Nanotubes from Pyrrole Polymerization in Reverse Water-Organic Emulsion (Adapted from ref. 75)... 

In this section we will describe the synthetic methods of pyrrole polymerization. The methods to synthesize substituted polypyrroles or to produce polypyrrole composites will be discussed in other sections. 

Table 10.1. Different oxidizing agents used for pyrrole polymerization from aqueous and organic solvents...

These facts can be explained if we consider the coexistence of a chemical pyrrole polymerization parallel to the formation of the polymer on the electrode. It is known that acidification of a pyrrole solution in an organic solvent gives a polymeric powder with alternating saturated and unsaturated pjnrole rings [21,136-9] (Figure 10.12). The kinetics of this homogeneous chemical proton-catalyzed polymerization of... 

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