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Oxidative chemical polymerization of pyrrole
Calorimetric and kinetic measurements
A reaction calorimeter has been used to determine at three different temperatures the enthalpy values for the polymerization of pyrrole dissolved in acetonitrile, by using FeCl3 as the oxidative agent. From the calorimetric data it has been found that the reaction is first-order with respect to the pyrrole. The rate constants at the same temperatures have also been determined. By using the Arrhenius equation we have obtained the activation energy for the formation of this electroconducting polymer.
Abstract
Three 1,2-diaryl pyrroles selective COX-2 inhibitors, 2-(4-fluorophenyl)-5-methyl-1-(4-methylsulfonyl-phenyl)-1H pyrrole, 2-(4-fluorophenyl)-1-[4-(methylsulfonyl) phenyl]-1H-pyrrole and 4-[2-(4-fluorophenyl)-1H-pyrrol-1-yl]benzenesulfon-amide, all three labeled with 14C in the 2-position were prepared from para-fluoro-benzaldehyde-[carbonyl-14C].
Abstract
Chemical polymerization of pyrrole (Py) was carried out in a reaction calorimeter by using FeCl3 or CuCl2 as an oxidant in an acetonitrile medium. The formation heat of polypyrrole (PPy), determined under a wide range of reactant concentrations and reaction temperatures, is directly related to the PPy yields and to the degree of polymerization. Due to the negative values of both the entropy and enthalpy of the reaction the gravimetric yield is inversely related to the temperature and directly to the Py concentration. The yields to the PPy and the related reaction heats, are close to zero when the 
ceiling temperatures
are reached (T
ceil=348 K for Fe-doped and T
ceil=313 K for Cu-doped PPys). It was observed that a ceiling concentration corresponds to each ceiling temperature and only light oligomers are formed if Py concentration is too low. The electric conductivity values of the products were also determined and a direct relationship to the yields was found as well. The highest electric conductivity value (C=0.6 S cm–1) was related to the PPy fresh synthesized from a 0.017 M Py solution.
Abstract
Conventionally polymerisation of pyrrole is carried out either by chemical or electrochemical oxidation. In the present study polymerisation of pyrrole was carried out in a novel way in order to investigate the kinetics of the reactions involved. Carbonate radical (CO3 −) generated either radiolytically or photolytically from a sodium carbonate solution, was employed as the oxidant for the polymerisation reaction Flash photolysis and steady state ψ-radiolysis of pyrrole solution containing sodium carbonate was used for generating different intermediate and stable polymeric species. The kinetics of the formation and decay of different intermediate species were studied using UV-VIS spectrophotometry and the disappearances of the monomer was ascertained using HPLC. After analysing the species and steps involved a plausible mechanism for the polymerisation of pyrrole is suggested.
Abstract
The overall tritium separation factor between molecular hydrogen and liquid pyrrole and pyrrolidine has been measured between 280 and 325 K. The data are comparable with values of α measured for similar exchange reactions involving ammonia and methylamine. There is a visible correlation of the isotope effect with the energy of hydrogen bond formed by NH groups of liquid ammonia, methylamine, pyrrole and pyrrolidine.
Abstract
The kinetics of tritium isotope exchange between liquid pyrrole and gaseous hydrogen has been studied over the temperature range of 290–303 K. The reaction was carried out in the presence of platinum black but in spite of that, it appeared to be relatively slow. The kinetics of the exchange reaction studied could be described by the simple McKay equation. The results obtained suggest that diffusion is the rate-determining step. A mechanism of exchange is proposed.
Abstract
We have studied the synthesis of polypyrrole-clay nanocomposites by the in situ oxidative polymerization of pyrrole in the interlayer space of vermiculites with different layer charges from Santa Olalla and Ojén, Spain. Moreover, the influence of different interlayer cations (Na+, Mg2+, Fe3+) on the interaction between pyrrole and the vermiculties was studied. The resulting materials were characterized by means of DTA-TG, XRD, FTIR and Mössbauer spectroscopy. In all samples polymerization of pyrrole was observed, presumably triggered by the structural iron. In most cases it was found to be externally deposited. An uptake of pyrrole in the interlayer space and PPy formation is observed in the case of the Fe3+-intercalated Ojén vermiculite, which has a lower layer charge than the Santa Olalla vermiculite.
The calorimetric determination of the ceiling temperature for the chemical polymerization of pyrrole
Implications on the electrical conductivity
Abstract
The previously found strong dependence of the polymerization enthalpy on the reaction temperature has been rationalized. The temperature dependence is to be ascribed to the existence of a ‘ceiling temperature’ for the polymerization process of the pyrrole monomer. The determined ceiling temperature has beenT≊350 K when FeCl3 was used as the oxidizing agent in CH3CN solution. The existence of a ceiling temperature together with its already determined exoenthalpic nature allows to classify the polymerization reaction as an exoentropic one. From the dependence of the yield of insoluble polymer on the reaction temperature, the trend of the relative mean numeral molecular massM n for the different obtained polymers has been determined. Measurements of electrical conductivity on pressed pellets of the different polymers allowed to establish a correlation between theM n value and the conductivities The dependence of the conductivity on the exposition time to the air allowed to do some essays on the aging behaviour of the obtained polypyrrole. By making some assumptions, an absolute calorimetric determination of the value ofM n of polypyrrole was tempted together with that of the related poly-N-vinilpyrrole.
Abstract
N-(2-oxo-5-phenyl-2,3-dihydro-1H-benzo[e][1,4]diazepin-3-yl)-1H-pyrrole-2-carboxamide-[carboxy-14C] was prepared as part of a five-step sequence from pyrrol-2-carbonitrile-[cyano-14C] as a key synthetic intermediate which has been synthesized from 2-bromopyrrole and zinc [14C]-cyanide in the presence of tetrakis (triphenylphosphine)palladium.
on their optical properties, but also on physical–chemical characteristics such as solubility, resistance against various influences such as oxygen or temperature fluctuation. 3,6-diphenyl-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione known as
