Francesco Pergola

Electrochemical synthesis of intrinsically conducting polymers of 3-alkylpyrroles

Abstract In the present work the electrochemical polymerization of pyrrole (Py) derivatives has been performed in order to identify the conditions for obtaining intrinsically conducting polymers, checking film morphology and conductivity. The study mainly concerns 3-alkylsubstituted pyrroles with different chain lengths (3-hexylpyrrole (3HP), 3-decylpyrrole (3DP), 3-hexadecylpyrrole (3HDP)). In the case of 3DP (0.01 M) various experimental conditions have been adopted: different solvents (propylene carbonate, acetonitrile), different counterions (ClO 4 − , BF 4 − , NO 3 − , PF 6 − , TsO − ) with the same cation Bu 4 N + and different current densities (0.05, 0.1, 0.2, 0.4 mA cm −2 ) in the case of BF 4 − in propylene carbonate. Porous and elastic films are obtained when the substituent alkyl side chain is longer and the supporting electrolytes are ClO 4 − , BF 4 − , PF 6 − ; with these last electrolytes the best conductivity is also obtained (0.1–0.8 S cm −1 for poly(3-decylpyrrole), P3DP). P3DP(TsO) and P3DP(NO 3 ), aside from the type of solvent, show poor mechanical properties and low electrical conductivity (10 −3 and 10 −6 S cm −1 for P3DP(TsO) and P3DP(NO 3 ), respectively). The conductivity decreases as the alkyl side chain becomes longer. When the polymerization is performed at low monomer concentration (of the order of 0.001 M), the surface properties of P3DP(ClO 4 ) are very poor and the conductivity is only 10 −3 S cm −1 . The obtained polymers have also been electrochemically characterized through cyclic voltammetry. The voltammetric evolution observed during cycling is studied under different experimental parameters (counterion type, solvent nature and electrochemical cycling). The cyclic voltammetry change, regarding the gradual shift to negative potentials of the redox process on P3DP with ClO 4 − , BF 4 − and PF 6 − as counterions, seems to be ascribed to a gradual deprotonation process. Analysing the voltammetric profile change from the point of view of a deprotonation process, it can be concluded that this process is speeded up by the basic character of the solvent (propylene carbonate) and in the presence of a basic counterion (tosylate) this is almost complete and immediate. P3DPNO 3 , although conductive (10 −6 S cm −1 ), can be switched from the oxidized form to the reduced one only a few times in acetonitrile and never in propylene carbonate, showing the difficulty of the polymer in being reduced and oxidized several times.

Anodic oxidation of chlorides, bromides and iodides on a platinum microelectrode with periodical renewal of the diffusion layer

Abstract The redox process, Cl2+2 e→ 2 Cl−, occurs reversibly on a platinized-platinum microelectrode with periodical renewal of the diffusion layer. the processes, Br2+2e → 2 Br− and I2+2e→2I− occur reversibly in 1 N HCIO4 either on a smooth or platinized electrode. In 1 N Nano3 the first of these reactions occurs only on a smooth electrode. the voltammetric curves obtained with a 5.10−4M Iodide solution in Hcl at a concentration between 1 and 10−3N (the ionic strength being kept constant by the addition Of HCIO4) show two anodic waves of about the same height. the first wave is due to the oxidation of iodide ion to iodine, the second to the reaction 12+4 Cl−→ 2 ICl−2 +2 e or I2+2 Cl−→ ICl− +2 e, according to the activity of the chloride ion in the solution. the voltammetric curves obtained with 5.10−4M iodide ion in HBr at a concentration between 1 and 0.28 N show a single anodic wave corresponding to the oxidation, I− +2 Br− → IBr2− + 2 e. Decreasing the bromide ion concentration below 0.28 N causes a distortion of the wave and finally a splitting : the two waves thus obtained correspond to the oxidation reactions of iodide ion to iodine and of this iodine to IBr2− or to IBr. the reversibility of the various oxidation-reduction systems and also the E 1 2 -values of the corresponding waves as functions of the concentrations of halide ions, have been verified. a strict relation between the e 1 2 -potentials and the electrode characteristics has been established. The results are in very good agreement with the values calculated on the basis of the equation valid for spherical diffusion.

Voltammetric behaviour of chlorites and chlorine dioxide on a platinized-platinum microelectrode with periodical renewal of the diffusion layer and its analytical applications

Summary Chlorite and chlorine dioxide solutions show an analogous voltammetric behaviour on a platinized-platinum micro-electrode with periodical renewal of the diffusion layer. Dilute chlorite solutions at pH>5 shows two distinct waves, one in the anodic and the other in the cathodic range. The anodic wave is due to the oxidation of chlorite to chlorine dioxide and the cathodic to its reduction to chloride. At pH≥10.5, the anodic wave is influenced by the disproportionation of chlorine dioxide produced at the electrode. Thus its height is doubled and the final oxidation product is chlorate. At pH A new polarographic method is reported for the determination of chlorites and chlorine dioxide, based on the measurements of the height of the waves given by these species.

Polarographic behaviour of alachlor application to analytical determination

Abstract A DC polarographic reduction wave independent of pH, with a half-wave potential of about −1.30 V (S.C.E.) is shown by Alachlor This reduction wave is characterized by the attainment of a current maximum, which vanishes in the presence of small amounts of a cationic surfactant The presence of strong surfactants prevents the adsorption of the reaction product on the electrode, thus eliminating the current maximum. The results of polarographic, coulometric and preparative electrolysis measurements are consistent with a reaction mechanism of reductive cleavage, which is shown by several organic halides. For analytical applications the DP polarographic technique is more usefuL In this case the adsorption of reactant or product on the electrode surface increases DPP currents. The peak current is proportional to the concentration over the range 1×10−7-1×10−5 M.

Halogenatedp-quinols of marine sponges. Synthesis via anodic oxidation of phenols and NHI-like rearrangement

Abstract Oxidation of either 2,6-dibromo- ( 1 ), 2-bromo- ( 3 ), or 2-bromo-chloro- p -acetamidophenol ( 5 ) at a Pt anode in aq. HClO 4 affords the corresponding common, 2 , or rare, 4 and 6 , marine halo- p -quinols in practicable yields, whereas literature recipes as to either chemical or electrochemical proved to be ineffective; these halo- p -quinols proved to be extremely alkali-labile, in part due to a rearrangement

Colchicine red-ox chemistry revisited: Cathodic behavior and EPR observation of an intermediate radical anion

Abstract Colchicine ( 1 ), a potently antimitotic alkaloid and useful laboratory tool in cancer research, undergoes cathodic reduction in DMF forming and ESR-observable radical anion ( 1r ) which is characterized by the isotropic hyperfine coupling constants 8.9, 4.3, 0.75, 0.49 and 0.48 G for H-8, H-12, OCH 3 , H-11 and H-4, respectively, and a much flattened troponoid ring. Assignments are aided by selective deuteriation of colchicine at C-8, C-11 and COCH 3 , as well as by spectral simulation and ab initio calculations of electron spin densities. Whether the colchicine radical anion may exist in nature is also discussed.

Voltammetric behaviour of the aqueous system I−I2IBrBr−Cl− on platinum

Abstract The voltammetric behaviour of the aqueous system I − I 2 IBrBr − Cl − on a platinum microelectrode with periodical renewal of the diffusion layer allowed the nature of the equilibria present in the solution to be determined. The constants of the disproportionation equilibrium I 2 Br − ⇌ I − + IBr and of the dissociation equilibrium IBrCl − ⇌ IBr + Cl − were shown to be about 3·9· 10 −7 and 2·9· 10 −2 moles/l. respectively.

Voltammetric determination of bromite with a platinized platinum microelectrode with periodical renewal of the diffusion layer

Summary A new method is presented for the polarographic determination of bromite alone or in the presence of bromate, hypobromite and chlorite, with a cell with platinized platinum electrode with periodical renewal of the diffusion layer. The simultaneous determination of bromite, bromate and hypobromite is also possible. Dilute bromite solutions with pH>8 show two distinct waves, the amplitude of which is proportional to the concentration, one in the anodic range and the other in the cathodic range; the former is caused by the oxidation of bromite to bromate and the latter by the reduction of bromite to bromide. Above pH 11.5 the anodic step is masked by the oxygen discharge. The presence of two independent polarographic steps enables either the anodic or the cathodic step to be chosen for the quantitative determination of bromite when compounds that interfere in the cathodic or anodic zone, respectively, are present in the test solution. The method gives good reproducibility in a wide field of concentrations, is sensitive and simple to use.

Anodic oxidation of 3,5-dihalogenotyrosines as a model reaction for the biogenesis of the cavernicolins, metabolites of the verongid sponge Aplysina cavernicola

Anodic oxidation of 3,5-dibromo-4-methoxyphenylalanine methyl ester 3, led to cavernicolin [3,3a,7,7a-tetrahydro-3a-hydroxyindole-2,6(1H)-dione] model compounds although equilibration to all four possible stereoisomers 4α, 4β, 5α and 5β was a special characteristic of the model compounds only. This may constitute a new model for the biogenesis of the cavernicolins as an alternative to a spirolactone route from oxidation of amino-protected tyrosines. Chemical oxidation gave poor results.

N-allylpyrrole as a bifunctional precursor to electrically conducting and filmable organic polymers: synthesis and preliminary characterization

Abstract We have begun to evaluate the potentialities of N -allypyrrole as a precursor monomer to electrically conducting organic polymers. Ab initio calculations carried out on tetramers of the correlated poly( N -vinylpyrrole) are reported and evaluated. A chemical synthetic route using FeCl 3 as the oxidizing agent allowed us to obtain a dark product which is presumably the poly(2,5- N -allypyrrole). An electrochemical synthesis carried out at constant applied potential gave very good black films on a Pt electrode. The chemical and the electrochemical polymers have nearly the same conductivity which is of the order of 10 −4 S/cm. IR spectra demonstrate the survival of the allyl double bond in the conductive materials. Attempts to polymerize the N -allylpyrrole on the allyl double bond in order to obtain a polymeric insulating precursor to a ladder conducting polymer were largely unsuccessful.