Lamberto Nucci

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.

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.

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.