Gerhard Kossmehl

Reactive groups on polymer covered electrodes—I. Electrochemical copolymerization of thiophene-3-acetic acid with 3-methylthiophene

Cyclic voltammetry (cv) experiments at Pt electrodes were carried out to produce copoly(3-methyl-2,5-thiophenediyl-2, 5-thiophenediyl-3-acetic acid) (3a) from the monomers 3-methylthiophene (1) and thiophene-3-acetic acid (2a), and to study the mechanism of electrocopolymerization. It was found by means of esteriflcation and amidation and further chemical reactions of the copolymers thus obtained that the COOH groups are covalently bound to the copolymer structure. The charge/discharge reversibility and the overoxidation (irreversible redox process occurring when the covered electrode is scanned beyond the positive potential limit) of 3a and some of its derivatives are demonstrated by representative cyclic voltammograms. In a series of copolymerization experiments the positive potential limit (Epos) was lowered step by step from 2.20 to 1.70V (vs. s AgAgCl) below the potential for the oxidation of 2a (Emox = 2.11 V vs. s AgAgCl) and, yet, the copolymer 3a was obtained. The results of the examination are discussed with the aid of data from cv, MS, FTIR-GIR (Fourier-Transform-Infrared-Grazing Incidence Infrared) spectroscopy, 1H NMR13C NMR spectroscopy, and elementary analyses.

Reactive groups on polymer covered electrodes 6-Copolymerization of 2,2′-bithiophene with methyl thiophene-3-acetate and 3-methylthiophene

Abstract Polythiophene films at the surface of electrodes containing ester groups are interesting potential carrier materials for reagents. Methyl thiophene-3-acetate (2) can be copolymerized with 3-methylthiophene (1) by means of cyclic voltammetry at potentials of 0–2.2 V. Higher potentials (0–2.4 V) lead to overoxidation of the copolymers. The ester groups were proved by FTIR spectra. Electrochemical investigations of 2,2′-bithiophene (4) and 2 at equimolar ratios shows no successful copolymerization at potentials of 0–1.3 V. If the copolymerization experiments of 4 with 1 or 2 were carried out at molar ratios of 1:50 at 1.3 V 4 with its low oxidation potential can be polymerized without copolymerization of the other monomers. However, if the oxidation potential is increased stepwise arising from 1.3 V the oxidation of 1 or 2 takes part forming copolymers containing both the monomer components. HPLC investigations of solutions containing mixtures of 4 and 2 and also 4 and 1 in acetonitrile/TEABF4 shows after exhaustive oxidation at a potential of 1.3 V the complete absence of 4. 1 and the ester 2 were not oxidized and copolymerized at this potentials. From the results of the copolymerization experiments as well as the HPLC investigations, it can be concluded that the dominant mechanism of the electrochemical polymerization is the radical cation dimerization.

Synthesis and reactivity of antioxidants based on vernolic acid and 3‐(3,5‐di‐tert‐butyl‐4‐hydroxyphenyl)propionic acid

The reactivity of sterically hindered phenols toward free radicals of the hydrocarbon cumene was studied. New compounds, i. e. methyl cis-13(12)-{3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxy}-12(13)-hydroxyoleate and cis-13(12)-{3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxy}-12(13)-hydroxyoleic acid were synthesized starting from vernolic acid and its methyl ester, respectively, and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid. Both new compounds possess antioxidant activities similar to those of commercially available antioxidants. Die Reaktivitat von sterisch gehinderten Phenolen gegenuber freien Radikalen des Kohlenwasserstoffes Cumol wurde untersucht. Die neuen Verbindungen Methyl-cis-13(12)-{3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxy}-12(13)-hydroxyoleat und cis-13(12)-{3-(3,5-Di-tert-butyl-4-hydroxyphenyl)propionyloxy}-12(13)-hydroxyolsaure wurden ausgehend von Vernolsaure bzw. dessen Methylester und 3-(3,5-Di-tert-butyl-4-hydroxyphenyl)propionsaure synthetisiert. Die beiden neuen Verbindungen besitzen antioxidative Aktivitaten ahnlich denen kommerziell erhaltlicher Antioxidantien.

Reactive groups on polymer covered electrodes-3. Electrochemical copolymerisation of nitrofunctionalized 3-substituted thiophene derivatives

Abstract Electrochemical copolymerization of 3-(2,4-dinitrostyryl) thiophene (4) and 3-(2,4,6-trinitrostyryl)-thiophene (5) with 3-methylthiophene (6) produced interesting new functionalized polythiophene layers at the surfaces of electrodes suitable for further reactions and which have potential NLO properties.

Studies on β-methylated end-capped bithiophenes

The reactivity of a variety of differently β-methylated oxidized α,α′-blocked (end-capped) bithiophenes has been studied. Electroanalytical methods such as cyclic voltammetry and studies with a rotating-ring disc electrode (RRDE) are employed, revealing two oxidation peaks. While the first electron transfer yields radical cations of increased stability as the number of β-methyl groups is increased, the second electron transfer is irreversible. For the first time, a dependence of the stability of radical cations (first oxidation step) on the degree of β-methylation is reported. Compounds with methylated 3-β-positions form more stable radical cations than 4-β-methylated ones. The stability of the oxidized end-capped bithiophene 6 can be explained by a reversible dimerization. The presence of β-substitution also exerts an influence on the reaction products of the chemical oxidation with FeCl3·6H2O, which have been isolated and purified by chromatography. In the case of bithiophene derivatives with methylated 3,3′-positions the main products are bithiophene-5-carbaldehydes; bithiophene derivatives with free 3-positions form bis(bithiophene)methanes. The reactive centers are α-methyl groups, not, as one might expect, free β-ring positions. In neither case has a β,β′-linkage between two thiophene rings been observed.

Study of the electrosynthesis of poly(3-butylthiophene) and its semiconductor properties

Abstract The mechanism of the electrosynthesis of poly(3-butylthiophene) (PBuT) was studied by cyclic voltammetry and potential step methods in comparison with polybithienyl. The anodic oxidation polymerization of the 3-butylthiophene underwent two steps: oligomer formation and further polymerization to form the polymer. The doping level of the PBuT increases with the cycle number of the potential sweeps during polymerization. The current responses to the potential steps indicate a nucleation and nuclei growth process which is repeated layer to layer. The differential capacity (Cd) and photocurrent were measured at the PBuT films in the aqueous electrolyte solution. The Cd−2 vs. E plot shows two regions of linearity, one with a negative slope and the other with a positive slope in different potential regions, which give the same flat-band potential. This indicates that the PBuT film exhibits both p-type and n-type features of a semiconductor at differrent potential regions. The cathodic photocurrent spectrum was analysed by the (jphhν)2/n vs. hν plots, giving band gap energies of 2.41 eV for n=1 and and 2.01 eV for n=4.