James Grimshaw

Carbon dioxide fixation by electrochemical reduction in water to oxalate and glyoxylate

Abstract Carbon dioxide, in aqueous solution containing tetramethylammonium ions at pH 9 was reduced in two steps to yield oxalic acid at −0.9 V and glyoxylic acid at −1.8 V on carbon and on mercury. Products were analysed by HPLC and confirmed by specific colorimetric measurements.

The cyclic voltammetry of some sulphonated transition metal phthalocyanines in dimethylsulphoxide and in water

Abstract The aqueous voltammetry of Co, Ni, Cu and Zn sulphonated metallophthalocyanines has been examined and compared to the voltammetry in DMSO. In DMSO, Ni, Cu and Zn phthalocyanines exhibit two quasi-reversible, phthalocyanine ligand based, one-electron transfers. Two reduction waves were also observed for Co phthalocyanine. However, the first reduction wave appeared to involve both a metal based electron transfer and a change in the coordination of the metal. The aqueous voltammetry of the cobalt phthalocyanine was similar to its non-aqueous behaviour. The other three phthalocyanines did not show the quasi-reversible behaviour in aqueous solution. Reversibility was much diminished and the forms of the waves changed greatly, indicating the involvement of protons in the redox processes.

Solar energy fixation of carbon dioxide via cadmium sulphide and other semiconductor photocatalysts

Abstract Aqueous carbon dioxide is photochemically reduced in the presence of semiconductor suspensions and colloids. Experiments have been performed using CdS, ZnO, SiC, Ba TiO3, and SrTiO3, dispersions. Product analysis showed the formation of formic acid formaldehyde, sometimes methanol and in the presence of tetramethylammonium chloride, two-carbon products such as glyoxylic and acetic acids and sometimes acetaldehyde. Product yields and photochemical yields were studied as a function of pH, solution composition, added sacrifical electron donors and catalysts, irradiation intensity and irradiation time. A demonstration experiment with a flat-bed solar collector showed the formation of formic acid and formaldehyde using direct sunlight.

Redox behaviour of polypyrrole films containing naphthoquinone and benzoquinone groups

Abstract The synthesis and electropolymerization of 2-[2-(1-pyrrolyl)ethylamino]-3-chloronaphthoquinone (PNQ) and 2,5-bis[2-(1-pyrrolyl)ethylamino]-2,6-dichlorobenzoquinone (PBQ). are described. Electrochemical behaviour of poly(PNQ) and poly(PBQ) films on platinum electrodes was investigated in acetonitrile media. A stable composite film was obtained by the oxidation of PNQ on a polypyrrole coated Pt electrode.

An isoflavone and a coumestan from eysenhardtia polystachya—Robert Boyle's fluorescent acid—base indicator

Abstract 7-Hydroxy-2′,4′,5′-trimethoxyisoflavone is the principal fluorescent phenolic constituent of the heartwood of Eysenhardtia polystachya , Robert Boyles fluorescent acid—base indicator. The bark yielded 9-methoxy-2,3-methylenedioxycoumestan.

Dissociative electron transfer between arene radical anions and halogenoalkanes: a pulse radiolysis study

Rate constants have been determined at room temperature (20 ± 1 °C) for a number of examples of the dissociative electron-transfer reaction between arene radical anions and the haloalkanes 1-iodobutane, 2-iodo-2-methylpropane and 2-bromo-2-methylpropane in the organic amide solvents N-methylpyrollidin-2-one N,N′-dimethylformamide. The data, when combined with the results of other workers using electrochemical techniques, indicate a linear relationship between log(kET) and the reduction potential of the donor radical anion (E°D) spanning eight orders-of-magnitude of kET up to the diffusion-controlled limit. The effect of temperature on kET was investigated for the reactions of 1-iodobutane with a number of the radical anions.The factors which affect the rates of these reactions and the success of current theory in explaining them are discussed.

The voltammetry of mixed solutions of carbon dioxide and metal phthalocyanines in DMSO

Abstract In order to look for new catalytic routes in the electroreduction of carbon dioxide, the voltammetry of mixed solutions of carbon dioxide and sulphonated phthalocyanines in DMSO has been investigated. An additional reduction wave was observed at more negative potentials than the second (−1.3 V SCE ) phthalcyanine reduction wave, for both copper and nickel phthalocyanines. No additional waves were observed with cobalt phthalocyanine, though shifts were observed in the second phthalocyanine reduction wave for all three phthalocyanines. The additional waves are thought to indicate the formation of a complex between CO 2 and the reduced phthalocyanine ion.

Electrochemical behaviour of poly(thiophene-benzoquinone) films

Abstract Poly(thiophene-benzoquinone) films were prepared on platinum spheres by electropolymerization of the monomer 1-[3-(3-thienyl)propyl]2,4,5-trichloro-3,6-dioxo-1,4-cyclohexadiene-1-acetate (TBQ) in acetonitrile. These films were studied mainly by cyclic voltammetry and chronoamperometry in acetonitrile containing tetraalkylammonium salts as the supporting electrolyte.

Electrochemical reactions. Part XV. Factors which determine the rate of carbon–halogen bond fragmentation in radical anions illustrated by some halogenated derivatives of quinoline, quinoxaline, and phenazine

The behaviour of some halogen-derivatives of quinoline, quinoxaline, and phenazine in the potential region of the first reduction waves has been examined by polarography and cyclic voltammetry in dimethylformamide at a mercury cathode. 2-Chloro- and 2-bromo-phenazine, 6-chloroquinoxaline, and 6-fluoroquinoline form radical anions which show no tendency to fragment with loss of halide ion at room temperature on the time scale of cyclic voltammetry. 2-Iodophenazine, 6-bromo- and 6-iodo-quinoxaline, and 6-chloroquinoline form radical anions which fragment to halide ion and, after further reactions, the parent heterocycle. Radical cations from the diprotonated halogeno-quinoxaline and -phenazine salts are stable in perchloric acid. The stability of the carbonhalogen bond in a halogenated radical anion depends upon the strength of this bond and the redox potential of the substrate–radical anion couple. For the isomeric halogeno-derivatives of a given aromatic system we have shown previously that the rate of carbon–halogen bond cleavage is dependent on the free electron density in the radical anion at the carbon terminus of the cleaving bond.

Formation of two-carbon acids from carbon dioxide by photoreduction on cadmium sulphide

Aqueous solutions of CO2 containing tetramethylammonium chloride were photolysed with visible light in the presence of colloidal CdS to yield glyoxylic acid as well as formic and acetic acids and CH2O.