Polarograph carbonate

Polarography is used extensively for the analysis of metal ions and inorganic anions, such as lOg and NOg. Organic compounds containing easily reducible or oxidizable functional groups also can be studied polarographically. Functional groups that have been used include carbonyls, carboxylic acids, and carbon-carbon double bonds. 

Berck B. 1962. Polarographic determination of methyl bromide, ethyl dibromide, acrylonitrile, chloropicrin, and carbon tetrachloride in air. J Agric Food Chem 10 158-162. 

The rotating disc electrode is constructed from a solid material, usually glassy carbon, platinum or gold. It is rotated at constant speed to maintain the hydrodynamic characteristics of the electrode-solution interface. The counter electrode and reference electrode are both stationary. A slow linear potential sweep is applied and the current response registered. Both oxidation and reduction processes can be examined. The curve of current response versus electrode potential is equivalent to a polarographic wave. The plateau current is proportional to substrate concentration and also depends on the rotation speed, which governs the substrate mass transport coefficient. The current-voltage response for a reversible process follows Equation 1.17. For an irreversible process this follows Equation 1.18 where the mass transfer coefficient is proportional to the square root of the disc rotation speed. 

Tlte reduction potential for an alkyl or benzyl radical, relative to that of the carbon-halogen bond from which it is derived, is important in determining the isolated products. Products are derived either by radical or by carbanion chemistry. The half-wave potential for the second polarographic wave of alkyl halides is connected with reduction of the radical. Sophisticated methods have been devised for deducing radical reduction potentials in cases where (his second wave is not seen. Values are collected in Table 4.4. 

Cyclopropyl carbanions are capable of maintaining their configuration whereas the CT-radical has been shown to reach inversion equlibrium with a rate constant of lO" s". ITie cyclopropyl bromide 13, and the corresponding iodide, are reduced in a single two-electron polarographic wave and the S +)-isomer yields the R(-)-hydrocarbon with 26% enantiomeric excess [67, 68]. Such a substantial retention of configuration during reduction of the carbon-bromine bond indicates a very fast second electron transfer process. Results from reduction of the cyclopropyl bro-... 

Reduction of sulphonium salts polarographic half-wave potentials, Ey. ref. [54], in water cyclic voltammetry peak potentials, Ep ref. [55], in acetonitrile at glassy carbon, scan rate 50 mV s. ... 

Carbon-heteroatom bonds of a-substituents to a carbonyl function are cleaved at less cathodic potentials than those required in the absence of the carbonyl group. The polarographic reduction of these systems has been extensively studies in aqueous media. Tie half-wave potentials are also less negative than those of the non-substituted carbonyl compounds. Electron addition involves an interaction between the n -orbital of the carbonyl group and the o-orbital of the departing group. 

Ebel et al. have used a microliter vessel in the voltammetry and polarographic determination of small sample volumes of chlorpromazine [166]. The concentration of cells in glass or PTFE was described for use with a dropping-mercury electrode (sample volume 180 pL), a rotating disc electrode (sample volume 1 mL), or a stationary vitreous-carbon electrode (sample volume 80 pL). Chlorpromazine was determined using oxidative voltammetry at a 3 mm vitreous-carbon or a rotating electrode. 

A mathematical analysis of all four isomeric thiadiazoles by the simple molecular orbital method has provided molecular diagrams of the free base and conjugate acid of each thiadiazole, with electron densities, bond orders, and free valencies. On this basis, predictions have been made concerning the reactivities of the six non-equivalent carbon atoms, the basicities of the nitrogen atoms, and the delocalization energies in these molecules. The 5-position in free 1,2,4-thiadiazole should possess maximum reactivity in nucleophilic substitution reactions. The treatment also accounts for the order of the polarographic half-wave potentials and the position of the absorption maxima in the ultraviolet region of the spectra of 1,2,4- and 1,3,4-thiadiazoles.4... 

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