Polarographic Behaviour

A compound 148 which shows stomach secretion inhibition (80EUP48555) and the aminotriazolopyridine 149 (90JHC1649) are reduced catalytically to the 5,6,7,8-tetrahydro derivatives. The polarographic behaviour of Trazodone has been studied (87M12). The quaternary salts 150 are reduced by borohydride to the 4,5,6,7-tetrahydro derivatives (94ZOK440). 

When information regarding the polarographic behaviour of a substance is not available, cognisance must be taken of the fact that in addition to the normal polarographic wave associated with the reduction and the diffusion of the species... 

Polarographic behaviour of coordination compounds. A. A. Vlcek, Prog. Inorg. Chem., 1963, 5, 211-384 (191). 

Polarographic behaviour of the system containing peroxydisulphate, arsenic-... 

Polarographic studies are reported on thioesters, mainly of the type (140) and (141), and on trichloroethylphosphonites. In the field of nucleotides and nucleosides it is found that ATP has a very high surface activity at the mercury electrode, which is strongly dependent upon complex formation with transition metals. The polarographic behaviour of cobalt complexes with triphenylphosphine and its oxide has been studied in order to estimate extraction efficiencies. 

Vlcek, A. A., Relation between electronic structure and polarographic behaviour of inorganic depolarizers. VII. Determination of activation energy of electrode processes. Coll. Czech. Chem. Comm., 24, 3538 (1959). 

Stolzberg [143] has reviewed the potential inaccuracies of anodic stripping voltammetry and differential pulse polarography in determining trace metal speciation, and thereby bio-availability and transport properties of trace metals in natural waters. In particular it is stressed that nonuniform distribution of metal-ligand species within the polarographic cell represents another limitation inherent in electrochemical measurement of speciation. Examples relate to the differential pulse polarographic behaviour of cadmium complexes of NTA and EDTA in seawater. 

Vanadium(n) Complexes.—Dehydration of VSO. THjO has been shown to proceed via the formation of VS04,mH20 (where n = 6, 4, or 1) and V(OH)-(SO4), which were characterized by X-ray studies. The polarographic behaviour and the oxidation potential of the V -l,2-cyclohexanediamine-tetra-acetic acid complex, at pH 6—12, have been determined.Formation constants and electronic spectra have been reported for the [Vlphen),] " and [V20(phen)] complexes. The absorption spectrum of V ions doped in cadmium telluride has been presented and interpreted on a crystal-field model. The unpaired spin density in fluorine 2pit-orbitals of [VF ] , arising from covalent transfer and overlap with vanadium orbitals, has been determined by ENDOR spectroscopy and interpreted using a covalent model. " ... 

Anionic and Cationic Carbonyls. The polarographic behaviour of Et N-[Fe(CO)3NO] at dropping mercury and stationary platinum electrodes has been studied. Two anodic waves and one cathodic wave were observed and the following reactions were suggested ... 

Only non-enolizable eneones give satisfactory yields of hydrodiroer on reduction in aptotic solvents [83]. A suitable aqueous buffer is needed with enolizable eneones to control base catalysed side reactions of condensation and oligomerisation. The polarographic behaviour of eneones in buffers is illustrated using cyclo-... 

The cross-redox reaction discussed above and formation of the Vm dimers has also been reported in the case of the edta complexes. Scheme 12 summarizes part of the equilibria proposed to explain potentiometric and spectroscopic data at t = 25 °C and I = 0.20 M in NaC104.336-338 The polarographic behaviour of V111 complexes of edta and analogous ligands has also been studied.339... 

The assumption of this scheme could explain the d.c. polarographic behaviour of manganous ions in alkaline tartrate solutions [11]. 

Apart from the polar effects of substituents discussed in the preceding paragraph, steric effects can also alter the polarographic behaviour of organic compounds (114). 

Data on such densely sterically hindered compounds that would hinder the attack by the electron have not been reported. There are two cases in which such an effect can be expected to operate. Whereas dial-kylperoxides are generally reducible at positive potentials, di-tert-butylperoxide has been reported as irreducible (139). Similarly for cyclic diketones (140), the unreducibility of 3,3,8,8-tetramethyl-l,2-cyclo-octanedione can arise from a similar effect, but the steric hindrance of coplanarity of the diketo grouping cannot be excluded in this case. A more detailed examination of these and similar systems would be necessary to reach a decision as to whether this type of steric effect can change the polarographic behaviour or not. 

The UV absorption spectra, in neutral aqueous medium, of pyrimidone-2 and its dimer reduction product, 6,6 -6u-(3,4-dihydropyrimidone-2), are exhibited in Fig. 2 Particularly interesting was the finding that irradiation of the dimer at 254 nm under these conditions led to the stepwise disappearance of its characteristic absorption spectrum, with the simultaneous appearance o the spectrum of the parent monomer. Additional evidence for the identity of the photoproduct with the parent pyrimidone-2 was furnished by chromatography and polarographic behaviour. The photochemical conversion reaction was shown to be quantitative (under these conditions pyrimidone-2 itself is quite radiation resistant), and to proceed with a quantum yield of 0.1, both in the presence and absence of oxygen 2). This value was unchanged when irradiation was conducted in 2H20 the absence of an isotope effect is clearly of relevance to the mechanism of the photodissociation reaction. 

The polarographic behaviour of 1-methylcytosine and 1, N4-dimethylcytosine at pH 3-7 was, as expected, similar to that for cytosine. Reduction led to formation, from each compound, of a dimer of l-methylpyrimidone-2, accompanied by quantitative elimination of ammonia and dimethylamine, respectively. The dimer reduction product in each case underwent photochemical conversion to 1-methylpyrimidone-2 84). 

Following initial studies by Cavalieri Lowy 96), it was shown by Smith Elving74) that the polarographic behaviour of 2-aminopyrimidine in acid medium is similar to that for the parent pyrimidine, which exhibits three waves at the dropping mercury electrode 74). The initial le step involves formation of a free radical which dimerizes and, at the potential of the second le reduction step, 2-amino-3,4-dihydropyrimidine is formed. But, unlike pyrimidine, 2-aminopyrimidines do not undergo a second 2e reduction to tetrahydro derivatives. Wave III (pH 7-9) involves two electrons and two protons, and is due to the combined processes responsible for waves I and II at lower pH. Both Smith Elving 74), and Sugino 104>, found that reduction of 2-aminopyrimi-dine on a mercury electrode 74) and lead cathode 104) resulted in the formation of unstable products. 

It is of additional interest that the product of reduction of wave I (1-electron) of 2-methylaminopyrimidine is a dimer (as shown by mass spectroscopy), which is photo-chemically converted in aqueous medium at 254 nm to 2-methylaminopyrimidine. Since the polarographic behaviour of 2-methylaminopyrimidine is similar to that... 

As might have been anticipated from the behaviour of 2-thiouracil (see above), 2,4-dithiouracil exhibits polarographic behaviour similar to that for 4-thiouracilI40). In the pH range 3-11 it gives three waves, the first two of which are due to the catalytic activity of dithiouracil, and the third to the catalytic activity of the reduction product(s) formed at the potential of wave II. As for 4-thiouracil, wave II overlaps the electro-... 

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