Polarographic reduction

In the presence of many metal ions, diorthohydroxyazo dyes exhibit two polarographic reduction waves, the first due to free dye and the second to metal-dye complex. Highly sensitive analytical methods based on this principle have been developed for example, Ni or Fe may be determined in the presence of an excess of aluminum thank to thiazolylazo derivatives (563). 

Iversen and Lund have realized the polarographic reduction of 2-thiazolecarboxylic acid and some of its derivatives in acid solution. They obtained 2-thiazolecarboxaldehyde (58),... 

The validity of the Hammett relationship log K/Ko = pa- has been extensively investigated for five-membered heteroaromatic compounds and their benzo analogues. The ratio Pheterocycie/Pbenzene is closest to Unity for thiophene. Judged from work on the polarographic reduction of nitro compounds, the ability to transmit electronic effects is HC=CH = S < O < NH. 

A comparison of the polarographic reduction of 2- and 3-substituted thiophenes have shown that the 2-isomers are more easily reduced than the 3-isomers. Polarography has also been used for the quantitative study of the dehalogenative reduction of 2-halo-5-carbonyl thiophenes and for the study of the hydroxychalcone-chromanone equilibrium in thienylsubstituted compounds. ... 

Kubota and Miyazaki studied the polarographic reduction of pyridine N-oxides and found a satisfactory correlation with the <7-values. The values increase with increasing pH. 

Example 3-4 A sample containing cadmium gives a polarographic reduction current of 6.0 pA. The current increases to 9 and 12 pA upon increasing the cadmium concentration in two steps of 2mM each. Calculate the cadmium concentration in the original sample. 

Quaternary salts, pKa value of, 7] polarographic reduction potentials, 71 Quinaldinium salts, in Mills reaction, 37,45 Quinoline-4)(4-methvlthiazole-2) trimethine cyanine, 62... 

In the Me2dtc complex, a unique, 15-line, epr spectrum was reported (69) that was peculiar only to the tetraphenylborate salt. This suggests a V-V interaction in the lattice. Electrochemical studies on these [CpjVLJ complexes (L = dithiocarboxylato ligand) shows two well defined, polarographic, reduction waves, and, for the process at most positive potential, the reversible formation of a V(III) species was postulated (72-74). 

The chemistry of tetrazolium thiolates and other mesoionic tetra-zoliums has been extensively reviewed.297,298 Tho ugh there are no reports of the chemical reduction of thiolates to formazan-like structures, the polarographic reduction of the complex betaines (146) to formazans has been reported.655... 

A discussion along this line has been made in regard to the orientation of the hydrogen molecule in the dissociative adsorption on metals 82>. Thus, the interpretation of the function of heterogeneous catalysis on a molecular basis is no longer beyond our reach. The important role of LU MO in the process of polarographic reductions has also been discussed... 

Polarographic reduction of l-methyl-5-nitroimidazole (97 R = Me, R2 = H) has been shown to proceed in two distinct steps, probably via the hydroxylamine derivative (102), to give the amino compound (96 R = Me, R2 = H) (62CR2603). 

The polarographic behavior of nalidixic acid has been studied by Staroscik and co-workers.(35) The pH range of -2.9 to 11 in 20% DMF was investigated in the concentration range of 5 x 10-V and three stages of reduction were found. The potentials were found to vary linearly with pH for the first two reduction stages, while the third was constant and appeared at pH >8. The carbonyl on C-4 was shown to be reduced to the 4-hydroxy product. Nalidixic acid was reduced with sodium borohydride and the product was demonstrated to be the same as that in the polarographic reduction by TLC. 

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