Redox methods

Oxidation-reduction potential Because of the interest in bacterial corrosion under anaerobic conditions, the oxidation-reduction situation in the soil was suggested as an indication of expected corrosion rates. The work of Starkey and Wight , McVey , and others led to the development and testing of the so-called redox probe. The probe with platinum electrodes and copper sulphate reference cells has been described as difficult to clean. Hence, results are difficult to reproduce. At the present time this procedure does not seem adapted to use in field tests. Of more importance is the fact that the data obtained by the redox method simply indicate anaerobic situations in the soil. Such data would be effective in predicting anaerobic corrosion by sulphate-reducing bacteria, but would fail to give any information regarding other types of corrosion. 

We noticed that the gelation of polymers by the redox method is promoted if 2-3 times the calculated molar ratio of thiosulfite is used (see half Equation 9 below). The gelation rate was very slow when x=l or x=4 (Table V). 

One redox method we have discussed is called iodometry. What is iodometry and why is it called an indirect method ... 

Why is bromine preferred to iodine in redox methods for the assay of pharmaceutical organic substances Explain with suitable examples. 

J. Barbier, Redox method of bimetallic catalysts. In Handbook of Heterogeneous Catalysis edited by G. ErtI, H. Knozinger, and J. Weitkamp (Wiley-VCH, Weinheim 1997) pp. 257-264. 

Refs on Analysis of NG 1) Marshall 2(1917), pp 739—40 (Estimation of small quantities by reaction with phenol disulfonic acid to form. PA and colorimetric measurement against K nitrate standards) 2) Koehler et al, AnnChimAnal-ChimAppl 2, 271-2(1920) CA H 3794(1920) (Devarda method) 3) W.W. Becker, lECAnalEd 5, 152-4(1933) CA 27, 2909U933)(Redox method for NG and NGc in the presence of DNT)... 

St CA 45, 6l56(1951)(Reverse Redox method) 9) M. Halse, MeddNotskFarm-Selskap 16, 166-9(1954) CA 49, 13024(1955) (Determination of NG in mixtures with PETN) (Saponification to nitrite at 20°, then reaction with sulfanilic acid and a-naphthyl amine for a colorimetric measurment against nitrite standards) 10) P. Lhoste, MP 37, 149-52(1955)... 

The first combined HPLC-electrochemical measurements of vitamin K used the reductive mode, but this technique suffered from interference from the reduction of oxygen. A redox method was later developed that eliminated this interference, and provided a 10-fold increase in sensitivity over photometric detection and an improved selectivity. The coulometric detector employed in the redox mode is equipped with a dual-electrode cell in which phylloquinone is first reduced upstream at the generator electrode and the hydroquinone is reoxidized downstream at the detector electrode. 

In redox methods, radicals are generated and removed either by chemical or electrochemical oxidation or reduction. Initial and final radicals are often differentiated by their ability to be oxidized or reduced, as determined by substituents. In oxidative methods, radicals are removed by conversion to cations. Such oxidations are naturally suited for the additions of electrophilic radicals to alkenes (to give adduct radicals that are more susceptible to oxidation than initial radicals). Reductive methods are suited for the reverse addition of alkyl radicals to electron poor alkenes to give adducts that are more easily reduced to anions (or organometallics). 

Bimetallic catalysts can be prepared by a direct redox method when a cationic complex of a metal of higher electrochemical potential is reduced by another metal of lower electrochemical potential that has been deposited and reduced first187 (see Table 4.10) PdAu/SiO 88 and PdAu/C189 have been made in this way, gold being deposited after the palladium. Small amounts of the metals were found in filtrates, and XRD and temperature-programmed decomposition of palladium hydride indicated a substantial... 

In most cases, the solids prepared according to the methods described in Section A 2 2 1 are not cataly-tically active as such The only exceptions are some grafted catalysts (2 2 1 2), most heterogenized complexes (2 2 14) and a large proportion of the catalysts prepared by redox methods (2 2 16) In the other cases, the substance deposited on the support must be transformed to a suitable compound (e g transformation of hydroxide or oxide to metal or to sulfide) m order to acquire the desired activity... 

Lab 12, 553-4(1946) fit CA 41, 1954(1947)(De-termination of small quantities of NG in the air. in the presence of nitrogen oxides)(Involves saponification to nitrite which is determined colorimetrically) 8) P. Fainer, CanJChem. 29, 46-53(1951) CA 45, 6156(1951)(Reverse Redox method) 9) M. Halse, MeddNorskFarm-Selskap 16, 166-9(1954) CA 49, 13024(1955) (Determination of NG in mixtures with PETN) (Saponification to nitrite at 20°, then reaction with sulfanilic acid and a-naphthyl amine for a colorimetric measur ment against nitrite standards) 10) P. Lhoste, MP 37, 149-52(1955) fit CA 50, 17451 (I956)(Rapid analysis of NG tablets) (Dewarda method) 10a) G.C. Whitnack et al, AnalChem 27, 899—901 (1955)(Polaro-graphic detn of NG in double-base proplnts)... 

Because it is a potent reducing agent, vittunin C is commonly determined by titrimetric or potentiometric redox methods. Such methods underestimate the amount of the vitamin present because dehydroascorbate - which has vitcunin activity - is formed by atmospheric oxidation of ascorbate in the sample, especially under neutral conditions, and is not detected by redox assay methods. 

Interlayer distance data of DA intercalated OL-l samples show that only one layer of amines was intercalated into the layers with average intercalation angles of about 40, 69, and 61°, respectively, for en-OL-1, 1,6-DHA-OL-l, and 1,10-HOA-OL-1. TMA intercalated H-OL-1 had two kinds of interlayer distances of 2.58 and 1.18 nm. The larger interlayer structure may include two layers of TMA and three layers of water molecules according to diameters of these molecules/ions. The small one included one layer of TMA cations and one layer of water molecules corresponded to the type II model of TMA manganese oxide prepared by redox methods using tetramethylammonium permanganate [33]. The structures of TEA, TPA, and TBA... 

FIGURE 4. Redox methods for deposition of metal films... 

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