Dehydration polarography

The mechanism of the global 4-electron electrochemical reduction of aromatic nitro compounds to hydroxylamines in aqueous medium shown in reaction 37 was investigated by polarography and cyclic voltametry. The nitro group is converted first to a dihy-droxylamine, that on dehydration yields a nitroso group the latter is further reduced to a... 

The only tetrahedral IrIV compound so far known is the tetramesityl,98 Ir(mes)4, made by the interaction of Li mes with partially dehydrated IrCl3 nH20 in Et20. It can be oxidized by AgPF6 to [Irv(mes)4]PF6- This cation is also tetrahedral. Polarography shows the reversible system Irin(mes)4 IrIV(mes)4 Irv(mes)4 but the anion could not be isolated. 

Dehydration is one of the important acid-base-catalyzed reactions of carbohydrates. In alkaline media, a deoxyaldosulose is formed from a carbohydrate molecule after one molecule of water has been split oflF this product then usually undergoes an intramolecular, oxidoreductive disproportionation to give the corresponding saccharinic acid in acidic media (with pentoses and hexoses), up to three molecules of water are split oE per molecule, with formation of 2-furaldehyde or 5-(hydroxymethyl )-2-furaldehyde. In many cases, polarography makes possible the monitoring of carbohydrate dehydration and the determination of its final products. 

Sulfur dioxide in shrimps, orange juice, peas, dried apricots, and dehydrated potatoes may be determined by differential pulse polarography, as described in AOAC method 987.04. The sulfur dioxide is purged with nitrogen from an acidified sample, and collected in electrolyte trapping solution comprising ammonium acetate buffer prior to analysis by differential pulse polarography. 

STUDIES ON ACID-BASE, HYDRATION-DEHYDRATION AND KETO-ENOL EQUILIBRIA IN AQUEOUS SOLUTIONS OF a-KETOACIDS BY POLAROGRAPHY, LINEAR SWEEP VOLTAMMETRY AND SPECTROSCOPY... 

Values of Kd can be obtained by electrochemical or spectroscopic techniques. In polarography, the equilibrium between the hydrated and carbonyl form is perturbed and limiting currents governed both by the position of equilibrium (Equation 9) and by the rate of dehydration 13 D.c. polarographic limiting currents thus offer only information about the upper limit of the value of Kd. In linear sweep voltammetry (LSV) the measurement of the current can be carried out over such a short period of time that the equilibrium cannot be reestablished . The current is then proportional to the concentration of the carbonyl form in the bulk of the solutions and can be used for determination of values of Kd, as discussed in detail elsewhere . 

Studies of Acid-Base, Hydration-Dehydration and Keto-Enol Equilibria in Aqueous Solutions of a-Ketoacids by Polarography, Linear Sweep Voltammetry and Spectroscopy... 

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