M. Aijaz Beg

Kinetics and mechanism of the epoxidation of fumaric acid with aqueous hydrogen peroxide catalyzed by sodium tungstate or sodium molybdate

Abstract The kinetics of epoxidation of fumaric acid by hydrogen peroxide in the presence of sodium tungstate or molybdate have been studied. Tungstate catalyzed epoxidation of fumaric acid to trans -epoxysuccinic acid is faster than that for molybdate catalysis. The reaction is first order with respect to substrate and catalyst and zero order with respect to hydrogen peroxide. Based on substituent, solvent, and salt effects, our opinion is that the mechanism of the epoxidation step is related to polar (electrophilic) character.

Studies on membrane concentration potentials across parchment-supported silver iodide membrane in solutions of some alkaline earth chlorides

Summary Membrane concentration potentials across a parchment-supported silver iodide membrane in solutions of BaCl 2 , CaCl 2 and MgCl 2 of different concentrations have been measured. The effect of the external electrolyte concentration on the membrane potential, membrane permselectivity ( P s ), cationic transport number in the membrane ( + ) and apparent anionic mobility have been studied. Membrane potential, P s and E + fall, whereas apparent anionic mobility increases, with increase in external electrolyte concentration. This behaviour has been attributed to the loss of membrane selectivity with increase in external electrolyte concentration as well as to the reduction in the membrane fixed charge density due to adsorption of cations at higher electrolyte concentrations. In the case of BaCl 2 at a concentration ratio of 1 N /0.1 N the membrane charge reverses its sign from electronegative to electropositive.

Fixed charge density of manganese ferrocyanide membrane. Comparison of the altug and TMS methods

Summary The fixed charge density of parchment-supported manganese ferrocyanide membrane has been determined by the TMS method and compared with that obtained by the method of Altug and Hair. The deviation has been ascribed to the difference between the mobility ratio inside the membrane and that in the free solution. The cationic transport numbers have also been determined using the TMS method and compared with those derived from membrane potentials.

Polarographic Study of trans-Dioxotetracyanotungstate(IV) Ion

The Polarographie behaviour of tetrapotassium dioxotetracyanotungstate (IV), Ki [W1V 0% (CN)i] · 6H2O at dropping mercury electrode (dme) has been investigated in aqueous medium in the presence of 0.1 M KNO3 and 0.01 °/o gelatin. The complex was found to be oxidized step-by-step to the tungstate (VI) state. The resulting tungstate (VI) complex is presumed to be hexa-coordinated trans[WVIO2 ( ) ]*~ like the original tungstate (IV) complex, and the electrode process can be given as: lW^02(CN)t]*-j—> [Wv02(CN)4]3-

Polarographic study of oxohydroxocyanomolybdate(IV) ion

Abstract The polarographic behaviour of tripotassium oxohydrocyanomolybdate(IV), K 3 [Mo IV O(OH)(CN) 4 ]·2H 2 O, was studied. The complex was found to be oxidized step-by-step to the molybdate(VI) state at the dropping mercury electrode in an aqueous solution which contained 0·1 M potassium nitrate and 0·01% gelatin. The resulting molybdate(VI) complex is presumed to be hexa-coordinated [Mo VI O(OH)(CN) 4 ] 1− , like the original molybdate(IV) complex, and the electrode process can be given as: .

Studies of concentration potentials across heavy metal soap liquid ion-exchange membranes

Abstract Concentration potentials in zinc sulphate, copper sulphate, nickel sulphate and cobalt sulphate solutions across liquid membranes based on myristates and laurates of zinc, copper, nickel and cobalt and caprate and caprylate of copper have been studied in concentration cells in which the liquid membrane separates the two solutions of the same electrolyte. The behaviour of the cell with heavy metal soap liquid ion-exchange membranes becomes more and more nernstian as the number of carbon atoms in the hydrocarbon chain of the fatty acid soap increases. Concentration potential values with copper, zinc, nickel or cobalt soap follow the order of their insolubility in water. The failure to record the theoretical potentials as calculated by Nernsts equation has been explained by considering the transport of water across organic phase by hydrated ions and the dissolution of heavy metal soaps in aqueous solutions. Liquid membranes based on heavy metal myristate soaps when used in concentration cells could measure the activities of zinc, copper, nickel and cobalt ions in the concentration range of 10−4–10−1 M.

Changes in the zeta-potential of copper ferrocyanide sol by gradual addition of electrolytes

SummaryZeta-potential of copper ferrocyanide sol falls, and its hydrogen ion concentration increases continuously with the addition of chlorides of potassium, barium, and aluminium till the sol falls to coalescence. The effect of thorium nitrate on the above sol is quite distinct from the rest in the sense that with its addition zeta-potential first falls rapidly, attains a minima, and then it again rises. The lowering of zeta-potential as well as the increase in hydrogen ion concentration of this sol by the cations of different valencies follows the Hardy-Schulze rule.ZusammenfassungDas Zeta-Potential von Kupfer-Ferro-Cyanid-Sol sinkt, und seine Wasserstoffkonzentration steigt kontinuierlich mit Zufügung der Chloride von Kalium, Barium und Aluminium, bis das Sol ausfällt. Der Effekt von Thoriumnitrat ist völlig verschieden. Das Zeta-Potential fällt zuerst sehr stark, erreicht ein Minimum und steigt dann wieder. Die Erniedrigung des Zeta-Potentials wie auch der Anstieg der Wasserstoffionenkonzentration dieses Soles durch Kationen verschiedener Wertigkeit entspricht der Hardy-SchulzeRegel.

The poisoning and charge reversal of manganese ferrocyanide impregnated parchment paper membrane

Summary The influence of the counterions on the charge reversal of parchment-supported inorganic membranes, during the transport of electrolytes through the manganese ferrocyanide membrane, has been studied. The transport number of counterions and the permselectivity of the membrane have also been evaluated during the course of transport. It has been found that the hydrated ionic radii and the adsorbability of the soluble hydrolysed poisoning counterions are mainly responsible for the charge reversal. The results have been discussed in the light of views given by Gregor, Willis and Boyd.

Potentiometric estimation of potassium hydroxotetracyanotungstate(IV) and determination of standard potential

Summary The potentiometric determination of tetrapotassium tetrahydroxytetracyanotungstate(IV) using I2, Cr2O72− and Ce(IV) as oxidants is reported. Studies relating to the determination of the oxidation potential (Eo) by the potential mediator method for W(IV)-W(VI) hydroxocyanide complex ion couple in alkaline medium are described. The Eo-value depends on the concentration of KOH and the relationship, E=E°-[RT/nF] ln [ox]/[red][KOH]1.5 has been found to hold for the couple. The thermodynamic quantities, ΔG°, ΔH° and ΔS°, have also been calculated.

Kinetic studies on slow coagulation of hydrophobic sols

Coagulation of molybdenum blue sol by thorium-nitrate has been followed by measuring the turbidity at intervals. The study has been done in presence of a number of non-electrolytes.Ghosh equation for slow coagulation holds valid in this case. The constants of the equation have been characterised.