Homogeneous catalytic hydrogenation of liquid carboxylated nitrile rubber

Homogeneous catalytic hydrogenation of olefinic bonds in liquid carboxylated nitrile rubber (L-XNBR) has been carried out selectively in the presence of nitrile and carboxyl functionality using a six-membered cyclopalladate complex of 2-benzoyl pyridine as catalyst. The degree of hydrogenation has been calculated from IR and NMR spectroscopic studies. For example, 68% hydrogenation has been obtained for a sample (containing 0.057 carboxyl equivalent/100 g and 26.1% acrylonitrile) under 2.7 MPa hydrogenation pressure, 0.18 mmol/L catalyst, at 333 K for 1 h in acetone solution. The overall extent of hydrogenation depends on the catalyst-to-double-bond ratio. The kinetics of hydrogenation of L-XNBR has been investigated. The reaction exhibits a pseudo-first order dependence on the concentration of the substrate. The rate constant of the reaction is reduced by the increase in carboxyl and nitrile content of the polymer. The effect of temperature on reaction kinetics has also been studied and the activation energy of hydrogenation of L-XNBR is 20.2 kJ/mol. Intrinsic viscosity of the polymer remains unchanged during the reaction. A significant lowering of the glass transition temperature and improvement of thermal stability have been observed on hydrogenation. © 1992 John Wiley & Sons, Inc.     

Effect of additives on electrokinetic properties of colloidal alumina suspension

Additive interactions and their effects on electrokinetic properties of colloidal alumina suspension are presented in this study. Dibasic ammonium citrate (DAC), natural egg albumin, and octanol-2 are chosen as additives. The surface charge behavior of a 5% (w/v) colloidal alumina suspension in the presence of these additives has been studied in detail. The optimum dosage of DAC to have a stable suspension is found to be 3 mg/g of alumina whereas it is 105 and 164 mg/g of alumina for albumin and octanol-2, respectively. Albumin was found to be a better dispersant than DAC and interacts more strongly than DAC with the surface of alumina, while octanol-2 shows physisorbing characteristics. Turbidity measurements indicate that albumin and DAC interact. When the DAC : albumin molar ratio exceeds 10, the turbidity of the solution is higher than the turbidity of pure albumin, indicating the formation of complexes.     

Theoretical conformational study of the molecular structures of some bipyridine cardiotonics

Conformational features of amrinone and milrinone have been examined viaab initio (at STO-3G and 3–21G levels) MO theory. The calculated results suggest twisted structures for both the molecules. The higher barrier to rotation of the pyridine ring and restricted conformational flexibility of milrinone are observed to be two significant factors responsible for its greater cardiotonic activity as compared to that of amrinone.     

Nickel(II) and copper(II) complexes of ONS ligands formed from 2-hydroxyacetophenone and S-alkyldithiocarbazates and the X-ray crystal structure of the [Ni(Ap-SMe)py] complex (Ap-SMe = anion of the 2-hydroxyacetophenone Schiff base of S-methyl-dithiocarbazate)

Summary New nickel(II) and copper(II) complexes of general formulae [M(Ap-SR)] and [Ap-SR)B] (Ap-SR = dianionic forms of the Schiff bases of 2-hydroxyacetophenone and S-alkyl esters of dithiocarbazic acid; M = Ni^II or Cu^II; R = Me or CH₂Ph; B = py, phen or dipy have been synthesized and characterized by a variety of physicochemical techniques. Magnetic and spectroscopic data support an oxygen-bridged binuclear structure for the [M(Ap-SR)] complexes. The [M(Ap-SR)py] complexes are four-coordinate and square planar, whereas the [M(Ap-SR)B] complexes (B = phen or dipy) are five-coordinate and probably trigonal bipyramidal. The [Cu(Ap-SR)B] complexes (B = py, phen or dipy) obey the Curie-Weiss law over the 298-93 K range.The structure of the [Ni(Ap-SMe)py] complex has been determined by X-ray crystallography. It has an approximately square-planar structure in which the doubly-deprotonated Schiff base is coordinated to the Ni^II ion via the azomethine N atom, the phenolic O atom and the thiolato S atom. The fourth coordination position around the Ni^II ion is occupied by the N of the pyridine ligand.     

Preparation of hydrogenated nitrile rubber using palladium acetate catalyst: Its characterization and kinetics

Hydrogenated nitrile rubber was prepared by using palladium acetate as the homogeneous catalyst system. The effect of different reaction parameters on the level of hydrogenation was studied. The extent of hydrogenation increased with increase in reaction time, temperature, pressure, and catalyst concentration. A maximum conversion of 96% could be achieved. The degree of hydrogenation was estimated from IR and NMR spectroscopy. The selectivity of the catalyst in reducing ? C?C? in presence of ? C?N was supported by IR and ¹³C-NMR spectra. ESCA studies further confirmed this observation. Properties of hydrogenated nitrile rubber were investigated by various techniques such as gel permeation chromatography (GPC), glass transition temperature (T_g), stress-strain behavior and rheological measurements. GPC studies showed no significant change in molecular weights of the products after the reaction. T_g value decreased with an increase in the level of hydrogenation. The ultimate stress improved significantly with the increase in the extent of hydrogenation. The die swell decreased with hydrogenation at a particular shear rate. The kinetics of the NBR hydrogenation were investigated. With the increase of the hydrogen pressure and catalyst concentration, the rate of the reaction increased. The reaction was apparently first order with respect to olefinic substrate at higher hydrogen pressure. The apparent activation energy, enthalpy, and entropy of the reaction were calculated as 29.9 kJ/mol, 27.42 kJ/mol, and –0.20 kJ mol^?1 K^?1, respectively.     

Kinetics and mechanism of oxidation of sulfanilic acid by periodate ion in aqueous medium

Results of kinetic studies of the sodium metaperiodate oxidation of sulfanilic acid in aqueous medium are discussed. A mechanism for the formation of azobenzene-4,4-disulfonic acid, isolated and characterized as its S-benzylisothiuronium derivative, is proposed.

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. -4,4- , S- .

     

Electrostatic double layer force between a sphere and a planar substrate in the presence of previously deposited spherical particles

A finite element model of the electrostatic double layer interaction between an approaching colloidal particle and a small region of a charged planar surface containing four previously deposited particles is presented. The electrostatic interaction force experienced by the approaching particle is obtained by solving the Poisson-Boltzmann equation with appropriate boundary conditions representing this complex geometry. The interaction forces obtained from the detailed three-dimensional finite element simulations suggest that for the many-body scenario addressed here, the electrostatic double layer repulsion experienced by the approaching particle is less than the corresponding sphere-plate interaction due to the presence of the previously deposited particles. The reduction in force is quite significant when the screening length of the electric double layer becomes comparable to the particle radius (kappaa approximately 1). The results also suggest that the commonly used technique of pairwise addition of binary interactions can grossly overestimate the net electrostatic double layer interaction forces in such situations. The simulation methodology presented here can form a basis for investigating the influence of several previously deposited particles on the electrostatic repulsion experienced by a particle during deposition onto a substrate.