T. Demappa

Oxidation of some primary amines by bromamine-B in alkaline medium: A kinetic and mechanistic study

The kinetics of oxidation of the aliphatic primary amines, n-propylamine, n-butylamine, and isoamylamine, by sodium N-bromobenzenesulfonamide or bromamine-B (BAB) in sodium hydroxide medium has been studied at 35 degrees C. The reaction rate shows a first-order dependence each on [BAB] and [amine], and fractional order on [OH-]. Additions of halide ions and the reduction product of BAB (benzenesulfonamide), and variation of ionic strength and dielectric constant of the medium do not have any significant effect on the reaction rate. Activation parameters have been evaluated. A Taft linear free-energy relationship is observed for the reaction with p*=-3.0 and delta=-2.0 indicating that electron-donating groups enhance the rate. An isokinetic relationship is observed with beta=393 K indicating that enthalpy factors control the rate. The existence of the relationship has been supported by the Exner criterion. Mechanisms consistent with the observed kinetic data have been proposed

Mechanical, thermal and flame-retardant properties of epoxy-nylon fabric-clay hybrid laminates

Epoxy–nylon fabric laminate composites containing 0.1–0.7 phr clay reinforcements were prepared using a hand layup technique. The fabricated laminates were tested for thermal stability, impact resistance, mechanical properties and flame retardancy. The results indicated an increase in impact resistance, tensile strength, flexural strength and Young’s modulus to an extent and then a decrease as the clay content is increased. Overall results show that a 0.2-phr clay reinforcement into the epoxy–nylon fabric laminate has shown better impact resistance (33.9% more than the neat epoxy–nylon fabric laminate), tensile strength (nearly two times the neat sample), flexural strength (nearly five times the neat sample) and Young’s modulus (39.4% more than the neat sample). Thermal stability is found to decrease slightly upon addition of clay. UL-94 tests conducted on the composite laminate samples have shown a reduction in the burning rate. Also, the tests performed in the present study indicate that the materials under investigation have promising applications in construction, agriculture and decorative purposes.

Oxidation of primary amines by bromamine-B catalyzed by Osmium(VIII) in alkaline medium: A kinetic and mechanistic study

The kinetics of oxidation of the aliphatic primary amines, n-propylamine, n-butylamine, and isoamylamine, by N-sodio-N-bromobenznesulfonamide or bromamine-B (BAB), in the presence of osmium(VIII), has been studied in alkaline medium at 35 degrees C. In the presence of the catalyst, the experimental rate law for the oxidation of the amine substrate (S) takes the form, rate = k[BAB][OsO4][OH-](x), which in the absence of the catalyst changes to the form, rate = k[BAB][S][OH-](y), where x and y are less than unity. Additions of halide ions and the reduction product of BAB (benzenesulfonamide). and the variation of ionic strength of the solvent medium have no effect on the reaction rate. Activation parameters have been evaluated. The proposed mechanism assumes the formation of a complex intermediate between the active oxidant species, PhSO2NBr-, and the catalyst, OsO4, in the rate determining step This complex then interacts with the substrate amine in fast steps to yield the end products. The average value for the deprotonation constant of monobromamine-B, forming PhSO2NBr-, is evaluated for the Os(VIII) catalyzed reactions of the three amines in alkaline medium as 9.80 x 10(9) at 35 degrees C. The average Value for the same constant for the uncatalyzed reactions is 1.02 x 10(4) at 35 degrees C

Polymeric degradation of water soluble chitosan/HPMC films using WAXS data

Abstract Films of cationic chitosan and non-ionic hydroxypropyl methyl cellulose (HPMC) have been prepared by solvent casting method, using glycerol as a plasticiser, from aqueous lactic acid medium. Here, an attempt is made to compare the degradation effect of neutral HPMC and chitosan on water uptake and flexibility in terms of microstructural parameters obtained from X-ray line profile analysis. The intension of this study is to investigate properties for the potential use of chitosan/HPMC films to improve flexibility for packaging, solubility of drug, drug release and biodegradability. Fractured surfaces of the films were examined through wide angle X-ray diffraction and the intensity profiles were used to determine the microstructural parameters. Chitosan and HPMC films have more water retentiveness property compared to other blends studied here.

Microstructural Parameters of HPMC/PVP Polymer Blends Using Wide Angle X-Ray Technique

Hydroxypropylemethylecellulose (HPMC) and Polyvinylpyrrolidone (PVP) polymer virgin and blend films were prepared and investigated using wide angle X-ray scattering method. Microstructural parameters like lattice strain (g %), the crystallite size for individual the Braggs reflection (hkl) have been computed using line profile analysis and hence by whole pattern fitting method. The X-ray diffraction study reveals that the blending of PVP decreases the crystallanity of HPMC up to 5:4 concentration and then increases. Measured tensile strength decreases, Youngs Modulus decreases, and % elongation increases as the concentration of PVP increases. The surface morphology investigated using scanning electron microscope, shows that the two polymers were miscible in all concentration range.

RUTHENIUM(III) CATALYZED KINETICS OF OXIDATION OF PRIMARY ALCOHOLS BY BROMAMINE-B IN HYDROCHLORIC ACID SOLUTION

The kinetics of the ruthenium(lll) catalyzed oxidation of the primary alcohols, methanol, ethanol, 1-propanol, and 1-butanol by sodium N-bromobenzenesulfonamide (bromamine-B or BAB) in HCl solution has been studied at 30 degrees C. The reaction rate shows a first-order dependence each on [BAB], [alcohol], and [ruthenium(III)]. The reaction also shows inverse fractional-order dependence on [acid]. Additions of halide ions and the reduction product of BAB (benzenesulfonamide), and variation of the ionic strength of the solvent medium have no effect on the rate. Activation parameters have been evaluated. A general mechanism consistent with the above kinetic data has been proposed. The protonation constant of monobromamine-B has been evaluated to be 12.6. A Taft LFE relationship is noted for the ruthenium(lll) catalyzed reaction with p* = -0.77 indicating that a positive charge develops on the transition state and the electron-donating groups favor the reaction rate. An isokinetic relationship is observed with beta = 386 K indicating that enthalpy factors control the rate.

Effects of CdCl 2 concentration and gamma irradiation on the structural, thermal and electrical conductivity properties of HPMC polymer electrolyte films.

Solid polymer electrolyte films based on hydroxypropyl methylcellulose (HPMC) with different concentrations of cadmium chloride (CdCl2) were prepared by solution cast method. Different techniques has been employed to investigate the effects of structural, thermal and ionic conductivity behavior of these polymer electrolyte films upon gamma irradiation with different doses of 20, 60 and 100 kGy. The dissolution of the salt into the polymer host and the structural properties of pure and CdCl2 (1% - 4%) (wt. %) complexed HPMC polymer electrolyte films before and after irradiation was confirmed by X - ray diffraction (XRD) studies. XRD results revealed that the amorphous domains of HPMC polymer matrix was increased with increase in the salt concentration and with the gamma dose. The percentage of crystallinity is found to be high in pristine unirradiated HPMC films. The thermal properties of these polymer electrolyte films before and after irradiation were studied using differential scanning calorimetry (DSC). The results revealed that the presence of CdCl2 in the polymer matrix increases the melting temperature, however it is observed that the total enthalpy of fusion ( ) is maximum for unirradiated pristine HPMC films. The variation of film morphology was examined by scanning electron microscopy (SEM). Direct current (dc) conductivity was measured in the temperature range of 313-383K. The magnitude of conductivity was found to increase with increasing concentration of the salt, temperature and for higher dose of radiation. The composition HPMC:CdCl2 (5:4) for unirradiated and irradiated samples, found to exhibit the least crystallanity and the highest conductivity.

Thermal Degradation of HDPE Short Fibers Reinforced Epoxy Composites

Thermogravimetric analysis was carried out to investigate the thermal degradation of High Density Poly Ethylene (HDPE) short fibers reinforced epoxy composites. Three composites with 5, 10 and 15 % by weight of HDPE short fiber composition were prepared using epoxy as matrix material. The HDPE short fiber used as reinforcing material into the resin helps in retarding the thermal degradation of epoxy. It has been noted that there is a composition dependence on the course of kinetic slower of epoxy with fiber loading. Of three compositions, the 10 % HDPE filled Epoxy composite shows better thermal resistance. This has been understood from the derivative peak temperatures 365°C and 391°C corresponding to 5% and 10 % levels of fiber loading respectively. Similarly the weight retention at IDT for neat epoxy, 5% and 10% fiber levels in epoxy were 83%, 84% and 87% respectively. The 15 % HDPE filled Epoxy composite shows downward trend with respect to derivative peak temperature and weight retention at IDT. The Horowitz-Metzger method was used to calculate the activation energies and results are tabulated. Morphological analysis was carried out with scanning electron microscopy (SEM) to evaluate the dispersion of the fibers in the epoxy matrix. UL-94 Horizontal and Vertical Burning tests conducted for the samples indicated that these materials can be used in structural, agricultural and decorative applications.

A study on refractive index, orientational order parameter and distribution function in the nematic phase of a nematogenic compound

ABSTRACT The refractive indices (ne no) and density have been measured at various temperature in the nematic-isotropic phases of nematogenic Methoxy-41-Pentyl-41-tolane. The molecular polarizability, nematic orientational order parameter are evaluated by Neugebauer anisotropic local field model. The distribution function f(β) and hence the higher order parameter ⟨P4⟩ at different temperatures in the nematic phases have been estimated.

Structural and ionic conductivity behavior in hydroxypropylmethylcellulose (HPMC) polymer films complexed with sodium iodide (NaI)

Solid polymer electrolyte films based on Hydroxypropylmethylcellulose (HPMC) complexed with Sodium Iodide (NaI) were prepared using solution cast method. The dissolution of the salt into the polymer host and the micro structural properties of pure and NaI complexed HPMC polymer electrolyte films were confirmed by X – Ray diffraction (XRD) studies. The XRD results revealed that the amorphous domains of HPMC polymer matrix was increased with increase in the NaI salt concentration. The degree of crystallanity and crystallite size is high for pure HPMC samples. Direct current (dc) conductivity was measured in the temperature range of 313–383k. Temperature dependence of dc electrical conductivity and activation energy regions data indicated the dominance of ion type charge transport in these polymer electrolyte films.