Enthalpies of mixing of acetonitrile with isomeric butanols: Enthalpies of hydrogen-bonded complexes

The enthalpies of mixing of four isomeric butanols with acetonitrile were determined at 30°C by a Calvet type microcalorimeter. All the four systems showed endothermic behaviour. The enthalpies of hydrogen bonded complex formation were determined by means of a thermochemical cycle. 1-butanol formed a stronger bonding (−13kJ/mole) than the other three isomers (−11.20kJ/mole). The strength of the H-bond of alcohol with C ≡ N is much less than that with C-N. NCL communication no. 4883     

Sorption and diffusion in heteropolyoxometalates : I. Aromatic hydrocarbons

The sorption capacities and diffusivities of benzene, toluene, xylene, mesitylene, and m-diethylbenzene have been measured at 293, 308, and 323 K on three solid heteropolyoxometalates, 12-tungstophosphoric, 12-molybdophosphoric, and 12-tungstosilicic acids, and their ammonium salts. Heats of adsorption were calculated from the former data. The microporous salts show considerably larger sorption capacities than the nonporous solid acids, not surprisingly, and the former show sorption properties which are evidently related to both the micropore size distributions and the nature of the sorbate molecules. Diffusivities of aromatic hydrocarbons were found to decrease with the increase in molecular weight and kinetic diameter, and were also dependent on the particular heteropolyoxometalate being examined. Heats of adsorption, in general, show no evidence of chemisorption effects. However, the sorption of mesitylene and of m-diethylbenzene on ammonium 12-tungstosilicate was found to be irreversible. Little or no evidence was found for the penetration of aromatic hydrocarbons into the bulk structure of the solid heteropolyacids.     

EPR and optical investigations of manganese ions in alkali lead tetraborate glasses

Electron paramagnetic resonance (EPR) and optical absorption spectra of Mn2+ ions in different alkali lead tetraborate glasses 90R2B4O7+9.25PbO+0.75MnSO4 (R=Li, Na and K) and 90Li2B4O7+(10-x)PbO+xMnSO4 (x=0.1, 0.25, 0.5, 0.75, 1.0, 1.25, 1.5 and 2 mol%) have been studied. The EPR spectrum of all the glass samples exhibit three resonance signals at g=2.0, 3.3 and 4.3. The resonance signal at g=2.0 is attributed to the Mn2+ ions in an environment close to an octahedral symmetry. The resonance signals at g=3.3 and 4.3 have been attributed to the rhombic symmetry of the Mn2+ ions. The effect of temperature (123-433 K) and the composition dependence of EPR signals have been studied for Mn2+ ions in lithium lead tetraborate glasses. It is interesting to observe that the variation of paramagnetic susceptibility (chi) with temperature obeys Curie-Weiss law. From the slope of 1/chi versus T graph, the Curie constant (C) has been evaluated. The zero-field splitting (zfs) parameter D has been calculated for different alkali lead tetraborate glasses from the intensities of the allowed hyperfine lines. The optical absorption spectrum exhibits three bands. An intense and broad band at lower energy side has been assigned to the spin-allowed (5Eg-->5T2g) transition of Mn3+ ions in an octahedral symmetry. The intense and sharp band and a broad band at higher energy side have been assigned to charge transfer bands. A red shift is observed with increase of alkali ion size. The optical band gap energy (Eopt) decreases, whereas the Urbach energies (DeltaE) increases with increase of Mn content. The theoretical values of optical basicity (Lambdath) of the glasses have also been evaluated.     

Catalytic synthesis of low molecular weight polyethylene by S-bridged Ti-complexes

A series of novel titanium(IV) complexes with S-bridged biphenol such as 5-tert-butyl-4-hydroxy-2-methyl phenyl sulfide (BHMPS) have been synthesized. These catalytic precursors formulated as [R₃Ti (O^O) TiR₃]_n were found to be highly active in polymerization of ethylene at high temperatures and pressures in combination with ethyl aluminium sesquichloride (Et₃Al₂Cl₃) as co-catalyst. The polyethylene yields range from 250–1600 Kg PE/mmole catalyst. The GPC of polymers typically correspond to ultra low molecular weight polyethylene with narrow polydispersities     

Determination of rosuvastatin in the presence of its degradation products by a stability-indicating LC method

A forced degradation study was successfully applied for the development of a stability-indicating assay method for determination of rosuvastatin Ca in the presence of its degradation products. The method was developed and optimized by analyzing the forcefully degraded samples. Degradation of the drug was done at various pH values. Moreover, the drug was degraded under oxidative, photolytic, and thermal stress conditions. Mass balance between assay values of degraded samples and generated impurities was found to be satisfactory. The proposed method was able to resolve all of the possible degradation products formed during the stress study. The developed method was successfully applied for an accelerated stability study of the tablet formulation. The major impurities generated during the accelerated stability study of the tablet formulation were matches with those of the forced degradation study. The developed method was validated for determination of rosuvastatin Ca, and the method was found to be equally applicable to study the impurities formed during routine and forced degradation of rosuvastatin Ca.     

57Fe Mössbauer spectroscopy of banded iron formations from eastern India

Samples of the mosses Hylocomium splendens and Pleurozium schreberi, collected in the summer of 1998, were used to study the atmospheric deposition of heavy metals and other toxic elements in the Chelyabinsk Region situated in the South Urals, one of the most heavily polluted industrial areas of the Russian Federation. Samples of natural soils were collected simultaneously with moss at the same 30 sites in order to investigate surface accumulation of heavy metals and to examine the correlation of elements in moss and soil samples in order to separate contributions from atmospheric deposition and from soil minerals. A total of 38 elements (Na, Mg, Al, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, As, Se, Rb, Sr, Zr, Mo, Sb, Cs, Ba, La, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Yb, Hf, Ta, W, Au, Th, U) in soil and 33 elements Na, Mg, Al, Cl, K, Ca, Sc, V, Cr, Mn, Fe, Co, Ni, Zn, As, Se, Br, Rb, Ag, Sb, Cs, Ba, La, Ce, Sm, Tb, Yb, Hf, Ta, W, Au, Th, U) were determined by epithermal neutron activation analysis. The elements Cu, Cd and Pb (in moss samples only) were obtained by atomic absorption spectrometry. VARIMAX rotated principal component analysis was used to identify and characterize different pollution sources and to point out the most polluted areas.     

Solubility studies in formamide: III. Solubility product of silver bromate and standard electrode potential of silver—silver bromate electrode in formamide

The solubility and solubility product of silver bromate in formamide in sodium perchlorate solutions have been determined at 25, 30 and 35°C. At these temperatures, the solubilities in pure formamide are found to be 1.837 × 10^?2, 1.967 × 10^?2, and 2.092 × 10^?2 moll^?1, respectively, and the corresponding solubility products are 3.375 × 10^?4, 3.869 × 10^?4, and 4.377 × 10^?4 mol² l^?2. The standard potentials of the Ag(s)/AgBrO₃(s)/BrO^?₃ electrode have been calculated and found to be 0.4997, 0.4948, and 0.4892 V, at 25, 30, and 35°C, respectively. The mean activity coefficients of silver bromate at various rounded molarities of sodium perchlorate solutions, and the standard thermodynamic quantities for the process AgBrO₃(s) → Ag⁺(solvated) + BrO^?₃(solvated) have been calculated at these three temperatures and compared with those for the process AgIO₃(s) → Ag⁺(solvated) + IO^?₃(solvated) in formamide.     

Polymerization of acrylonitrile: Kinetics of the reaction initiated by the Fe2+/BrO3− redox system

The aqueous polymerization of acrylonitrile initiated by the bromate—ferrous redox system in aqueous sulfuric acid was studied under nitrogen atmosphere. The rate of polymerization increased with increasing concentration of ferrous in the range of 0.25-1 × 10^?2M. The percentage of conversion increased with increasing concentration of the catalyst, but beyond 2.5 × 10^?3M there was a decreasing trend in the rate of polymerization. The rate varied linearly with [monomer]. The initial rate of polymerization as well as the maximum conversion increased within the range of 1–2.5 × 10^?3M KBrO₃, but beyond 2.5 × 10^?3M the rate of polymerization decreased. The initial rate and limiting conversion increased with increasing polymerization temperature in the range 30–40°C; beyond 40°C they decreased. The effect of certain neutral salts, water-miscible solvents, complexing agents, and copper sulfate concentration on the rate of polymerization was investigated.     

Studies in sesquiterpenes—LV: Isolongifolene(part 6): Mechanism of rearrangement of longifolene to isolongifolene-I

The gross mechanism of rearrangement of longifolene to isolongifolene has been elucidated by using site-specifically labelled longifolene-4, 4, 5, 5-d₄ and shown to follow the pathway proposed by Berson et al., which involves an exo, exo Me shift, in preference to the endo, endo Me migration route proposed earlier. An efficient synthesis of longifolene-4, 4, 5, 5-d₄, the key compound in the present investigation, is described.