Systematic studies on adsorption of lead on sea nodule residues

Lead adsorption from aqueous solutions was studied with the aim of detoxifying industrial effluents before their safe disposal onto land or into river waters. Sea nodule residue (SNR), a waste material containing oxides and oxyhydroxides of manganese, iron, silicon, etc., was used as an effective adsorbent for lead in this study. The effect of various parameters such as contact time, initial lead concentration, pulp density, particle size of the adsorbent, pH, and temperature was studied to optimize the conditions for maximum adsorption. Adsorption followed first-order kinetics and 99% of lead adsorption was achieved at a solid:liquid ratio of 1:330, in the pH range 5.5-6.0 at a particle size of -150 microm in 8 h for solution containing 200 ppm lead. The adsorption capacity was found to be 99.0 mg of lead per gram of SNR and the adsorption isotherms followed the Langmuir and Freundlich adsorption models. The mechanism of adsorption of lead onto the sea nodule residue was also investigated. It was possible to reduce the lead level from 25-200 ppm to acceptable levels (0.1 ppm) by adsorption over this solid waste.     

Thin Layer Chromatography of Purines on Silica Gel G Impregnated with Transition Metal Ions; Assay of Caffeine and Theophylline in Pharmaceutical Formulations

This study was undertaken to develop thin layers of silica gel G impregnated with transition metal ions for separation, identification and estimation of purines. The influence of transition metal ions and eluting solvents on chromatographic behaviour (hR_f) has been studied. The method was applied for qualitative analysis of purines in the mixtures and quantitative analysis of purine bases in the mixture as well as in pharmaceutical formulations. The results were compared statistically with those obtained by official methods. The method is simple, reproducible, and accurate within 1.3 ± 0.6%.     

Gas chromatographic determination of nitrite in water by precolumn formation of 2-phenylphenol with flame ionization detection

Nitrite can be determined by its reaction with 2-aminobiphenyl in acidic medium to produce 2-phenylphenol which is quantified by gas chromatography with flame ionisation detection using biphenyl as an internal standard. The hydrolysis of the intermediate diazonium ion avoids many of the problems encountered in the conventional determination of nitrite by the diazotization of an aromatic amine (usually sulphanilamide) and coupling with N-(1-napthyl)ethylenediamine dihydrochloride to yield an azo dye followed by spectrophotometry. Unlike this method, the proposed reaction is rapid and does not suffer from interferences by copper(II), iron(III) and lead(II). The calibration graph was linear over the range 5–1000 μg/l NO₂-N and the limit of detection found to be 0.5 μg/l NO₂-N. A single analysis can be completed within 20 min. The method was not affected by coloured or turbid analyte solutions and has been used to determine nitrite in natural waters.     

Determination of nitrate in environmental water samples by conversion into nitrophenols and solid phase extraction−spectrophotometry, liquid chromatography or gas chromatography-mass spectrometry

Conversion of nitrate into a nitro-phenol derivative by reaction with 2-methylphenol or 2,6-dimethylphenol allowed at least 100-fold enrichment of the derivative on Lichrolut EN polymeric cartridge, and it is stable for up to 1 month on the cartridge. The derivative could be eluted with ammonia-methanol mixture. This reaction for nitrate determination has permitted a choice of final measurement by UV-Vis spectrophotometry, liquid chromatography or gas chromatography-mass spectrometry when the limits of detection were 10, 6 and 3 μg l⁻¹, respectively, and the calibration range 20 μg to 10 mg l⁻¹ nitrate. The method has been validated by spiking natural water samples, when the recovery of nitrate was 98.5-108.4% (relative standard deviation 2.5-6.1%).     

Theoretical studies of some nonbenzenoid hydrocarbons—IV : Pleiadiene and related compounds

Pleiadiene and other similar compounds have been studied by the semi-empirical SCFMO method of Pariser, Parr and Pople using the core resonance integral value developed by Lo and Whitehead, Dewar et al. and Yamaguchi et al. It has been found that π^*←π transitions predicted by the methods of Lo and Whiteheadand Dewar et al. suitable for the prediction of ground state properties are also in good agreement with experimental results where available and comparable to those predicted by the method of Yamaguchi et al. developed for the prediction of spectral transitions. The resonance stabilization of the molecules 3,4.5,7,8 and 9 have also been studied. It is found that ethylinic linkage across the naphthalene moity in pleiadiene increases the resonance energy of the final compound, in contrast to our previous observation, i.e. ethylinic linkage across the naphthalene moiety reduces the resonance energy of the final compound.     

Coordination complexes of PdII with benzothiazolines

Summary Some new Pd^II complexes have been synthesized by reacting PdCl₂ with monofunctional bidentate Schiff bases (condensation product of furfuraldehyde, pyridine-2-aldehyde and thiophene-2-aldehyde witho-amino-thiophenol) in different molar ratios. The i.r. and n.m.r. spectra reveal that the nitrogen of azomethine and sulphur of thiol are coordinating sites. Electronic spectral data suggests square planar geometry for these complexes.     

Mechanochemical Synthesis and Reactivity of a Stable Nickel Borohydride

We report the solvent-assisted mechanochemically synthesised mononuclear Ni(II) borohydride complex supported by a macrocyclic tetradentate ligand. It was characterised as stable high-spin [(L^Me)Ni(η²-BH₄)]⁺ cation in solid-state and in solution by various physicochemical methods and capable of transferring hydride. The stoichiometric reactivity of [(L^Me)Ni(η²-BH₄)]⁺ cation was examined with trityl cation, alkyl halide, disulphide, thiol, carboxylic acid and enol at room temperature.     

Efficient Hydroboration of Esters and Nitriles Using a Quinazolinone-Supported Titanium(IV) Multitasking Catalyst

We report catalytic hydroboration of esters as well as nitriles under solvent-free and mild conditions using single titanium(IV) metal complex, [{κ²-C₆H₄C(O)N(ⁱPr)C(N-ⁱPr)=N}{κ³-(ⁱPr)N=C(O)−C₆H₄−NC(NMe₂)N(ⁱPr)}TiNMe₂] 1 as a sustainable, economical, and efficient pre-catalyst. The molecular structure of the Ti^IV complex in the solid state reveals the unique coordination of Ti^IV metal with N, N, and O atoms of one quinazolinone unit via in-situ rearrangement, while another quinazolinone moiety coordinates in bidentate fashion via both N atoms only. The Ti^IV complex demonstrates excellent activity as a pre-catalyst towards the hydroboration of a wide array of esters and nitriles with pinacolborane (HBpin) to afford alkoxyboranes and diboryl amines in high yield (up to 99 %) with greater tolerance to a variety of electron-withdrawing and electron-donating functional groups. A most plausible mechanism of hydroboration of esters is also proposed based on kinetics and NMR studies, which suggests the formation of titanium-hydride species as an active catalyst.