Reactions of 2,4,6-tripyridyl-1,3,5-s-triazine and its Fe(ii) complex with OH· and eaq-

Summary Pulse radiolysis studies indicated that OH^· and e_aq^- formed adducts with 2,4,6-tripyridyl-1,3,5-s-triazine (tptz). The OH-adduct showed an absorption maximum at 290 nm, while the adduct formed from the attack of e_aq^- and subsequent protonation of the anion, has an absorption maximum at 300 nm. In case of the complex, Fe(tptz)₂²⁺, both OH^· and e_aq^- gave ligand centered adducts. All the adducts decayed by second order dimerization or disproportionation, a disproportionation reaction in case of the complex.     

Spectrophotometric determination of rhenium using 2-pyridyl thiourea

The reagent 2-pyridyl thiourea produces a reddish brown complex with rhenium in hydrochloric acid medium in the presence of tin(II) chloride. The complex shows absorption maxima at 405 nm, obeys Beer's law for a range of 1–16 ppm of rhenium. The sensitivity and molar absorptivity is found to be 0.0115g cm^–2 and 1.603×10⁴ 1 mol^–1 cm^–1 respectively showing an improvement over other sulphur-nitrogen bearing ligands. Composition found by Job's and mole ratio method, indicates that the complex contains metal and reagent in the ratio 12. Stability constant and stepwise formation constants of the complex have been evaluated by Harvey-Manning's method (logK _overall=8.825), Leden's method (logK _overall=8.3096), Rossotti-Rossotti's method (logK _overall=8.653) and Yatsimirskii's method (logK _overall=8.740). The relative error per 1% absolute photometric error is found to be 2.7%.     

Oxidation of ketones by cerium(IV) in presence of iridium(III) chloride

Kinetic data, in iridium(III) chloride catalyzed oxidation of ethyl methyl ketone (EMK) and methyl propyl ketone (MPK) by cerium(IV) perchlorate in aqueous perchloric acid medium, suggest the formation of complex C₁ between cerium(IV) and organic substrate in the first equilibrium step, which in turn gives rise to another complex C₂ with the catalyst. This second complex in the rate-determining step gives rise to the intermediate products. Interestingly IrCl_3, which is considered to be a sluggish catalyst in alkaline media, was found to surpass the catalytic efficiency of even osmium and ruthenium in acidic media. Rate decreases in the beginning at low acid concentrations, but after reaching to a minimum it becomes directly proportional to acid concentrations. Probably on increasing the acid concentrations hydrolyzed species of ceric perchlorate gradually converts into the un-hydrolyzed species, which then accelerates the rate at higher [H⁺], resulting in the observed peculiar effect of hydrogen ions on the rate. Initial concentrations of cerium(IV) and acid determine the extent of reduction of cerium(IV) by water. Order of the reaction shows direct proportionality with respect to the oxidant and ketones at their low concentrations, but tends to become zeroth order at their higher concentrations. Rate of the reaction shows direct proportionality with respect to [IrCl₃] while change in ionic strength of the medium does not affect the reaction velocity. Parameters such as the energy of activation, free energy of activation and entropy data suggest that methyl propyl ketone forms the activated complex more easily compared to ethyl methyl ketone.     

Tandem one-pot intra- and inter-molecular McMurry coupling for the synthesis of bisindolostilbenophanes

Treatment of 3 equiv of indole-3-aldehyde with 1,3,5-trimethyl-2,4,6-tris(bromomethyl)benzene and 1,3,5-tris(bromomethyl)benzene gave the tris-alkylated products, which underwent both intra- and inter-molecular McMurry coupling in one-pot with low valent titanium to give indole-based stilbenophanes.     

Some new aromatic hydroxylamines as spectrophotometric reagents for vanadium

A comparative study is described of the use of N-benzoyi-o-tolyl-, N-benzoyl-m-tolyl, N-benzoyl-p-tolyl-, N-benzoyl-p-chlorophenyl- and N-phenylacetylphenyl-hydroxylamines, as spectrophotometric reagents for the determination of vanadium, after extraction with chloroform. All the reagents form 1:2 (metal:reagent) complexes in hydrochloric acid media or at pH 4.8–6.0; the dissociation constants of the complexes are of the order of 10^-9 and 10^-8, respectively, except those of N-benzoyl-p-chloro-phenylhydroxylamine which are of the order of 10^-8 in both media. The reactions in hydrochloric acid media are more selective and sensitive than those at pH 4.8–6.0. In presence of alcohol, the wavelengths of maximum absorption decrease. The pK_a values of the hydroxylamines were determined in water and in alcohol-water (1:1) solutions.     

Simultaneous LC Estimation of Glimepiride and Metformin in Glimepiride Immediate Release and Metformin Sustained Release Tablets

In the present study, a simple, rapid and precise liquid chromatographic method was developed and validated for the simultaneous determination of glimepiride and metformin in sustained release formulation. The separation was achieved on a Nucleosil 100-5SA column, 250 × 4.6 mm i.d., 5 μm using a mobile phase composed of 1.7 % ammonium dihydrogen phosphate buffer pH 3.0: acetonitrile (70:30 v/v).The instrumental settings were a flow rate of 1.0 ml min^?1 and a detector wavelength of 230 nm. The retention time of glimepiride and metformin were 5.1 and 11.3, respectively. The developed method was validated in terms of specificity, sensitivity, linearity, range, accuracy, precision and ruggedness. The proposed method was successfully applied to the sustained release pharmaceutical dosage form for the simultaneous determination of glimepiride and metformin without any interference by excipients.     

Cascade synthesis of dihydrobenzofuran via Claisen rearrangement of allyl aryl ethers using FeCl3/MCM-41 catalyst

Dihydrobenzofuran as one of the active ingredients of the naturally occurring motif is synthesized by using in situ generation of ortho allyl phenols. Aryl allyl ethers on reacting with catalytic amounts of non noble metal iron (III) chloride supported on MCM-41 under moderate reaction conditions yield dihydrobenzofuran. First step via Claisen rearrangement gives ortho allyl phenol followed by its in situ cyclization to yield dihydrobenzofuran in very good yields. Both Lewis as well as Brønsted acidity of the catalyst as evidenced by Py-FTIR studies was found to catalyze the cascade synthesis of dihydrobenzofuran. The scope of the present strategy was successfully demonstrated for several substrates with varying electronic effects for the synthesis of corresponding dihydrobenzofuran with high yields in a range of 71–86%.     

Acetanilide palladacycle: an efficient catalyst for room‐temperature Suzuki–Miyaura cross‐coupling reaction

The catalytic activity of three acetanilide palladacycles derived from easily accessible and commercially available acetanilide derivatives, viz. N‐phenylacetamide ( L1 ), N‐(4‐chlorophenyl)acetamide ( L2 ) and N‐(4‐methylphenyl)acetamide ( L3 ) has been examined in Pd‐catalyzed Suzuki–Miyaura reaction of arylboronic acid with aryl bromides at room temperature. The complex 1L3 exhibited efficient activity in the Suzuki–Miyaura reaction (up to 99% isolated yield) under mild reaction conditions. Copyright © 2014 John Wiley & Sons, Ltd.     

Alcoholic solvent‐assisted ligand‐free room temperature Suzuki–Miyaura cross‐coupling reaction

We have observed the enhancing effect of alcoholic solvents in palladium‐catalysed ligand‐free Suzuki–Miyaura reactions. No extra additives or ligands are required for the Suzuki–Miyaura reaction of aryl bromides with arylboronic acids when we carried out the reaction in alcoholic or aqueous alcoholic solvents. Moreover, ethanol or aqueous ethanol is found to be a very good solvent for the Suzuki–Miyaura reaction involving electronically diverse aryl bromides and arylboronic acids under mild and ligand‐free conditions with low catalyst loading. It is observed from Hg(0) poisoning tests that the in situ generated palladium(0) species is the actual catalytic species for the reaction. Copyright © 2015 John Wiley & Sons, Ltd.