An Efficient Procedure for the Synthesis of Spiro (3H-Indole-3,4′ (1′H)pyrano[2,3-C]pyrrole]-5′-carbonitriles Using Solid Inorganic Supports and Microwave Activation

Microwave irradiation accelerates the Michael condensation of 3-dicyanomethylene-2H-indole-2-one with 2-pyrrolidone/ N-methy1-2-pyrrolidone (i) adsorbed on neutral alumina in “dry media” (ii) using absolute ethanol as energy transfer medium. 3-Dicyanoniethylene-2H-indol-2-one was synthesized under microwave irradiation using indole-2,3-dione and malononitrile. The results were compared with those obtained following the classical method. The advantages obtained by the use of microwave irradiation are demonstrated.     

Herringbone and Helical Self‐Assembly of π‐Conjugated Molecules in the Solid State through CH/π Hydrogen Bonds

Self‐organization of organic molecules through weak noncovalent forces such as CH/π interactions and creation of large hierarchical supramolecular structures in the solid state are at the very early stage of research. The present study reports direct evidence for CH/π interaction driven hierarchical self‐assembly in π‐conjugated molecules based on custom‐designed oligophenylenevinylenes (OPVs) whose structures differ only in the number of carbon atoms in the tails. Single‐crystal X‐ray structures were resolved for these OPV synthons and the existence of long‐range multiple‐arm CH/π interactions was revealed in the crystal lattices. Alignment of these π‐conjugated OPVs in the solid state was found to be crucial in producing either right‐handed herringbone packing in the crystal or left‐handed helices in the liquid‐crystalline mesophase. Pitch‐ and roll‐angle displacements of OPV chromophores were determined to trace the effect of the molecular inclination on the ordering of hierarchical structures. Furthermore, circular dichroism studies on the OPVs were carried out in the aligned helical structures to prove the existence of molecular self‐assembly. Thus, the present strategy opens up new approaches in supramolecular chemistry based on weak CH/π hydrogen bonding, more specifically in π‐conjugated materials.     

Evaluation of kinetic parameters for oxidation of thioacids by benzimidazolium dichromate: A mechanistic study

In a non-aqueous medium, oxidation kinetics of thioglycolic, thiolactic and thiomalic acids by benzimidazolium dichromate have been studied. In the temperature range of 20°C–50°C, oxidation kinetics were examined by spectrophotometry. In terms of oxidant, the reaction is dependent on the unitary order. In the case of thioacids, we find the Michaelis-Menten type kinetics. Hydrogen-ions act as catalyst in this process. The reaction rate slows down as the Mn²⁺ ion concentration increases. The reaction does not cause acrylonitrile to polymerize. The formation of a thioester into the pre-equilibrium followed by its progressive degradation was postulated as a mechanism.     

Diazotized reagent for spectrophotometric determination of glyphosate pesticide in environmental and agricultural samples

A new sensitive spectrophotometric method for the determination of glyphosate herbicide in environmental and agricultural samples is developed. The reaction is based on diazotization followed by coupling of glyphosate with p-dimethyl amino benzaldehyde. The resulted complex absorption spectra was observed at λ_max = 420 nm. The effects of other metal ions and pesticides were also tested for selective determination of glyphosate. The analytical parameters were optimized and have been successfully applied for determination of glyphosate in various environmental samples such as soil, water and vegetables. This method has a lower limit detection of 6 μg of glyphosate. Beer's law is obeyed over the concentration range of 6.0 μg–24.0 μg glyphosate in 25 mL of the final solution at 420 nm. The standard deviation and relative standard deviation calculated are 0.0055 and 1.023, respectively. The molar absorptivity of the colored system is 1.91 × 10¹⁰ L mol^?1cm^?1 and Sandell's sensitivity is found 0.408 × 10^?5 μg cm^?2. The proposed method is simple, sensitive, highly reproducible and time saving as compare to those complicated time consuming methods.     

Nanocomposite interface coupled with thickness optimization promoting water dissociation in heterogeneous bipolar membrane

Bipolar membranes (BPMs) are multilayered composite film containing an interface layer sandwiched between cation exchange layer (CEL) and anion exchange layer (AEL), and are capable of dissociating water molecules under reverse bias potential. Woven fabric supported heterogeneous bipolar membranes (HBMs) were synthesized adopting layer-by-layer solvent casting technique. Nanocomposite layer based on sulfonated polyether ether ketone (SPEEK) and GO (graphene oxide) were applied at the interface of CEL/AEL made of cation/anion exchange resins and poly (vinyl chloride) as binder to advance water dissociation in HBMs. Thickness of monopolar layers were initially optimized without any interfacial layer. Introduction of SPEEK interface substantially lowered onset water dissociation potential, U_diss (~1.87 V) relative to the HBM without interface (~3.27 V), which got further reduced (~1.80 V) by nanocomposite (GO + SPEEK) interface. U_diss recorded with SPEEK + GO as interface was much lower than some of the recently reported homogeneous BPM. The NaOH production from NaCl (1.0 mol?L^?1) solution in a bipolar membrane electrodialysis set up containing synthesized HBM with nanocomposite interface (SPEEK + GO) was double than that of NaOH concentration obtained with HBM having no interface, where the current density was fixed at 50.0 mA·cm^?2. Careful optimization of monopolar/interface layer thickness and composition of nanocomposite interface results in developing cost effective HBMs facilitating water dissociation at lower potential.     

Synthesis and X-ray structural studies of pyrimidin-2,4-dione and 2-thioxo-1H-pyrimidin-4-one bearing chloroethyl moiety

The present work is aimed to investigate non-covalent bonding capabilities of uracil derivative bearing hydrophobic side chain in solid crystalline state. The synthesis and crystal structure of 5-(2-chloro-ethyl)-6-methyl-uracil 3 and 5-(2-chloro-ethyl)-6-methyl-2-thiouracil 4 are described, which revealed sulfur-π interaction including resonance-induced intermolecular H-bonding in 4 whereas compound 3 showed only strong H-bonding and formed a dimer. Thus the analysis of such moieties in solid state provides useful structural information on the binding characteristics of functional groups and has implications for the de novo design of drugs and enzyme's inhibitors.     

EPR evidence for a single electron transfer mechanism in reactions of aromatic ketones with lithium amides

Direct spectroscopic evidence (EPR) supporting a single electron transfer mechanism in the reaction of lithium amides with aromatic ketones is presented.     

One-pot regioselective synthesis of dihydronaphthofurans and dibenzofurans

A regioselective approach for the synthesis of substituted naphthofurans and dibenzofurans has been demonstrated through a ring transformation reaction of suitably functionalized 2H-pyran-2-ones by reaction with 6,7-dihydro-5H-benzofuran-4-one and 7-methoxybenzofuran-3-one, respectively, in high yields. The novelty of the procedure lies in the creation of an aromatic ring transformed by 2H-pyran-2-one involving the -COCH₂- moiety of a cyclic ketone.     

IR and thermal studies on a new oxomolybdenum(VI) oxalato complex

A new molybdenum(VI) oxalato complex K₄(NH₄)₁₀[Mo₁₄O₄₂(C₂O₄)₇] (PAMO) was prepared and characterized by chemical analysis, IR spectral and X-ray studies. Its thermal decomposition was studied using TG, DTA and DTG techniques. The compound is anhydrous and decomposes between 235° and 335°C in three steps. The first and the second steps occur in the temperature ranges 235°–290°C and 290–310°C to give the intermediate compounds having the tentative compositions K₄(NH₄)₈[Mo₁₄O₄₂(C₂O₄)₆] and K₂(NH₄)₂[Mo₁₄O₄₂(C₂O₄)₃], respectively, the later than decomposing to give a mixture of potassium tetramolybdate and molybdenum trioxide at 335°C. DTA also shows a peak at 530°C which corresponds to the melting of potassium tetramolybdate. An examination of the products obtained at 340° and 535°C by chemical analysis, IR spectra and X-ray studies reveals them to be identical.The authors are grateful to Dr. M. C. Jain, Head of the Department of Chemistry, for providing research facilities.     

Metal derivatives of amidoximes I. Mono-, bis- and tris-(trimethylsilyl)amidoximes

The preparation and properties of mono-, bis- and tris-(trimethylsilyl)amidoximes are described.