Kinetic studies on saponification of ethyl acetate using an innovative conductivity‐monitoring instrument with a pulsating sensor

An innovative conductometric measurement technique using a nonconventional but high‐performance (high‐precision, high‐resolution, rapid response features for online graphic display) in house–built pulsating conductivity monitoring instrument has been deployed to study the kinetic behavior during the reaction of ethyl acetate and NaOH. A laboratory‐made constant temperature reaction bath with the facility of continuous stirring of solution for homogeneous mixing was used to carry out experiments at desired solution temperatures. Rate constants of the saponification reaction in the temperature range at various temperatures (30–55°C) were determined, and the results were compared with the reported values. Although the reported data exhibit wide scatter, our data are in agreement with some of the literature data. From these data, thermodynamic parameters such as activation energy, activation enthalpy, activation entropy, and activation free energy have been evaluated. With the introduction of this novel conductometric measurement technique, the determination of rate constants at various solution temperatures becomes much simpler and faster. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 648–656, 2011     

A new Cu(II) three-dimensional network with 4,4′-oxybis benzoic acid: structural diversity,EPR, and magnetism

The copper derivative {[Cu₄(oba)₄(H₂O)₄]?H₂O}_n (1) has been hydro(solvo)thermally synthesized by combining flexible 4,4′-oxybis benzoic acid (oba) and divalent copper nitrate. As a result of the potential coordination modes of carboxylate oxygens from the oba ligand, the aforementioned complex leads to the formation of an interesting 3D framework, as evidenced by single-crystal X-ray diffractometry. Concerning the topology in 1, the dimers [Cu₂C₄O₈] are nodes of a 5-fold 4-connected uninodal net of the type lvt, with point symbol {4².8⁴} and vertex symbol [4.4.8₄.8₄.8₈.8₈]. The encapsulation of the copper coordination polymer displays a moderate luminescent property. On temperature-dependent magnetic study, it reveals that the magnetic behaviour of 1 can be associated to a strong antiferromagnetic coupling between the two Cu(II) ions.     

Studies on oscillating chemical reaction in Cu(II)‐catalyzed thiocyanate–hydrogen peroxide–NaOH system using pulsating sensor

We present a novel measurement technique to study an oscillating chemical reaction using a new class of sensor, viz. a pulsating sensor developed in‐house. A halogen‐free oscillating chemical reaction in the Cu(II)‐catalyzed H₂O₂‐KSCN–NaOH system reported by Orban was chosen to examine the performance of this technique. Shift in potential during the oscillating reaction was captured online with high precision and excellent resolution using this simple but high‐performance pulsating potentiometric measurement technique. In this work, the influence of bath temperature and flow rate of reagents on the Cu(II)‐catalyzed H₂O₂–KSCN–NaOH oscillating chemical reaction is investigated to optimize the conditions for rapid oscillations. This, in turn, helps to evolve analyte pulse perturbation techniques for rapid assay of hydrazine, uranium(VI), and sodium thiosulfate in aqueous solutions using the above oscillating reaction. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 19–29, 2013     

Structural Aspects and Spectroscopic Characterization of a Mn(II) Complex with Unsymmetrical NNO-Donor Hydrazone Ligand

Abstract  

The manganese(II) complex, Mn[C₅H₄N–C(CH₃)=N–N=C(O)–C₆H₅]₂ (1) containing N,N,O-donor hydrazone ligand is characterized by X-ray diffraction study. The ligand is the 1:1 condensation product of benzhydrazide and 2-acetylpyridine. The spectral, cyclic voltammetric and room-temperature magnetic moment data are used to establish structure and electronic structure of the compound. Structural investigation shows that 1 crystallizes to a monoclinic system, space group C2/c, a = 22.8367(13), b = 10.1523(6), c = 12.0736(7) Å, α = γ = 90°, β = 116.5930(10)°, and Z = 4. The central manganese atom is in an N₄O₂ coordination sphere constituted by the NNO donor sets of the two independently hydrazone ligands. The Mn–N1, Mn–N2 and Mn–O1 bond distances are 2.3255(15), 2.1854(13) and 2.1361(13) Å, respectively. The effective magnetic moment (μ_eff) value of 1 is found to be 5.92 B.M. at 300 K. Cyclic voltammetry shows Mn(III)/Mn(II) couple at 0.9 V and imine reductions at −0.68 and at −1.3 V.     

Effect of hetero atom on the conformational stability of the forming ring in the transition structures of Type-II ene cyclization: a theoretical study

The chair conformation of the forming ring in the transition structure, for its high stability, is usually considered for the determination of the overall stereoselectivity in a type-II ene cyclization reaction. However, present theoretical investigation reveals that the presence of a heteroatom like oxygen or nitrogen in the tether of type-II carbonyl ene cyclization stabilizes the transition structure, in which the forming ring adopts a boat conformation. Due to such stability of the boat conformer the overall stereoselectivity of some type-II reactions may differ from the expected one.     

Comparative study on the transition structures of (3,4) and (3,5) ene cyclizations: A theoretical approach

Possible transition structures (TSs) of (3,4) and (3,5) ene cyclizations of 7-methyl-1,6-octadiene and 7-methylocta-1,6-dien-3-one were constructed and optimized by DFT method. Product proportions were calculated using the relative energies of the transition structures and these results are found to be in good agreement with the experimental one. Variation of the product proportions was explained using some model TSs of intermolecular ene reactions. The change of the dihedral angle around the forming carbon–carbon bond in the model transition structures was found to play a crucial role in determining the overall selectivities of cyclized products.     

Effect of the heteroatomic substituent on the pi-facial diastereoselectivity in Lewis acid catalyzed carbonyl ene reaction: A theoretical study

Quantum chemical investigation on the optimized transition structures of intermolecular ene reaction containing various heteroatomic substituents at the -carbon atom reveal that, the electrostatic effect produced by the ene moiety plays a crucial role in controlling the conformation of the transition structure. The stereoselectivity calculated from the proposed model agreed nicely with the reported experimental results.     

End-to-End Thiocyanato-Bridged Helical Chain Polymer and Dichlorido-Bridged Copper(II) Complexes with a Hydrazone Ligand: Synthesis,Characterisation by Electron Paramagnetic Resonance and Variable-Temperature Magnetic Studies,and Inhibitory Effects on Human Colorectal Carcinoma Cells

The reactions of the tridentate hydrazone ligand, N′-[1-(pyridin-2-yl)ethylidene]acetohydrazide (HL), obtained by condensation of 2-acetylpyridine with acetic hyadrazide, with copper nitrate trihydrate in the presence of thiocyanate, or with CuCl₂ produce two distinct coordination compounds, namely a one-dimensional helical coordination chain of [CuL(NCS)]_n (1) units, and a doubly chlorido-bridged dinuclear complex [Cu₂L₂Cl₂] (2) (where L=CH₃C(O)=N–N=CCH₃C₅H₄N). Single-crystal X-ray structural determination studies reveal that in complex 1, a deprotonated hydrazone ligand L⁻ coordinates a copper(II) ion that is bridged to two neighbouring metal centres by SCN⁻ anions, generating a one-dimensional helical coordination chain. In complex 2, two symmetry-related, adjacent copper(II) coordination entities are doubly chlorido-bridged, producing a dicopper entity with a Cu⋅⋅⋅Cu distance of 3.402 (1) Å. The two coordination compounds have been fully characterised by elemental analysis, spectroscopic techniques including IR, UV–vis and electron paramagnetic resonance, and variable-temperature magnetic studies. The biological effects of 1 and 2 on the viability of human colorectal carcinoma cells (COLO-205 and HT-29) were evaluated using an MTT assay, and the results indicate that these complexes induce a decrease in cell-population growth of human colorectal carcinoma cells with apoptosis.     

Hetero-aromatic N-base-promoted oxidation of 4-chlorobenzyl alcohol by Cr(VI) in micellar media

Research on Chemical Intermediates - A little attempt has been made to get in touch with the green chemistry studying the successful occurrence of oxidation of 4-chlorobenzyl alcohol to...     

Structural aspects of a trimetallic CuII derivative: cytotoxicity and anti-proliferative activity on human cancer cell lines

A trimetallic Cu^II derivative, [Cu₃(L)₂(CF₃COO)₂] (1) (where H₂L = N,N′-bis(salicylidene)-1,3-propanediamine), was prepared and characterized. In 1, the two terminal Cu^II ions are linked to the central Cu^II by trifluoroacetato and doubly bridging phenoxido. Both the square-pyramidal and octahedral geometries are observed among two different Cu^II centers in the linear arrangement of the trimetallic unit. Compound 1 is characterized by IR and UV-Vis spectra. Compound 1 has high cytotoxic activity in breast adenocarcinoma (MCF-7), colorectal carcinoma (HCT116) and particularly, in ovarian carcinoma (A2780) cell line compared to a lung adenocarcinoma cell line. The IC₅₀ in A2780 cells is 25 times lower than the respective value for normal human primary fibroblasts demonstrating 1 has higher cytotoxicity towards cancer cells. Additionally, combination of DOX with 1 induces a higher loss of HCT116 cell viability compared with each drug alone.