Synthesis of N-alkylimidazolium salts and their utility as solvents in the Beckmann rearrangement

Six different room temperature ionic liquids (RTILs) based on N-methyl or N-isopropyl imidazolium cations with counteranions, such as , , and OTf⁻, have been synthesized by exchanging the counteranions of the corresponding N-methyl or N-isopropylimidazolium bromides using appropriate salts such as NH₄BF₄, KPF₆, and AgOTf. Catalytic amounts of these ionic liquids (ILs) have been used as the reaction medium for the Beckmann rearrangement of oximes to amides in the presence of PCl₅. A moderate to good conversion of oximes to amides in all the six ILs was observed.     

Spectroscopic and spectrofluorimetric studies on the interaction of irbesartan with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and iodine

Raman, UV-vis, 1H NMR, FT-IR, mass and fluorescence spectral techniques were employed to investigate the mechanism of interaction of irbesartan (IRB) drug with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and iodine. Interaction of IRB with iodine yields triiodide ion and its formation was confirmed by electronic and Raman spectra. The peaks appeared in Raman spectrum of the isolated product at 143, 113 and 76 cm(-1) are assigned to νas(I-I), νs(I-I) and δ(I3-) respectively, confirmed the presence of I3- ion. The interaction of DDQ with irbesartan was found to proceed through the formation of outer complex and its conversion to the CT complex. Formation constant (K), molar extinction coefficient (?) and thermodynamic properties ΔH#, ΔS# and ΔG# were determined and discussed. Fluorescence quenching studies indicated that the interaction between the IRB and the acceptors are spontaneous and the IRB-DDQ interaction is found to be stronger than that the other system. Solvent variation studies indicated that the binding constant increased with an increase in polarity of the medium.     

Metal-Free,One-Pot,Rapid Synthesis of Tetrahydropyridines Using Acetic Acid as Solvent and Catalyst at Room Temperature

Acetic acid–promoted, one-pot synthesis of tetrahydropyridines has been developed under metal-catalyst-free conditions via a tandem reaction. High atom economy, good yield, simple procedure, no expensive column chromatography, shorter reaction time, and metal-free and mild reaction conditions are some of the important features of this protocol. The current methodology provides an alternative approach for not only highly substituted tetrahydropyridines (THPs) but also fully substituted tetrahydropyridines (FTHPs) in moderate to good yields. The plausible mechanism for the formation of THPs was greatly promoted by the H⁺ ion coming from acetic acid.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]     

Spectroscopic and kinetic studies on the interaction of ketoconazole and povidone drugs with DDQ

The kinetics and mechanism of the interaction between 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and ketoconazole and povidone drugs has been investigated spectroscopically. In the presence of large excess of donor, the 1:1 CT complex is transformed into a final product, which has been isolated and characterized by FT-IR and GC-MS techniques. The rate of formation of product has been measured as a function of time in different solvents at three temperatures. The thermodynamic parameters, viz. activation energy, enthalpy, entropy and free energy of activation were computed from temperature dependence of rate constants. Based on the spectro-kinetic results a plausible mechanism for the formation of the complex and its transformation into final product is presented and discussed.     

Hydrogen peroxide clusters: the role of open book motif in cage and helical structures

Hartree-Fock (HF) calculations using 6-31G*, 6-311++G(d,p), aug-cc-pVDZ, and aug-cc-pVTZ basis sets show that hydrogen peroxide molecular clusters tend to form hydrogen-bonded cyclic and cage structures along the lines expected of a molecule which can act as a proton donor as well as an acceptor. These results are reiterated by density functional theoretic (DFT) calculations with B3LYP parametrization and also by second-order M?ller-Plesset perturbation (MP2) theory using 6-31G* and 6-311++G(d,p) basis sets. Trends in stabilization energies and geometrical parameters obtained at the HF level using 6-311++G(d,p), aug-cc-pVDZ, and aug-cc-pVTZ basis sets are similar to those obtained from HF/6-31G* calculation. In addition, the HF calculations suggest the formation of stable helical structures for larger clusters, provided the neighbors form an open book structure.     

Preferential solvational effects on the Cr(VI) oxidation of benzylamines in benzene/2‐methylpropan‐2‐ol mixtures

Imidazolium fluorochromate (IFC) oxidation of 11 meta‐ and para‐substituted benzylamines, in varying mole fractions of benzene/2‐methylpropan‐2‐ol binary mixtures, is first order in IFC and acid and zero order in substrate. The Hammett correlation yielded a U‐shaped curve, indicating a change in the relative importance of bond formation and bond fission in the transition state. The rate data failed to correlate with macroscopic solvent parameters such as ε_r and E. The correlation of k_obs with Kamlet–Taft solvatochromic parameters suggests that H‐bonding between the reacting species and the solvent plays a major role in governing the reactivity. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 159–167, 2010     

ChemInform Abstract: Structure and Stability of Water Chains (H2O)n,n = 5—20

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