Recyclable clay supported Cu (II) catalyzed tandem one-pot synthesis of 1-aryl-1,2,3-triazoles

Montmorillonite KSF clay supported CuO nanoparticles efficiently catalyzes one-pot aromatic azidonation of aryl boronic acids followed by regioselective azide–alkyne 1,3-dipolar cycloaddition (CuAAC) reaction producing corresponding 1-aryl-1,2,3-triazole derivatives at room temperature in excellent yields without use of any additives. Investigations on mechanism of CuAAC revealed that sodium azide, which is used as azidonating reagent in one-pot protocol reduces Cu(II) to click-active Cu(I). The catalytic efficiency of another Cu(II) source CuSO₄ in combination with NaN₃ for this one-pot CuAAC protocol, further supported our mechanism. This is the first report for use of Cu(II)/NaN₃ catalytic system for CuAAC protocol. The clay–Cu(II) catalyst being ligand-free, leaching-free, easy to synthesize from inexpensive commercially available precursors, recyclable, and environmentally friendly will be highly useful for economical synthesis of 1,4-disubstituted 1,2,3-triazoles.     

Stereoselective synthesis of methyl branched chiral deoxypropionate units: a new route for synthesis of insect pheromone (−)-lardolure and (2R,4R,6R,8R) 2,4,6,8-tetramethylundecanoic acid

(−)-Lardolure and (2R,4R,6R,8R)-2,4,6,8-tetramethylundecanoic acid have been synthesized via lipase catalyzed desymmetrization strategy to create two methyl chiral centers. Other key steps involved in the synthesis are Wittig reaction, Evan’s asymmetric alkylation, Grignard reaction, Pd-catalyzed isomerization of primary allylic alcohol to corresponding saturated aldehyde, and PhNO/proline catalyzed MacMillan α-hydroxylation.     

Synthesis of optically active seven-membered 1,5-anhydrocarbasugars and 1,4,5-tribenzoyloxy-2-ethoxy cycloheptanes via [5+2] cycloaddition

[5+2] Cycloaddition followed by asymmetric dihydroxylation procedure have been utilized to prepare novel cyclitols. Accordingly, rac-2α-hydroxy-6α-ethoxy-1,5-anhydro cyclohept-3-ene, 10 derived from [5+2] cycloaddition of 3-oxidopyrylium ylide and vinyl ether has been recognized as a seven-membered carbasugar equivalent and elaborated to 1,4,5-tribenzoyloxy-2-ethoxy cycloheptanes through a flexible, regio- and stereoselective strategy involving Sharpless asymmetric dihydroxylation conditions to resolve the compounds obtained. The structures and relative configurations of newly synthesized (+)-2α-acetoxy-6α-ethoxy-3β,4β-dihydroxy-1,5-anhydro cycloheptane ((+)-12)); (−)-1β,4β,5β-tribenzoyloxy-6α-ethoxy cycloheptane ((−)-17) and (+)-1α,4α,5α-tribenzoyloxy-6β-ethoxy cycloheptane ((+)-17) are unambiguously established by single crystal X-ray analysis and duly supported by ¹H and ¹³C NMR spectroscopy data.     

Microwave-assisted synthesis of 1,3-dialkyl ethers of calix[4]arenes: application to the synthesis of cesium selective calix[4]crown-6 ionophores

Partial etherification of phenolic-OH groups of calix[4]arenes with various alkyl halides/tosylates and K₂CO₃ under microwave irradiation afforded 1,3-dialkoxycalix[4]arenes in their cone conformation only as predominant/sole product in good yields (71–85%). The protocol was found to be much superior to conventional heating both in terms of yield and reaction time. Some of the 1,3-dialkoxycalix[4]arenes were elaborated further to the syntheses of cesium selective calix[4]crown-6 ionophores.     

Dynamic viscosity versus probe-reported microviscosity of aqueous mixtures of poly(ethylene glycol)

Correlation between the dynamic viscosity (η) and the microviscosity of a hybrid green medium constituted of water and poly(ethylene glycol) (PEG) of average molar mass (200, 400, and 600) g · mol^?1, respectively, is explored over the temperatures range (10 to 90) °C across the complete composition regime. The microviscosity is obtained using a fluorescence probe 1,3-bis-(1-pyrenyl)propane (BPP), which is manifested through the ratio of the monomer-to-intramolecular excimer intensities (I_M/I_E). Aqueous PEG mixtures are observed to behave similar to Newtonian fluids as the temperature dependence of dynamic viscosity follows Arrhenius-type behavior. Surprisingly, a simple and convenient linear dependence of ln η with wt% PEG of the mixture is established. The BPP I_M/I_E is observed, in general, to increase with the bulk dynamic viscosity of the mixture having >10 wt% PEG suggesting a good correlation between the bulk dynamic viscosity and BPP-reported microviscosity when the viscosity of the aqueous PEG mixture is relatively high.     

Solvent and Zn2+ Binding Effects on the Photo-physical Properties of (Dibenzoylmethanato)boron Difluoride

Absorption and emission spectroscopic studies of (dibenzoylmethanato)boron difluoride (1bf) in various polar and non-polar, protic and aprotic solvents are reported. The solvatochromic shifts of the spectral bands were examined in terms of solvent properties, including donor and acceptor numbers, followed by multilinear regression in which several solvent parameters were simultaneously analyzed. This π-conjugated positively charged system exhibits excellent solvatochromism. Variations in the electronic absorption spectral characteristics of 1bf were studied in solution in the presence of zinc perchlorate. Absorption spectral studies indicate stable complex formation between the zinc ion and 1bf in the ground state in aprotic dipolar benzonitrile rather than in protic polar solvent methanol. Zinc ion binding of 1bf was theoretically rationalized through frontier molecular orbital interaction.     

Efficiency of diffusion controlled miscible displacement in fractured porous media

Experiments were performed to study the diffusion process between matrix and fracture while there is flow in fracture. 2-inch diameter and 6-inch length Berea sandstone and Indiana limestone samples were cut cylindrically. An artificial fracture spanning between injection and production ends was created and the sample was coated with heat-shrinkable teflon tube. A miscible solvent (heptane) was injected from one end of the core saturated with oil at a constant rate. The effects of (a) oil type (mineral oil and kerosene), (b) injection rates, (c) orientation of the core, (d) matrix wettability, (e) core type (a sandstone and a limestone), and (f) amount of water in matrix on the oil recovery performance were examined. The process efficiency in terms of the time required for the recovery as well as the amount of solvent injected was also investigated. It is expected that the experimental results will be useful in deriving the matrix–fracture transfer function by diffusion that is controlled by the flow rate, matrix and fluid properties.     

Tertiary phosphine-appended transition metal ferrocenyl dithiocarbamates: Syntheses,Hirshfeld surface,and electrochemical analyses

Five new heteroleptic complexes of Cu(I), Ag(I), and Ni(II) having formulae [Cu₃(dtc)₂(dppf)₂]PF₆ ( Cu-I ), [Cu₃(dtc)₂(dppe)₂]PF₆ ( Cu-II ), [Cu(PPh₃)₂(dtc)] ( Cu-III ), [Ag₃(dtc)₂(PPh₃)₂]NO₃ ( Ag-I ), and [Ni(dtc)(dppf)]PF₆ ( Ni-I ) (dtc = N-ethanol-N-methylferrocenyl-dithiocarbamate; dppf = 1,1′-bis(diphenylphosphino)ferrocene; dppe = 1,1′-bis(diphenylphosphino)ethane; PPh₃ = tripheylphosphine) have been synthesized and characterized using elemental analysis, Fourier-transform infrared, multinuclear nuclear magnetic resonance, UV–Vis spectroscopy, and single-crystal X-ray diffraction. The single-crystal X-ray diffraction studies indicate that Ag-I forms a rare trinuclear cluster in which the geometry around the two silver centers Ag1 and Ag3 is distorted tetrahedral, whereas the third silver center Ag2 shows a distorted trigonal planar geometry. The Ni-I complex has a distorted square-planar geometry around the Ni center. In addition, a side product [Ag₂{S₂(dppf)₂}] ( Ag-II ) was obtained during an attempt to synthesize [Ag(dppf)(dtc)], where the two Ag centers are bridged by two sulfido centers and coordinated with two phosphorus centers of the dppf ligand to give rise to a distorted tetrahedral geometry. The solid-state structures of Ag-I , Ni-I , and Ag-II are stabilized by a variety of weak interactions. The nature of these interactions has been addressed with the help of Hirshfeld surface analyses. In addition, the weak argentophilic interaction in Ag-I and Ag-II have been studied using quantum theory of atoms in molecules and natural bond orbital calculations. The electrochemical properties of the complexes have been investigated using cyclic voltammetry, where Cu-I and Cu-II exhibited two quasi-reversible waves, whereas Cu-III , Ag-I , Ag-II , and Ni-I exhibited only one quasi-reversible peak.     

Synthesis of 3-keto-quinolines from enaminones,anilines and DMSO: Transition metal free one pot cascade

An efficient and transition metal-free approach for the synthesis of functionalized 3-ketoquinolines from readily available anilines, enaminones and DMSO in the presence of K₂S₂O₈ has been conducted. This one pot tandem reaction proceeds through [3+2+1] cycloaddition reaction involving DMSO, enaminones and amines. In this environmental benign approach, DMSO acts as both a one carbon source and the solvent. A broad range of variously substituted amines and enaminones are successfully employed in this one pot tandem process to access a broad range of substituted 3-ketoquinolines.     

The effect of the finite size of ions and Debye layer overspill on the screened Coulomb interactions between charged flat plates

Screened repulsion between uniformly charged plates with an intervening electrolyte is analyzed for strongly overlapped electrical double layers (EDL), accounting for the steric effect of ions and their expulsion from EDL edges into the surrounding solution. As a generalization of a study by Philipse et al. which does not account for these effects, an analytical expression is derived for the repulsion pressure in the limit of infinitely long plates with a zero-field assumption, which agrees closely with the corresponding numerical solution at low inter-plate separations. Our results show an augmented repulsive pressure for finite-sized ions at strong EDL overlaps. For plates with a finite lateral size, we demonstrate a further extended domain of low inter-plate gaps where the repulsion pressure increases with ion size due to a strong interplay between the steric interaction of ions and the EDL overspill phenomenon, considered earlier in a study by Ghosal & Sherwood limited to the linear Debye-Hückel regime (which cannot account for the steric effect of ions). This investigation on a simple model should enhance our understanding of the interaction between charged particles in electrophoresis, nanoscale self-assembly, active particles, and various other electrokinetic systems.