Highly Enantioselective Hydrogenation of β‐Alkyl and β‐(ω‐Chloroalkyl) Substituted β‐Keto Esters

Highly enantioselective hydrogenation of β‐alkyl and β‐(ω‐chloroalkyl) substituted β‐keto esters was achieved with Ru catalysts based on chiral diphosphines in EtOH at 50°C under 50‐bar initial hydrogen pressure, affording the corresponding β‐hydroxy esters in >98% ee.     

Ionic conductivity enhancement of PVA: carboxymethyl cellulose poly-blend electrolyte films through the doping of NaI salt

Cellulose - In this paper, we report the effect of doping sodium iodide (NaI) salt into a polymer blend matrix of sodium carboxymethyl cellulose (NaCMC) and poly(vinyl alcohol) (PVA). Solution...     

Mechanochemical reaction of TiO<Subscript>2</Subscript> with β-alanine for the preparation of visible light active nitrogen doped titania: adsorption and kinetic studies

Nitrogen doped TiO₂ (TiO_2−xN_x) with a homogenous anatase phase was synthesized, using β-alanine as a nitrogen precursor and ethanol as a oxygen depriving agent in the concentration range of 0.05, 0.10, 0.15 and 0.2 at% and were characterized by Powder X-ray Diffraction (PXRD), X-ray Photoelectron Spectra (XPS), Scanning Electron Microscope (SEM), Fourier Transform Infrared (FT-IR) and UV–visible Diffused Reflectance Spectroscopic (DRS) techniques. Ethanol deprives the surface oxygen, thereby generating oxygen defects whose concentration was evaluated by FTIR, Photoluminescence (PL) and Electron Spin Resonance (ESR) studies. FTIR analysis reveal that concentration of oxygen vacancies/defects (V_o) decreases as the nitrogen concentration increases leading to the reduction in the Ti–O bond length. This results in a shift of the IR absorption peak towards a low wave number as predicted by simple physical harmonic oscillator model. The Ti 2p_3/2 XPS spectra of TiO_2−xN_x shifts to lower binding energies due to the increase in the electron densities around the Ti atoms indicating the formation of Ti³⁺ in the doped samples. N₂ adsorption–desorption isotherms measurements show a slight increase in the Brunner–Emmet–Teller (BET) surface area, pore diameter, mesopore volume, while the crystallite size and the morphology were also effected by the nitrogen doping. The equilibrium adsorption of Toluene molecules on the photocatalyst surface follows Langmuir theory and the rate controlling step could be the surface reaction of the adsorbed Toluene molecules.     

Removal of copper by oxygenated pyrolytic tire char: kinetics and mechanistic insights

The kinetics of copper ion (Cu(II)) removal from aqueous solution by pyrolytic tire char was modeled using five different conventional models. A modification to these models was also developed through a modified equation that accounts for precipitation. Conventional first- and second-order reaction models did not fit the copper sorption kinetics well, indicating a lack of simple rate-order dependency on solute concentration. Instead, a reversible first-order rate reaction showed the best fit to the data, indicating a dependence on surface functional groups. Due to the varying solution pH during the sorption process, modified external and internal mass transfer models were employed. Results showed that the sorption of copper onto oxygenated chars was limited by external mass transfer and internal resistance with and without the modification. However, the modification of the sorption process produced very different results for unoxygenated chars, which showed neither internal nor external limitation to sorption. Instead, its slow sorption rate indicates a lack of surface functional groups. The sorption of Cu(II) by oxygenated and unoxygenated chars was also found to occur via three and two distinct stages, respectively.     

Experimental investigation of natural convection heat transfer characteristics in MWCNT-thermal oil nanofluid

Journal of Thermal Analysis and Calorimetry - The carbon nanotubes are considered as one of the highest thermal conductive material which is having a variety of heat transfer applications. The...     

The Effect of Rotation on the Onset of Double Diffusive Convection in a Horizontal Anisotropic Porous Layer

The effect of rotation and anisotropy on the onset of double diffusive convection in a horizontal porous layer is investigated using a linear theory and a weak nonlinear theory. The linear theory is based on the usual normal mode technique and the nonlinear theory on the truncated Fourier series analysis. Darcy model extended to include time derivative and Coriolis terms with anisotropic permeability is used to describe the flow through porous media. The effect of rotation, mechanical and thermal anisotropy parameters, and the Prandtl number on the stationary and overstable convection is discussed. It is found that the effect of mechanical anisotropy is to allow the onset of oscillatory convection instead of stationary. It is also found that the existence of overstable motions in case of rotating porous medium is not restricted to a particular range of Prandtl number as compared to the pure viscous fluid case. The finite amplitude analysis is performed to find the thermal and solute Nusselt numbers. The effect of various parameters on heat and mass transfer is also investigated.     

Linear and nonlinear double diffusive convection in a rotating sparsely packed porous layer using a thermal non-equilibrium model

Double diffusive convection in a fluid-saturated rotating porous layer is studied when the fluid and solid phases are not in local thermal equilibrium, using both linear and nonlinear stability analyses. The Brinkman model that includes the Coriolis term is employed as the momentum equation. A two-field model that represents the fluid and solid phase temperature fields separately is used for the energy equation. The onset criterion for stationary, oscillatory, and finite amplitude convection is derived analytically. It is found that small inter-phase heat transfer coefficient has significant effect on the stability of the system. There is a competition between the processes of thermal diffusion, solute diffusion, and rotation that causes the convection to set in through either oscillatory or finite amplitude mode rather than stationary. The effect of solute Rayleigh number, porosity modified conductivity ratio, Lewis number, diffusivity ratio, Vadasz number, and Taylor number on the stability of the system is investigated. The nonlinear theory based on the truncated representation of Fourier series method predicts the occurrence of subcritical instability in the form of finite amplitude motions. The effect of thermal non-equilibrium on heat and mass transfer is also brought out. Some of the convection systems previously reported in the literature is shown to be special cases of the system presented in this study.     

Linear and non-linear double diffusive convection in a rotating porous layer using a thermal non-equilibrium model

Double diffusive convection in a fluid-saturated rotating porous layer heated from below and cooled from above is studied when the fluid and solid phases are not in local thermal equilibrium, using both linear and non-linear stability analyses. The Darcy model that includes the time derivative and Coriolis terms is employed as momentum equation. A two-field model that represents the fluid and solid phase temperature fields separately is used for energy equation. The onset criterion for stationary, oscillatory and finite amplitude convection is derived analytically. It is found that small inter-phase heat transfer coefficient has significant effect on the stability of the system. There is a competition between the processes of thermal and solute diffusions that causes the convection to set in through either oscillatory or finite amplitude mode rather than stationary. The effect of solute Rayleigh number, porosity modified conductivity ratio, Lewis number, diffusivity ratio, Vadasz number and Taylor number on the stability of the system is investigated. The non-linear theory based on the truncated representation of Fourier series method predicts the occurrence of subcritical instability in the form of finite amplitude motions. The effect of thermal non-equilibrium on heat and mass transfer is also brought out.     

Synthesis of 2-alkylidenepyrrolidines, pyrroles, and indoles by condensation of silyl enol ethers and 1,3-bis-silyl enol ethers with 1-azido-2,2-dimethoxyethane and subsequent reductive cyclization

The condensation of 1,3-bis-silyl enol ethers with 1-azido-2,2-dimethoxyethane and subsequent reductive cyclization allowed an efficient regio- and diastereoselective synthesis of a variety of 2-alkylidene-4-methoxypyrrolidines. The thermal elimination of methanol resulted in the formation of functionalized pyrroles. Similarly, 2,3,3a,4,5,6-hexahydro-2,3-benzopyrroles were prepared and transformed into 4,5,6,7-tetrahydro-2,3-benzopyrroles. In contrast, treatment of 2-alkylidenepyrrolidines with trifluoroacetic acid resulted in formation of indoles by [4 + 2] cycloaddition and subsequent extrusion of a nitrogen atom.     

Synthesis,characterization and control of eight process-related and two genotoxic fingolimod impurities by a validated RP-UPLC method

An HPLC method has been described in the European Pharmacopoeia and United States Pharmacopeia for the determination of nine organic impurities (imp A–I) in fingolimod hydrochloride, a synthetic sphingosine-1-phosphate receptor modulator. The manufacturing process of fingolimod hydrochloride consists of multistep chemical synthesis wherein controls of precursors, intermediates and process steps should be performed to assure the final quality of the drug substance. We synthesized and isolated eight process-related impurities (FINI imp A–H) of fingolimod, which were different from the pharmacopoeial impurities. One unknown process-related impurity was found as a key intermediate (FINI) and was identified by LC–MS. Characterization of all of the impurities were done using spectroscopic techniques (¹H and ¹³C NMR, FTIR, MS), and the mechanistic pathways to the formation of these impurities were also discussed. Two of these impurities were evaluated as potential genotoxic impurities owing to their alerting structures and alkylating properties (alkyl sulfonates and alkyl halides, class 3, ICH M7). We also developed and validated an RP-UPLC method in line with ICH Q2 guidelines for control these impurities (FINI imp A–H) and to assure the pharmacopoeial quality drug substance.