Synthesis of aryl alkynyl carboxylic acids and aryl alkynes from propiolic acid and aryl halides by site selective coupling and decarboxylation

The coupling of propiolic acid with aryl iodides afforded the aryl alkynyl carboxylic acids and aryl alkynes in generally good yields. Aryl alkynyl carboxylic acids were obtained when the reaction was performed in the presence of Pd(PPh₃)₂Cl₂ (2.5 mol %), dppb (5.0 mol %) and DBU (5 equiv) at 50 °C. For the synthesis of the terminal aryl alkynes, the reaction was conducted in the presence of Pd(PPh₃)₂Cl₂ (2.5 mol %), dppb (5.0 mol %), DBU (5.0 equiv), and Cu(acac)₂ (10 mol %) at 25 °C for 5 h, and further reacted at 60 °C for 6 h.     

Facile domino reactions in the statistically controlled product- and stereoselective synthesis of densely functionalized cis-1,4-cyclohexa-1,4-dienes and trans,trans-trisubstituted-1,2,5,6-tetrahydropyridines

The domino reactions of ethyl 3-oxo-4-(arylsulfonyl)butanoates with aromatic aldehydes in a 2:1 molar ratio in the presence of a catalytic amount of ammonium acetate furnished densely functionalized cyclohexa-1,4-dienes stereoselectively, while the domino reactions of ethyl 3-oxo-4-(arylsulfonyl)butanoates, aromatic aldehydes, and ammonium acetate in a 1:2:2 molar ratio afforded highly functionalized 1,2,5,6-tetrahydropyridines stereoselectively.     

Numerical study on a vertical plate with variable viscosity and thermal conductivity

Free convection over an isothermal vertical plate immersed in a fluid with variable viscosity and thermal conductivity is studied in this paper. We consider the two-dimensional, laminar and unsteady boundary layer equations. Using the appropriate variables, the basic governing equations are transformed to non-dimensional governing equations. These equations are then solved numerically using a very efficient implicit finite difference scheme known as Crank–Nicolson scheme. The fluid considered in this study is of viscous incompressible fluid of temperature dependent viscosity and thermal conductivity. The effect of varying viscosity and thermal conductivity on velocity, temperature, shear stress and heat transfer rate are discussed. The velocity and temperature profiles are compared with previously published works and are found to be in good agreement.     

One-pot synthesis of [2+2]-helicate-like macrocycle and 2+4-μ4-oxo tetranuclear open frame complexes: Chiroptical properties and asymmetric oxidative coupling of 2-naphthols

Synthesis of binuclear Cu(II) terminally closed [ 2+2 ]- double-stranded helicate-like macrocycles 1, 1′ , 1″ , 2 , 2′ , 2″ and 2+4- μ₄-oxo tetranuclear open frame complexes 3 , 3′ , 3″ , 4 , 4′ , 4″ are established. Adapting one-pot self-assembly technique from simple three components systems: 1,1′-binaphthyl-2,2′-diamine, 4-methyl-2,6-diformyl phenol and cupric salts, the helicate-like [ 2+2 ]- macrocyclic complexes 1–1″, 2–2″ and 2+4- μ₄-oxo tetranuclear complexes 3–3″ , 4–4″ were obtained by appropriately altering the reaction condition such as temperature and subcomponent ratio. Density Functional Theory (DFT) calculations were carried out for understanding the structural geometries, intermediates involved in the diverse formation of [ 2+2 ] and 2+4 frameworks. The single crystal X-ray structures obtained for 1′ , 2 and 3 confirms the self-assembly process in line with DFT. This detailed analysis tempted us to derive a plausible mechanism for this long standing challenge in the synthesis of such macrocycles using 1,1′-binaphthyl-2,2′-diamine (BNDA) and aromatic aldehyde. The chiroptical properties of enantiopure complexes and their catalytic applications in asymmetric oxidative coupling of 2-naphthol to chiral 1,1’-Bi-2-naphthol (BINOL) achieved in good yield and ee were discussed.     

Effect of NiO/Ni(OH)2 nanostructures in graphene/CNT nanocomposites on their interfacial charge transport kinetics for high-performance supercapacitors

Journal of Solid State Electrochemistry - Graphene sheet/multiwall carbon nanotube (GMC) and its composites with NiO and Ni(OH)2 are synthesized by microwave-assisted technique for the application...     

On the diffusion of a chemically reactive species in a convective flow past a vertical plate

A numerical solution of the first-order homogeneous chemical reaction in an unsteady free convective flow past a semi-infinite vertical plate is studied. The dimensionless governing equations are solved by an efficient, more accurate, unconditionally stable, and rapidly converging implicit finite-difference scheme. The effect of various parameters, such as the Prandtl number, Schmidt number, buoyancy ratio parameter, and chemical reaction parameter on flow velocity and temperature is determined. The velocity profiles are in excellent agreement with available results in the literature. The local and average values of skin friction and Nusselt and Sherwood numbers are calculated. The effects of the chemical reaction parameters on these values are discussed for both generative and destructive reactions. Owing to the presence of the first-order chemical reaction, the velocity is found to increase in the generative reaction and to decrease in the destructive reaction.     

Guest⊂Guest⊂Host Multicomponent Molecular Crystals: Entrapment of Guest⊂Guest in Honeycomb Networks Formed by Self‐Assembly of 1,3,5‐Tri(4‐hydroxyaryl)benzenes

Sterically‐engineered rigid trigonal molecular modules based on 1,3,5‐tri(4‐hydroxyphenyl)benzenes H1 and H2 undergo O‐H???O hydrogen‐bonded self‐assembly into eight‐fold catenated hexagonal (6,3) and two‐fold interpenetrated undulated square (4,4) networks, respectively. In the presence of [18]crown‐6 as a guest, the triphenol H1 is found to self‐assemble into a honeycomb network with hexagonal voids created between three triphenol building blocks. The guest [18]crown‐6 molecules are found to be nicely nested in hexagonal enclosures. The empty spaces within the crowns can be further filled with neutral (MeOH/water, MeOH/MeNO₂) or ionic guest species such as KI/KAcAc to furnish novel multicomponent assemblies, that is, guest ? guest ? host, that typify Russian dolls. In contrast, triphenol H2 is found to yield analogous multicomponent molecular crystals in which the guest crown–K⁺ acts as a spacers in the hydrogen‐bonded self‐assembly that leads to distorted chicken wire networks.     

Alkylation of Cyclic 1,3-Diketones

A simple procedure for the C-alkylation of cyclic 1,3-diketones have been reported using Triton B as base in aqueous conditions.     

Determination of total nitrogen in atmospheric wet and dry deposition samples

A microwave-assisted persulfate oxidation method followed by ion chromatographic determination of nitrate was developed for total nitrogen determination in atmospheric wet and dry deposition samples. Various operating parameters such as oxidation reagent concentrations, microwave power, and extraction time were optimized to maximize the conversion of total nitrogen to nitrate for subsequent chemical analysis. Under optimized conditions, 0.012 M K₂S₂O₈ and 0.024 M NaOH were found to be necessary for complete digestion of wet and dry deposition samples at 400 W for 7 min using microwave. The optimized extraction method was then validated by testing different forms of organic nitrogen loaded to pre-baked filter substrates and NIST SRM 1648 (urban particulate matter), and satisfactory results were obtained. In the case of wet deposition samples, standard addition experiments were performed. The suitability of the method for real-world application was assessed by analyzing a number of wet and dry deposition samples collected in Singapore during the period of March-April 2007. The organic nitrogen content was 15% (wet) and 30% (dry) of the total nitrogen. During the study period, the estimated wet fluxes for nitrate (NO₃⁻), ammonium (NH₄⁺), organic nitrogen (ON), and total nitrogen (TN) were 16.1 ± 6.5 kg ha⁻¹ year⁻¹, 11.5 ± 5.7 kg ha⁻¹ year⁻¹, 3.8 ± 1.5 kg ha⁻¹ year⁻¹and 31.5 ± 13.2 kg ha⁻¹ year⁻¹, respectively, while the dry fluxes were 2.5 ± 0.8 kg ha⁻¹ year⁻¹, 1.4 ± 0.9 kg ha⁻¹ year⁻¹, 2.3 ± 1.4 kg ha⁻¹ year⁻¹ and 7.5 ± 2.6 kg ha⁻¹ year⁻¹, respectively.