Iodine-catalyzed,one-pot,three-component aza-Friedel–Crafts reaction of electron-rich arenes with aldehyde/carbamate combinations

Iodine is shown to be an efficient catalyst for a one-step, three-component aza-Friedel–Crafts reaction of activated arenes or heteroarenes with benzyl or tert-butyl carbamates in combination with a wide variety of aldehydes in toluene under ‘open-flask’ and mild conditions. In the presence of 5 mol % of iodine in toluene at room temperature, the reaction gives the corresponding N-CBz or N-Boc protected α-branched amines, selectively, in good to excellent yields.     

Influence of surface oxygen groups on V(II) oxidation reaction kinetics

The role of surface oxygen groups on the kinetics of the V(II) oxidation reaction was studied on modified glassy carbon (GC) electrodes by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The reaction was found to be sensitive to the presence of oxygen groups on the electrode surface. Higher O/C ratios determined by X-ray photoelectron spectroscopy (XPS) corresponded to higher reactivities and lower charge transfer resistances measured in a 1 M V(II) electrolyte. The stability of an oxidised GC surface was also investigated in a 1 M V(II) electrolyte by potential holding and cycling experiments. It was found that after holding and cycling to successively more negative potentials up to − 0.8 V/RHE, the electrode surface lost its initial reactivity.     

Gold-catalyzed intramolecular hydroalkoxylation/cyclization of conjugated dienyl alcohols

Catalytic intramolecular additions of hydroxyl groups to tethered conjugated dienes are described. The reactions proceed smoothly at 60 °C in the presence of 5 mol % of (PPh₃)AuCl/AgOTf as a catalyst. A broad range of structurally diverse conjugated dienes produce substituted tetrahydrofurans and tetrahydropyrans in good yields. This reaction represents an atom-economic route to construct five- and six-membered cyclic ethers.     

Selective pyrolysis of Organosolv lignin over zeolites with product analysis by TG-FTIR

Organosolv lignin has been selected to investigate the thermal behavior of lignin over zeolites by using a thermogravimetric analyzer coupled with a Fourier-transform infrared spectrometer (TG-FTIR). The chemical structure of this lignin has been determined by ¹H NMR to obtain the distribution of main functional groups such as methoxyl groups and free aliphatic and phenolic hydroxyl groups. All three zeolite catalysts tested, HZSM-5, H-β, and USY, exerted significant influences on the dehydration reaction in the initial stage, the deoxygenation reaction of oxygenated compounds such as methanol and phenols, and the char-forming process during lignin pyrolysis in the range 30–800 °C. The dehydration reaction was enhanced in the order USY > HZSM-5 > H-β, while char formation was suppressed in the reverse order. The presence of HZSM-5 and H-β catalyzed the conversion of both oxygenated compounds and chars into the low-molecular-weight gases CO, CO₂, and methane. The addition of USY clearly aided decomposition of the oxygenated compounds, but had little effect on the char degradation.     

Solid phase modification of carbon nanotubes with anthraquinone and nitrobenzene functional groups

A new solid phase modification method is developed for chemical attachment of anthraquinone (AQ) and nitrobenzene (NB) functional groups to surface of carbon nanotubes (CNTs) through aminomethyl benzene (− C₆H₄CH₂NH −) linker. The benzyl amine linker was spontaneously grafted onto the CNTs by refluxing in the C₆H₄CH₂NHBoc diazonium salt at 60 °C in acetonitrile solution. After the removal of the Boc protecting group, AQ and NB groups were attached to the benzyl amine linker by solid-phase amide coupling. The grafted CNTs were characterized using FTIR and cyclic voltammetry techniques, surface coverage and stability of the tethered functional groups was evaluated. The dispersion of modified CNTs is significantly improved in organic solvent and the surface loading reaches up to 0.20 mmol/g for both anthraquinone and nitrobenzene.     

Impact of the alkali cation on the electrocatalytic oxidation of urea and benzyl alcohol on nickel electrode

The effect of electrolyte alkali metal cations (Li⁺, Na⁺, or K⁺) on the electro-oxidation of urea and benzyl alcohol on NiOOH catalyst has been investigated by means of cyclic voltammetry and chronoamperometry in the presence of an electrolyte containing LiOH, NaOH, or KOH. The catalytic activity toward the electro-oxidation of urea and benzyl alcohol was found to increase in the sequence Li⁺ < Na⁺ < K⁺. This activity's difference is partly caused by different surface blockage abilities by OH–M⁺(H₂O)_x (M: Li, Na, K) clusters, which is similar to many electrocatalytic reactions on Pt reported previously, additionally, incorporation of various cations to the catalyst may induce the activities difference as well.     

Organocatalytic selective benzoylation of alcohols with trichloromethyl phenyl ketone: inverse selectivity in benzoylation of alcohols containing phenol or aromatic amine functionality

Trichloromethyl phenyl ketone benzoylates primary and secondary aliphatic alcoholic groups in compounds also containing a phenolic group in the presence of 2–10 mol % of PMDETA organocatalyst at room temperature in high yields and excellent selectivity. It also shows the potential to selectively benzoylate primary alcoholic groups of aminoarylalkanols and primary-secondary diols as well as primary amino group of alkyl amines in the presence of aryl amines under similar conditions. A rationale for the selectivity and efficiency of the reaction has been provided.     

Nickel-catalyzed decarboxylative coupling of an alkynyl carboxylic acid with aryl iodides

A decarboxylative coupling reaction with an alkynyl carboxylic acid and aryl iodides in the presence of a nickel catalyst was developed. When the reaction was conducted with NiCl₂ (10 mol%), Xantphos (15 mol%), Mn (1.0 equiv), and Cs₂CO₃ (1.5 equiv), the desired diaryl alkynes were formed in moderated to good yields. Furthermore, this method does not produce the diyne, which is formed in the homocoupling of alkynyl carboxylic acids.     

Toughening of in situ polymerized cyclic butylene terephthalate by chain extension with a bifunctional epoxy resin

Cyclic butylene terephthalate (CBT) was polymerized in the presence of a low molecular weight bifunctional epoxy resin. The resultant chain extended polymerized CBT (pCBT) showed an increased ductility compared to that of conventionally polymerized pCBT for all analyzed epoxy concentrations (1–4 wt.%). The best results were obtained with 2 wt.% of epoxy resin. Other mechanical properties remained relatively unaffected by the epoxy resin. ¹H NMR analysis suggested an esterification reaction of the carboxyl end groups of pCBT and the glycidyl functional groups of the diepoxide. With increasing epoxy content, the chain extended pCBT showed an increasing molecular weight and a decreasing glass transition. Crystallization and melting temperatures as well as crystallinity also decreased with increasing epoxy concentration.     

High-energy ionising radiation initiated decomposition of acetovanillone

Hydroxyl radical, hydrated electron and hydrogen atom intermediates of water radiolysis react with acetovanillone with rate coefficients of (1.05±0.1)×10¹⁰, (3.5±0.5)×10⁹ and (1.7±0.2)×10¹⁰mol^?1 dm³ s^?1. Hydroxyl radical and hydrogen atom attach to the ring forming cyclohexadienyl type radicals. The hydroxyl–cyclohexadienyl radical formed in hydroxyl radical reaction in dissolved oxygen free solution partly transforms to phenoxyl radical. In the presence of O₂ phenoxyl radical formation and ring destruction are observed. Hydrated electron in O₂ free solution attaches to the carbonyl oxygen and undergoes protonation yielding benzyl type radical. In air saturated 0.5 mmol dm^?3 solution using 15 kGy dose most part of acetovanillone is degraded, for complete mineralisation five times higher dose is required. The experiments clearly show that acetovanillone can be efficiently removed from water by applying irradiation technology.     

Synthesis of covellite (CuS) from the elements

A one-step, corrosion-assisted reaction was developed to synthesize copper sulfide (CuS) from elemental copper and sulfur in water at 60 °C. The as-prepared polycrystalline CuS consists of polyhedral-shaped 2–3 μm crystallites. CuS forms by the oxidation of copper metal in the presence of sulfur, whereas in the presence of water, a continuous solid-state reaction occurs without passivation by the product.     

Reduction of aromatic compounds with Al powder using noble metal catalysts in water under mild reaction conditions

In water, Al powder becomes a powerful reducing agent, transforming in cyclohexyl either one or both benzene rings of aromatic compounds such as biphenyl, fluorene and 9,10-dihydroanthracene under mild reaction conditions in the presence of noble metal catalysts, such as Pd/C, Rh/C, Pt/C, or Ru/C. The reaction is carried out in a sealed tube, without the use of any organic solvent, at low temperature. Partial aromatic ring reduction was observed when using Pd/C, the reaction conditions being 24 h and 60 °C. The complete reduction process of both aromatic rings required 12 h and 80 °C with Al powder in the presence of Pt/C.     

Spectroscopic investigation of the interaction of p-benzoquinone with casein in the solid state

The reaction between p-benzoquinone (PBQ) and casein (protein) in the solid state was studied. After reaction with protein, the FT-IR spectra showed a new band at 1215 cm^?1, with an intense sign attributed for casein/PBQ product. An optimum amount of PBQ for determination of the product when mixed with casein was 100 mg and a reaction time of 30 min. The product was stable for a period of 24 h after the reacting by heating. The interaction of PBQ with casein was investigated by FT-IR, reflectance, Raman and EPR spectroscopies. The reaction between PBQ and casein in the solid state yields a radical species (p-benzosemiquinone) that it is stabilized by the presence of p-biphenolate and p-benzoquinone species in the solid state.     

Plasmon heating mediated Friedel-Crafts alkylation of anisole using supported AuNP@Nb2O5 catalysts

Two different hybrid materials composed of gold nanoparticles (AuNPs) supported on either commercial niobium oxide HY 340 or mesoporous niobium oxide catalyzed the Friedel-Crafts alkylation of anisole by benzyl chloride. Excitation of the surface plasmon of the supported AuNPs allowed the reaction to occur at lower temperatures by acting as an alternative heat source. The localized heating produced via plasmon excitation permitted the acid catalyzed reaction to occur - at the Lewis acid sites on the Nb₂O₅ support - at 80 °C while thermal-dark reactions using a conventional heat source, required temperatures of 120 °C or higher. The catalytic activity of the tested hybrid materials decreased with storage time. However, the deactivation showed to be reversible upon lyophilisation indicating that the nature of the deactivation could be due to water adsorption.     

Photolysis of methyl-parathion thin films: Products,kinetics and quantum yields under different atmospheric conditions

The present study focuses on the photodegradation of methyl-parathion thin films, an organophosphate insecticide, under different atmospheric conditions. The latter include nitrogenated, oxygenated and ozonated atmospheres, under low and high relative humidity conditions. Addition of oxygen to the atmospheric mixture did not seem to affect the reaction rates and quantum yields. Relative humidity affect was minor, with a small enhancement in reaction rate under 254 nm radiation. The addition of ozone (to either dry or humid atmosphere), at all concentrations tested, largely enhanced degradation rates. In the absence of ozone, the obtained quantum yields for photolysis of methyl-parathion thin films under 254 and 313 nm were 0.024 ± 0.007 and 0.012 ± 0.005, respectively. These values are higher than the values previously reported for solutions of methanol and water. Although the presence of molecular oxygen and water vapors did not seem to affect much the reaction rates, it did have a certain effect on the resulted products. More polar products were obtained under oxygenated and ozonated atmospheres, as well as dimers under ozone conditions. The reaction on thin films has yielded more toxic products than usually found in solutions, adding alkylphosphate esters in addition to the oxons formed normally.     

Primary amine catalyzed direct asymmetric aldol reaction assisted by water

l-Valine was found to be an active catalyst in the asymmetric direct aldol reaction. The aldol reaction of a variety of aromatic aldehydes with acetone was catalyzed by 20 mol % of l-valine at 35 °C with the aldol products obtained in moderate to good yields (48–83%) and enantiomeric excesses (42–72%). The reaction was more efficient catalytically with best results observed in the presence of 1 mol equiv of water, with respect to the aldehyde, in either DMSO or DMF as solvent. The effect of water concentration on the reaction rate and enantioselectivity was also investigated. Thus, with increasing water concentration in DMSO there was decreasing enantioselectivity. However, the reaction in the presence of l-phenylalanine showed a lower level of reactivity and enantioselectivity to afford the aldol in 25% with 31% ee. In marked contrast, reaction with l-phenylglycine resulted in the negligible formation of the aldol (<5%). Our results, suggest a new strategy in the design of new bioorganic catalysts for direct asymmetric aldol reactions.     

High performance bioanode based on direct electron transfer of fructose dehydrogenase at gold nanoparticle-modified electrodes

The direct electron transfer reaction of fructose dehydrogenase (FDH) from Gluconobacter sp. on alkanethiol-modified gold nanoparticles (AuNPs) was examined. AuNP-modified electrodes were simply fabricated by depositing citrate-reduced gold nanoparticles onto a gold electrode and carbon fiber paper and then covering the surface with a self-assembled monolayer of alkanethiols. The immobilization of AuNPs provided a large effective surface area for the adsorption of FDH. Catalytic oxidation currents based on the direct electron transfer reaction of FDH were observed from a potential about ?100 mV (vs. Ag/AgCl, 3 M NaCl) in the presence of d-fructose without a mediator. The current density reached as high as 14.3 ± 0.93 mA/cm² (at +500 mV), which was achieved in the presence of 200 mM d-fructose by immobilization of FDH on 2-mercaptoethanol-modified AuNP/carbon fiber paper electrodes.     

Preparation of monoalkylpiperidines via the mild hydrogenation of monoalkynylpyridines

Monoalkynylpyridines were prepared via a Sonogashira cross-coupling reaction between monoiodopyridines and alkynes. Mild hydrogenation of the obtained monoalkynylpyridines was then conducted to produce the corresponding monoalkylpiperidines in moderate to excellent yields. The hydrogenation reaction was carried out under H₂ (1 atm) in the presence of 10 wt% Pd/C (5 eq) in either AcOH or MeOH at room temperature. The present mild method is therefore useful for the quick and easy preparation of monoalkylpiperidines.     

New,simple and validated kinetics spectrophotometric method for determination of moxifloxacine in its pharmaceutical formulations

The objective of this research was to develop a kinetic spectrophotometric method for determination of moxifloxacine (MOXF) in pure form and pharmaceutical formulations. The method was based on the formation of a colored N-vinyl chlorobenzoquinone derivative of MOXF by its reaction with 2,3,5,6-tetrachloro-1,4-benzoquinone in presence of acetaldehyde.The formation of the colored product was monitored spectrophotometrically by measuring the absorbance at 652 nm. Factors affecting the reaction were studied and optimized. The stoichiometry of the reaction was determined, and the reaction pathway was postulated. The activation energy of the reaction was calculated and found to be 6.65 kJ mol^?1. Under the optimized conditions, the initial rate and fixed time (at 5 min) methods were utilized for constructing the calibration graphs. The graphs were linear in concentration ranges 5–100 and 15–150 μg ml^?1 with limit of detection of 2.0 and 5.0 μg ml^?1 for the initial rate and fixed time methods, respectively. The analytical performance for both methods was fully validated, and the results were satisfactory. No interference was observed from the excipients that are commonly present in the pharmaceutical formulations. The proposed method was successfully applied to the determination of MOXF in its pharmaceutical formulations. The label claim percentages were 101.25 ± 0.73% and 100.92 ± 0.65% for the initial rate and fixed time method, respectively. Statistical comparison of the results with those obtained by a reference spectrophotometric method showed excellent agreement between the accuracy and precision of the two methods. The proposed method has great value in its application to the analysis of MOXF in quality control laboratories.     

Crucial effect of rubidium cation on catalytic activity of a polycrystalline gold electrode toward oxygen reduction reaction in alkaline media

Catalytic activity of a polycrystalline gold electrode toward oxygen reduction reaction (ORR) in aqueous alkaline media in the presence of various alkali-metal sulfates (M₂SO₄, M = Li, Na, K, Rb and Cs) was investigated by hydrodynamic voltammetry. The fraction of 4e^? pathway in low overpotentials (? 0.1 to ? 0.3 V) depended on the alkali-metal cations (Rb ? Na, K, Cs, Li). A complete 4e^? reduction of O₂ was only attained in the presence of Rb⁺ cation in the solution, which was comparable or even superior to that reported at the Au(100) single crystal electrode.