Effect Of Base Concentration Research Articles

Investigation of hydrogen production from sodium borohydride by carbon nanotube‐graphenesupportedPdRubimetallic catalyst forPEMfuel cell application

In this study, hydrogen (H2) generation from the hydrolysis of sodium borohydride (NaBH4) catalyzed by bimetallic Palladium-Ruthenium (PdRu) supported on multiwalled carbon nanotube-graphene (MWCNT-GNP) hybrid material is investigated. The effect of various parameters such as temperature, NaBH4 concentration, and catalyst loading and effect of base concentration are examined to observed optimum operating conditions. Experimental results show that the PdRu/MWCNT-GNP bimetallic catalyst has high catalytic activity on NaBH4 hydrolysis reaction. It has been found that PdRu/MWCNT-GNP catalyst shows low activation energy of 22.33 kJ/mol for hydrolysis reaction of NaBH4. The PdRu/MWCNT-GNP catalyst also exhibits H2 generation rate of 79.2 mmol/min·gcat at 45°C. It shows good cycle stability in the catalyst reusability test and retained 89% of its initial catalytic activity after fifth use. The high catalytic activity of the PdRu/MWCNT-GNP catalyst makes it promising in H2 generation from NaBH4 hydrolysis for commercial proton exchange membrane fuel cell (PEMFC) applications.

Effect of solution composition on the recrystallization of kaolinite to feldspathoids in hyperalkaline conditions: limitations of pertechnetate incorporation by ion competition effects

AbstractThe incorporation of pertechnetate (TcO4–) into feldspathoids produced by alkaline alteration of aluminosilicate clays may offer a potential treatment route for 99Tc-containing groundwater and liquors. Kaolinite was aged in NaOH to determine the effect of base concentration, temperature, and solution composition on mineral transformation and pertechnetate uptake. In all reactions, increased temperature and NaOH concentration increased the rate of kaolinite transformation to feldspathoid phases. In reactions containing only NaOH, sodalite was the dominant alteration product; however, small amounts (6–15%) of cancrinite also formed. In experiments containing NaOH/Cl and NaOH/NO3 mixtures, sodalite and nitrate cancrinite were crystallized (at 70°C), with no reaction intermediates. The addition of SO42– crystallized sulfatic sodalite at 40 and 50°C, but at higher temperatures (60 and 70°C) sulfatic sodalite transforms to vishnevite (sulfatic cancrinite). In experiments where a pertechnetate tracer was added (at ∼1.5 μmol l–1), only 3–5% of the 99Tc was incorporated into the feldspathoid phases. This suggests that the larger pertechnetate anion was unable to compete as favourably for the internal vacancies with the smaller OH–, NO3–, SO42– or Cl– anions in solution, making this method likely to be unsuitable for groundwater treatment.

Superparamagnetic Cobalt Ferrite Nanoparticles: Effect of Temperature and Base Concentration

Cobalt ferrite nanoparticles were coprecipitated in air medium using NH3, and the effects of tempera- ture and base concentration on the properties were studied. X-ray diffraction (XRD) technique and Fourier transform infrared spectroscopy were used to investigate the structural properties of the samples. Particle sizes and shapes were determined by a transmission electron microscope (TEM). Magnetic measurements were done using vibrating sam- ple magnetometer at room temperature. The proper reaction temperature was found to be 80 °C for the synthesis of superparamagnetic cobalt ferrite nanoparticles. The effect of base concentration on the properties of the superparamag- netic nanoparticles was investigated under this temperature. The magnetization values of cobalt ferrite nanoparticles increased as the base concentration increased and reached to a value of 32.4 emu/g with zero coercivity. The particle sizes (dXRD, dTEM ,a nddVSM) of cobalt ferrite nanoparticles were calculated from XRD patterns, TEM images, and mag- netic data, respectively. It was observed that the dTEM and dVSM are similar to each other, and the dXRD are bigger than those with the similar trend of increase with the increase of base concentration.

CFD simulation of ZnO nanoparticle precipitation in a supercritical water synthesis reactor

Continuous hydrothermal flow synthesis process has shown great advantages concerning the control of particle size and morphology through the optimization of supercritical water processing parameters. In particular, micromixing is a key issue of the process for controlling the nucleation mechanism. A Computational Fluid Dynamics (CFD) model is suggested for nanoparticle size determination using a population balance approach. Models for reaction kinetics, thermodynamics, nucleation and growth are presented. The effects of base concentration and hydrodynamics are investigated. Results show that the CFD may be valuable simulation tool for controlling the size and the shape of nanoparticles from a good adjustment of processing parameters. However, some additional knowledge on nucleation, crystal growth and aggregation mechanisms are useful in order to get a better agreement.

An investigation of the bromination of 1,4-dihydropyridine rings

Conditions for bromination at the C3 and C5 positions of a 1,4-dihydropyridine (DHP) were investigated. The effect of base concentration, base type, reaction temperature, and solvent were examined. DHP derivatives with ester and amide moieties were synthesized and brominated. The bromine atoms can be replaced by other substituents, utilizing Suzuki cross coupling.

Effects of base concentration and cation on hydrothermal processes of cetyltrimethylammonium permanganate in various aqueous media

Hydrothermal reactions of cetyltrimethylammonium permanganate (CTAMnO4) in various aqueous media were systematically studied. The final products were strongly dependent on base concentrations and alkali metal cations in the medium. The transformation of CTAMnO4 into CTAOH was faster in 1.5 M LiOH solution than in 0.3 M LiOH solution, and the Hofmann elimination of CTAOH resulted in the formation of 1-hexadecene. The reaction of the alkene with lithium permanganate resulted in the co-precipitated phase of lithium carbonate and manganese dioxide, in which Li4Mn5O12 was formed. Further reaction between Li4Mn5O12 and lithium carbonate produced a stable compound Li2MnO3 in the environment that contained organic compounds. No precipitated phase of lithium carbonate was observed in 0.3 M LiOH solution, and manganese dioxide was formed which could further react with organic compounds in dilute base environments, leading to the formation of Li-birnessite. Li-birnessite was transformed into the spinel with an extended reaction time. In KOH or NaOH solution, the molar ratio of Mn3+/Mn4+ in final products decreased with increasing base concentration. Mn3+-based compounds (Mn2O3 and γ-MnOOH) were observed in 0.1 M KOH solution, whereas K-birnessite was a stable product in 1.5 M KOH solution. The mesophase was observed in KOH solution, and its diffraction intensity increased with increasing base concentration. The effects of base concentration and alkali metal cation on the products were discussed as well.

An Expeditious Synthesis of 1‐(4‐Chlorophenyl)‐3,3‐dimethyl‐2‐butanone by a Ligand‐Free Palladium‐Catalyzed α‐Arylation of Pinacolone: Scale‐Up and Effect of Base Concentration

AbstractAn efficient and large‐scale synthesis of 1‐(4‐chlorophenyl)‐3,3‐dimethyl‐2‐butanone (1) by an α‐arylation of pinacolone (2) with 1‐bromo‐4‐chlorobenzene (3) in the presence of palladium acetate and sodium t‐butoxide in toluene is described. An increase in the concentration of sodium t‐butoxide to 2.5–3.0 equivalents suppressed the formation of over‐arylated products. These ligand‐free conditions afforded a yield of 1 that was comparable to those obtained by using a ligand.

Competing base-promoted E2 and E1 reactions of an acidic tertiary substrateElectronic supplementary information (ESI) available: the effect of base concentration on rate constant and product composition. See http://www.rsc.org/suppdata/p2/b2/b200758d/

The solvolysis of 4-chloro-4-(4′-nitrophenyl)pentan-2-one (1-Cl) in aqueous acetonitrile yields the alcohol 4-hydroxy-4-(4′-nitrophenyl)pentan-2-one (1-OH) and the elimination products 4-(4′-nitrophenyl)-2-oxopent-4-ene (2), (E)-4-(4′-nitrophenyl)-2-oxopent-3-ene (3), and (Z)-4-(4′-nitrophenyl)-2-oxopent-3-ene (4). Addition of thiocyanate ion does not increase the total reaction rate in 25 vol% acetonitrile in water, but gives rise to the substitution products 1-SCN and 1-NCS, at the expense of 1-OH, and a small increase in the fraction of alkene 3. Addition of acetate ion and other weak bases gives rise to base-promoted E2 (or E1cB) to give alkene 3 (and 4). The Bronsted parameter for this reaction was measured as β = 0.76. Water-promoted E2 (or E1cB) reaction was not observed.

ChemInform Abstract: Effect of Base Concentration on the Rate of the Vicarious Nucleophilic Substitution of Hydrogen and on the Kinetic Isotope Effect.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Effect of base concentration on the rate of the vicarious nucleophilic substitution of hydrogen and on the kinetic isotope effect

Varying concentration of the chloromethyl tolyl sulfone carbanion influences the rate of its VNS reaction with 2-fluoro-4-bromonitrobenzene and changes the mechanistic scheme from thermodynamic to kinetic control. Both primary and secondary kinetic isotope effects are observed and are clearly connected with particular kinetic relations.

Chemiluminescence involving acidic and ambident ion light emitters. The chemiluminescence of 9-acridinepercarboxylate anion

The reaction of phenyl 9-acridinecarboxylate with an excess of peroxide ion in THF/water (67/33 mol %) leads to the emission of either bright yellow-green light or bright blue light, depending on the reaction conditions. The blue emission is favored by high concentrations of hydrogen peroxide and water, for example. 9-Acridinepercarboxylic acid is a common intermediate in the reactions. The light emitter responsible for the blue chemiluminescence is acridone, whereas that responsible for the yellow-green chemiluminescence is the anion of acridone. The effects of base concentration and solvent composition on the relative proportions of these two emitters have produced evidence that, contrary to the expectation of simple theory, a dioxetanone is not an intermediate in the reaction. Other cases where chemiluminescence may involve percarboxylate and peroxide ions are discussed.

The effect of base concentration on orientation in E2 reactions: A common feature in metal alkoxide promoted olefin formation from alkyl halides and tosylates

The title effect has been investigated in the reactions of three 2-butyl (X = I, Br, OTs) and four 2-decyl (X = I, Br, Cl, OTs derivatives with t-C4H9OK/t-C4H9OH, t-C4H9OK/tetrahydrofuran and t-C4H9ONa/t-C4H9OH as the base-solvent system. It has been found that a gradual increase of base concentration induces marked changes in positional as well as geometrical orientation by simultaneously increasing the 1-alkene/2-alkene and cis-2-alkene/trans-2-alkene ratios. The variations in orientation observed for the different substrates and/or base-solvent combinations are very similar. Concentration-dependent competition of dissociated and associated alkoxide species in the reaction or concentration-dependent solvation of leaving group by metal alkoxides are proposed to account for the changes in orientation.

The search for the active base operating in alkoxide promoted E2 reactions in low polar solvents: A kinetic analysis of the elusive problem

Partial kinetic orders in base for 1-decene, cis-2-decene and trans-2-decene formation from the reaction of 2-decyl bromide with t-C4H9OK in tetrahydrofuran and in tert-butanol and with t-C4H9ONa in tert-butanol have been determined and their significance for assessment of active base has been probed. It has been ascertained that assessment of active base in alkoxide promoted E2 reactions is model-dependent. An unambiguous evidence has been provided by a kinetic analysis of the effect of base concentration on olefin-isomer distribution in the reaction. Two alternative kinetic models of this effect have been devised, the one assuming a competition of several active base species for a single substrate and the other a competition between an uncomplexed and alkoxide-complexed substrate for a single active base. Compatibility of both kinetic models with experimental data has been demonstrated.

Studies in cyclophosphazenes. Part 11. Geminal amination of (alkylamino)pentachlorocyclotriphosphazenes via a conjugate-base mechanism

Geminal amination of aminocyclotriphosphazenes is believed to proceed via a conjugate-base mechanism, but no study of this mechanism has been reported. Therefore in an endeavour to test this the effect of base concentration on the ratio of geminal to non-geminal products in the general reaction N3P3Cl5(NRR′)+ NHR″R‴ [graphic omitted] N3P3Cl4(NRR′)(NR″R‴)+ base·HCl (R,R′,R″,R‴= H or alkyl) has been investigated. The influence of the substituent groups, the amine, the solvent, and the base and its concentration have been studied. Geminal isomer formation was found to be enhanced by increased base concentration, but only if the phosphazene had a primary amine substituent. These findings conform with the proposed proton abstraction mechanism but conflict with another postulated mechanism.

A near infrared study of neteroassociation by di- T-butyl carbinol and choice of concentration scale for molecular complex equilibria

A study of the heteroassociation of di- t-butyl carbinol with seventeen organic bases in carbon tetrachloride solution mostly at −10° has been carried out using near infrared spectroscopy. The effect of base concentration on the constancy of apparent equilibrium constants favors molarity over molality as the most appropriate concentration scale for use in studies of molecular complex equilibria.

Rearrangement and Decomposition of Phosphoranyl Peroxides Produced in situ from Alkylidenephosphoranes and t-Alkylperoxy Anions

Abstract The reactions of alkylidenephosphoranes(I), produced in situ from the corresponding phosphonium salts and sodium ethoxide, with sodium salt of t-butyl hydroperoxide (II) were carried out in absolute ethanol. Carbanion (III) of phosphoranyl peroxide, formed by the reaction of I with II, underwent a rearrangement to produce t-butyl phenyl ether, alkyl t-butyl ether, and two kinds of phosphine oxides. Phosphoranyl peroxide (IV), formed by abstraction of proton from ethanol, decomposed in homolytic fashion to yield t-butyl alcohol and hydroxyphosphorane (V) as an intermediate, the decomposition of which gave benzene, hydrocarbon and corresponding phosphine oxides. Homolytic decomposition of IV was supported by the reaction of tetraphenylphosphonium bromide with II. The contribution of III was confirmed by the effect of base concentration on the amounts of rearrangement products. The reaction with cumylperoxy anion gave similar results. The mechanisms of these reactions were discussed.

Effect of base concentration upon the reactivities of the hydroxyl groups in methyl d-glucopyranosides

The anomeric methyl D-glucopyranosides were treated with N, N-diethylaziridinium chloride in various molarities of aqueous sodium hydroxide at variable ionic strength and constant ionic strength. It was found that the extent of reaction of the hydroxyl groups at C-2, C-3, and C-4 decreased with increasing concentration of base. Reaction at the C-6 hydroxyl group remained essentially constant with increasing concentration of base. Neither varying the ionic strength nor the concentration of reagent affected the distribution of substituents at any given concentration of base.

The Effect of Base Concentration and Solvent Polarity on the Base-Catalyzed Decomposition of Camphor Tosylhydrazone under Aprotic Conditions

The Effect of Base Concentration and Solvent Polarity on the Base-Catalyzed Decomposition of Camphor Tosylhydrazone under Aprotic Conditions