Strong Acidic Properties Research Articles

Fluorinated antimony(v) derivatives: strong Lewis acidic properties and application to the complexation of formaldehyde in aqueous solutions.

As part of our ongoing studies of water tolerant Lewis acids, we have synthesized and investigated the properties of Sb(C6F5)3(O2C6Cl4), a fluorinated stiborane whose Lewis acidity approaches that of B(C6F5)3. While chloroform solutions of this Lewis acid can be kept open to air or exposed to water for extended periods of time, this new Lewis acid reacts with P t Bu3 and paraformaldehyde to form the corresponding formaldehyde adduct t Bu3P-CH2-O-Sb(C6F5)3(O2C6Cl4). To test if this reactivity can also be observed with systems that combine the phosphine and the stiborane within the same molecule, we have also prepared o-C6H4(PPh2)(SbAr2(O2C6Cl4)) (Ar = Ph, C6F5). These yellow compounds, which possess an intramolecular P→Sb interaction, are remarkably inert to water but do, nonetheless, react with and accomodate formaldehyde into the P/Sb pocket. In the case of the fluorinated derivative o-C6H4(PPh2)(Sb(C6F5)2(O2C6Cl4)), formaldehyde complexation, which occurs in water/dichloromethane biphasic mixtures, is accompanied by a colourimetric turn-off response thus highlighting the potential that this chemistry holds in the domain of molecular sensing.

Efficient conversion of acids and esters to amides and transamidation of primary amides using OSU-6

OSU-6, an MCM-41 type hexagonal mesoporous silica with strong Bronsted acid properties, has been used to promote the high-yield conversion of carboxylic acids and esters to carboxamides as well as transamidations of primary amides in a one-pot solventless approach. A metal-free heterogeneous catalyst that promotes all of these processes has not been previously reported. OSU-6 enables these transformations to proceed in shorter times and at lower temperatures for a broad range of substrates. An added benefit is that the catalyst can be recycled and reused multiple times without significant loss of activity.

The influence of artificially introduced N-glycosylation sites on the in vitro activity of Xenopus laevis erythropoietin.

Erythropoietin (EPO), the primary regulator of erythropoiesis, is a heavily glycosylated protein found in humans and several other mammals. Intriguingly, we have previously found that EPO in Xenopus laevis (xlEPO) has no N-glycosylation sites, and cross-reacts with the human EPO (huEPO) receptor despite low homology with huEPO. In this study, we introduced N-glycosylation sites into wild-type xlEPO at the positions homologous to those in huEPO, and tested whether the glycosylated mutein retained its biological activity. Seven xlEPO muteins, containing 1–3 additional N-linked carbohydrates at positions 24, 38, and/or 83, were expressed in COS-1 cells. The muteins exhibited lower secretion efficiency, higher hydrophilicity, and stronger acidic properties than the wild type. All muteins stimulated the proliferation of both cell lines, xlEPO receptor-expressing xlEPOR-FDC/P2 cells and huEPO receptor-expressing UT-7/EPO cells, in a dose-dependent manner. Thus, the muteins retained their in vitro biological activities. The maximum effect on xlEPOR-FDC/P2 proliferation was decreased by the addition of N-linked carbohydrates, but that on UT-7/EPO proliferation was not changed, indicating that the muteins act as partial agonists to the xlEPO receptor, and near-full agonists to the huEPO receptor. Hence, the EPO-EPOR binding site in X. laevis locates the distal region of artificially introduced three N-glycosylation sites, demonstrating that the vital conformation to exert biological activity is conserved between humans and X. laevis, despite the low similarity in primary structures of EPO and EPOR.

Catalytic behaviors of chloromethane combustion over the metal-modified ZSM-5 zeolites with diverse SiO2/Al2O3 ratios

A series of M/ZSM-5 (M=Co, Fe, Ce, and Mn) catalysts with different molar ratios of SiO2/Al2O3 (30, 107) was prepared via a traditional wetness impregnation, and further characterized by XRD, BET, H2-TPR, NH3-TPD, and XPS as well as activity test for the catalytic combustion of chloromethane. Characteristic structure of ZSM-5 is basically maintained even after impregnating the various metallic components. Catalytic activities achieving under an atmosphere of 1500ppm CH3Cl, 10% O2, and GHSV of 15,000h−1 of the investigated catalysts follow a trend of Co/ZSM-5-30, Ce/ZSM-5-30>Co/ZSM-5-107, Ce/ZSM-5-107, Fe/ZSM-5-30, Mn/ZSM-5-30>Mn/ZSM-5-107, Fe/ZSM-5-107>H-ZSM-5-30>H-ZSM-5-107. The binary Co/ZSM-5-30 and Ce/ZSM-5-30 show the satisfactory conversions of CH3Cl (87% and 95%) associated with a low yield of CO (9.6% and 16%) at 400°C, owing to the excellent redox properties (determined by the chemical nature of the loaded metallic components) and strong acidic properties (modified by Al isomorphic substitution) of the as-prepared zeolitic catalysts.

Mechanism of the initiation of low-temperature radiation telomerization of tetrafluoroethylene in hexafluoroisopropanol

ESR and IR spectroscopy and scanning calorimetry are used to investigate the mechanism of low-temperature radiation telomerization of tetrafluoroethylene (TFE) in hexafluoroisopropanol (HFIP). It is found that the low-temperature telomerization of TFE in HFIP proceeds via an ion-radical mechanism. This process is initiated by the radical anions (CF3)2C·-O− formed during the deprotonation of OH groups of primary hydroxyl radicals (CF3)2C·-OH exhibiting strong acidic properties. An interpretation of ESR spectra of irradiated HFIP recorded at 230–240 K is proposed with regard to the anisotropy on β-fluorine atoms and estimates of the angles between the corresponding C-F bonds and the axis of the unpaired electron orbital.

Dissolved organic matter in lysimetric water of mountain forest soils in the southern Sikhote Alin

The fractional composition of dissolved organic matter and the chemical nature of humic and fulvic acids were studied in lysimetric waters from forest soils of different altitudinal zones in the Sikhote Alin Range. The elemental composition, infrared absorption spectra, concentrations of acid functional groups, and pK spectra of humic and fulvic acids were determined. Fulvic acids predominated in the upper soil horizons, and fraction of nonspecific dissolved organic substances predominated in the lower mineral horizons. The portion of humic acids in the humus horizons markedly decreased from the low-mountain soils to the high-mountain soils; the nitrogen content of humic and fulvic acids decreased in the same direction. Three classes of carboxyl and phenolic groups were determined in pK-spectra of humic and fulvic acids. The soils of high-mountain zones had stronger acidic properties of humic and fulvic acids in comparison with the soils of low-mountain zones. The determined characteristics of the composition of dissolved organic matter and the trends of their changes contribute to our knowledge of pedogenetic processes in the altitudinal sequence of forest landscapes of the Sikhote Alin Range.

Arene–Ruthenium Chemistry and Brønsted Acid Catalysis of a Chiral Phosphane-Hydroxyl Ligand

The phosphane-hydroxyl ligand (SC1,RC2)-Ph2PC(Ph)HC(OH)HCH2OMe (POH) displays κ1P, κ2P,O, κ3P,O,O′, and anionic deprotonated κ3P,O,O′ coordination modes toward the metallic (η6-p-MeC6H4iPr)Ru moiety. The hydroxyl group in [(η6-p-MeC6H4iPr)Ru(κ3P,O,O′-POH)][SbF6]2 (3) has strong acidic properties. This complex catalyzes the Diels–Alder reaction between cyclopentadiene and trans-β-nitrostyrene or methacrolein as well as the Friedel–Crafts reaction between indole and methyl 3,3,3,-trifluoropyruvate or trans-β-nitrostyrene. Solution studies strongly indicate that complex 3 acts as a metallic Lewis acid assisted Brønsted-acid catalyst.

Dispersibility of HCl-treated Cellulose Nanocrystals with Water-dispersible Properties in Organic Solvents

Abstract The dispersibility of cellulose nanocrystals (CNCs) with water-dispersible properties, which were prepared by HCl treatment of cellulose resources, in organic solvents was investigated by cross-polar images. It was found that the CNCs were dispersed well in amphoteric solvents with strong Lewis acid and base properties, similar to the original water solvent.

Chemical characterisation of humic-like substances from urban, rural and tropical biomass burning environments using liquid chromatography with UV/vis photodiode array detection and electrospray ionisation mass spectrometry

Environmental contextOne of the most important classes of water-soluble organic compounds in continental fine and tropical biomass burning aerosol is humic-like substances (HULIS), which contain components with strong polar, acidic and chromophoric properties. We focus on the chemical characterisation of HULIS and provide evidence that nitro-aromatic catecholic compounds are among the major species of HULIS. This indicates that volatile aromatic hydrocarbons emitted during biomass burning are important gas-phase precursors for HULIS. AbstractHumic-like substances (HULIS) are ubiquitously present in the troposphere and make up a major fraction of continental fine-sized water-soluble organic compounds. They are regarded as material with strong polar, acidic and chromophoric properties; however, structural information at the individual component level is rather limited. In the present study, we have characterised HULIS from different locations using liquid chromatography coupled to photodiode array detection and negative ion electrospray ionisation mass spectrometry. Aerosol samples with particles less than 2.5 μm in diameter (PM2.5) were collected in Budapest and K-puszta, Hungary, during 2007 and 2008 spring and summer periods, and in Rondônia, Brazil, during a 2002 biomass burning experiment. Major components of the Budapest 2007 and Brazil 2002 HULIS corresponded to chromophoric substances, of which 4-nitrocatechol (molecular weight (MW) 155) was identified as the most abundant organic species and less abundant ones were attributed to mono- and dimethyl nitrocatechols (MWs 169 and 183). The mass concentrations of 4-nitrocatechol in the water-soluble organic carbon (WSOC) of the Budapest 2007 and day- and night-time Brazil 2002 HULIS were 0.46, 0.50 and 1.80 %. Abundant components of K-puszta 2008 HULIS were assigned to α-pinene secondary organic aerosol (SOA) tracers, i.e. 3-methyl-1,2,3-butanetricarboxylic acid and terpenylic acid; their mass concentrations in the HULIS WSOC were 0.75 and 0.40 %. Tere- and ortho-phthalic acids (MW 166) were major components of the Budapest and K-puszta HULIS, but only minor ones of the Brazil 2002 biomass burning HULIS, consistent with a source that is different from biomass burning and likely related to open waste burning of phthalate ester-containing material such as plastic.

Effect of silica on the selective oxidation of methanol to dimethoxymethane over vanadia–titania catalysts

V–Ti–O oxides with about 4% sulfate were prepared by a co-precipitation method, which showed strong surface acidic and redox properties, and therefore exhibited good performance for the selective oxidation of methanol to dimethoxymethane (DMM) at relatively low reaction temperatures (e.g., 443 K). However, the selectivity to DMM substantially decreased when reaction temperature increased to higher than 453 K. Addition of SiO2 significantly weakened the surface acidity and redox ability of V–Ti–O, and significantly improved the selectivity to DMM above 453 K. Ninety-three percentage selectivity to DMM with 66% conversion of methanol was obtained over a Si–V–Ti–O catalyst at 483 K.

IR spectroscopic and catalytic characterization of the acidity of imogolite-based systems

This paper studies the surface properties of three systems based on imogolite, as it concerns the type, acidic strength, accessibility and stability of hydroxyl groups. Proper imogolite presents a peculiar nanotube structure with remarkable surface features being the outer surface covered by Al(OH)Al groups and the inner surface lined by abundant, but presumably non-interacting, SiOH groups. As a hydrated alumino-silicate, the behaviour of imogolite is very sensitive to thermal pre-treatments. Molecular water is removed only at 300 °C: this makes inner silanols accessible to probes such as CO, ammonia, methanol and, partially, to phenol. Silanols are as acidic as those of amorphous silica, but their abundance enhances the interaction with adsorbed molecules: on the one hand, ammonia is observed to form ammonium species, and on the other hand, diffusion is difficult. At temperatures around 500 °C, the nanotube structure is lost with the formation of a lamellar phase showing new stronger acidic properties, resembling those of amorphous alumino-silicates with high Al content. An amorphous precursor phase with the same chemical composition (proto-imogolite) is also available, and has been studied as were the other forms of imogolite. Catalytic tests of gas-phase phenol reaction with methanol showed that the aromatic compound has a limited access to inner silanols at high temperature, whereas methanol interacts with both inner silanols and outer Al(OH)Al groups. Proto-imogolite shows a remarkable acid-type behaviour in phenol methylation, which, however, rapidly declines because of deactivation phenomena. A peculiar reactivity is shown by the lamellar phase: its amphoteric character, combining both basic and acidic Lewis sites, leads to a high regio-selective behaviour, and to the preferred formation of o-cresol.

Evaluation of strong acid properties of layered HNbMoO 6 and catalytic activity for Friedel–Crafts alkylation

The acid properties and catalytic activity of layered HNbMoO 6 for liquid-phase Friedel–Crafts alkylation are examined. 31P MAS NMR spectroscopy using trimethylphosphine oxide as a probe molecule reveals that HNbMoO 6 possesses strong acid sites in the interlayer region. Layered HNbMoO 6 is demonstrated to display remarkable catalytic performance for this reaction, substantially exceeding the activities of niobic acid, niobium–molybdenum mixed oxide, ion-exchange resins, and zeolites. It is determined that benzyl alcohol is intercalated into the HNbMoO 6 interlayer during alkylation to form a monolayer configuration, allowing the strong interlayer acid sites to participate in the reaction.

Catalytic activity of zeolitic and mesostructured catalysts in the cracking of pure and waste polyolefins

Six acid solids of varying acid and textural characteristics has been investigated for their catalytic activity in the degradation of plastic polymers using thermogravimetric and differential thermal analysis. The polymers included pure low-density polyethylene, pure high-density polyethylene and two samples of recycled polyethylene of urban and agricultural origins. The catalysts were three zeolitic materials (standard ZSM-5, nanocrystalline n-ZSM-5 and Beta) and three mesostructured solids (sol–gel Al-MCM-41 (sg), hydrothermal Al-MCM-41 (hy) and Al-SBA-15). The catalytic activity of each acid solid has been related to its capacity to shift the degradation reaction to lower temperatures. Despite showing strong acid properties, standard ZSM-5 zeolite exhibited a very low catalytic activity on most plastics, which was attributed to diffusional impediments that affected the access of the bulky polymer molecules to its internal active sites. These impediments were partly overcome in the case of Beta zeolite and even more markedly with nanocrystalline n-ZSM-5, which exhibited the strongest catalytic activity due to a combination of strong acid properties and large external surface area. Owing to their non-crystalline nature, mesostructured solids showed weaker acid properties than their zeolitic counterparts. However, this disadvantage was partly compensated by the presence of larger pores that reduced diffusional hindrances. Thus, Al-MCM-41 (hy) exhibited one of the highest catalytic activities, largely surpassing the performance of crystalline solids with stronger acid properties. The catalytic activity of all the acid solids tested in this work was significantly reduced when they were used on waste plastics. This deactivating effect was more notable in mesostructured solids.

The transformations of toluene on alumina and bifunctional catalysts

The activity of Pt, Rh, and Ni catalysts deposited on Al2O3 and tungsten-containing catalysts 20% H4SiW12O40/ZrO2 and 15% WOx/ZrO2 in the hydrogenation of toluene and toluene ring opening and isomerization in the presence of hydrogen was studied. Under experimental conditions (160–360°C, 2.2 MPa), the main reactions on Rh/Al2O3 were the hydrogenation of toluene into methylcyclohexane, hydrogenolysis into isoheptanes, and hydrocracking into alkanes C1–C6. On Pt, Rh, and Ni catalysts on carriers with strong acid properties, the isomerization of the six-membered into five-membered ring followed by hydrogenolysis (hydrocracking) of alkylcyclopentanes occurred. The yield of heptane isomers, however, did not exceed 13%. The activity of Pt and Rh catalysts on a high-acidity carrier (WOx/ZrO2) in hydrocracking was much higher than that of catalysts based on deposited heteropoly acid. The yields of hydrogenolysis (hydrocracking) products on Ni/WOx/ZrO2 were much lower than on Pt(Rh)/WOx/ZrO2. The highest yield of ring opening products (isoheptanes and n-heptane) was obtained with layered loading of two catalysts; it reached 58 wt % at 300°C and a 2.2 MPa pressure, which was 4.5 and 2 times higher than the yield obtained on Ni-Pt/WOx/ZrO2 and 2% Rh/Al2O3 catalysts. Hydrodemethylation was not the main direction of toluene transformations on any of the catalysts studied.

Self-Humidifying Cs2.5H0.5PW12O40 / Nafion / PTFE Composite Membrane for Proton Exchange Membrane Fuel Cells

A Cs2.5H0.5PW12O40/Nafion/polytetrafluoroethylene (PTFE) self-humidifying composite membrane was developed for proton exchange membrane fuel cells. It was prepared by recasting the Cs2.5H0.5PW12O40/Nafion self-humidifying layer onto the two sides of a Nafion/PTFE composite membrane with a solution-recast method. Due to the strong acidic, hydrophilic, and redox properties of Cs2.5H0.5PW12O40, the Cs2.5H0.5PW12O40/Nafion self-humidifying layer not only contributes to humidify the membrane but also contributes to the improvement of the open-circuit voltage of the fuel cell. When the self-humidifying composite membrane was employed as an electrolyte in H-2/O-2 PEMFC, a higher maximum power density value (1.1 W/cm(2)) was obtained than that of Nafion/PTFE composite membrane (0.6 W/cm(2)), under the operating conditions of 70 degrees C and at the humidified temperature of 20 degrees C. (c) 2005 The Electrochemical Society.

Study of the acid character of some palladium-modified pillared clay catalysts: Use of isopropanol decomposition as test reaction

Preparation, textural and structural characterizations as well as acid properties of some aluminium, zirconium pillared montmorillonite (from Algerian bentonite) and including alumina or zirconium pillared montmorillonite supported palladium are reported. Heat resistant basal spacings of 1.7 nm, surface areas in the range of 250–300 m 2/g and micropore volumes of about 0.1 cm 3/g were obtained. The acid activation of montmorillonite prior pillaring conduces to a resulting material with significantly higher pore volume and acidity. The improvement in acidity is mainly of the Brønsted acid type. The modification of zirconium-pillared montmorillonite with sulfate ions affects the structural properties of the pillared sample but gives a material with strong acid properties and both Lewis and Brønsted acid types are enhanced. It is reported also that textural and structural properties are not affected by the impregnation of a metallic function (1 wt.% Pd loading) but the acid properties changed. The pillared montmorillonite supported palladium has more Brønsted acidity than does the pillared montmorillonite. Decomposition of isopropanol was studied on these systems at low reaction temperature.

Fabrication of Nafion- and heteropoly acid-containing thin catalytic films without failure

It has been shown that homogeneous thin films of silica heavily loaded with phosphotungstic acid (30 wt.%) or Nafion (50 wt.%) can be uniformly deposited on various substrates by a dip-coating to give effective structured catalysts with strong acidic properties. Experiments indicate that the use of well condensed silica sols, with over 75% of Q n population in the form of Q 3 sites, is a precondition to obtain crack-free films and that the withdrawal speed plays a second order role, especially at lower viscosities. Based on the quality maps of the films prepared under various conditions we conclude that defect-free coatings can be obtained provided that sol viscosity is above the specific threshold value and still within a linear part of the viscosity dependence upon time.

Adsorption of Pd atoms on γ-Al2O3: a density functional study of metal–support interactions

The Pd/γ-Al2O3 interface at low coverage has been theoretically studied by means of periodic-supercell density functional calculations. The most stable (110) γ-Al2O3 clean surface plane has been modelled by using a six layers slab stoichiometric model of 40 atoms. A single Pd atom has been deposited on top of the surface in different positions, first freezing the surface structure and later allowing the surface to relax. The results indicate that the metal–support interaction is dominated by the strong Lewis acid properties of the tetrahedral cationic sites. It is also shown that in the octahedral cationic sites, adsorption of single Pd atoms induces a significant relaxation of the substrate. While the interaction energy with the preferred site is strong (∼3.8eV), small differences are found for nearby sites, indicating a high mobility of Pd atoms on the surface, at least on the channels.

Efficient Synthesis of N‐(Trifluoromethylsulfonyl)trifluoromethanesulfonimidoyl Fluoride — The Key Agent in the Preparation of Compounds with Superstrong Electron‐Withdrawing Groups and Strong Acidic Properties.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Opposite activation conditions of acid and metal functions of Pt/SO 42−-ZrO 2 catalysts

The influence of the thermal treatments of Pt/SO 4 2−-Zr(OH) 4 catalysts on the activity for the metal-catalyzed reaction of cyclohexane dehydrogenation and the acid-catalyzed reaction of n-butane isomerization, were studied in this work. A mutual antagonism between the conditions for optimal activity of the acid and metal functions was found and was seemingly related to the crystallization of the support. In order to be able to isomerize n-butane, SO 4 2−-Zr(OH) 4 had first to be calcined in air at T calc>400 °C. The onset of activity and strong acid properties coincided with the appearance of the tetragonal crystal phase. SO 4 2−-Zr(OH) 4 supported Pt, prepared from chloroplatinic acid, was tried to be converted to the metal state (Pt 0) in order to have full catalytic capacity. When Pt/SO 4 2−-Zr(OH) 4 was first calcined in air at T calc>400 °C, Pt remained in a seemingly oxidized state, with no de/hydrogenation properties even after reduction in H 2 at 300 °C. Under certain conditions, Pt metal properties were improved: (i) calcining Pt/SO 4 2−-Zr(OH) 4 in air at T calc<400 °C; (ii) calcining Zr(OH) 4 at T calc>400 °C before sulfating the support; and (iii) calcining Pt/SO 4 2−-Zr(OH) 4 in N 2 instead of air. In these cases, though Pt dehydrogenation activity increased, the activity of the acid function decreased (iii) or was practically null ((i) and (ii)). The support was amorphous in case (i) and mainly monoclinic in case (ii). Sulfate loss and conversion into the monoclinic phase occurred in case (iii). As compared to sulfate-free Pt/ZrO 2, sulfur poisoning always decreased the metal activity of sulfated catalysts but the decrease was higher for mainly tetragonal sulfate-doped catalysts. The final conclusion is that the optimum activation conditions for the metal and acid functions in Pt/SO 4 2−-Zr(OH) 4 are mutually excluding. The deleterious effect of SO 4 2−-ZrO 2 (SZ) on Pt metal activity is closely related to the growth and/or the presence of the tetragonal phase and cannot be prevented if a high activity of the acid function is demanded by the reacting system.