Strong Acidic Conditions Research Articles

Formation of N,O-Acetals in the Production of X-ray Contrast Agents

Acetylation of 1 with acetic anhydride, an important step in the preparation of iohexol, gave the corresponding acetanilide and minor amounts of a few byproducts, whose structures have been elucidated. Among the byproducts were some 1,3-oxazolidines which survived when the reaction was quenched by adding methanol and water under strong acidic conditions.

Novel cookie-with-chocolate carbon dots displaying extremely acidophilic high luminescence.

A fluorescent carbon dot with a cookie-with-chocolate film structure (about 5 × 5 μm(2)) showed a high fluorescence quantum yield (61.12%) at low pH. It was hydrothermally synthesized from l-serine and l-tryptophan. The formation mechanism of the film with carbon dots (CDs) was investigated. The film structure was formed by hydrogen bonding and π-π stacking interactions between aromatic rings. The strong blue fluorescence of the CDs increased under strong acidic conditions owing to the changes in the N-groups. These cookie-like CDs are attractive for their potential use as effective fluorescent probes for the sensitive detection of aqueous H(+) and Fe(3+).

Electrokinetic delivery of persulfate to remediate PCBs polluted soils: Effect of injection spot

Persulfate-based in situ chemical oxidation (ISCO) is a promising technique for the remediation of organic compounds contaminated soils. Electrokinetics (EK) provides an alternative method to deliver oxidants into the target zones especially in low permeable-soil. In this study, the flexibility of delivering persulfate by EK to remediate polychlorinated biphenyls (PCBs) polluted soil was investigated. 20% (w/w) of persulfate was injected at the anode, cathode and both electrodes to examine its transport behaviors under electrical field, and the effect of field inversion process was also evaluated. The results showed that high dosage of persulfate could be delivered into S4 section (near cathode) by electroosmosis when persulfate was injected from anode, 30.8% of PCBs was removed from the soil, and the formed hydroxyl precipitation near the cathode during EK process impeded the transportation of persulfate. In contrast, only 18.9% of PCBs was removed with the injection of persulfate from cathode, although the breakthrough of persulfate into the anode reservoir was observed. These results indicated that the electroosmotic flow is more effective for the transportation of persulfate into soil. The addition of persulfate from both electrodes did not significantly facilitate the PCBs oxidation as well as the treatment of electrical field reversion, the reinforced negative depolarization function occurring in the cathode at high current consumed most of the oxidant. Furthermore, it was found that strong acid condition near the anode favored the oxidation of PCBs by persulfate and the degradation of PCBs was in consistent with the oxidation of Soil TOC in EK/persulfate system.

Development of wheat glutenin nanoparticles and their biodistribution in mice.

Wheat glutenin nanoparticles intended for targeted drug delivery were biocompatible and were detected in the kidney, liver, and spleen in mice. Protein-based nanoparticles are preferred for therapeutic drug and gene delivery owing to their biocompatibility and ability to load various types of drugs. However, proteins such as a collagen and albumin are unstable in aqueous environments and are not ideal for drug delivery applications. Wheat glutenin has been demonstrated to be biocompatible and have good stability under aqueous conditions. Films and fibers have been made from wheat glutenin for medical applications but there are no reports on developing micro- or nanoparticles. In this research, wheat glutenin nanoparticles (70-140 nm) were prepared and the stability of the nanoparticles under various physiological conditions was investigated. Nanoparticles were fluorescently labeled and later injected into mice and the ability of the nanoparticles to penetrate into the cells in various organs was studied. Strong acidic or alkaline conditions provided glutenin nanoparticles with low diameters and the particles were more stable under the pH 7 rather than pH of 4. Glutenin nanoparticles were predominantly found in the liver in mice. Our in vivo and in vitro studies suggest that glutenin nanoparticles are suitable for drug delivery applications.

Characteristics of Pd-Pt Nanoparticles with Core-Shell Structure on Polybenzimidazole-Wrapped Graphene for Fuel Cell Electrocatalyst

Introduction Pt has received unremitting interest in the proton-exchange polymer electrolyte fuel cell (PEFC) technology as electrocatalysts for both the hydrogen oxidation and oxygen reduction reactions [1]. However high cost limits its application and the reduction of the amount of Pt in the catalyst is required (it was ca. 48.83 $ per gram at the beginning of 2014) [2].To reduce the usage of Pt, arranging Pt as shell on proper metal core is promising “core-shell approach”. This strategy is attractive and practical because only the outmost few layers of Pt atoms in a catalyst are actually needed in facilitating a reaction while most atoms in the bulk are more or less wasted [3, 4]. Among various metal, we chose Pd as a core metal due to the stability under strong acidic condition in PEFC [5]. Here, we attached Pd-Pt core-shell nanoparticles on Graphene which are ideal materials as conductive supporting due to the large surface area, remarkable electric conductivity and excellent electrochemical durability. This study, we utilize polybenzimidazole (PBI) as a polymeric anchor to load Pd-Pt core-shell nanoparticles on to the surface of Graphene. Experiments Graphene wrapped with PBI (Graphene/PBI) (5.0 mg) was added to a 60-vol% aqueous ethylene glycol (EG) solution (20 mL) and dispersed by sonication. Pd (OAc)2 (3.3 mg) dissolved in the methanol (5.0 mL) was added to the Graphene/PBI dispersion, and then the mixture was heated at room temperature for 3 h. H2PtCl6 •6 H2O (0.45 mg) dissolved in a 60 vol% aqueous EG solution (20 mL) was added to the Graphene/PBI/Pd dispersion and the mixture was stirring for room temperature for 24 h. The solid material was collected by filtration and washed with water and then dried under vacuum to obtain Graphene/PBI/Pd-Pt (Figure 1). Results and Discussion To inspect the structure of Pd-Pt core-shell nanoparticles, we observed scanning transmission electron microscopy (STEM). STEM operated at 200 kV are presented in Figure 2.Figures 2a and 2b show the STEM image of a Graphene/PBI/Pd-Pt. Figures 2c and 2d show the EDS mapping of Pd (red) and Pt (blue). It is obvious that Pd is surrounded by Pt as indicated in overlay (Figure 2e). The results strongly indicate the successful formation of Pd-Pt core-shell structure on Graphene/PBI. Conclusions We fabricated Graphene/PBI/Pd-Pt core-shell composite. STEM results indicate that the Graphene /PBI/Pd-Pt core-shell catalyst exhibited the core-shell nanostructure. References N. Nakashima et. al, Adv. Funct. Mater . 18, 1776 (2008)T.Fujigaya et. al, Adv. Mater. 25,1666–1681(2013)R. R. Adzic et. al, Angew. Chem. Int. Ed. 49, 8602 (2010)Y. Xia et. al. Science . 324, 1302 (2009)Y. Xia et. al. Chem. Soc. Rev. 41, 8035-8049 (2012)

Superhydrophobic mesoporous material as a pH-sensitive organic dye adsorbent

A superhydrophobic material was synthesized using a one-pot approach via the self-hydrolysis and condensation of polymethylhydrosiloxane (PMHS) under a base catalyst in ethanol and water media. The obtained superhydrophobic polymethylhydroxysiloxane (PMHOS) material was stable up to temperatures as high as 500°C, even under strong acidic and basic pH conditions. The micro–nano particles of PMHOS exhibited a hierarchical morphology with a mesoporous structure. The superhydrophobic PMHOS, however, become superhydrophilic by calcination at 600°C. The superhydrophobic and superhydrophilic PMHOS exhibited a good ability to adsorb organic dyes at a certain pH (pH 12).

Acid-Resistant Catalysis without Use of Noble Metals: Carbon Nitride with Underlying Nickel

A nanocomposite able to function as a hydrogenation catalyst under strongly acidic conditions without the presence of noble metals is synthesized and thoroughly studied. This specially designed catalyst possesses a unique structure composed of carbon nitride (CN) with underlying nickel, in which the nickel endows the CN with new active sites for hydrogen adsorption and activation while it itself is physically isolated from the reactive environment and protected from poisoning or loss. The CN is inert for hydrogenation without the help of nickel. The catalyst shows good performance for hydrogenation of nitro compounds under strong acidic conditions, including the one-step hydrogenation of nitrobenzene in 1.5 M H2SO4 to produce p-amoniophenol, for which the acid in the reaction system has restricted the catalyst only to noble metals in previous studies. Further characterization has demonstrated that the nickel in the catalyst is in an electron-deficient state because some of its electron has been donated to...

Towards a zero-waste oxidative coupling of nonactivated aromatics by supported gold nanoparticles.

We show that gold nanoparticles are able to perform the direct oxidative coupling of nonactivated aromatics with O2 as the only co-reagent. In this reaction, the aromatic acts both as reactant and solvent. Biphenyl, for example, can be obtained from benzene with high selectivity and a turnover number (TON) of 230 per pass. Similarly, several substituted biaryls can be prepared. Pd performs only one TON and even when a second catalytic functionality is introduced, together with strong acidic conditions, TON is always lower than 100. Other catalysts require iodine for performing the reaction, leading to 2 kg of waste for 1 kg of biphenyl formed, whereas no waste is created by the oxidative coupling with gold nanoparticles.

Adsorption mechanism of mixed anionic/cationic collectors in Muscovite – Quartz flotation system

The flotation separation of muscovite from quartz was investigated using mixed sodium oleate/dodecylamine acetate (NaOL/DDA) collectors. The experiments were conducted on single minerals and on a mixture of minerals, and their collecting performances were studied by means of Fourier transform infrared (FTIR) spectroscopy, zeta potential technique and X-ray photoelectron spectroscopy (XPS). The results show that neither muscovite nor quartz is floated with NaOL alone, while using DDA alone, they can be separated only at strong acid conditions (pH<3). Mixed NaOL/DDA collectors exhibits excellent performance in the flotation separation of muscovite from quartz at pH 10. The ratio of the mixed collectors is found to be an important criterion in the flotation tests. The best separation result (muscovite recovery of 80% and quartz recovery of 10%) could be achieved with NaOL/DDA molar ratios of 3/1 and 2/1 at pH 10. The co-adsorption of NaOL and DDA is found on muscovite surface by strong electrostatic interaction, hydrogen bonding and chemical adsorption. This study may provide guidance for the flotation mechanism and application of mixed anionic/cationic collectors.

Design of Multi‐Stage Thermal Responsive Wettable Surface

Design of Multi‐Stage Thermal Responsive Wettable Surface

Research and application of a novel strong acidic clean fracturing fluid

Clean fracturing fluids used in the oil-fracturing field are basically alkaline currently. The insoluble precipitate which produced from the reaction of strong alkaline liquid and reservoir formation will cause serious injury to the reservoir's permeability, and the dirt onthe surface of construction equipment is difficult to remove. The strong acidic clean fracturing fluid described here is a novel clean fracturing fluid for proppant-fracturing. It is a viscoelastic solution formed by surfactant and counter ion salt in acid solution, whichcan work in strong acid condition(pH2). It can carry and transport proppant into the specified formation location effectively in the reservoir formation up to 80°C. It has excellent shear-resistant performance and sand-carrying properties, and erode-inhibiting effectalso. The demulsification rate can reach to 90% and more. The novel acidic clean fracturing fluid will break completely when it have encountered hydrocarbons or water but no permanent damage to the formation was caused. The fracturing fluid has both etching effectand proppant-fracturing effect to calcium sandstone reservoir yield significantly. The novel acidic clean fracturing fluid has been successfully applied to the Daqing Oilfield and got remarkable results. Increasing production reached to 9 times for single well, and thestimulation ratio is 2–4 times to ordinary fractured wells.

ChemInform Abstract: Iodine Promoted Simple Synthesis of Benzimidazole Acyclonucleosides.

In nature, 5,6-dimethyl-1-(α-D-ribofuranosyl)benzimidazole exists as a moiety of vitamin B12 (Ref 1). The furanosyl benzimidazole can be considered as Cnucleoside mimic. Due to its structural similarity to purine, benzimidazole is also an important chemical entity in pharmaceuticals 2 . In one approach, aldobenzimimdazoles are prepared by the condensation of aldonic acid or aldonic δ-lactones with o-phenylenediamine 3 . The condensation reactions are often conducted in strong acidic conditions at elevated temperature (e.g.135°C) 4 . The teritol-1-yl benzimidazoles can be further converted to furanosyl benzimidazoles by Lewis acid promoted dehydrative cyclization 5 . In another approach, aldoses are subjected to oxidative condensation with o-phenylenediamine to give aldobenzimidazoles in a direct manner 6 . This approach mitigates the laborious work in the prior preparation of aldonic acids from the corresponding aldoses 7 . For example, Moore and Link 4 have previously applied this approach to synthesize two monosaccharides benzimidazoles, D-gluco and Dgalactobenzimidazoles, in 24% and 50% yields from D-glucose and D-galactose, respectively, by heating with cupric acetate (2 equiv) at 53°C for 14 hr in aqueous acetic acid solution. Some saccharide bisSchiff bases and quinaxolines also form as side products under such reaction conditions 4-6 . However using catalytic amounts of CuSO4 or replacing the AcOH solvent with MeOH does not give any desired aldo-benzimidazoles 8 . Considering the acid-sesitive internal glycosidic bonds in disaccharides and higher saccharides, it is questionable that the corresponding aldo-benimidazoles can be obtained by the above mentioned reactions involving acidic conditions at high reaction temperature. In continuation of our study, the novel transformation of aldehyde and aldoses by use of amines and iodine 9-12 , we describe herein an improved protocol for the synthesis of various aldo-benzimidazoles by direct oxidative condensation of aldoses, including different mono-saccharides with substituted ophenylenediamine in the presence of iodine.

Investigations on the degradation of aspartame using high-performance liquid chromatography/tandem mass spectrometry

Abstract Aspartame is a widely used sweetener, the long-term safety of which has been controversial ever since it was accepted for human consumption. It is unstable and can produce some harmful degradation products under certain storage conditions. A high-performance liquid chromatography/tandem mass spectrometry method was developed for the simultaneous analysis of aspartame and its four degradation products, including aspartic acid, phenylalanine, aspartyl-phenylalanine and 5-benzyl-3,6-dioxo-2-piperazieacetic acid in water and in diet soft drinks. Aspartame and its four degradation products were quantified by a matrix matched external standard calibration curve with excellent correlation coefficients. The limits of detection were 0.16–5.8 μg/L, which exhibited higher sensitivity than common methods. This method was rapid, sensitive, specific and capable of eliminating matrix interferences. It was also applied to the study of the degradation of aspartame at various pH and temperatures. The results indicated that aspartame was partly degraded under strong acidic or basic conditions and the extent of degradation increased with increasing temperature.

The influence of pH on organovermiculite structure stability

There is a large amount of research and application studies in the topic of organically modified vermiculites and their properties. In this work, the stability of two organovermiculites, one modified with hexadecyltrimethylammonium (HDTMA+) and the other modified with hexadecylpyridinium (HDP+) ions, was investigated at pH values from 1 to 14 at laboratory temperature. The organovermiculites in the pH range of 4–10 were stable. In addition, the HDTMA+-vermiculite was stable in strong alkaline media and under extreme acidic conditions as well. However, HDP+-vermiculite underwent significant decomposition when exposed to strong acidic or alkaline conditions (pH 1, 2 and 12, 14). The prepared and tested materials were investigated using X-ray diffraction (XRD) method, Fourier transform infrared (FTIR) spectrometry, total organic carbon content (TOC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The leaching of structural cations was determined as well.

The Significant Role of Carboxylated Carbonaceous Fragments in the Electrochemistry of Carbon Nanotubes

Carbon nanotubes (CNTs) have been widely employed as electrode materials in diverse branches of electrochemistry, which are claimed to display dramatically improved electrochemical behaviour compared to the conventional carbon materials. But a series of recent publications have demonstrated that the electrocatalysis of CNTs might be due to the presence of some impurities, such as metallic catalysts, nanographitic particles and amorphous carbon. For this reason, CNTs are usually purified or treated with nitric acid or nitric and sulphuric acid prior to their versatile applications. However, the strong acidic and oxidative conditions are so aggressive that serious erosion of the tube structures has inevitably taken place, which creates defects on the sidewalls and gives rise to numerous molecular byproducts, commonly referred as carboxylated carbonaceous fragments (CCFs). The adsorption of CCFs on CNTs greatly alters the surface conditions of CNTs which may significantly impact on their electrochemical properties. To this end, we wish to disclose whether the electrocatalysis of the nitric acid purified CNTs is affected by the adsorption of the CCFs. Ascorbic acid (AA) and β-nicotinamide adenine dinucleotide (NADH) as selected as the targeting benchmarks that are known to be insensitive to the presence of metallic impurities, which may guarantee the preclusion of the promoting contributions from the metallic catalysts resident in CNTs. We have demonstrated that the electrocatalytic activities of the CNTs are actually dominated by the adsorbed CCFs generated during the acidic pre-treatment. After removal of the CCFs by base rinse, the electrocatalytic properties of CNTs are greatly deteriorated and degraded to the level similar to the conventional graphite powder. We believe this finding is particularly meaningful to uncover the mysterious electrocatalysis of CNTs.

Fractionation Behavior of Metals (Al, Ni, V, and Mo) During Bioleaching and Chemical Leaching of Spent Petroleum Refinery Catalyst

We analyzed, for the first time, the different fractions of metals present in the spent catalyst and changes they undergone during bioleaching and chemical leaching. Before bioleaching, Al (83.9 %) was found mainly in the residual fraction of the pretreated spent catalyst. Ni (61.3 %) was mainly present in the exchangeable fraction exhibiting its high environmental mobility. V (58.5) and Mo (49.3 %) mainly existed in the oxidizable fraction suggesting that highly oxidizing conditions would liberate these metals from the spent catalyst. During bioleaching with Acidithiobacillus thiooxidans, almost complete solubilization of the exchangeable as well as of reducible fraction was observed. Due to strong acidic conditions, part of oxidizable fraction of these metals was also solubilized. Bioleaching also affected the fractionation of metals remaining in the treated spent catalyst. At the end of the process, most of the metals remaining in the spent catalyst were found in the more stable fractions ensuring the safe disposal of spent catalyst. The leaching yields and fractionation behavior of metals during chemical leaching was found to be identical. The results of the present study strongly suggest that bioleaching is an effective method for removing metals from the spent catalyst.

The formation mechanism and photocatalytic activity of hierarchical NiAl–LDH films on an Al substrate prepared under acidic conditions

NiAl-LDH films with hierarchical morphology have been fabricated by immersion of an Al substrate in Ni(2+)-containing solutions under strong acidic conditions, and the growth processes of the films are discussed in this communication. The as-prepared LDH films exhibit high activity in the photocatalytic degradation of organic contaminants.

A novel polyvinyltetrazole-grafted resin with high capacity for adsorption of Pb(ii), Cu(ii) and Cr(iii) ions from aqueous solutions

A novel polyvinyltetrazole-grafted resin with high capacity for the adsorption of heavy metal ions was prepared via surface-initiated atom transfer radical polymerization (SI-ATRP) of acrylonitrile on chloromethylated crosslinked styrene–divinylbenzene resin and a subsequent cyano-tetrazole conversion reaction under microwave assistance. Fourier-transform infrared spectrometry and X-ray photoelectron spectroscopy were used to characterize the surface composition of the polyvinyltetrazole-grafted resin. It was found that the grafting amount of acrylonitrile increased linearly with the polymerization time, and approximately 70% of the cyano groups on the resin surface were converted to tetrazolyl groups, as estimated by elemental analysis. The maximum adsorption capacity of the resin was up to 1.52 mmol g−1 for Pb(II), 2.65 mmol g−1 for Cu(II) and 3.36 mmol g−1 for Cr(III) at pH 5.0. The effects of pH and salt concentration on the adsorption suggested that the adsorption of metal ions was governed mainly by the chelation interaction. The adsorption isotherms of the three metal ions were best described by the Langmuir model, and their adsorption kinetics followed the pseudosecond-order kinetic equation. The adsorption of the three concerned metal ions was hardly affected by common coexisting ions such as Na(I), K(I), Ca(II) and Mg(II), whereas it was slightly decreased when Fe(III) and Zn(II) coexisted in the solution, which illustrates the selective adsorption of Pb(II), Cu(II) and Cr(III) from wastewater. The resin has a good desorption rate and is reusable. In addition, the resin exhibited excellent chemical stability under strong acidic and alkaline conditions. These findings suggest that the resin could be potentially applied to the efficient removal of heavy metal ions from wastewater.

N-Aminomethylation vs. C-Aminomethylation of Indole and Pyrrole with an N,O-Acetal Controlled by the Hardness of a Counter Ion of an Iminium Compound

Abstract Under relatively strong Lewis acidic conditions (a softer counter ion) using TMSOTf and TMSI, the aminomethylation of indole or pyrrole with a typical N,O-acetal preferentially produced the kinetically favored N-aminomethylated indole or pyrrole derivative. Use of a relatively weak Lewis acid (a harder counter ion), such as TMSCl and TMSBr, preferentially produced the thermodynamically favored C-aminomethylated indole and pyrrole derivative.

Quasi All‐Silica Zeolite Obtained by Isomorphous Degermanation of an As‐Made Germanium‐Containing Precursor

Ge-containing ITQ-22 zeolites have been almost completely degermanated under strong acidic conditions without modifications of the framework topology. Simultaneous to Ge extraction, the framework was partially dissolved; mesopores were formed but the structure was maintained through the re-incorporation of some of silicon species at vacant sites. The presence of many defects in the degermanated framework enabled the incorporation of tetrahedral aluminum, opening the way to the preparation of new and stable acid catalysts with original topologies.