Aqueous Hydrolysis Research Articles

Straightforward Synthesis of Aromatic Imines from Alcohols and Amines or Nitroarenes Using an Impregnated Copper Catalyst

AbstractThe impregnated copper on magnetite catalyst is a versatile system for the synthesis of imines starting from alcohols and amines. This catalyst does not require any type of expensive and difficult to handle organic ligand or typical transition metals, and provides excellent yields achievable under mild reaction conditions. Moreover, the catalyst is very easy to remove from the reaction medium by simply using a magnet. The one‐pot process of dehydrogenation of alcohols in the presence of aniline followed by aqueous hydrolysis gave pure alcohols in excellent yields. In addition to amines, nitroarenes could be used as the nitrogen‐containing reagent. In the case of primary amines the expected imines were successfully prepared under similar reaction conditions.

LIQUID CHROMATOGRAPHIC METHOD FOR THE SEPARATION OF ANOMERS OF MIGLITOL

A simple, inexpensive, and rapid liquid chromatography (LC) method has been developed for the quantitative determination of anomers of Miglitol, an oral anti diabetic drug. Degradation studies were performed on the bulk drug by heating to 60°C, exposure to UV light at an energy of 200 Watt hours/m2and to Visible light at an illumination of not less than 1.2 million lux hours, acid (0.1 N hydrochloric acid), base (0.1 N sodium hydroxide) aqueous hydrolysis, and oxidation with 6.0% v/v hydrogen peroxide. Good resolution between the peaks corresponding to anomeric impurities, degradation products, and the analyte was achieved on a Waters amino column using a mobile phase consisting of a mixture of aqueous ammonium dihydrogen phosphate and acetonitrile. The degradation samples were assayed against the reference standard of Miglitol and the mass balance in each case was close to 99.0%. Validation of the method was carried out as per International Conference on Harmonization (ICH) requirements.

Hydrolysis-Induced Aqueous Gelcasting: The Latest Concept for Net-Shape Consolidation of Ceramics—A Review

This is a review article covering literature reported on consolidation of ceramic components out of aqueous-based Al2O3, MgAl2O4 spinel, β-Si4Al2O2N6, β-SiAlON-SiO2 composite, and zirconia toughened alumina (ZTA) slurries following hydrolysis induced aqueous gelcasting (henceforth referred to as GCHAS) route. GCHAS is a combination of aqueous gelcasting (GC) and hydrolysis assisted solidification (HAS) routes. The advantages of GCHAS over other net-shape forming techniques in the fabrication of certain important ceramic structures such as thin wall radomes have been reviewed in this article. Interestingly, among the various colloidal-based net shape forming techniques available, GCHAS has been found to be a most promising one for consolidating complex-shaped ceramic structures with significantly high green strength and high product yield. Sintered properties of ceramics consolidated by GCHAS are compared and discussed with those of similar ceramics consolidated by aqueous slip casting (SC), GC, HAS, and a conventional dry-powder pressing (DP) of freeze dried granules in this article.

Electrochemical Studies of the Kinetics and Mechanism of Aqueous Iron Hydrolysis Reactions in Mine Water Solutions

not Available.

Conversion of cellulose to polyols over promoted nickel catalysts

Sorbitol is one of the key platform chemicals that can be applied to several industrial applications, including bio-fuels and hydrogen production. Presently there is no commercial heterogeneous catalytic process to produce sorbitol from cellulose due to the low yield and high cost of noble metals required for the conversion. In this paper we describe an aqueous phase hydrolysis–hydrogenation process to convert cellulose to sorbitol using a cheap Ni based catalyst. Monometallic Ni catalysts showed little activity for the reaction, but with the addition of a small amount of Pt to the Ni catalyst (Ni : Pt = 22 : 1 atom ratio), the activity was greatly enhanced. Results showed that the bimetallic Ni–Pt catalysts supported on mesoporous alumina gave a hexitol (sorbitol + mannitol) yield of 32.4% compared to only 5% with a Ni catalyst. Moreover, Ni–Pt supported on a mesoporous beta zeolite support provided even higher yield of 36.6%. These results were obtained after only 6 hours of run at 200 °C and 50 bar H2 pressure (at room temperature). The presence of a small amount of Pt promotes the protonation of water and hydrogen molecules, which spill over to Ni sites creating in situ acid sites to catalyse hydrolysis of cellulose.

Development and Validation of Stability Indicating LC Method for Olmesartan Medoxomil

The present method provides the detailed description of development and validation of a simple stability indicating re- verse phase column liquid chromatographic method for Olmesartan in the presence of its impurities namely Imp-A, Imp-B, Imp-C, Imp-D, Imp-E, Imp-F and Imp-G and degradation products generated from forced degradation studies. The drug substance was subjected to stress conditions of aqueous hydrolysis, Oxidative, photolytic and thermal stress degradation. The degradation of Olmesartan was observed under acid hydrolysis, base hydrolysis and peroxide. The drug was found to be stable to other stress conditions attempted. Successful separation of the drug from synthetic impu- rities and degradation products formed under stress conditions was achieved on symmetry C18, 150 mm × 4.6 mm, 5μ column using a phosphate buffer, Acetonitrile and Milli Q water. The developed LC method was validated with respect to specificity, linearity, accuracy, precision, raggedness and robustness. The assay method was found to be linear in the range of 250 μg?mL–1 to with 1000 μg?mL–1 correlation coefficient of 0.9999 and the linearity of the impurities was es- tablished from LOQ to 0.4%. Recoveries of assay and impurities were found between 98.5% and 101.2%. The devel- oped LC method to determine the related substances and assay determinations of Olmesartan can be used to evaluate the quality of regular production samples and stability samples. To best of our knowledge, the validated stability indi- cating LC method which separates all the impurities disclosed in this investigation was not published elsewhere.

Investigation of the WO3/ZrO2 surface acidic properties for the aqueous hydrolysis of cellobiose

A series of WOx/ZrO2 with various tungsten oxide loadings (1–20) wt.% was prepared by co-precipitation. The catalysts were characterized by XRD, BET, XPS, Raman spectroscopy, TPR, ammonia adsorption microcalorimetry and pyridine FT-IR spectroscopy. XRD and Raman results showed that the ZrO2 support is predominantly present in the monoclinic phase when the WO3 loading was less than 5 wt.% and predominantly in the tetragonal phase above 10 wt.%. No formation of bulk WO3 was detected for the catalysts calcined at 700 °C, which is also the case for the highest loaded samples. TPR results revealed that isolated WO3 species are easier to reduce than amorphous WOx. The ammonia adsorption microcalorimetric study evidenced acid sites with adsorption heats in the range 90 < Qdiff < 130 kJ.mol−1, in amounts which increase with increasing WO3 loading until reaching the monolayer. Concerning the acid site nature, a progressive increase of the amount of Brønsted sites with the WO3 loading was observed. The catalytic reaction of cellobiose disaccharide hydrolysis showed a better catalytic performance on the highest WO3 loaded catalysts, associated to the presence of Zr-stabilized WOx clusters and a strong protonic acidity.

Temperature effects on the stereospecificity of nucleophilic fluorination: formation of trans‐[18F]4‐fluoro‐l‐proline during the synthesis of cis‐[18F]4‐fluoro‐l‐proline

Fluorine‐18 labeled (2S,4S)‐4‐fluoro‐l‐proline (cis‐[18F]4‐FPro) has been reported to be a potential positron emission tomography tracer to study abnormal collagen synthesis occurring in pulmonary fibrosis, osteosarcomas, mammary and colon carcinomas. In this paper, we report the stereospecific radiofluorination of (2S,4R)‐N‐tert‐butoxycarbonyl‐4‐(p‐toluenesulfonyloxy) proline methyl ester (at 110°C) to produce diastereomerically pure cis‐[18F]4‐FPro in 38% radiochemical yield at the end of a 90‐min synthesis. Investigation of the effect of temperature on the stereospecificity of nucleophilic fluorination showed that diasteriomerically pure cis‐[18F]4‐FPro or trans‐[18F]4‐FPro was produced at lower temperatures (85°C–110°C) during the fluorination of (2S,4R) or (2S,4S) precursors, respectively. However, at higher temperatures (130°C–145°C), fluorination of (2S,4R) precursor produced a mixture of cis‐[18F]4‐FPro and trans‐[18F]4‐FPro diastereomers with cis‐[18F]4‐FPro as the predominant isomer. Hydrolysis of the purified fluorinated intermediate was carried out either in one step, using 2 m triflic acid at 145°C for 10 min, or in two steps where the intermediate was heated in 1 m HCl at 110°C for 10 min followed by stirring at room temperature in 1 N NaOH for 5 min. The aqueous hydrolysis mixture was loaded onto an anion exchange column (acetate form for one‐step hydrolysis) or an ion retardation column (two‐step hydrolysis) followed by a C18 Sep‐Pak® (Waters Corporation, Milford, MA, USA). Pure cis‐[18F]4‐FPro was then eluted with sterile water. We also report that epimerization of cis‐[18F]4‐FPro occurs during the two‐step hydrolysis (H+ followed by OH−) of the intermediate, resulting in 5 ± 3% trans‐[18F]4‐FPro, whereas the one‐step acid hydrolysis yielded pure cis‐[18F]4‐FPro in the final product. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Fabrication of near net shape magnesium aluminate (MgAl2O4)spinel components via aqueous processing

Net shape fabrication of magnesium aluminate (MgAl2O4)spinel (MAS) components like domes and radomes is of great importancebecause they are employed in certain important strategic applications. Environmentallyand economically benign net-shape forming techniques such as aqueous gelcasting (GC)and hydrolysis induced aqueous gelcasting (GCHAS) cannot be employedto MAS powder as it reacts with water during processing and makes the processcumbersome. The processes reported in the literature to overcome this problemand for successful fabrication of net shape MAS components like thin wallradomes/crucibles following aqueous colloidal processing routes such as GCand GCHAS are reviewed in this paper. This article also reviews the effectof surface treatment of MAS powder against hydrolysis and of consolidationroute on net shape forming capability and the sintering ability of MAS powder.Furthermore, various other net shaping techniques reported for MAS are alsoreviewed in this article.

ChemInform Abstract: Superelectrophilic Chemistry of Aminonitriles and Related Substrates.

AbstractIn the presence of superacid TfOH, Houben—Hoesch reaction of amino nitriles or cyanopyridines with benzene affords aryl ketones after aqueous hydrolysis.

In-vitro evaluation of biphenylyl acetic acid-beta-cyclodextrin conjugates as colon-targeting prodrugs: drug release behaviour in rat biological media.

Biphenylyl acetic acid was selectively conjugated to one of the primary hydroxyl groups of beta-cyclodextrin through an ester- or amide-linkage, and the physicochemical properties (aqueous solubility and hydrolysis) were investigated. Aqueous solubility of the conjugates was lower than those of either drug or parent beta-cyclodextrin. The amide conjugate was stable in aqueous solution and in rat biological fluids and gastrointestinal contents. The ester conjugate was hydrolysed to beta-cyclodextrin and biphenylyl acetic acid at moderate rates resulting in a V-shaped rate-pH profile in aqueous solution. The ester conjugate released the drug preferentially when incubated with the contents of caecum or colon, whereas no appreciable drug release was observed on incubation with contents of stomach or intestine, nor on incubation with intestinal or liver homogenates, nor on incubation with rat blood. The present results suggest that the ester-type drug conjugate of beta-cyclodextrin may serve as a colon-targeting prodrug.

Ordering Double Perovskite Hydroxides by Kinetically Controlled Aqueous Hydrolysis

The precipitation of crystals with stoichiometric and ordered arrangements of distinct metal cations often requires carefully designed molecular precursors and/or sufficient activation energy in addition to the necessary mass transport. Here, we study the formation of ordered double perovskite hydroxides, MnSn(OH)(6) and CoSn(OH)(6), of the generic chemical formula, BB'(OH)(6) (no A site), using kinetic control of aqueous hydrolysis from simple metal salt solutions. We find that the precipitation yields ordered compounds only when the B ion is Mn(II) or Co(II), and not when it is any other divalent transition metal ion, or Zn(II). The key step in forming the compounds is the prevention of rapid and uncontrolled hydrolysis of Sn(IV), and this is achieved by a fluoride counteranion. The two compounds, MnSn(OH)(6) and CoSn(OH)(6), are studied by high-resolution synchrotron X-ray diffraction and from the temperature dependence of magnetic behavior. From maximum entropy image restoration of the electron density and from Rietveld analysis, the degree of octahedral distortion and tilting and the small extent of anti-site disorder are determined. From the nonoverlapping electron density, we infer strongly ionic character of bonding. As the first magnetic study of such materials, we report simple paramagnetic behavior with no long-range magnetic order down to 2 K for the Mn(II) compound, while the cobalt compound presents uncompensated antiferromagnetic interactions, attributed to the single-ion anisotropy of octahedral Co(II).

Ionic liquid aqueous solvent‐based microwave‐assisted hydrolysis for the extraction and HPLC determination of myricetin and quercetin from Myrica rubra leaves

An ionic liquid aqueous solvent-based microwave-assisted hydrolysis (ILAS-MAH) approach was proposed for the rapid extraction and accurate determination of myricetin and quercetin from Myrica rubra (M. rubra) leaves for the first time. The effects of the ionic liquid class and concentration, liquid-solid ratio, hydrolysis temperature and time were investigated to obtain the optimal ILAS-MAH conditions. The optimized conditions were 2.0 mol/L [bmin][HSO4] or 2.5 mol/L acidified [bmin]Br solution, liquid-solid ratio 30:1 (mL : g), hydrolysis temperature 70°C and hydrolysis time 10 min. Under these conditions, the recoveries of myricetin and quercetin were in the range of 86.3-107.3% with relative standard deviation lower than 5.8%. Compared with conventional heating hydrolysis and regular MAH, the proposed approach reduced hydrolysis time and improved yields. The mechanism of ILAS-MAH was also investigated.

Production of hemicellulosic sugars from Pinus pinaster wood by sequential steps of aqueous extraction and acid hydrolysis

Pinus pinaster wood samples were subjected to aqueous extraction at 130°C to remove extractives and to a sequential stage of hydrothermal processing under selected operational conditions to obtain hemicelluloses-free solids and liquors containing hemicelluloses-derived products (mainly oligomeric saccharides and monosaccharides). Liquors were separated from the media, supplemented with sulfuric acid (4%), and heated to cause the posthydrolysis of oligomeric saccharides to yield hemicellulosic sugars. The effects of the major operational conditions on the yields of the target products were assessed in selected experiments. The considered process enabled the recovery of hemicellulosic sugars (mannose, glucose, xylose, and galactose) at almost quantitative yields.

Aqueous slip casting and hydrolysis assisted solidification of MgAl2O4 spinel ceramics

This paper reports on synthesis of MgAl2O4 spinel (MAS) powders with six different chemical compositions and the consolidation of the synthesised MAS powders following an aqueous slip casting and hydrolysis assisted solidification (HAS) routes. The synthesised MAS powders were surface passivated against hydrolysis before being dispersed in distilled water to obtain suspensions with 41–45 vol.‐% solid loading using suitable dispersing agents. In the case of the HAS process, the consolidation of suspensions was achieved in non‐porous moulds under ambient conditions by the incorporation of AlN equivalent to 1–5 wt‐%Al2O3 into the suspension. The stoichiometric MAS powder consolidated by slip casting and dry pressing routes was sintered along with those consolidated by HAS route at 1550–1650°C for 1 h. Various characterisation techniques were utilised to evaluate the effect of composition and consolidation technique on slurry characteristics and sintered properties of MAS ceramics.

Preformulation Studies of Zidovudine Derivatives: Acid Dissociation Constants, Differential Scanning Calorimetry, Thermogravimetry, X-Ray Powder Diffractometry and Aqueous Stability Studies

As part as of the preformulation studies of new 5′-OH derivatives of zidovudine, compounds 2–6, their acid dissociation constants, Differential Scanning Calorimetry (DSC) and Thermogravimetry (TG) curves, X-Ray Powder diffractograms and aqueous stability are reported. A sensitive technique such as differential scanning potentiometry was used to determine the pKa constants of the above mentioned compounds. In addition, pKa values were calculated from theoretical methods, and no significant differences with those of experimental ones were observed. X-Ray Powder Diffractometry data demonstrated that compounds 2–4 were crystalline while 5 and 6 were amorphous. DSC analysis indicated that all of them presented an exothermic decomposition peak above 150 °C which is accompanied by a weight loss in the respective TG curves. The stability of these compounds in aqueous medium at different pH values was investigated, using a validated High Performance Liquid Chromatography (HPLC) method, which demonstrated to be rapid, selective, sensitive, accurate and stability-indicating. Good recovery, linearity and precision were also achieved. For all compounds the aqueous hydrolysis followed a pseudo-first-order kinetics, depending on pH and the union existing between AZT and the associate moiety. The hydrolysis was catalyzed by hydroxide ion in the 7.4–13.2 pH range, while all compounds exhibited pH-independent stability from acidic to neutral media (pHs 1.0–7.4).

Discovery of 4-tert-Butyl-2,6-dimethylphenylsulfur Trifluoride as a Deoxofluorinating Agent with High Thermal Stability as Well as Unusual Resistance to Aqueous Hydrolysis, and Its Diverse Fluorination Capabilities Including Deoxofluoro-Arylsulfinylation with High Stereoselectivity

Versatile, safe, shelf-stable, and easy-to-handle fluorinating agents are strongly desired in both academic and industrial arenas, since fluorinated compounds have attracted considerable interest in many areas, such as drug discovery, due to the unique effects of fluorine atoms when incorporated into molecules. This article describes the synthesis, properties, and reactivity of many substituted and thermally stable phenylsulfur trifluorides, in particular, 4-tert-butyl-2,6-dimethylphenylsulfur trifluoride (Fluolead, 1k), as a crystalline solid having surprisingly high stability on contact with water and superior utility as a deoxofluorinating agent compared to current reagents, such as DAST and its analogues. The roles of substituents on 1k in thermal and hydrolytic stability, fluorination reactivity, and the high-yield fluorination mechanism it undergoes have been clarified. In addition to fluorinations of alcohols, aldehydes, and enolizable ketones, 1k smoothly converts non-enolizable carbonyls to CF(2) groups, and carboxylic groups to CF(3) groups, in high yields. 1k also converts C(=S) and CH(3)SC(=S)O groups to CF(2) and CF(3)O groups, respectively, in high yields. In addition, 1k effects highly stereoselective deoxofluoro-arylsulfinylation of diols and amino alcohols to give fluoroalkyl arylsulfinates and arylsulfinamides, with complete inversion of configuration at fluorine and the simultaneous, selective formation of one conformational isomer at the sulfoxide sulfur atom. Considering the unique and diverse properties, relative safety, and ease of handling of 1k in addition to its convenient synthesis, it is expected to find considerable use as a novel fluorinating agent in both academic and industrial arenas.

Mesoporous zeolites as enzyme carriers: Synthesis, characterization, and application in biocatalysis

We study the application of hierarchical ZSM-5 zeolites, combining micropores and intracrystalline mesopores, as carriers for lipase enzymes compared with purely microporous ZSM-5 and mesoporous MCM-41. Strategies to improve enzyme immobilization by modification of the support porosity and surface properties ( e.g. by reaction with organosilane, or by treatment with the enzyme cross-linking agent glutaraldehyde) are also reported. Spectroscopic screening of catalyst activity and recyclability for the aqueous phase hydrolysis of p-nitrophenyl esters, permits evaluation of the influence of support properties and immobilization conditions on the performance of the resulting biocatalysts. An excellent correlation is observed between the mesopore surface area, the enzyme uptake, and the corresponding biocatalyst activity, demonstrating the functional character of mesopores in hierarchical zeolites. Modification of the mesopore walls prior to enzyme immobilization is essential to attain an active and recyclable biocatalyst. Enzymes immobilized on purely inorganic supports exhibit rapid loss of activity attributed to enzyme leaching. Despite the high mesopore surface area of surface-functionalized MCM-41, the mono-dimensionality of the mesopores results in restricted accessibility and a reduced enzyme uptake. In comparison, the interconnected mesopores of the hierarchical zeolites remain accessible after surface functionalization showing good adsorption properties. Lipase immobilized on thiol-functionalized mesoporous ZSM-5 was found to be the most efficient biocatalyst.

Radiation-induced graft polymerization of functional monomer into poly(ether ether ketone) film and structure-property analysis of the grafted membrane

Radiation-induced graft polymerization of sulfo-containing styrene derivatives into crystalline poly(ether ether ketone) (PEEK) substrates was carried out to prepare thermally and mechanically stable polymer electrolyte membranes based on an aromatic hydrocarbon polymer, so-called “super-engineering plastics”. Graft polymerization of the sulfo-containing styrene, ethyl 4-styrenesulfonate (E4S) into a high crystalline PEEK substrate (degree of crystallinity: 32%) hardly progressed, whereas graft polymerization into a low crystalline PEEK substrate (degree of crystallinity: 11%) gradually progressed, achieving a grafting degree of more than 50% after 72 h. Oxygen radicals appeared in the ESR spectra of irradiated PEEK films, indicating that graft polymerization initiates from the phenoxy radicals generated by scission of PEEK main chains and proceeds so as to yield block type grafts. The PEEK-based polymer electrolyte membrane (PEM) converted by aqueous hydrolysis of grafted films exhibited mechanical strength (100 MPa), being 88% of the original PEEK substrates. These mechanical properties of PEEK-based PEM are much higher than those of graft-type fluorinated PEM reported previously and almost three times higher than that of Nafion (35 MPa). Wide- and small-angle X-ray scattering (WAXS and SAXS) indicated that the graft polymerization was accompanied with recrystallization of the amorphous phase of PEEK substrate, the well known solvent-induced recrystallization of amorphous PEEK solids, to form a weak lamellar structure with 8 nm spacing. Complementary SAXS and small-angle neutron scattering (SANS) observations clearly showed that the graft-type PEEK membranes possessed ion channel domains with the average distance of 13 nm, being larger than that of Nafion. Furthermore, there was a micro-structure in the ion channels with the average distance of 1.8 nm.

Epimerization and hydrolysis of 3,6-dimethyl-2,3,5,6-tetrahydro[1,2,4]thiadiazino[6,5,4- hi]indole 1,1-dioxide

In this study, configurational and chemical stability of (R,R),(S,S),(R,S),(S,R)-3,6-dimethyl-2,3,5,6-tetrahydro[1,2,4]thiadiazino[6,5,4- hi]indole 1,1-dioxide ( 1) were investigated by dynamic and stopped-flow HPLC methods. Single epimeric mixtures (R,R),(R,S)- 1 and (S,S),(S,R) -1 were obtained combining synthetic and chromatographic strategies. Separation of (R,R) -1 and (R,S)- 1 was achieved by chiral chromatography and absolute configuration of eluted epimers has been assigned basing on molecular modelling calculations. Epimerization and hydrolysis of (R,R),(R,S)- 1 have been studied by classical off-column, dynamic HPLC and stopped-flow HPLC methods. The influence of different parameters, such as temperature, pH and dielectric constant was evaluated. The data obtained indicate that (R,R),(R,S)- 1 undergoes to a rapid epimerization in aqueous solvent and hydrolysis in acidic conditions. Moreover, epimerization and hydrolysis were investigated in presence of an artificial membrane and in physiological buffers (pH 2.2 and 7.0 at 37.5 °C) to simulate in vivo conditions.