Showing papers on "Anhydrous published in 2003"

Fast and Easy Multiresidue Method Employing Acetonitrile Extraction/Partitioning and "Dispersive Solid-Phase Extraction" for the Determination of Pesticide Residues in Produce

Abstract: A simple, fast, and inexpensive method for the determination of pesticide residues in fruits and vegetables is introduced. The procedure involves initial single-phase extraction of 10 g sample with 10 mL acetonitrile, followed by liquid-liquid partitioning formed by addition of 4 g anhydrous MgSO4 plus 1 g NaCl. Removal of residual water and cleanup are performed simultaneously by using a rapid procedure called dispersive solid-phase extraction (dispersive-SPE), in which 150 mg anhydrous MgSO4 and 25 mg primary secondary amine (PSA) sorbent are simply mixed with 1 mL acetonitrile extract. The dispersive-SPE with PSA effectively removes many polar matrix components, such as organic acids, certain polar pigments, and sugars, to some extent from the food extracts. Gas chromatography/mass spectrometry (GC/MS) is then used for quantitative and confirmatory analysis of GC-amenable pesticides. Recoveries between 85 and 101% (mostly > 95%) and repeatabilities typically < 5% have been achieved for a wide range of fortified pesticides, including very polar and basic compounds such as methamidophos, acephate, omethoate, imazalil, and thiabendazole. Using this method, a single chemist can prepare a batch of 6 previously chopped samples in < 30 min with approximately 1 dollar (U.S.) of materials per sample.

Crystallization and phase stability of CaSO4 and CaSO4- based salts

Abstract: Calcium sulfate occurs in nature in form of three different minerals distinguished by the degree of hydration: gypsum (CaSO4·2H2O), hemihydrate (CaSO4·0.5H2O) and anhydrite (CaSO4). On the one hand the conversion of these phases into each other takes place in nature and on the other hand it represents the basis of gypsum-based building materials. The present paper reviews available phase diagram and crystallization kinetics information on the formation of calcium sulfate phases, including CaSO4-based double salts and solid solutions. Uncertainties in the solubility diagram CaSO4–H2O due to slow crystallization kinetics particularly of anhydrite cause uncertainties in the stable branch of crystallization. Despite several attempts to fix the transition temperatures of gypsum–anhydrite and gypsum–hemihydrate by especially designed experiments or thermodynamic data analysis, they still vary within a range from 42–60°C and 80–110°C. Electrolyte solutions decrease the transition temperatures in dependence on water activity. Dry or wet dehydration of gypsum yields hemihydrates (α-, β-) with different thermal and re-hydration behaviour, the reason of which is still unclear. However, crystal morphology has a strong influence. Gypsum forms solid solutions by incorporating the ions HPO4 2−, HAsO4 2−, SeO4 2−, CrO4 2−, as well as ion combinations Na+(H2PO4)− and Ln3+(PO4)3−. The channel structure of calcium sulfate hemihydrate allows for more flexible ion substitutions. Its ion substituted phases and certain double salts of calcium sulfate seem to play an important role as intermediates in the conversion kinetics of gypsum into anhydrite or other anhydrous double salts in aqueous solutions. The same is true for the opposite process of anhydrite hydration to gypsum. Knowledge about stability ranges (temperature, composition) of double salts with alkaline and alkaline earth sulfates (esp. Na2SO4, K2SO4, MgSO4, SrSO4) under anhydrous and aqueous conditions is still very incomplete, despite some progress made for the systems Na2SO4–CaSO4 and K2SO4–CaSO4–H2O.

Physicochemical Properties of 1,3-Dialkylimidazolium Fluorohydrogenate Room-Temperature Molten Salts

Abstract: Reaction of some N-alkylimidazolium chlorides with anhydrous hydrogen fluoride (HF) gave nonvolatile room temperature molten salts (room temperature ionic liquids), RMImF.2.3HF where RMIm = 1,3-dimethylimidazolium (DMIm), 1-ethyl-3-methylimidazolium (EMIm), 1-methyl-3-propylimidazolium, 1-butyl-3-methylimidazolium, 1-methyl-3-pentylimidazolium, and 1-hexyl-3-methylimidazolium. Vacuum stable salts at room temperature exhibited similar stoichiometry regardless of the type of cation. In the differential scanning calorimetry (DSC) curve, DMImF.2.3HF exhibited both the freezing and melting on the cooling and heating process, respectively, while EMImF.2.3HF showed the glass transition on the cooling process and devitrification and melting on the heating process. The other salts show only the glass transition on the DSC curves. High specific conductivities, 110 and 100 mS cm -1 , were observed at 298 K for DMImF.2.3HF and EMImF.2.3HF, respectively. Introduction of the longer alkyl side chains to the imidazolium cation increased the viscosity and decreased the conductivity. These salts were stable in air and did not etch a Pyrex glass container at ambient conditions. The dissociation pressures of HF from the salts were negligibly small at ambient condition. The electrochemical windows of these salts was about 3 V.

A computational and experimental study of anhydrous phosphotungstic acid and its interaction with water molecules

Abstract: The hydration state of phosphotungstic acid (H 3 PW 12 O 40 ) was explored through the use of in situ Fourier transform infrared (FT-IR) spectroscopy, water sorption microcalorimetry, and density functional theory (DFT) quantum chemical calculations. In addition, the proton affinities of the various sites on the Keggin unit were evaluated. The small differences ( −1 ) between the proton affinities of bridge and terminal oxygen atoms indicate that protons likely reside on both types of sites on the Keggin unit. Vibrational spectra calculated by DFT and measured experimentally by in situ FT-IR spectroscopy compare very well. The adsorption energy of a water molecule on an anhydrous Keggin unit was calculated to be approximately −55 to −70 kJ mol −1 for the formation of H 3 O + , independent of protonic site. The range compares well to the heat of water sorption (−65 kJ mol −1 ) determined from microcalorimetry on a sample dehydrated at 573 K. The uptake of gaseous water molecules was found to be five times higher on a sample pretreated at 473 K than on one pretreated at 573 K, indicating that the hydrated secondary structure does not reform after the high temperature pretreatment. In situ FT-IR spectroscopy confirms the lack of reversibility during dehydration/rehydration treatment for samples heated to 573 K.

A Novel Self-generating Liquid MOCVD Precursor for Co3O4 Thin Films

Abstract: The novel [Co(C5F6HO2)2·2H2O·CH3(OCH2CH2)4OCH3] low-melting adduct has been synthesized and characterized. Very mild heating results in the anhydrous Co(hfac)2tetraglyme liquid and thermal stable complex that evaporates intact. This adduct has proven to be a well-suited precursor for MOCVD of cobalt oxide films.

Synthesis of Coinage-Metal Nanoparticles from Mesityl Precursors

Abstract: An anhydrous route for the synthesis of amine-capped coinage-metal nanoparticles (NP) has been developed using coinage-metal mesityl (mesityl = 2,4,6-Me3C6H2) derivatives. Under an argon atmosphere, crystalline [Cu(μ-mesityl)]5, [Ag(μ-mesityl)]4, and [Au(μ-mesityl)]5 were readily dissolved in octylamine (0.3 M solution) and subsequently injected into a heated hexadecylamine solution (300 °C), generating the corresponding metal nanoparticles. After washing with methanol and extracting with toluene, oxide-free coinage NPs were isolated and characterized by UV−vis spectroscopy and transmission electron microscopy. Under these conditions, the spherical NPs were found to be 8−9 nm in size for Cu° (no surface oxide present), 9 nm for Ag°, and 8−80 nm for Au°. Reducing the concentration of the precursor solution, the temperature of the solution, and the time of reaction led to the synthesis of Au° NPs that were 12 ± 1 nm in size.

Sodium carbonate and sodium bicarbonate production from nahcolitic oil shale

Abstract: A method for solution mining nahcolite, capable of extracting nahcolite from geological formations lean in nahcolite comprising injecting high pressure water (which may include recycled aqueous solution of bicarb and sodium carbonate) at a temperature of at least 250° F. into the formation, dissolving nahcolite in the hot water to form a production solution and recovering the production solution. The invention also includes the processing of the production solution to provide sodium carbonate and, optionally, sodium bicarbonate, comprising: decomposing the sodium bicarbonate portion of the hot aqueous production solution to form a hot aqueous solution of sodium carbonate; evaporating water from the hot aqueous solution comprising sodium carbonate to form a concentrated solution of sodium carbonate; producing sodium carbonate monohydrate from the concentrated solution of sodium carbonate by crystallization; and dewatering and calcining the sodium carbonate monohydrate to produce anhydrous sodium carbonate.

Liquid−Liquid and Solid−Liquid Equilibrium of the Ternary System Ethanol + Cesium Sulfate + Water at (10, 30, and 50) °C

Abstract: The phase diagrams of the CH3CH2OH + Cs2SO4 + H2O system were determined at (10, 30, and 50) °C. The binodal curves were given using a five-parameter equation. The tie lines were correlated by the Othmer-Tobias and Bancroft equations. Samples of the solid phase analyzed by thermogravimetric analysis showed that it was the anhydrous salt.

Modeling anhydrous and aqua copper(II) amino acid complexes: a new molecular mechanics force field parametrization based on quantum chemical studies and experimental crystal data.

Abstract: This paper presents the vacuum structures of aquacopper(II) bis(amino acid) complexes with glycine, sarcosine, N,N-dimethylglycine, and N-tert-butyl-N-methylglycine estimated using the B3LYP method. The differences between the B3LYP vacuum structures and experimental crystal structures suggested considerable influence of crystal lattice packing effects on the changes in the complexes' geometries. A previously developed molecular mechanics force field for modeling anhydrous copper(II) amino acidates was reoptimized to simulate these changes and predict the properties of both trans and cis anhydrous and aqua copper(II) amino acid complexes. The modeling included experimental molecular and crystal structures of 13 anhydrous and 10 aqua copper(II) amino acidates with the same atom types (Cu(II), C, H, N, and O) but various copper(II) coordination polyhedron geometries, crystal symmetries, and intermolecular interactions. The empirical parameters of the selected potential energy functions were optimized on the...

Solvothermal Synthesis and Structure of Anhydrous Manganese(II) Formate, and Its Topotactic Dehydration from Manganese(II) Formate Dihydrate

Abstract: Recrystallization of manganese(II) formate dihydrate from formic acid under solvothermal conditions results in single crystals of anhydrous manganese(II) formate Mn(O2CH)2, and the structure of this phase has been determined by X-ray diffraction. The same product can be obtained by solid-state dehydration of single crystals of manganese formate dihydrate, giving crystals that, although of poor quality, still allow for a single crystal structure determination. The structural relationship between the hydrated and anhydrous phases and the nature of the transformation have been determined. Given the nature of the rearrangement involved in the solid-state reaction, it is remarkable that a crystalline product is obtained. Magnetic measurements of the anhydrous manganese(II) formate show it to be a three-dimensional antiferromagnet. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Process for producing biodiesel fuel using triglyceride-rich oleagineous seed directly in a transesterification reaction in the presence of an alkaline alkoxide catalyst

Abstract: An integrated process is described for producing biodiesel from oleaginous seeds, preferably castor bean seeds. The inventive process includes a transesterification reaction where the seeds themselves react with anhydrous ethyl alcohol in the presence of an alkaline catalyst. The resulting ethyl esters are then separated by decantation and neutralized and used as fuel for diesel engines, co-solvents for diesel and gasoline mixtures with anhydrous or hydrated ethyl alcohol. The solid fractions may be used as fertilizers, for feeding cattle and as a raw material for producing ethyl alcohol.

A novel Brønsted acid-base system as anhydrous proton conductors for fuel cell electrolytes

Abstract: A super-strong acid, bis(trifluoromethanesulfonyl)amide, was combined with 4,4′-trimethylenedipyridine at various molar ratios to prepare a novel series of Bronsted acid–base ionic liquids. The protic neutral salt was electroactive for H2 oxidation and O2 reduction at a platinum electrode under non-humidifying condition, which shows the potential of pyridinal systems as new fuel cell electrolytes for elevated temperature operation and foretells the polymeric model of solid-state anhydrous proton conductors.

Regioselectivity in Palladium−Indium Iodide-Mediated Allylation Reaction of Glyoxylic Oxime Ether and N-Sulfonylimine

Abstract: Allylation reaction of electron-deficient imines with allylic alcohol derivatives in the presence of a catalytic amount of palladium(0) complex and indium(I) iodide was studied. The reversibility of allylation was observed in the reaction of glyoxylic oxime ether having camphorsultam. As the important effect of water on regioselectivity, the γ-adducts were kinetically formed from monosubstituted allylic reagents in the presence of water. The selective formation of thermodynamically stable α-adducts was observed in anhydrous THF. In contrast, the allylation of N-sulfonylimine gave the γ-adducts with high regioselectivities even under anhydrous reaction conditions.

The reactive surface sites and the H2S sensing potential for the SnO2 produced by a mechanochemical milling

Abstract: SnCl 2 powder was milled with Ca(OH) 2 and K 2 CO 3 powder respectively in a ball mill at room temperature and in an air atmosphere. Pure SnO 2 was obtained by removal of the CaCl 2 or KCl by-product by washing the powder. An initial composition of SnCl 2 . K 2 CO 3 , and Cr(NO 3 ) 3 .9H 2 O was milled to produce the doped SnO 2 phase with Cr on the surface. Heat-treatment results in the formation of a tetragonal phase. The infrared spectra for the different powders and from thick films of these materials are reported. An important finding is that during milling in the presence of water, OH groups are formed at the surface in great numbers. After heat-treatment at 400°C or higher, the OH bonds of adjacent grains are probably transformed into Sn-O-Sn bridges. Washing the material with pure ethanol, instead of water, can result in the reduction of intensity for the band at 1450 cm -1 due to the presence of the bridge bonding Sn-O-Sn. On exposure to H 2 S and CO gas, the SnO 2 film prepared from anhydrous powder. has higher sensitivity than the SnO 2 film, prepared from hydrated powder. It is shown that the SnO 2 produced by mechanochemical synthesis can be successfully applied to a H 2 S gas sensor.

Crystal structure of anhydrous δ-D-mannitol

Abstract: The crystal structure of anhydrous δ-D-mannitol (C6H14O6) was solved from high-resolution synchrotron X-ray powder diffraction data collected on a mixture containing 20% and 80% w/w of β- and δ-D-mannitol, respectively. The direct space simulated annealing program PSSP, and Rietveld analysis employing GSAS were used to determine and refine the structure. The polymorph has monoclinic symmetry, space group P21 with a=5.089 41(5) A, b=18.2504(2) A, c=4.917 02(5) A, and β=118.303(2)°. There is one molecule in the irreducible volume of the unit cell. The pattern of hydrogen bonding is significantly different than the previously known α and β forms.

Partition of five aroma compounds between air and skim milk, anhydrous milk fat or full-fat cream

Abstract: The present study deals with the physicochemical interactions between aroma compounds and various dairy media used as models of complex food matrices, as well as the consequences of the interactions on aroma partitioning between the air and matrix. Five aroma compounds were investigated: amyl and isoamyl acetate, ethyl pentanoate, hexanal and t-2-hexenal. Skim milk, anhydrous milk fat and full-fat cream were chosen as dairy media, while water was used as a reference medium. Apparent partition coefficients of the five aromas were determined between the air and media between 30 and 80 °C by static headspace-gas chromatography. Partition coefficients over full-fat cream were also calculated from partition coefficients over skim milk and anhydrous milk fat. Compared with water, a significant retention of t-2-hexenal was observed in skim milk (nearly 90% whatever the temperature), whereas the retention of the other aromas varied from 6% for isoamyl acetate to 40% for hexanal in skim milk. Hydrophobic interactions were responsible for the retention of esters, whereas covalent binding of t-2-hexenal by dairy proteins was probably involved. The volatility of the 5 aromas was drastically reduced over anhydrous milk fat, because of their hydrophobic nature (log P > 1). There were discrepancies between calculated and measured partition coefficients over full-fat cream, which depended on aroma compounds and temperature. Measured and calculated ethyl pentanoate retentions were similar whatever the temperature. For isoamyl acetate, hexanal and, to a lesser extent, t-2-hexenal, aroma retention was greater than expected. The reverse phenomenon was observed with amyl acetate. The so-called "enthalpy of affinity" was calculated from the variation of the partition coefficient with temperature. This parameter allowed an overview of the relative importance of aroma compounds-matrices interactions. Anhydrous milk fat / aroma compounds / cream / skim milk / partition coefficient

Epoxidation of Styrene by Anhydrous H2O2 over TS-1 and γ-Al2O3 Catalysts: Effect of Reaction Water, Poisoning of Acid Sites and Presence of Base in the Reaction Mixture

Abstract: The styrene conversion and product (viz. styrene oxide, phenyl acetaldehyde, benzaldehyde) selectivity in the liquid-phase epoxidation of styrene by H2O2 (H2O2/styrene = 2) over TS-1 (Si/Ti = 80) and γ-Al2O3 are strongly influenced by the presence of water and/or base (viz. urea and pyridine) in the reaction mixture. The TS-1 showed high styrene conversion activity but no epoxide selectivity in the absence of any base. When anhydrous H2O2 (24% H2O2 in ethyl acetate), with the continuous removal of the reaction water (using the DeanStark trap), was used instead of 50% aqueous H2O2, both the conversion and epoxide yield are increased drastically for the γ-Al2O3, whereas for the TS-1, the increase in the conversion was quite small and there was also no improvement in the epoxide selectivity and/or yield. However, when urea or pyridine was added in the reaction mixture, the epoxide selectivity for both the catalysts was increased depending on the concentration of the base added; the increase in the selectivity was very large for the TS-1 but small for the γ-Al2O3. Poisoning of the acid sites of the γ-Al2O3 by the chemisorbed ammonia or pyridine (at 100 °C) caused a small decrease in the conversion, but it also caused a large decrease in the epoxide selectivity. However, the pyridine poisoning of the TS-1 caused a little beneficial effect, a small increase in the epoxide selectivity. The ammonia poisoning of the TS-1, however, resulted in a small decrease in the conversion with no improvement in the epoxide selectivity. As compared to the TS-1, the γ-Al2O3 catalyst showed a much better performance in the epoxidation by anhydrous H2O2 with the continuous removal of the reaction water. However, the reaction water, if not removed continuously, is detrimental to the γ-Al2O3, causing a large decrease in the catalytic activity and selectivity for styrene oxide but an increase in the selectivity for benzaldehyde.

Phase diagram calculation of molten salt hydrates using the modified BET equation

Abstract: From water activity data within the concentration range of molten salt hydrates the parameters ri and ei of the modified Brunauer, Emmett and Teller (BET) equation have been determined for several salts i. The parameters were used to model the solid–liquid phase diagrams and to extract the temperature functions of the Gibbs energy of formation of all occurring solid phases with respect to pure liquid water and anhydrous molten salts as reference states. Applying the multi-component formulation of the BET model according to Ally and Braunstein, phase diagrams of aqueous ternary systems composed of the salts LiNO3, NaNO3, Mg(NO3)2, Ca(NO3)2, Zn(NO3)2, LiCl, CaCl2, LiClO4, and Ca(ClO4)2 were predicted and compared with available experimental data. Good agreement with the experimental data was found, when the presumptions of the BET model in respect to water activity and chemical interactions are satisfied. Based on the BET calculations, a list of new eutectic temperatures and compositions of salt hydrate mixtures is given.