Basic hydrolysis of glyceryl nitrate esters. II. 1,2-glyceryl and 1, 3-glyceryl dinitrate esters

Kinetics of the basic hydrolysis of 1,2-glyceryl dinitrate (1,2-DNG) and 1,3-glyceryl dinitrate (1,3-DNG) esters were investigated in CO₂-free aqueous calcium hydroxide solutions. The hydrolysis reactions were carried out in a temperature controlled reactor vessel with provision for continuous N₂ sparging of the reaction mixture. Both glyceryl dinitrate esters hydrolyzed via second-order reaction at 25°C. 1,2-DNG in basic solutions isomerized to 1,3-DNG which subsequently hydrolyzed to yield products. The main hydrolysis product of 1,3-DNG was identified as glycidyl nitrate. Other products formed during the basic hydrolysis of DNGs were nitrites and nitrates.     

Basic hydrolysis of glyceryl nitrate esters. I. 1-glyceryl and 2-glyceryl nitrate esters

Kinetics of the basic hydrolysis of 1-glyceryl mononitrate (1-MNG) and 2-glyceryl mononitrate (2-MNG) were investigated in CO₂-free aqueous calcium hydroxide solutions. The hydrolysis reactions were carried out in a temperature-controlled reactor vessel with provision for continuous N₂ sparging of the reaction mixture. Both glyceryl nitrate esters hydrolyzed via second-order reaction at 25°C. 2-MNG in calcium hydroxide solution isomerized to 1-MNG, which subsequently hydrolyzed to form NO. In strongly basic aqueous solutions of NaOH (30%), 2-MNG is converted to glycidol and NO.     

Intercalation studies of zinc hydroxide chloride: Ammonia and amino acids

Zinc hydroxide chloride (ZHC) is a layered hydroxide salt with formula Zn₅(OH)₈Cl₂·2H₂O. It was tested as intercalation matrix for the first time and results were compared with intercalation products of the well-known zinc hydroxide nitrate and a Zn/Al layered double hydroxide. Ammonia was intercalated into ZHC, while no significant intercalation occurred in ZHN. Aspartic acid intercalation was only achieved by co-precipitation at pH=10 with ZHC and pH=8 with zinc hydroxide nitrate. Higher pH resistance in ZHC favored total deprotonation of both carboxylic groups of the Asp molecule. ZHC conferred more thermal protection against Asp combustion presenting exothermic peaks even at 452 °C while the exothermic event in ZHN was 366 °C and in the LDH at 276 °C.     

Physicochemical transformations during synthesis of double K−Zr phosphates in a melt of potassium nitrate

Double phosphates of K and Zr with three-dimensional and layered structure were synthesized in a melt of potassium nitrate in the temperature range of 300–550°C. The double phosphates were formed with participation of three components of a reaction mixture: ZrOCl₂·8H₂O−(NH₄)₂HPO₄−KNO₃, in which potassium nitrate was both an active component of the reaction mixture and the reaction medium. The influence of the nature of the starting reagents on the composition of the reaction products and on the sequence and stoichiometry of the reactions proceeding, in the reaction mixture were studied by thermogravimetry and mass-spectrometry. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 666–670, April, 1997.     

Fabrication of mesoporous ZnO nanosheets from precursor templates grown in aqueous solutions

Mesoporous ZnO nanosheets were successfully prepared by pyrolytic transformation of zinc carbonate hydroxide hydrate, Zn₄CO₃(OH)₆·H₂O. The nanosheets were initially formed as assemblies on glass substrates during chemical bath deposition (CBD) in aqueous solutions of urea and zinc acetate dihydrate, zinc chloride, zinc nitrate hexahydrate, or zinc sulfate heptahydrate at 80°C. It was key to induce heterogeneous nucleation of Zn₄CO₃(OH)₆·H₂O by promoting a gradual hydrolysis reaction of urea and controlling the degree of supersaturation of zinc hydroxide species. Morphology of Zn₄CO₃(OH)₆·H₂O was largely influenced by the anions present in the CBD solutions. The Zn₄CO₃(OH)₆·H₂O nanosheets were transformed into wurtzite ZnO by heating at 300°C in air without losing the microstructural feature.     

The mechanism of selective NO<Subscript>x</Subscript> reduction by hydrocarbons in excess oxygen on oxide catalysts: VI. Spectroscopic and kinetic characteristics of surface complexes on a Ni-Cr oxide catalyst

The reaction mechanism of the selective catalytic reduction of NO_x by propane in the presence of O₂ on a commercial Ni-Cr oxide catalyst was studied using in situ IR spectroscopy. It was found that nitrite, nitrate, and acetate surface complexes occurred under reaction conditions. Considerable amounts of hydrogen were formed in the interaction of NO + C₃H₈ + O₂ or C₃H₈ + O₂ reaction mixtures with the catalyst surface. The rates of conversion of the surface complexes detected under reaction conditions were measured. The resulting values were compared to the rate of the process. It was found that, at temperatures lower than 200°C, nitrate complexes reacted with the hydrocarbon to form acetate complexes; in this case, the formation of reaction products was not observed. In the temperature region above 250°C, two reaction paths took place. One of them consisted in the interaction of acetate and nitrate complexes with the formation of reaction products. The decomposition of NO on the reduced surface occurred in the second reaction path. Nitrogen atoms underwent recombination, and oxygen atoms reoxidized the catalyst surface and reacted with the activated hydrocarbon to form CO₂ and H₂O in a gas phase.     

Characterisation and performance of three promising heterogeneous catalysts in transesterification of palm oil

In this work, the performance of three heterogeneous catalysts, namely potassium hydroxide/γ-alumina, bulk calcium oxide, and nano-calcium oxide, in comparison with the homogeneous potassium hydroxide was studied in the transesterification of palm oil to produce methyl esters and glycerol. The physical and chemical properties of the heterogeneous catalysts were thoroughly characterised and determined using a number of analytical methods to assess their catalytic activities prior to transesterification. The reaction products were analysed using liquid chromatography and their properties were quantified based on the American Society of Testing and Materials and United State Pharmacopoeia standard methods. At the 65°C reaction temperature, the oil-to-methanol mole ratio of 1: 15, 2.5 h of the reaction time, and catalyst (φ _r = 1: 40), potassium hydroxide, potassium hydroxide/γ-alumina, nano-calcium oxide, and bulk calcium oxide gave methyl ester yields of 97 %, 96 %, 94 %, and 90 %, respectively. The impregnation of γ-alumina with potassium hydroxide displayed a catalytic performance comparable with the performance of potassium hydroxide where the former could be physically separated via filtration resulting in a relatively greater purity of products. Other advantages included the longer reusability of the catalyst and more active sites with lower by-product formation.     

Thermal decomposition of nickel aluminium mixed hydroxides and formation of nickel aluminate spinel

Various nickel aluminium mixed hydroxide samples of different compositions were prepared by co-precipitation from their nitrate solutions using dilute NH₄OH. Additional samples were prepared by impregnation of hydrated Al₂O₃, preheated at 600 and 900°C, with nickel nitrate solution in an equimolar ratio. The thermal decomposition of different mixed solids was studied using DTA. The X-ray investigation of thermal products of the mixed solids was also studied.The results obtained revealed that the presence of NiO up to 33.3 mole % with aluminium oxide much enhanced the degree of crystallinity of the γ-Al₂O₃ phase. In contrast, the presence of Al₂O₃ much retarded the crystallization process of the NiO phase. With the exception of samples containing 20 mole% NiO, all the mixed hydroxide samples, when heated in air at 900°C, led to the formation of well-crystalline Ni Al₂O₄ spinel, alone, or together with either NiO or γ-Al₂O₃, depending on the composition of the mixed oxide samples. The solid containing 20% NiO and heated at 900°C was constituted of amorphous NiO dispersed in γ-Al₂O₃. Heating the nickel nitrate-impregnated Al₂O₃ in air at 800–1000°C led to the formation of Ni Al₂O₄ together with non-reacted NiO and γ-Al₂O₃. The degree of crystallinity of the spinel was found to increase by increasing the calcination temperature of the impregnated solids from 800 to 1000°C and by increasing the preheating temperature of the hydrated Al₂O₃ employed from 600 to 900°C.     

Cathodic electrodeposition and characterization of nanostructured Y2O3 from nitrate solution. Part I: Effect of current density

Particle, plate and flaky-like nanostructures of Y(OH)₃ and Y₂O₃ were prepared via cathodic electrodeposition from nitrate bath by applying different current densities. In the first step, yttrium hydroxide precursors were cathodically grown on the cathode surface at the current densities of 2, 1, 0.5, 0.25 and 0.1 mA cm^?2. The obtained hydroxide powders were heat-treated at 600°C for 3 h. The products were characterized by means of carbon, hydrogen and nitrogen (CHN), differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and FT-IR spectroscopy. From the CHN, XRD and TG results, the mechanism of base electro generation at the applied conditions and the intercalation of nitrate ions in the deposit structure were proposed and confirmed. The results showed that the structural and morphological properties of the products are directly determined by the applied current density and it can be recognized as a main factor affecting in the cathodic electrodeposition of Y₂O₃.     

La matrice eau de mer et le signal du cuivre en spectrometrie d'adsorption atomique sans flamme : Partie 1: Etude de l'influence des principaux composants

(Copper signals from seawater matrices in electrothermal atomic absorption spectrometry. Part 1: study of the effects of principal inorganic ions.)The effects of the main inorganic ions of seawater (Na⁺, Mg²⁺, Ca²⁺, Cl^?, SO^2?₄), and of nitrate as modifier, on the electrothermal atomic absorption spectrometric signal of copper are studied. Sodium chloride, sulfate or nitrate, magnesium chloride or nitrate, and calcium chloride can cause serious interferences. Thermal treatment at about 700°C prevents the interference of MgCl₂ by its hydrolysis. Ashing can be done without loss of copper at higher temperatures in the presence of sulfate salts (1300°C) and nitrate salts (1200°C) than in the presence of chloride salts (1100°C). This is ascribed to the stabilising effect of oxides and sulfides. A study of the influence of two-component matrices, MCl-MNO₃ or MCl-MSO₄, on the atomization signal of copper confirms this stabilizing effect which adds to the decrease in interference connected with removal of chloride in acidic medium.     

The Ortho Effect on the Acidic and Alkaline Hydrolysis of Substituted Formanilides

The kinetics of formanilides hydrolysis were determined under first‐order conditions in hydrochloric acid (0.01–8 M, 20–60°C) and in hydroxide solutions (0.01–3 M, 25 and 40°C). Under acidic conditions, second‐order specific acid catalytic constants were used to construct Hammett plots. The ortho effect was analyzed using the Fujita–Nishioka method. In alkaline solutions, hydrolysis displayed both first‐ and second‐order dependence in the hydroxide concentration. The specific base catalytic constants were used to construct Hammett plots. Ortho effects were evaluated for the first‐order dependence on the hydroxide concentration. Formanilide hydrolyzes in acidic solutions by specific acid catalysis, and the kinetic study results were consistent with the A_AC2 mechanism. Ortho substitution led to a decrease in the rates of reaction due to steric inhibition of resonance, retardation due to steric bulk, and through space interactions. The primary hydrolytic pathway in alkaline solutions was consistent with a modified B_AC2 mechanism. The Hammett plots for hydrolysis of meta‐ and para‐substituted formanilides in 0.10 M sodium hydroxide solutions did not show substituent effects; however, ortho substitution led to a decrease in rate constants proportional to the steric bulk of the substituent.     

Investigation of the Reaction of Roasted Serpentine Ore with Some Ammonium Salts

The reaction between roasted serpentine ore and ammonium sulfate was studied at the range of temperature 250–1000°C using different molar ratios to determine the maximum extraction of magnesia and also to characterize the different reaction products. The maximum extraction of MgO from the roasted ore reached 92.4% at 400°C. It was found from XRD that ammonium magnesium sulfate [(NH₄)₂Mg₂(SO₄)₃] was produced as the main product at 400°C, which decomposes to magnesium sulfate at 500–600°C. The last compound decomposes to magnesium oxide at 900–1000°C. Thermal analysis of the reaction mixture confirmed the results obtained by XRD. Extraction of magnesia by ammonium chloride at 300–400°C showed low percentage of extraction (7.8%). Comparison was made between using ammonium chloride instead of sulfate taking into consideration the thermal decomposition products of both ammonium salts. Extraction of magnesia from the roasted ore by aqueous ammonium sulfate or ammonium chloride showed good results.     

Layered calcium phenylphosphonate: Synthesis and properties

Calcium phenylphosphonate, Ca(HO₃PPh)₂, was synthesized by the reaction of calcium nitrate and phenylphosphonic acid. A thorough investigation was performed to study the effect of reaction parameters on the synthesis and growth of crystalline product in a high yield. The compound was structurally characterized by single-crystal X-ray diffraction technique. It consists of a layered structure with inorganic framework of CaO₈ polyhedra from which phenyl groups are pointing out. The inorganic framework is also stabilized by the OH⋯O hydrogen bonds. Results from thermal analysis by thermogravimetry and thermodiffractometry revealed that calcium phenylphosphonate is stable up to 300°C. The compound undergoes consequent thermal decomposition and phase transitions above 300°C temperatures until it converts to δ-Ca(PO₃)₂ at 620°C.     

On the existence of bivalent ions in the apatite channels: A new example—Phosphocalcium cyanamido-apatite

A new apatite, phosphocalcium cyanamido-apatite Ca₁₀(PO₄)₆ CN₂ □, is obtained by treatment under low pressure at high temperature (900–1000°C) of a mixture of the corresponding hydroxyapatite and calcium cyanamide. In this apatite, one CN^2?₂ ion associated with a vacancy replaces two hydroxyl ions in the channels. The formation of a cyanamide-containing apatite also occurs by treatment of an A-type carbonated apatite by ammonia at 600–900°C: in the latter case, the reaction seems more difficult and more limited than in the former. The cyanamido apatite is decomposed by heating in air, and it gives rise first to an A-type carbonated apatite, with release of both ammonia and nitrogen oxide and second to hydroxyapatite by hydrolysis of the A-type carbonated apatite.     

Synthesis and phosphorescence properties of Dy3+ and (Pr3+–Dy3+) in MgTiO3

Using tetra-n-butyl titanate and magnesium nitrate as raw materials, Dy³⁺ and Pr³⁺ ions in the matrix of magnesium titanate (MgTiO₃) was successfully synthesized by a modified solid-state reaction. The mixtures to achieve a solid-state reaction were heated in porcelain crucibles at 600?°C for 2?h, 900?°C for 6?h, and 1000.0?°C for 2?h. The reaction products obtained in an air atmosphere were characterized by X-ray powder diffractions. The optimization of reaction conditions were carried out by thermal gravimetry and differential thermal analysis methods. Surface and elemental analyses were performed by using on SEM instrument. The excitation and emission spectra were recorded by photoluminescence spectrophotometer.     

Reaction of perfluoro-1-methylindan with SiO2-SbF5

The reaction of perfluoro-1-methylindan with SiO₂-SbF₅ depending on the amount of SiO₂ led to the formation after hydrolysis of the reaction mixture of perfluoro-3-methylindan-1-one, perfluoro-4-methylisochromen-1-one, 6-(1-carboxy-2,2,2-trifluoro-ethyl)-2,3,4,5-tetrafluoro-benzoic and 6-(carboxymethyl)-2,3,4,5-tetrafluorobenzoic acids. Heating in the SbF₅ medium perfluoro-1-methylindan in a glass ampoule at 130°C, or perfluoro-3-methylindan-1-one at 70°C provided a solution of a perfluoro-4-methylisochromenium salt that on treating with anhydrous HF was converted into perfluoro-4-methyl-1H-isochromen, and on hydrolysis, into perfluoro-4-methylisochromen-1-one.     

Explosion of acetylene–chlorine mixture at room temperatures initiated by small additions of oxygen: Kinetic study and mechanism

Oxygen added in amounts of 0.01-0.1% was found to cause the explosion of an acetylene–chlorine mixture at temperatures as low as ?78°C. Explosion occurrence and nature depend on the mode of mixing the reactants, the effect of oxygen being associated with concentration limits. The dependence of explosion-inducing oxygen amounts on temperature, pressure, concentrations of reactants, reactor surface type and area, additions of inert gases, and reaction products were investigated. The effect of light on the C₂H₂ + Cl₂ + O₂ was studied. The composition of gaseous products resulting from acetylene–chlorine mixture explosion in the presence of minute amounts of oxygen, from a slow reaction inhibited and noninhibited by oxygen, and also from explosion at 400°C in the absence of oxygen, was determined. The results obtained point to the fact that any acetylene–chlorine mixture flash caused by small amounts of oxygen is a branched chain reaction involving activated particles, chain branching presumably being associated with the decomposition of radical CHCl=CHOO* → CH + HCl + CO₂.     

Effect of alkaline earth metal dopants on the thermal decomposition of the CaCO3-SiO2 system: Part II. Formation of dicalcium silicate

Mixtures of calcium oxide (taken as carbonate) and silica in 2:1 molar ratio containing varying amounts of MgO, SrCO₃ and BaCO₃ as dopants were subjected to thermal treatment up to 1450°C. The exothermic peaks at 1200°C and above (beyond the decomposition temperature of calcium carbonate) have been examined to elucidate the phases formed. The exothermic peak at 1210°C without dopant was found to conform to the β-dicalcium silicate phase with a significant amount of free lime and cristobalite along with small amounts of the γ-C₂S phase. MgO at 0.1–1% leads to the formation of β- and γ-dicalcium silicate phases at 1420–1430°C, while 5% MgO results in the formation of the β-C₂ S phase at 1360°C. SrCO₃, in the concentration range studied, leads to the stabilization of β-C₂S, but does not lower its temperature of formation. BaCO₃ at 0.1–1% assists in the formation of the β-dicalcium silicate phase, but 5% BaO forms a mixture of β- and α'_H-C₂S phases at a lower temperature.     

Novel hybrid process for the conversion of microcrystalline cellulose to value-added chemicals: part 1: process optimization

In this paper, a novel hybrid process for the treatment of microcrystalline cellulose (MCC) under hot-compressed water was investigated by applying constant direct current on the reaction medium. Constant current range from 1A to 2A was applied through a cylindrical anode made of titanium to the reactor wall. Reactions were conducted using a specially designed batch reactor (450 mL) made of SUS 316 stainless steel for 30–120 min of reaction time at temperature range of 170–230 °C. As a proton donor H₂SO₄ was used at concentrations of 1–50 mM. Main hydrolysis products of MCC degradation in HCW were detected as glucose, fructose, levulinic acid, 5-HMF, and furfural. For the quantification of these products, High Performance Liquid Chromatography (HPLC) and Gas Chromatography with Mass Spectroscopy (GC–MS) were used. A ½ fractional factorial design with 2-level of four factors; reaction time, temperature, H₂SO₄ concentration and applied current with 3 center points were built and responses were statistically analyzed. Response surface methodology was used for process optimization and it was found that introduction of 1A current at 200 °C to the reaction medium increased Total Organic Carbon (TOC) and cellulose conversions to 62 and 81 %, respectively. Moreover, application of current diminished the necessary reaction temperature and time to obtain high TOC and cellulose conversion values and hence decreased the energy required for cellulose hydrolysis to value added chemicals. Applied current had diverse effect on levulinic acid concentration (29.9 %) in the liquid product (230 °C, 120 min., 2 A, 50 mM H₂SO₄).     

Hydrothermal Formation of Calcium Copper Tetrasilicate

We describe the first hydrothermal synthesis of CaCuSi₄O₁₀ as micron‐scale clusters of thin platelets, distinct from morphologies generated under salt‐flux or solid‐state conditions. The hydrothermal reaction conditions are surprisingly specific: too cold, and instead of CaCuSi₄O₁₀, a porous calcium copper silicate forms; too hot, and calcium silicate (CaSiO₃) forms. The precursors also strongly impact the course of the reaction, with the most common side product being sodium copper silicate (Na₂CuSi₄O₁₀). Optimized conditions for hydrothermal CaCuSi₄O₁₀ formation from calcium chloride, copper(II) nitrate, sodium silicate, and ammonium hydroxide are 350 °C at 3000 psi for 72 h; at longer reaction times, competitive delamination and exfoliation causes crystal fragmentation. These results illustrate that CaCuSi₄O₁₀ is an even more unique material than previously appreciated.