Acid-catalyzed isomerization of caryophyllene in the presence of SiO<Subscript>2</Subscript> and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> impregnated with sulfuric acid

The conversion of caryophyllene upon contact with Al₂O₃ and SiO₂ impregnated with sulfuric acid was carried out, and the components of the resulting mixtures were identified. Having in hands such “standard” mixtures greatly facilitates identification of components of sesquiterpene fractions of essential oils and other mixtures of natural origin. The catalytic activity of silica gel impregnated with sulfuric acid (H⁺-SiO₂) in the acid-catalyzed isomerization of caryophyllene is significantly higher than that for H⁺-Al₂O₃ and is comparable with the activity of concentrated sulfuric acid.     

Carbon-13 kinetic isotope effects in the decarbonylations of lactic acid containing13C at the natural abundance level

The¹³C kinetic isotope fractionation in the decarbonylation of lactic acid of natural isotopic composition by sulfuric acid has been studied in the temperature range of 20–80°C. The¹³C₍₁₎ isotope separation in the decarbonylation of lactic acid by concentrated sulfuric acid depends strongly on the temperature above 40°C. Below this temperature the¹³C isotope effect in the decarbonylation of lactic acid by concentrated sulfuric acid is normal similarly as has been found inthe decarbonylation of lactic [1-¹⁴C] acid. The experimental values of k(¹²C)/k(¹³C) ratios of isotopic rate constants for¹²C and¹³C are close to, but slightly higher than theoretical¹³C-kinetic isotope effects calculated (neglecting tunneling) under the asumption that the C₍₁₎-OH bond is broken in the rate-controlling step of the dehydration reaction. Dilution of concentrated sulfuric acid with water up to 1.4 molar (H₂O)/(H₂SO₄) ratio caused the increase of the¹³C isotope fractionation from 1.0273 found in concentrated sulfuric acid at 80.5°C to 1.0536±0.0008 (at 80.6°C). A discussion of the abnormally high temperature dependence of¹⁴C and¹³C isotope fractionation in this reaction and the discussion of the problem of relative¹⁴C/¹³C kinetic isotope effects is given.     

Kinetic study of the equilibrium in the methanesulfonic acid-water system

A kinetic study of the hydrolysis of ethyl isovalerate in the methanesulfonic acid-water system from pure water to 60.5% CH₃SO₃H at 25°C showed that the hydrolysis rate is directly proportional to the concentration of H₅O₂ ⁺ ions determined by IR spectroscopy. The hydrolysis mechanism is the same as in hydrochloric acid and sulfuric acid solutions. Evidence was found for correctness of the measurements of the equilibrium concentrations of molecules and ions in aqueous methanesulfonic acid solutions by multiple frustrated total internal reflection IR spectroscopy. The possibility was demonstrated for an independent measurement of the equilibrium concentrations of H₅O₂ ⁺ ions by a kinetic method in aqueous acid solutions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1694–1697, July, 1991.     

Inter- und intramolekulare Umlagerung der Sulfogruppe in 2-Naphtol-1-sulfonsäure

The isomerisation of 2-naphthol-1-sulfonic acid (potassium salt) into 2-naphthol-6-sulfonic acid has been studied using labelled sulfuric acid (H₂³⁵SO₄). In 40 to 50% aqueous sulfric acid the reaction takes place exclusively by an intermolecular mechanism (protio-desulfonation and resulfonation). In glacial acetic acid, in the presence of an excess of sulfuric acid, the rearrangement is partly intramolecular. With an equimolar amount of sulfuric acid the rearrangement is completely intramolecular. This reaction is first order with respect to 2-naphthol-1-sulfonic acid and zeroth order with respect to excess of sulfuric acid. A mechanism for the reaction is proposed.     

Stereoregularity of poly(2-vinylpyridine) determined by 1H-NMR and 13C-NMR spectroscopy

In order to determine the stereoregularity of poly(2-vinylpyridine), 2-vinylpyridine-β,β-d₂ was synthesized. The ¹H-NMR spectra of the deuterated polymer in D₂SO₄ and o-dichlorobenzene solutions showed three peaks, which were assigned to triad tacticities. Since the absorptions of heterotactic and syndiotactic triads of methine protons overlap those of methylene protons in nondeuterated polymers, only isotactic triad intensities can be obtained from the ¹H-NMR spectra of nondeuterated poly(2-vinylpyridine). The ¹³C-NMR spectra of poly(2-vinylpyridine) were obtained in methanol and sulfuric acid solutions. In methanol solution the absorption was split into three groups, which cannot be explained by triads, and in sulfuric acid solution several peaks were observed. These splittings may be due to pentad tacticity. The results show that poly(2-vinylpyridine) obtained by radical polymerization is an atactic polymer.     

Study on Apparent Kinetics of the Reaction between Sulfuric and Hydriodic Acids in the Iodine–Sulfur Process

The iodine–sulfur (IS) thermochemical process for hydrogen production is one of the most promising approaches in using high‐temperature process heat supplied by a nuclear reactor. This process includes three reactions that form a closed cycle: the Bunsen reaction, in which iodine, water, and sulfur dioxide react to form sulfuric acid and hydriodic acid (HI); HI decomposition; and sulfuric acid decomposition. However, the side reactions between H₂SO₄ and HI may disturb the operation of the IS closed cycle. For optimal process conditions, the reaction kinetics between H₂SO₄ and HI should be examined. In this work, a preliminary kinetic study was conducted. Using the initial reaction rate method, the kinetic parameters of the reaction between sulfuric acid and HI, such as the apparent reaction orders and rate constant were determined. For I^?, the apparent reaction order was approximately 1.77, whereas the orders for H⁺ and SO₄^2? were 7.78 and 1.29, respectively. The apparent rate constant at 85 ± 1°C was approximately 2.949 × 10^?11 min^?1 (mol/L)^?9.84. The H⁺ concentration had more significant influence on the reaction rate than those of SO₄^2? and I^?. Such basic data provide useful information for related process design and further kinetics study.     

A Fluorescence Quenching Method for the Determination of Bromate Ion with 4,5-Dibromophenylfluorone and Cetyltrimethylammonium Bromide

Abstract

A highly sensitive and selective fluorescence quenching method was developed to determine the bromate ion (BrO₃ ^?) with 4,5-dibromophenylfluorone (DB-PF) as fluorogenic reagent. BrO₃ ^? reacts with potassium bromide in sulfuric acid solution (0.6M) giving bromine (Br₂) which is estimated with fluorescence quenching method using DB-PF as fluorogenic reagent. Bromine reacts with DB-PF to produce a compound, whose maximum excitation wavelength and emission wavelength are 543nm, 560nm respectively. The linear calibration range is 0.05–0.5 μg/25ml. The detection limit is 0.05μg/25ml. The method may be used to determine microamounts of BrO₃ ^? in potassium chlorate with satisfactory results. The method offers the advantages of simplicity, rapidity and sensitivity.     

Diffusion with hydrolysis and ion association in aqueous solutions of beryllium sulfate

Taylor dispersion is used to measure mutual diffusion coefficients for aqueous solutions of beryllium sulfate at concentrations from 0.005 to 1 mol-L^–1 at 25°C. Least-squares analysis of the dispersion profiles shows that diffusion of the partially hydrolyzed salt produces a small additional flow of sulfuric acid, about 0.04 mol sulfuric acid per mole of total beryllium sulfate. Ternary diffusion coefficients measured for the aqueous BeSO₄–H₂SO₄ system are qualitatively consistent with Nernst-Planck predictions based on the formation of beryllium sulfate ion pairs, bisulfate ions, and the hydrolysis equilibria 2Be²⁺+H₂O= Be₂OH³⁺+H⁺, 3Be²⁺+2H₂O=Be₃(OH) ₂ ⁴⁺ +2H⁺. Except for very dilute solutions, the predicted flow of sulfuric acid is small compared to the flow of beryllium sulfate because most of the beryllium ions are protected from hydrolysis by the formation of BeSO₄ ion pairs, and most of the hydrogen ions produced by hydrolysis are converted to less-mobile bisulfate ions.     

Further improvements in the 2,4-xylenol spectrophotometric method for nitrate

Improvements are described for the 2,4-xylenol spectrophotometric method for nitrate that reduce the elapsed and working time. Diluted (22 + 3) sulfuric acid is added quickly to the sample solution while the flask is immersed in tap water. 2,4-xylenol solution is added, the 6-nitro-2,4-xylenol formed is steam-distilled into a composite ammonia—isopropanol reagent, and the absorbance of the ammonium salt of 6-nitro-2,4-xylenol is measured. Further possible interferences are described. Br₂, I₂, ClO^-, CIO₃^-, BrO₃^-, and I0₄^-, cause low results by deactivating or destroying the 2,4-xylenol. Azide, hydrazine, and elemental carbon cause low results by reducing the nitrate in the strong sulfuric acid solution. Se⁺ causes low results because 2,4-xylenol is consumed in reducing Se⁴⁺ to the element. Pt⁴⁺ and Os⁸⁺ cause high results. Interferences from Br₂, I₂, ClO^-, ClO₃^- lO₃^-, and I0₄^- can be eliminated by reduction to the halide with sulfurous acid and precipitation with silver sulfate. Sulfurous acid reduction also eliminates interferences from V⁵⁺. Mn⁷⁺, Cr⁶⁺, S₂O₈^2-, and H₂0₂. Interferences from N₃^-, Br₂, I₂, and S₂0₈^2- are eliminated merely by boiling a 0.5% sulfuric acid solution for 30 min (and precipitating any residual halide with silver sulfate).     

PANI/La2O3复合纳米材料的合成及其电化学降解的抑制作用

作为离子型表面活性剂, 对-甲基苯磺酸可用于氧化镧的预超声分散处理, 同时还可作为质子酸对聚苯胺(PANI)进行掺杂, 从而赋予聚苯胺导电性. 采用化学法合成了聚苯胺/氧化镧复合纳米材料, 用四探针法测定了材料的电导率, 用扫描电镜、电子能谱、X射线衍射、红外光谱等检测分析手段对材料进行了表征. 结果表明, 聚苯胺及聚苯胺/氧化镧复合纳米材料的电导率分别为1.0•和1.9 S•cm^－1, 粒子直径分别约为200和50 nm. 氧化镧的掺杂未降低聚苯胺的电导率, 并使粒径减小. 循环伏安实验结果说明, 氧化镧的掺杂可提高氧化还原峰的电流密度, 并能有效抑制聚苯胺在0.25～2.0 mol•L^－1的H₂SO₄及H₃PO₄水溶液中的电化学降解.     

Kinetics and Mechanism of the Electro-oxidation of Gold in Thiocarbamide Solutions

The kinetics and mechanism of the electrooxidation of gold and thiocarbamide in sulfuric acid solutions of thiocarbamide (TC) have been investigated. The potentials for the oxidation of gold in TC solutions to [Au(TC)₂]⁺ _ads and [Au(TC)₃]³⁺ _ads are 0.132 and 0.561 V (relative to the standard silver chloride electrode). The electrooxidation of thiocarbamide in sulfuric acid solution is characterized by two maximums on voltammograms at 0.983 V (formation of formamidine disulfide, FAD) and 1.437 V (oxidation of FAD, sulfides and hydrosulfides of gold(I)). The calculated rate constants for the electrosolution of gold at the maximum current of the voltammogram is k ₁ = 1.15·10^–5 cm/s and at the minimum current is k ₂ = 3.13·10^–6 cm/s in sulfuric solutions of TC. A mechanism is proposed for the electrosolution of gold and TC in sulfuric acid solutions of thiocarbamide.     

Fabrication of a magmolecule using nanoparticle and evaluation of its adsorption capacity for selenium ions from nuclear wastewater

The purpose of present study is to fabrication of a magmolecule (amino-functionalized magnetite nanoparticles) and evaluation of its adsorption capacity for selenite (SeO₃ ^2?) ions from nuclear wastewater. To accomplish this, synthesized magnetite nanoparticles is coated with a layer of SiO₂ in order to be chemically stable and then functionalized with 3-aminopropyl triethoxysilane (APTES) to be more effective. Adsorption of SeO₃ ^2? ions was investigated in batch technique. The effect of parameters such as solution pH, presence of competing anions using sulfuric acid and nitric acid (NO₃ ^?, HSO₄ ^? and SO₄ ^2?) and temperature were studied. Maximum adsorption occurred at pH 2.4 for magnetite (naked nanoparticle) and 1.7 for functionalized nanoparticles, while the dose of adsorbent was 1 g/L and selenite ion concentration was 50 mg/L. sulfuric acid was selected as the better acidic agent for controlling pH of solution. Thermodynamic parameters were also calculated and it has been found that the adsorption was endothermic. The obtained result showed that the naked particles had more adsorption capacity but it has been suggested usage of functionalized particles in the magmolecule process duo to stability and reusable capability.     

Sorption of radioactive technetium on pyrrhotine

The sorption behavior of technetium on pyrrhotine was studied with batch experiments and diluted sulfuric acid (less than 2.88 mol/l) was used to dissolve the technetium adsorbed on pyrrhotine. A significant sorption of technetium on pyrrhotine was observed under aerobic and anaerobic conditions, and the sorption on the mineral was supposed to be due to the reduction of TcO₄ ^- to insoluble TcO₂ ^.nH₂O. Sorbed technetium on the mineral could be desorbed by diluted sulfuric acid. The maximum desorption ratio under aerobic conditions was much higher than that of under anaerobic conditions, meanwhile, the desorption rates under anaerobic conditions were higher than that of under aerobic conditions in the initial stage of the experiments.     

Kinetics of the Electrocatalytic Oxidation of 2,2-Dimethylolpropionaldehyde

A new method of synthesis 2,2-dimethylolpropionic acid from 2,2-dimethylolpropionaldehyde was put forward. The electrochemical oxidation behavior of 2,2-dimethylolpropionaldehyde has been investigated on a Ti/SnO₂ + Sb₂O₄/PbO₂ electrode by cyclic voltammetry (CV) and stable polarization curves in sulfuric acid. The results showed that it was an irreversible reaction controlled by diffusion. The formation mechanism of 2,2-dimethylolpropionic acid in the sulfuric acid was then proposed and the transfer coefficients of the reaction were calculated. It was concluded that RCHO+ỌH_ads→RCHOỌH_ads was the rate-determining step in the electrolysis process. The rate of this step obtained from the assumed process agrees well with experiment.     

生物质炭基固体酸催化剂的制备

 以生物质木粉为原料, 采用炭化-磺化法制备了炭基固体酸催化剂, 并用于油酸与甲醇的酯化反应, 考察了制备条件对炭基固体酸催化剂活性的影响. 采用 X 射线衍射、红外光谱、热重分析、高分辨透射电子显微镜及元素分析等手段对催化剂进行了表征. 结果表明, 由生物质木粉制备的炭基固体酸催化剂具有较高催化酯化反应活性, 在 400 oC 下炭化 0.5 h, 135 oC 下磺化 1 h 制备的炭基固体酸催化剂在精馏分水连续酯化装置中催化油酸与甲醇的酯化反应 2 h 时, 酯化转化率达到 96%. 采用炭化-磺化法制备的生物质炭基固体酸催化剂具有蠕虫状的无序乱层炭结构, 磺酸基 (－SO3H) 含量高达 13.25%, 并且在 220 oC 以下时具有良好的热稳定性.     

Oxidation of benzyl alcohols by nitrous and nitric acids in strong sulfuric acid media

We have studied the oxidation of benzyl alcohols by nitrous and nitric acid in sulfuric acid media. The oxidation by nitrous acid is rapid and has an activation energy of 10.6 ± 0.8 kcal mol^?1. A Hammett plot of logk₂ vs. σ⁺ is linear with a ρ value of ?1.4. The oxidation by nitric acid in sulfuric acid media is autocatalytic. From the kinetic and product analyses, it is concluded that a common oxidant, the nitrosonium ion is involved when either nitrous or nitric acid is used. A mechanism is proposed which involves the abstraction of hydride from the alcohols as the rate determining step. It is demonstrated that the autoxidation of the alcohols is catalyzed by nitrous acid or nitric oxide.     

On the emitters of sulfuric acid sonoluminescence

A comparative study of the sonoluminescence spectra of water and argon-saturated aqueous H₂SO₄ solutions was carried out. At an H₂SO₄ concentration of 18 mol L⁻¹, the sulfuric acid sonoluminescence is fifty times more intense than water sonoluminescence. The sulfuric acid luminescence spectrum differs from the water sonoluminescence spectrum caused by the emission of excited water molecules and OH radicals from the gas phase of cavitation bubbles. The sulfuric acid sonoluminescence spectrum exhibits maxima at 330, 420, 500, and 630 nm. Emitters of sonoluminescence of sulfuric acid are the singlet (330–340 nm) and triplet (∼420 nm) excited SO₂ molecules formed by sonolysis of H₂SO₄ molecules. Another product of sonolysis of H₂SO₄, atomic oxygen, is assumed to be responsible for the luminescence at λ = 630 nm. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1742–1745, August, 2005.     

Production of High Purity Amorphous Silica from Rice Husk

Combustion of the rice husk produces rice husk ash, which consists of mainly silica. High purity silica can be produced by controlled combustion after acid treatment. In this study, leaching of rice husk with hydrochloric acid and sulfuric acid were carried out prior to combustion to obtain purer silica. It was found that pre-treatment of the rice husk with sulfuric acid had accelerated the hydrolysis and decomposition of organic components as revealed by thermogravimetry (TG) and Scanning Electron Microscopy (SEM) analyses. In a systematic study, the combustion of un-leached, hydrochloric acid-leached and sulfuric acid-leached rice husks were performed in a muffle furnace at 500, 600, 700, 800 and 900^oC for 2 h. Results demonstrated that all the samples produced amorphous silica (SiO₂) and the average particle size were in the range of 0.50 to 0.70 μm. The effect of combustion at different temperatures between 500^oC and 900^oC on the silica production is very small, particularly at temperature above 600^oC. Thus, amorphous silica with purity above 99% as confirmed by X-Ray Fluorescence (XRF) analysis can be produced by hydrochloric and sulfuric acids leaching of the rice husk, followed by controlled combustion at 600^oC for 2 h. The BET surface area of the silica produced after leaching the rice husk with hydrochloric acid was higher (218 m²/g) than with sulfuric acid (209 m²/g). The silica obtained has potential application as filler in plastics and rubber compounding.     

Resonance raman spectra and structure of p-aminoazobenzene dyes in diprotonated form

Resonance Raman spectra of methyl orange and its three ring deuterated and three ¹⁵N-azo derivatives have been measured in solutions in concentrated sulfuric acid and sulfuric acid-d₂. From the isotope shifts of the observed Raman bands, methylorange is confirmed to take the dicationic azo form protonated at the dimethylamino and the α-azo nitrogen atoms. The resonance Raman spectrum of tropaeolin OO is entirely different from that of methyl orange in concentrated sulfuric acid and is well elucidated on the basis of the protonated hydrazone-form, -NH-N⁺H =.