Near infrared study of aqueous rare-earth ethylsulfates

The near infrared spectra of aqueous solutions of the ethylsulfates of La, Nd, Gd, Tb, Er, Yb, Lu, Y, and Na have been determined from about 0.2 mol-dm^–3 to nearly saturation. The extinction coefficients of water have been calculated taking into account the absorption of ethylslfate anions determined in separate experiments. Their values appeared to be nearly the same as that of pure water. The relative contents of free OH groups in 0.5 and 0.7M solutions have been estimated from the absorbances at 1160 nm. They were lower in solutions of the heavy rare-earth ethylsulfates (Tb, Er, Yb, Lu) than in equimolar solutions of the lighter ones (La, Nd), confirming our previous view that secondary hydration of the heavy trivalent rare-earth cations is distinctly stronger than that of the lighter ones. A comparison of the spectra of these aqueous ethylsulfates with those of perchlorates shows that the structure-breaking ability of the C₂H₅SO ₄ ^– ion is much smaller than that of perchlorate anion.     

Effect of sulfuric and phosphoric acid pretreatments on enzymatic hydrolysis of corn stover

The pretreatment of corn stover with H₂SO₄ and H₃PO₄ was investigated. Pretreatments were carried out from 30 to 120 min in a batch reactor at 121°C, with acid concentrations ranging from 0 to 2% (w/v) at a solid concentration of 5% (w/v). Pretreated corn stover was washed with distilled water until the filtrate was adjusted to pH 7.0, followed by surfactant swelling of the cellulosic fraction in a 0–10% (w/v) solution of Tween-80 at room temperature for 12 h. The dilute acid treatment proved to be a very effective method in terms of hemicellulose recovery and cellulose digetibility. Hemicellulose recovery was 62–90%, and enzymatic digestibility of the cellulose that remained in the solid was >80% with 2% (w/v) acid. In all cases studied, the performance of H₂SO₄ pretreatment (hemicellulose recovery and cellulose digestibility) was significantly better than obtained with H₃PO₄. Enzymatic hydrolysis was more effective using surfactant than without it, producing 10–20% more sugar. Furthermore, digestibility was investigated as a function of hemicellulose removal. It was found that digestibility was more directly related to hemicellulose removal than to delignification.     

Solvent-Free One-Pot Synthesis of Sulfonephthaleins from Saccharin and Phenols

Sulfonephthaleins can be synthesized in a single pot from saccharin and phenol via the in situ formation of 2-sulfobenzoic anhydride, followed by its reaction with phenol using H₂SO₄ as the condensing agent, in the absence of any solvent. This solvent-free synthesis is more economical and environmentally benign.     

Removal of SO2 from Gas Streams by Oxidation using Plasma-Generated Hydroxyl Radicals

The key problem for the removal of SO₂ by electrical discharge methods is how to obtain the hydroxyl radicals at high concentration and large production rates. With the micro-gap discharge method, O₂ and H₂O in simulated gas streams (N₂/O₂/H₂O/SO₂) are ionized into a large number of OH^. radicals to oxidize SO₂ into SO₃ which reacts with H₂O forming H₂SO₄ droplets at 120 °C in the absence of any catalyst or absorbent. The droplets are captured with an electrostatic precipitator. As a result, conversion of SO₂ to primarily H₂SO₄ is limited by the generation of OH^. radicals. By increasing the reduced field and concentrations of O₂ and H₂O, the amount of OH^. radicals increase resulting in more removal of SO₂ from gas streams. The removal efficiency of SO₂ reaches 100% when the residence time is only 0.74 s. Therefore, a new gas-phase oxidation method for removal of SO₂ without NH₃ additive is found.     

H2SO4-Promoted Synthesis of (E)-Stilbenes from Substituted Phenylacetones and Substituted Benzaldehydes Through Tandem Aldol–Grob Reaction

Stilbene derivates (stilbenoids) are present in plants and show a wide range of biological activities and potential therapeutic value. In continuation of our natural product synthesis program, an efficient, simple, and practical method has been developed to regioselectively synthesize (E)-stilbenes using H₂SO₄ as a catalyst in a short time (30–60 s) at room temperature in good to excellent yields.

Enthalpy of solution and effect of temperature on activity coefficients in MSO4−H2SO4−H2O system

Results of calorimetric determination of integral enthalpies of solution of some hydrates (monohydrates and heptahydrates) of 3d transition metal sulphates such as FeSO₄, NiSO₄ and MnSO₄ in three-component systems at sulphuric acid concentrations up to 2M are reported. Measured values of integral enthalpies of solution are the basis for calculation of activity coefficient temperature dependences according to Pitzer's model.     

Influence of support acidity on electronic state of platinum in oxide systems promoted by SO4 2− anions

The electronic state of platinum supported on SO₄/ZrO₂, SO₄/TiO₂, SO₄/Al₂O₃, and SO₄/SiO₂ systems and on systems unpromoted by sulfur was investigated by diffuse-reflectance IR spectroscopy using CO as the probe molecule. The introduction of SO₄ ²⁻ anions increases the electron deficit on platinum particles. This suppresses the formation of bridging CO complexes with the metal, leads to the high-frequency shift of absorption maxima of CO adsorbed in the linear form, and stabilizes positively charged metal species (Pt^δ+ and Pt⁺) during the reduction process. The formation of the positively charged species includes the interaction between the acidic protons and the metal particles yielding [Pt−H]^δ+ adducts. The extent of the influence of the support on the electronic state of the metal increases in the series SO₄/SiO₂<SO₄/Al₂O₃<SO₄/TiO₂<SO₄/ZrO₂ in parallel with an increase in the strength of the acid sites in the system. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1094–1099, June, 1998.     

NMR relaxation study of the phase transitions and relaxation mechanisms of the alums MCr(SO4)2·12H2O (M=Rb and Cs) single crystals

The physical properties and phase transition mechanisms of MCr(SO₄)₂·12H₂O (M=Rb and Cs) single crystals have been investigated. The phase transition temperatures, NMR spectra, and the spin-lattice relaxation times T₁ of the ⁸⁷Rb and ¹³³Cs nuclei in the two crystals were determined using DSC and FT NMR spectroscopy. The resonance lines and relaxation times of the ⁸⁷Rb and ¹³³Cs nuclei undergo significant changes at the phase transition temperatures. The sudden changes in the splitting of the Rb and Cs resonance lines are attributed to changes in the local symmetry of their sites, and the changes in the temperature dependences of T₁ are related to variations in the symmetry of the octahedra of water molecules surrounding Rb⁺ and Cs⁺. We also compared these ⁸⁷Rb and ¹³³Cs NMR results with those obtained for the trivalent cations Cr and Al in MCr(SO₄)₂·12H₂O and MAl(SO₄)₂·12H₂O crystals.     

Synthesis and thermal investigation of Na2Cd(SO4)2·2H2O

The synthesis and thermal decomposition of Na₂(SO₄)₂·2H₂O in both air and nitrogen are described. The synthesis was performed by two different procedures, but in both cases the same product was obtained, corresponding to the general formula given above. The crystals obtained were investigated by methods of X-ray powder diffraction, and chemical and thermal analysis. The differences in thermal decomposition in air and nitrogen are discussed.     

丙炴醇聚合膜对铁在酸性溶液中的缓蚀作用

The formation of polymer film of propargyl alcohol(PA) and its protective ability against corrosion in Fe/H_2SO_4 and Fe/H_2SO_4+H_2S systems have been investigated using impedance measurement. The composition and morphology of the corrosion surface of iron, on which PA polymerized at different bines, were obtained with the aid of SEM and AFM as well as EDX. The results showed that PA polymerized into compact polymer film in Fe/H_2SO_4 and Fe/ H_2SO_4 + H_2S systems, which made iron surface smooth and have a morphologies of regular square structure in microscopic level. In Fe/H_2SO_4 system, macroscopic continuous polymer film of PA was not formed leading to local corrosion on electrode surface. In Fe/H_2SO_4 +H_2S system, the adsorption of H_2S and HS - on electrode surface slowed down the formation of polymer film of PA. However, the iron sulfide, produced after a longer time, increased the continuity of the polymer film of PA and therefore, the polymer film could perform its long-te...更多rm inhibition action.     

Silica-gel-supported Ce(SO4)2·4H2O-mediated cyclization of 2′-amino and 2′-hydroxychalcones under solvent-free conditions

A simple, efficient, and environmentally friendly approach for the synthesis of flavones, aza-flavones, and aza-flavanones from corresponding 2′-hydroxy or 2′-aminochalcones has been developed. The reactions are successfully conducted in presence of silica-gel-supported Ce(SO₄)₂·4H₂O under solvent-free conditions.     

Inhibitive,adsorption and synergistic studies on ethanol extract of Gnetum Africana as green corrosion inhibitor for mild steel in H2SO4

Abstract

The inhibitive and adsorptive characteristics of ethanol extract of Gnetum Africana for the corrosion of mild steel in H₂SO₄ solutions have been studied using weight loss, gasometric, thermometric, and IR methods of monitoring corrosion. Ethanol extract of Gnetum Africana is a good adsorption inhibitor for the corrosion of mild steel in H₂SO₄. The inhibitive property of the extract is attributed to the presence of alkaloid, saponin, tannin, terpene, anthraquinone, cardiac glycoside, and alkaloid in the extract. The adsorption of the inhibitor on mild steel surface is exothermic, spontaneous and is consistent with the mechanism of physical adsorption. In addition, Langmuir and Temkin adsorption isotherms best described the adsorption characteristics of the inhibitor. Efforts to improve the adsorption of the inhibitor through synergistic combinations with halides indicated that only KCl may enhance the efficiency of the inhibitor. The study provides information on the use of ethanol extract of Gnetum Africana as a corrosion inhibitor for mild steel.     

Steam pretreatment of acid-sprayed and acid-soaked barley straw for production of ethanol

Barley is an abundant crop in Europe, which makes its straw residues an interesting cellulose source for ethanol production. Steam pretreatment of the straw followed by enzymatic hydrolysis converts the cellulose to fermentable sugars. Prior to pretreatment the material is impregnated with a catalyst, for example, H₂SO₄, to enhance enzymatic digestibility of the pretreated straw. Different impregnation techniques can be applied. In this study, soaking and spraying were investigated and compared at the same pretreatment condition in terms of overall yield of glucose and xylose. The overall yield includes the soluble sugars in the liquid from pretreatment, including soluble oligomers, and monomer sugars obtained in the enzymatic hydrolysis. The yields obtained differed for the impregnation techniques. Acid-soaked barley straw gave the highest overall yield of glucose, regardless of impregnation time (10 or 30 min) or acid concentration (0.2 or 1.0 wt%). For xylose, soaking gave the highest overall yield at 0.2 wt% H₂SO₄. An increase in acid concentration resulted in a decrease in xylose yield for both acid-soaked and acid-sprayed barley straw. Optimization of the pretreatment conditions for acid-sprayed barley straw was performed to obtain yields using spraying that were as high as those with soaking. For acid-sprayed barley straw the optimum pretreatment condition for glucose, 1.0 wt% H₂SO₄ and 220°C for 5 min, gave an overall glucose yield of 92% of theoretical based on the composition of the raw material. Pretreatment with 0.2wt% H₂SO₄ at 190°C for 5 min resulted in the highest overall xylose yield, 67% of theoretical based on the composition of the raw material.     

Die Kristallstruktur von Dikalium-trikobalt(II)-dihydroxid-trisulfat-dihydrat,K2Co3(OH)2(SO4)3·2H2O

Crystals of K₂Co₃(OH)₂(SO₄)₃·2H₂O were synthesized under hydrothermal conditions. The crystal structure [a=17.945 (4) Å,b=7.557 (2) Å,c=9.760 (3) Å, space group Cmc2₁,Z=4] was determined by direct methods and refined with single crystal X-ray data. The H atoms were located byFourier syntheses. Their structural parameters were refined, too. The finalR-values areR=0.025 andR _w =0.028 (w=1/) for 612 reflections withF ₀>3 (F ₀). Both Co(II) atoms are octahedral six coordinated and form zigzag chains running parallel [001]. These chains are connected via sulfate groups to built up sheets parallel (100). The KO₉ polyhedron and one of the four hydrogen bonds link these sheets.

     

H_2SO_4-SiO_2:Highly efficient and novel catalyst for the Ferrier-type glycosylation

<正>Sulfuric acid immobilized on silica gel is designed as a very useful catalyst for synthesis of 2,3-unsaturated glycopyranosides. This handy,metal-free,environment friendly transformation provides high yields andα-stereoselectivities in a very few amount (0.02 eq.) of catalyst and in short reaction times(10 min).     

Investigation on The Thermal Properties of Fe2O(SO4)2. Part II

Fe₂O(SO₄)₂ is a secondary product of the decomposition of FeSO₄⋅H₂O. Part I of this study presents results on the synthesis of Fe₂O(SO₄)₂ in gaseous environment containing either low or high concentration of oxygen. In this paper the existence of differences between the structures of Fe₂O(SO₄)₂ and Fe₂(SO₄)₃ is proved on the basis of a detailed thermal study of Fe₂O(SO₄)₂ upon dynamic heating (differential thermal analysis) and upon isothermal heating (thermal-analytic balance) in various gaseous environments as well as by presenting kinetic data on the processes of decomposition of both compounds. This revised version was published online in July 2006 with corrections to the Cover Date.     

Boric Acid–Catalyzed One-Pot Access to 7-Aryl-benzopyrano[4,3-b] benzopyran-6,8-diones Under Aqueous Micellar Conditions

A mild protocol for the synthesis of 7-arylbenzopyrano[4,3-b]benzopyran-6,8-diones by three-component reaction of 4-hydroxycoumarin, aromatic aldehyde, and 5,5-dimethylcyclohexane-1,3-dione (dimedone) with boric acid catalyst under aqueous micellar conditions is described. Good to excellent yield, high selectivity, tolerance of several common functional and protecting groups, and green features including avoidance of organic solvent in the reaction as well as isolation stage and use of nontoxic water-compatible mild Lewis acid catalyst are key attractive features of the protocol.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]