Thermodynamic properties of transition metals in aqueous solution. 2. The enthalpies of mixing of aqueous solutions of CoCl2, CuCl2, and MnCl2 with NaCl at varying ionic strength at 25°C

Enthalpies of mixing (_m H) aqueous solutions of CoCl₂, CuCl₂, and MnCl₂ with NaCl solutions were measured at constant ionic strengths of 0.5, 1.0, and 3.0 molal at 25°C. The excess enthalpy equations of Pitzer were then fit to the resulting _m H data. The resulting parameters are the temperature derivatives of the activity coefficient mixing parameters in the Pitzer system. The heat of mixing data for CoCl₂ and CuCl₂ were in agreement with earlier isomolal results by other workers.     

The Effect of Preparation Method and Calcination Temperature on the Crystallite Size and Surface Area of Perovskite-Type SrFeO x

We have investigated the synthesis of perovskite-type SrFeO_x (2.5 x 3.0) using three preparative methods: sol-gel, mechanochemical processing and solid state reactions at high temperature of the corresponding oxides. The sample obtained after calcination of the gel from sol-gel method, contained the least amount of strontium carbonate impurity. The amount of strontium carbonate impurity decreased with the increase in calcination temperature. Perovskites obtained have been characterized by X-ray diffraction (XRD) and nitrogen adsorption isotherms. Samples obtained from three methods have been compared with respect to calcination temperature, crystallite size and specific surface area.Issued as NRCC No. 46479.     

An Efficient and Facile Synthesis of Quinoxaline Derivatives Catalyzed by KHSO4 at Room Temperature

Summary. A facile synthesis of quinoxaline derivatives catalyzed by KHSO₄ in very high yields at room temperature is reported.     

Headspace solvent microextraction of trihalomethane compounds into a single drop

Headspace solvent microextraction (HSME) into a single drop is developed for the determination of six trihalomethanes, CH2Cl2, CHCl3, C4H9Cl, CCl4, C2HCl3, and C2Cl4, in aqueous solution. A drop of benzyl alcohol containing bromoform, as an internal standard, is used for extraction. The analytes are extracted by suspending a 3-microL drop directly from the needle of a microsyringe. The needle passes through the septum of a vessel, and the needle tip appears above the surface of the solution. After the prescribed extraction time, the drop is drawn back into the syringe. The syringe is then removed, and its content is injected directly into a gas chromatography column for analysis. The main parameters affecting the HSME process, such as stirring speed, microdrop volume, sample solution temperature, microsyringe needle temperature, sample volume, solution pH, extracting solvent, and ionic strength of the solution, are studied. Also, the linear range and precision of the method are examined.     

The effect of the physical and chemical characteristics of activated carbons on the adsorption energy and affinity coefficient of Dubinin equation

The dependency of adsorption energy (E) and affinity coefficient (beta) of Dubinin equations (Dubinin-Radushkevich (DR) or Dubinin-Astakhov (DA)) on surface chemistry and porosity of activated carbons was investigated by analyzing adsorption of nitrogen, benzene, trichloroethylene (TCE), and water vapor by several surface-modified activated carbons and carbon fibers. For all studied nonpolar adsorbates, carbons with smaller average micropores showed higher adsorption energies independent of their surface chemistry. For water vapor, carbons with higher surface polarities showed higher adsorption energies due to specific adsorbate-adsorbent interactions. Adsorption energies increased with decreasing average micropore widths. betaN2,DR for different carbons were observed to vary in the 0.292-0.539 range. Carbons with higher degrees of mesoporosity had higher betaN2,DR values, while no dependency was observed between betaN2,DR and surface chemistry. A comparison of DR and DA cases indicates that: (1) the average value of betaN2,DA is considerably above the classical value of this parameter; and (2) the range of betaN2,DA values were smaller compared to betaN2,DR, despite a wide range of mesoporosity of carbons examined. Obtained beta(TCE,DR) values varied in the 0.952-1.243 range, with an average value of 1.085+/-0.083, independent of surface chemistry or porosity of activated carbons. A similar result was observed for beta(TCE,DA). betaH2O,DR values of different granular and fibrous activated carbons changed in the range of 0.081-0.271. They depended more on the carbon surface chemistry and less on the porosity. A similar result was obtained when DA equation was considered.     

Joule-Thomson inversion curve prediction by using equation of state

In this paper five equations of state are tested for checking their ability to predict the Joule-Thomson inversion curve.These five equations of state are:Mohsennia-Modarres-Mansoori(MMM),Ji-Lemp(JL),modified Soave-Redlich-Kwang(SRK)equation of state by Graboski(MSRK1),modified SRK equation of state by Peneloux and Rauzy(MSRK2),and modified Peng-Robinson (PR)equation of state by Rauzy(PRmr).The investigated equations of state give good prediction of the low-temperature branch of the inversion curve,except for MMM equation of state.The high-temperature branch and the peak of the inversion curve have been observed,in general,to be sensitive to the applied equation of state.The values of the maximum inversion temperature and maximum inversion pressure are calculated for each component used in this work.     

Deprotection of Thioacetals Using K2S2O8/[bmim]Br as a Mild and Efficient Reagent under Solvent-Free Conditions

Summary. A straightforward and effective procedure for the deprotection of thioacetals to the corresponding carbonyl compounds using potassium persulfate and the ionic liquid [bmim]Br under solvent-free conditions is reported. A variety of aliphatic and aromatic 1,3-dithiolanes or 1,3-dithanes was deprotected to the corresponding carbonyl derivatives by this procedure.     

Selective Acetylation of Alcohols and Amines with Ethyl Acetate in the Presence of H<Subscript>6</Subscript>[PMo<Subscript>9</Subscript>V<Subscript>3</Subscript>O<Subscript>40</Subscript>] as the Catalyst

Summary. Acetylation of various alcohols and benzyl amine was tested in the presence of H₆[PMo₉V₃O₄₀], a mixed addenda heteropolyacid, in ethyl acetate under reflux condition. Phenols and anilines are not affected under the reaction conditions. Selective transestrification of alcohols can be achieved in the presence of phenol and aniline derivatives using this method.     

Kinetic studies on the solvolysis and axial ligand substitutions of bis-triphenylphosphine(cyclohexane-1,2-dione-dioximato)ruthenium(II) in non-aqueous solvents

Kinetic studies of ligand substitutions of the six-coordinated Ru^II pseudo-macrocyclic complex [Ru(CHDH)₂- (PPh₃)₂] (CHDH=cyclohexanedione-dioximato) have been spectrophotometrically investigated in a variety of solvents and at 70, 80, 85 and 90°C. The reactions studied are of the form:[(PPh₃)Ru(CHDH)₂(PPh₃)] + L =[(PPh₃)Ru(CHDH)₂L] + PPH₃ where L is imidazole, pyridine, piperidine or thiophene or a solvent molecule (PhCl, PhMe, MeCN, DMSO or DMF). The solvolysis reactions with chlorobenzene and toluene proceed to an equilibrium position favoring the bis-triphenylphosphine complex. All other reactions proceed to completion. From a mechanistic point of view the reactions were found to proceed through the formation of a five coordinate intermediate that possesses little or no discriminating ability towards the incoming nucleophiles. The rate data were thus interpreted in terms of a dissociative (D) or dissociative interchange (Id) mechanism. Activation parameters H and S are reported. Preliminary studies on the solvatochromic behavior of [Ru(CHDH)₂(PPh₃)₂] and the corresponding mixed complexes are discussed.     

Solid Phase Extraction and Flame Atomic Absorption Spectrometric Determination of Trace Amounts of Zinc and Cobalt Ions in Water Samples

A simple and rapid method for the preconcentration of Co²⁺ and Zn²⁺ as their 2-guanidino-benzimidazole chelates is proposed using an octadecyl silica cartridge. The retained analytes were recovered with a mixture of 5mL of 0.01M HNO₃ and 5mL of methanol. The metal ions in the effluent were determined by flame atomic absorption spectrometry. The effect of different parameters, such as sample matrix, amount of ligand, type of eluent for elution of ions from cartridge, flow rates of sample solution and eluent, breakthrough volume, and limit of detection, were evaluated. The effects of various cationic and anionic interferences on the percent recovery of Co²⁺ and Zn²⁺ were also studied. Quantitative extraction efficiencies were obtained by elution of the cartridge with a minimal amount of solvent. Hence, with a typical preconcentration factor of 50, the limits of detections of the proposed method are 0.26 and 1.62ngmL^–1 for Zn²⁺ and Co²⁺, respectively. The method was applied to the determination of zinc and cobalt ions in different water samples.