Mechanochemical reactions of telluric acid with alkaline fluorides

The mechanochemical reactions of telluric acid, Te(OH)₆ with alkaline fluorides (Na and K) have been studied using IR and XRD techniques. The reactions lead to the formation of hydrogen-bonding complexes, NaF.Te(OH)₆ and 2KF.Te(OH)₆. The reactions are free from side products such as alkali tellurates, alkali fluorotellurates or HF₂⁻ salts.     

Sol-gel powder synthesis in the TiO2-TeO2-ZnO system: Structural characterization and properties

The present study deals with the gel formation tendency in the ternary TeO₂-TiO₂-ZnO system. Depending on the TiO₂ amount, the gelation occurred at different times and subsequently several gel formation regions have been determined. Homogeneous, transparent and monolithic gels were obtained using combination of organic and inorganic precursors during the synthesis. Using XRD analysis it was established that upon the heating composites were obtained which contain an amorphous phase and different crystalline phases: TiO₂ (anatase), TiO₂ (rutile), α-TeO₂ and ZnTeO₃, depending on composition. The IR results showed that the short range order of the amorphous phases which are part of the composite materials consist of TiO₆, ZnO₄ and TeO₄ structural units. Using UV–Vis spectroscopy it was established that the absorption edge of the gels varied from 330 nm to 364 mm and the increase in TiO₂ content caused a red shifting of the cut-off. The calculated Eg values are in the range 3.41–3.75 eV higher than that of pure TiO₂, TeO₂ and ZnO oxides. The XPS results showed that the Te atoms in the surface layers of the samples studied exist in several chemical states as Te²⁺, Te⁰, but Te⁶⁺ dominates. Octahedrally coordinated Ti⁴⁺ ions are observed in the gels and in the samples annealed at 200 °C but a small amount of tetrahedrally coordinated Ti⁴⁺ is also detected, which indicates the incomplete polymerization of TiO₆ units.     

Micellar effect on the sensitivity of spectrophotometric Mo(VI) determination based on the formation of gallic acid complex providing evidence for the polyoxoanion structure of molybdate ions

In this study effects of anionic (sodium dodecyl sulfate, SDS), cationic (cetyltrimethylammonium bromide, CTAB) and nonionic (Triton X-100, TX100) micelles on the sensitivity of spectrophotometric molybdenum(VI) (Mo) determination based on the formation of a binary complex with gallic acid (GA) were investigated.

Micellar CTAB was found to enhance the formation of Mo–GA complex. SDS micelles exerted an inhibitory effect while TX100 micelles had no effect on the complex formation. By the optimization of experimental conditions, the determination limit of the method suggested in the literature was lowered from 5.2 × 10⁻⁵ to 4.6 × 10⁻⁶ and to 5.7 × 10⁻⁷ M, in the absence and presence of CTAB, respectively.

The mechanism of the effect of CTAB was investigated by spectrophotometric titrations and it was concluded that CTAB did not form a ternary complex with Mo and GA. The stoichiometry of the complex, deduced from the results of spectrophotometric titrations, provided evidence for the formation of para-Mo₇O₄⁶⁻ polyanions at pH 4.5, indicating to the formation of a charge transfer complex between these ions and GA in micellar medium.     

Calculation of reference pH values for standard solutions from the corresponding acid dissociation constants

Making the simplest possible assumption about the activity coefficient of the charged species, pH values of standard buffer solutions have been evaluated from the thermodynamic acidity constants, K, of the weak acids involved. A general equation is given for a triprotic acid, H₃A, as it can be simplified to derive the equations for other systems. A computer program for the solution of the equation was written giving m_H values, species distribution coefficients, α, buffer capacities, β, species activity coefficients, γ, and ionic strength, I. Iteration was continued until agreement between successive values to within 1 ± 10^?6 was reached.The activity coefficients of singly charged ions were taken as equal to γ_Cl, where log γ_Cl=?AI^1/2 (1 + 1.5I^1/2), which is the Bates-Guggenheim convention, and those of doubly and triply charged ions were given by the valence relations of the Debye-Hückel theory as γ⁴_Cl and γ⁹_Cl, respectively.     

Partial Molar Volumes and Refractions of Cobalt(III) Complexes, Part 2: Homologous Series of Nitrilopentaamminecobalt(III) Complexes

Both the partial molar volumes (V° _2m refractions (R° _2m ) of the solutes at infinite dilution have been determined at 20 °C for a series of six octahedral N₆-coordinated cobalt(III) species featuring five coordinated ammonia ligands along with a sixth N-coordinated organonitrile of increasing ligand size (from acetonitrile to sebaconitrile). The experimental values for V° _2m are consistent with the relative sizes of the ligands but show larger values than those generated by computer modeling as the size of the cation increases, presumably due to the void space of the cation which increases with the size of the nitrile ligand.     

Dependence of Surface Tension of Near-boiling Non-associated Liquids on Their Molar Volume and Some Critical Constants

Abstract

The equation proposed for near-boiling non-associated liquids describes a new functional dependence of their surface tension on such physico-chemical characteristics as: critical volume, critical temperature and molar volume at the temperatures which are near their normal boiling points. It is shown that, in the case of some low-boiling liquids, possessing small molecules, this equation can be used for the adequate calculation of surface tension at different temperatures in the liquid phase.     

Enhancement of hydrolysis through the formation of mixed hetero-metal species

In order to analyze the formation of hetero-metal polynuclear hydrolytic species, in this paper, we reported some results of an investigation (at I = 0.16 mol L⁻¹ in NaNO₃, at t = 25 °C by potentiometry, ISE-H⁺, glass electrode) on the hydrolysis of several mixtures (in different ratios) of two couples of cations: dioxouranium(VI)/copper(II) and dioxouranium(VI)/diethyltin(IV). The elevated total concentrations of cations 0.005 ≤ ΣC_M mol L⁻¹ ≤ 0.05) adopted in these measurements induced us to study again the hydrolysis of uranyl, for which no suitable literature data are available in these particular experimental conditions. All measurements were performed by two different operators, using completely independent instruments and reagents. Many different speciation models were considered in the calculations, including the simultaneous refinement of homo- and hetero-metal species, and a statistical analysis of obtained results was proposed too. Main results can be summarized as follows: UO₂²⁺ and Cu²⁺ form three hetero-metal polynuclear hydrolytic species [(UO₂)Cu(OH)³⁺, (UO₂)Cu₂(OH)²⁺ and (UO₂)₂Cu₄(OH)²⁺, with log β_pqr = −2.93 ± 0.01, −7.34 ± 0.03 and −13.78 ± 0.03, respectively], all those common to their simple speciation without the other cation; UO₂²⁺ and (C₂H₅)₂Sn²⁺ form seven mixed hydrolytic species [(UO₂)(DET)(OH)³⁺, (UO₂)(DET)₂(OH)²⁺, (UO₂)₂(DET)₄(OH)²⁺, (UO₂)(DET)₂₄(OH)²⁺, (UO₂)₂(DET)⁺₅(OH), (UO₂)(DET)₂⁺₅(OH) and (UO₂)₂(DET)⁻₇(OH), with log β_pqr = −2.5 ± 0.2, −4.74 ± 0.02, −10.70 ± 0.06, −10.34 ± 0.03, −15.70 ± 0.06, −15.58 ± 0.06 and −27.9 ± 0.1, respectively] that are of the same kind of those formed by uranyl; formation of mixed hydrolytic species causes a significant enhancement of the percentage of hydrolyzed metal cations, modifying the solubility and, therefore, the bioavailability of these cations. We also determined, for dioxouranium(VI)/copper(II) system, the corresponding complex formation enthalpies and entropies by direct calorimetric measurements. We obtained ΔH₁₁₂ = 47.9 ± 0.6 and ΔH₂₁₄ = 92.9 ± 0.5 kJ mol⁻¹, TΔS₁₁₂ = 6 ± 1 and TΔS₂₁₄ = 14 ± 1 kJ mol⁻¹ (±S.D.), respectively, for the formation of (UO₂)(Cu)₂(OH)²⁺ and (UO₂)₂(Cu)₄(OH)²⁺ species (according to reaction 2). We also calculated the single enthalpic and entropic contributes to the extra-stability that these species show with respect to the corresponding homo polynuclear ones.     

Synthesis, structural study and hydrolytic degradation of copolymer based on glycolic acid and bis-2-hydroxyethyl terephthalate

The current demand for environmentally degradable copolymers has initiated the use of novel degradable copolyesters. One of them is a copolyester based on poly(ethylene terephthalate-co-glycolic acid) (PET-GLA). The copolymer was synthesized by the melt reaction of bis-2-hydroxyethyl terephthalate (BHET) with glycolic acid (GLA) oligomers in the presence of Sb₂O₃ as a catalyst.Hydrolytic degradation of the copolymer was carried out in two buffered solutions at 45 °C: degradation was studied by incubating samples in powder form, in a concentrated solution from 30 to 150 days.The copolymer before and after degradation was characterized by means of different analytical techniques. ¹H and ¹³C NMR spectroscopy was used to confirm the incorporation of glycolide units in PET chains and to observe the structure and decomposition of the novel polyester. The thermal properties and morphology before and during the degradation were studied by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis for determining melting points as well as melting and decomposition temperatures of investigated copolyester.     

Polarographic behaviour of 2-benzilidenimino-benzohydroxamic acid (2-BIBH) and 2-BIBH-Mo(VI) system

The polarographic behaviour of 2-benzilideniminobenzohydroxamic acid (2-BIBH) solutions and of 2-BIBH solutions in the presence of Mo(VI) have been studied by using differential pulse polarography and cyclic voltammetry. The polarographic characteristics of the resulting waves have been studied and possible mechanisms of the processes involved have been proposed. A linear relationship has been observed betweenI _p and Mo(VI) concentration in the range 2×10^–6 to 1.6×10^–5 M when using 3×10^–4 M 2-BIBH. Standard deviations of 5.6×10^–8 and 1.2×10^–8 M were found for 3×10^–6 and 8 × 10^–6 M Mo(VI), respectively.     

Molar volume calculated at various pressures and the Pippard relations close to the melting point in benzene

The molar volume of solid and liquid benzene was calculated at various pressures (at constant temperatures), and the Pippard relations were examined close to the melting point in this organic molecule.

The molar volume calculated is in good agreement with the observed data, which decreases as the pressure increases up to about 150 MPa. The Pippard relations are also valid within this pressure range at constant temperatures studied here for the solid and liquid phases of benzene.     

Partial Molar Volumes of Cobalt(III) Complexes. Part 3: Homologous Series of Aminopentaamminecobalt(III) Complexes

Partial molar volumes (V ₂°) have been determined at infinite dilution in aqueous solution at 20 °C for a series of octahedral N₆-coordinated cobalt(III) species having five-coordinated ammonia ligands along with an N-coordinated linear alkyl amine whose alkyl chain was varied from ethylamine to octylamine. The experimental values for V ₂° are consistent with the relative sizes of the ligands but show increasing deviations from those predicted by computer modeling, as the size of the cation increases, presumably due to the void space of the cation that increases with the size of the amine ligand. The value of the partial molar volume at infinite dilution increased by about 16 mL⋅mol⁻¹ with each added methylene group.     

A DFT investigation of dissociation of nitrous acid,transformation of its monomeric isomers,their dimeric isomers,and dimerization

The structure optimization of the monomeric isomers of the nitrous acid HONO, their cyclic dimers (HONO)₂, and transition states of their transformations has been carried out using the density functional theory calculations at the B3LYP/6‐311++G(d,p) and B3LYP/aug‐cc‐pVQZ levels of theory. Three monomeric isomers (c, t, and z isomers) and six dimeric isomers (cc, ct, cz, tt, zz, and tz isomers) were found. Dissociation of the most stable of the HONO isomer (t isomer) was investigated and its rate constant was obtained at the UB3LYP/aug‐cc‐pVQZ level. Energetics, thermodynamic properties, rate, and equilibrium constants of the monomeric and dimeric isomerizations of the nitrous acid were obtained. Dimerization energies, enthalpies, and free energies of the dimeric isomers, (HONO)₂ were also obtained. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

A novel extractant-impregnated resin containing carminic acid for selective separation and pre-concentration of uranium(VI) and thorium(IV)

The present work proposes the use of a novel extractant-impregnated resin (EIR) as an adsorbent in trace separation and pre-concentration of U(VI) and Th(IV) ions. The new EIR was prepared by impregnating carminic acid onto Amberlite XAD-16 resin beads. The morphology of new EIR was studied by BET surface area measurements and SEM micrographs. A column packed with CA/XAD-16 was used for selective separation and pre-concentration of the metal ions. Maximum adsorption of Th(IV) and U(VI) ions occurred at pHs of 3.50–5.75 and 3.75–6.50, respectively. The adsorbed metals could be eluted sequentially using 0.55?mol?L^?1 HCl for U(VI) and 2.25?mol?L^?1 HCl for Th(IV). The dynamic capacity of EIR was found to be 0.832 and 0.814?mmol?g^?1 for Th(IV) and U(VI), respectively. The tolerance limit of some foreign ions was also studied. The proposed method showed a good performance in analyzing geological reference materials and a synthetic seawater sample. Furthermore, the above procedure was successfully employed for the analysis of natural water samples.     

Substituent effect on electrophoretic mobility for a series of poly(N-acryloyl-amino acid)s

In this study, the electrophoretic mobilities (μ) for a series of poly(N-acryloyl-amino acid)s were determined by capillary zone electrophoresis to investigate the effect of substituent on the electrophoretic behavior of polyelectrolytes. The μ values determined showed a strong correlation with the molar volume of the corresponding amino acids.     

The determination of the second dissociation constant of sulfuric acid

The second dissociation constant of sulfuric acid is determined in 1M NaClO₄ at 25°C using an electrochemical cell without liquid junction consisting of a glass and a perchlorate electrode. By taking into account the association between the Na⁺ and SO ₄ ^2– ions an average value of 0.0184±0.0005 is found using three different methods. This corresponds with an apparent acidity constant KA ₂ ^* of 0.095±0.003     

The Hydrolysis of AuCl<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack> and the Stability of Aquachlorohydroxocomplexes of Gold(III) in Aqueous Solution

The equilibria AuCl₄⁻+jOH⁻+kH₂O⇌AuCl_4−j−k (OH) _j (H₂O) _k ^k−1+(j+k)Cl⁻, β _jk (0≤j,k≤4) have been studied spectrophotometrically at 20 °C in aqueous solution. For I=2 mol⋅dm⁻³(HClO₄) the conventional constants, β _i ^*, of the equilibria, Au^*+iCl⁻ ⇌AuCl _i ^*, are equal to log ₁₀ β ₁^*=(6.98±0.08); log ₁₀ β ₂^*=(13.42±0.05); log ₁₀ β ₃^*=(19.19±0.09); and log ₁₀ β ₄^*=(24.49±0.07), where [AuCl _i ^*]=∑[AuCl _i (OH) _j (H₂O)_4−i−j ] at i=const. The hydrolysis and other transformations of AuCl₄⁻ in aqueous solution are discussed. On the basis of new and known data, a full set of equilibrium constants, β _jk , or their estimates has been obtained.     

Determination and comparison of stability constants of tungsten(VI) and molybdenum(VI) with nitrilotriacetic acid and glutamic acid at different ionic strengths

The formation constants of species formed in the systems H⁺?+?W(VI)?+?nitrilotriacetic acid (NTA) and H⁺?+?NTA have been determined in aqueous solution for pH?=?4–9 at 25°C and different ionic strengths ranging from 0.1 to 1.0?mol?dm^?3 NaClO₄, using potentiometric and spectrophotometric techniques. It was shown that tungsten(VI) forms a mononuclear 1?:?1 complex with NTA of the type WO₃L^3? at pH?=?7.5. The composition of the complex was determined by the continuous variations method. The complexation of molybdenum(VI) with glutamic acid was investigated in aqueous solution ranging in pH from 4 to 9, using polarimetric, potentiometric and spectrophotometric techniques. The composition of the complex was determined by the continuous variations method. It was shown that molybdenum(VI) forms a mononuclear 1?:?1 complex with glutamic acid of the type MoO₃L^2? at pH?=?6.0. The dissociation constants of glutamic acid and the stability constants of the complex were determined at 25°C and at ionic strengths ranging from 0.1 to 1.0?mol?dm^?3 sodium perchlorate. In both complex formation reactions the dependence of the dissociation and stability constants on ionic strength is described by a Debye-Huckel type equation. Finally, a comparison has been made between the patterns of ionic strength dependence for the two complexes and the results have been compared with data previously reported.     

聚6-羟基己酸碱性条件下的水解反应研究

探究了碱性条件下聚6-羟基己酸水解反应的机理和最优化工艺条件。实验过程中选用碱度较大的氢氧化钠及碱度较小的碳酸氢钠作为反应试剂。研究表明:碱度不同,其反应机理,反应工艺条件亦不同。碱度越大,OH~-浓度越大,亲核基团[OH~-]直接进攻聚6-羟基己酸的酯基结构,使酯基键发生断裂反应,生成小分子的6-羟基己酸;反应工艺条件缓和,在100℃的集热式恒温加热磁力搅拌器中既可完全解聚。碱度大的氢氧化钠参与反应的最优化工艺条件:氢氧化钠/聚6-羟基己酸摩尔比为4.4,乙二醇/聚6-羟基己酸摩尔比为6.5,水用量100g,催化剂0.1g,反应时间2h,反应温度100℃条件下,6-羟基己酸产率达到84.07%;碱度小的碳酸氢钠钠参与反应的最优化工艺条件:碱度越小,OH~-浓度越小,在反应初期亲核基团[-OCH_2CH_2OH]占主导地位,发生醇解反应的概率大,整个反应体系为醇解反应与水解反应相互促进进行;反应工艺条件苛刻,须在180℃密闭高压釜中完全解聚。碳酸氢钠/聚6-羟基己酸摩尔比为1.1,乙二醇/聚6-羟基己酸摩尔比为3,水用量100g,催化剂0.1g,反应时间1h,反应温度180℃~190℃条件下,6-羟基己酸产率达到90.38%。在整个反应系统中,乙二醇作为溶剂来使用。     

高效毛细管电泳大体积样品堆积在线富集法测定蒲公英中阿魏酸、绿原酸和咖啡酸

采用大体积样品堆积(LVSS)在线富集模式,建立了高效毛细管电泳(HPCE)测定蒲公英中阿魏酸、绿原酸和咖啡酸含量的方法。主要考察了在毛细管区带电泳(CZE)分离模式下,缓冲液的pH和浓度对分离效果的影响,以及在LVSS在线富集模式下,进样时间对富集效果的影响。在最优条件下阿魏酸、绿原酸和咖啡酸可在12 min内得到分离,3个成分在0.5~25.0μg/mL浓度范围内均有较好的线性关系(r2=0.999),平均加样回收率分别为104.9%,98.0%和100.1%,RSD(n=6)分别为3.6%,2.6%和1.0%。定量限(S/N=10)分别为0.10,0.10和0.03μg/mL,检出限(S/N=3)分别为0.03,0.03和0.01μg/mL。相对于常规CZE模式,本方法的富集效果倍数为17~19倍。建立的方法可用于蒲公英的日常检测与质量控制。     

Chromium(VI) oxide-mediated oxidation of polyalkyl-polypyridines to polypyridine-polycarboxylic acids with periodic acid

4,4′-Dicarboxy-2,2′-bipyridine was synthesized quantitatively by chromium(VI) oxide-mediated oxidation of 4,4′-dimethyl-2,2′-bipyridine or 4,4′-diethyl-2,2′-bipyridine with periodic acid as the terminal oxidant in sulfuric acid. 5,5′-Dicarboxy-2,2′-bipyridine and 6,6’-dicarboxy-2,2′-bipyridine were also synthesized by the method from the corresponding dimethyl bipyridines in excellent yields. 4,4′,4″-Tricarboxy-2,2′:6′,2″-terpyridine was obtained in 80% yield from 4,4′,4″-triethyl-2,2′:6′,2″-terpyridine, and 4,4′,4″,4′″-tetracarboxy-2,2′:6′,2″:6″,2′″-quaterpyridine was obtained in 72% yield from 4,4′,4″,4′″-tetraethyl-2,2′:6′,2″:6″,2′″-quaterpyridine by the same procedure.