The photocatalytic decomposition of chloroform by tetrachloroaurate(III)

Abstract  

Near-UV irradiation of solutions of (Bu₄N)AuCl₄ in aerated ethanol-stabilized chloroform causes the continuous decomposition of chloroform, as evidenced by the production of many equivalents of HCl and peroxides. At the outset of irradiation, most of the AuCl₄ ⁻ is reduced to AuCl₂ ⁻, but the reduction stops and is reversed. The same experiments done in ethanol-free chloroform cause chloroform decomposition only until the irreversible reduction of the gold is complete. In deoxygenated ethanol-free chloroform, irreversible reduction to AuCl₂ ⁻ is accompanied by the formation of HCl and CCl₄, while the main decomposition products in deoxygenated ethanol-stabilized chloroform are HCl and C₂Cl₆. It is proposed that, in ethanol-free chloroform, photoreduction of AuCl₄ ⁻ begins with the concerted elimination of HCl from an association complex of CHCl₃ with AuCl₄ ⁻, and that ethanol suppresses { \textCHCl₃ ·\textAuCl₄ ^- } \{ {\text{CHCl}}_{3} \cdot {\text{AuCl}}_{4}^{ - } \} complex formation, leaving a slower radical process to carry out the photoreduction of AuCl₄ ⁻ in ethanol-stabilized chloroform. In the presence of oxygen, the radical process causes a build-up of CCl₃OOH, which reoxidizes AuCl₂ ⁻ to AuCl₄ ⁻ and allows the photodecomposition of CHCl₃ to continue indefinitely.     

Photocatalytic degradation of chloroform by bis (bipyridine)dichlororuthenium(III/II)

Broadband (λ > 320 nm) irradiation of chloroform solutions of either [Ru(bpy)₂Cl₂] or [Ru(bpy)₂Cl₂]Cl exposed to air led to a photostationary state, in which [Ru(bpy)₂Cl₂]⁺ predominated, and to the continuous decomposition of CHCl₃, as evidenced by the accumulation of HCl, hydroperoxides (CCl₃OOH and CHCl₂OOH), and tetra-, penta-, and hexachloroethane. The addition of Cl^? increased the rate of photodecomposition, while the replacement of Cl^? by F^? greatly decreased the rate. The observations are consistent with a photocatalytic cycle in which [Ru(bpy)₂Cl₂]⁺ is photochemically reduced to [Ru(bpy)₂Cl₂], which is thermally reoxidized by CCl₃OO or CCl₃OOH. In the absence of air a much slower photodecomposition reaction takes place leading to continuously increasing concentrations of chloroethanes. The data are consistent with a catalytic cycle in which [Ru(bpy)₂Cl₂]⁺ is photoreduced, as in aerated solutions, while [Ru(bpy)₂Cl₂] is photooxidized with chloroform as the substrate.     

Thermal behaviour of nickel(II) sulphate,nitrate and halide complexes containing ammine and ethylenediamine as ligands

Thermal behaviour of nickel amine complexes containing SO₄ ²⁻, NO₃ ⁻, Cl⁻ and Br⁻ as counter ions and ammonia and ethylenediamine as ligands have been investigated using simultaneous TG/DTA coupled with mass spectroscopy (TG/DTA–MS). Evolved gas analyses detected various transient intermediates during thermal decomposition. The nickel ammonium sulphate complex produces NH, N, S, O and N₂ species. The nickel ammonium nitrate complex generated fragments like N, N₂, NO, O₂, N₂O, NH₂ and NH. The halide complexes produce NH₂, NH, N₂ and H₂ species during decomposition. The ligand ethylenediamine is fragmented as N₂/C₂H₄, NH₃ and H₂. The residue hexaamminenickel(II) sulphate produces NiO with crystallite size 50 nm. Hexaammine and tris(ethylenediamine)nickel(II) nitrate produce NiO in the range 25.5 nm and 23 nm, respectively. The halide complexes produce nano sized metallic nickel (20 nm) as the residue. Among the complexes studied, the nitrate containing complexes undergo simultaneous oxidation and reduction.     

The extraction of Cr(III) from aqueous thiocyanate solutions and its separation from Co(II) and Ni(II)

For the system liquid anion-exchanger—Cr(III)−NCS⁻, an investigation has been made of the dependence of the percentage extraction of Cr(III) on parameters such as standing time of the Cr(III)−NCS⁻ solution, temperature, pH and type of exchanger. Quantitative extraction of e.g. 4·10⁻⁴ M Cr(III) by 0.1M Aliquat in CCl₄ is easily achieved at room temperature, using 4.75M KNCS−0.05N HCl as aqueous phase. At high Cr(III) concentrations, the complex anion present in the organic phase is Cr(NCS) ₆ ³⁻ ; when working with dilute metal ion solutions, the species extracted is Cr(NCS)₄ (H₂O) ₂ ⁻ . Separations of mixtures containing 10⁻²−10⁻⁴ M Co(II), Ni(II) and Cr(III) have successfully been accomplished.     

FeCl3 solutions in isopropanol-water

Summary This paper is devoted to the characterization of FeCl₃ solutions in isopropanol containing water. For this goal optical absorption and e.p.r. techniques have been used in conjunction with magnetization and M?ssbauer data reported very recently. It is shown that in a 10⁻² M solution of FeCl₃ containing 0.4 M of water the main iron(III) species present in the solution are [FeCl₄]⁻ (55%) and [FeCl₂(H₂O)₄]⁺ (20%) while the remainding 25% is due to dihydroxo dimers, . When the water concentration increases the [FeCl₄]⁻ anions are progressively destroyed, the main iron(III) species present in the solution being the dihydroxodimers and [FeCl₂(H₂O)₄]⁺. The variation of the concentration of the three species mentioned with the water content and FeCl₃ concentration is presented in this paper.     

Étude par spectrométrie raman laser de l'extraction liquide-liquide du FeCl3 par le chlorhydrate de trilaurylamine

Raman spectra of aqueous 1 M chloroferrate(III) solutions indicate the presence of FeCl₃ and FeCl₄^- in proportion to the hydrochloric acid concentration, but FeCl₄^- is only present in solutions of acidity higher than 5 M HCl. The liquid-liquid extraction of the aqueous chloroferrate phases ( 1 M HCl) by trilaurylamine hydrochloride in cyclohexane, shows that iron(III) is extracted only in its FeCl₄^- form, even though this species does not appear in the aqueous solutions. A quantitative spectroscopic study of the organic phases by means of the v₁ line of FeCl₄^- at 332 cm^-1 leads to the following conclusions: (a) the plot of the scattering coefficient of the 332 cm^-1 line versus iron(III) concentration shows the presence of two complex species in the organic phase; (b) the distribution curves of the complex species could be calculated. On the basis of the Raman results, an ion-pair type compound is proposed for the two complexes.     

Application of the catalytic properties of N-methylthiourea to the determination of In(III) at low levels by square wave voltammetry

Abstract  

This article proposes a simple and fast method of In(III) determination in the presence of Cd(II) and Pb(II). The catalytic activity of N-methylthiourea was used in the In(III) electroreduction, which also had a slight effect on the electroreduction process of Cd(II) and Pb(II). By applying square wave voltammetry it was possible to determine 3 × 10⁻⁷ mol dm⁻³ In(III) in the presence of 5 × 10⁻⁵ mol dm⁻³ Cd(II) and 1 × 10⁻⁴ mol dm⁻³ Pb(II) in 5 mol dm⁻³ NaClO₄ at pH 2. The calibration curve for In(III) was linear from 3 × 10⁻⁷ to 5 × 10⁻⁴ mol dm⁻³. The relative standard deviation for In(III) determination was about 3.0%.     

Synthesis,characterization, and thermal behavior of palladium(II) coordination compounds containing isonicotinamide

Palladium(II) coordination compounds of general formula trans-[PdX₂(isn)₂], X = Cl⁻ (1), N₃ ⁻ (2), SCN⁻ (3), NCO⁻ (4), isn = isonicotinamide; were synthesized and characterized in solid state by elemental analysis, infrared spectroscopy, and simultaneous TG–DTA. TG experiments reveal that the compounds 1–4 undergo thermal decomposition in three or four stages, yielding Pd⁰ as final residue, according to calculus and identification by X-ray powder diffraction.     

From Cluster to Cluster: Structural Transformation Reactions Among Tungsten Chloride Clusters

Reactions between tungsten halides are discussed along the series of compounds WCl₆ → WCl₄ → W₆Cl₁₂ ↔ W₆Cl₁₈ → [W₆CCl₁₈]ⁿ⁻ ← [W₃Cl₁₃]^u−, focusing on the two closely related tungsten chloride compounds whose structures compromise the well-known octahedro W₆Cl₁₈ cluster and the carbon-centered triprismo W₆CCl₁₈ cluster. Both clusters can be regarded as being built by merging two trigonal [W₃Cl₁₃]^u− units in different ways. Syntheses, structural transformation reactions, and concepts regarding electronic structures are reported.     

Constants of keto-enol equilibrium of acetoacetyl- and 1,1′-bis(acetoacetyl)ferrocene in aprotic solvents at 20°

The keto-enol equilibrium of 2 × 10⁻³ M solutions of (acetoacetyl)ferrocene and 1,1′-bis(acetoacetyl)ferrocene was studied by ¹H NMR spectroscopy in a series of aprotic solvents such as DMSO-d ₆, (CD₃)₂CO, CDCl₃, CD₂Cl₂, CCl₄, and C₆D₆ at a temperature of 20°C. It was established that the calculated enolization constants increase with a decrease in the polarity of solvent molecules. The results complement and combine known empirical rules about the effect of the medium on keto-enol equilibria.     

Mechanistic studies on the intramolecular electron transfer in an adduct species of the oxo-centred trinuclear iron(III) cation and <Emphasis Type="SmallCaps">l</Emphasis>-ascorbic acid in aqueous solution

The kinetics of the intra-molecular electron transfer of an adduct of l-ascorbic acid and the [Fe₃^IIIO(CH₃COO)₆(H₂O)₃]⁺ cation in aqueous acetate buffer was studied spectrophotometrically, over the ranges 2.55 ≤ pH ≤ 3.74, 20.0 ≤ θ ≤ 35.0 °C, at an ionic strength of 0.50 and 1.0 mol dm⁻³ (NaClO₄). The reaction of l-ascorbic acid and the complex cation involves the rapid formation of an adduct species followed by a slower reduction in the iron centres through consecutive one-electron transfer processes. The final product of the reaction is aqueous iron(II) in acetate buffer. The proposed mechanism involves the triaqua and diaqua-hydroxo species of the complex cation, both of which form adducts with l-ascorbic acid. At 25 °C, the equilibrium constant for the adduct formation was found to be 86 ± 15 and 5.8 ± 0.2 dm³ mol⁻¹ for the triaqua and diaqua-hydroxo species, respectively. The kinetic parameters derived from the rate expression have been found to be: k ₀ = (1.12 ± 0.02) × 10⁻² s⁻¹ for the combined spontaneous decomposition and k ₁ = (4.47 ± 0.06) × 10⁻² s⁻¹ (ΔH ₁^‡ = 51.0 ± 2.3 kJ mol⁻¹, ΔS ₁^‡ = −100 ± 8 J K⁻¹ mol⁻¹), k ₂ = (4.79 ± 0.38) × 10⁻¹ s⁻¹ (ΔH ₂^‡ = 76.5 ± 0.8 kJ mol⁻¹, ΔS ₂^‡ = 6 ± 3 J K⁻¹ mol⁻¹) for the triaqua and diaqua-hydoxo species, respectively.     

N-functionalized cyclam based trinuclear copper(II) complexes: electrochemical,magnetic, catalytic and antimicrobial studies

A series of trinuclear Cu(II) complexes have been prepared by Schiff base condensation of 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-l,4,8,11-tetraazacyclotetradecane and 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-l,4,8,11-tetraazacyclotetradecane with aromatic and aliphatic diamines, Cu(II) perchlorate and triethylamine. The complexes were characterized by elemental and spectroscopic analysis. Electrochemical studies of the complexes in DMF solution show three irreversible one-electron reduction processes around E_pc ¹ = −0.73 to −0.98 V, E_pc ² = −0.91 to −1.20 V and E_pc ³ = −1.21 to −1.33 V. ESR spectra and magnetic moments of the trinuclear Cu(II) complexes show the presence of antiferromagnetic coupling. The rate constants for hydrolysis of 4-nitrophenylphosphate by the Cu(II) complexes are in the range of 3.33 × 10⁻² to 7.58 × 10⁻² min⁻¹. The rate constants for the catecholase activity of the complexes fall in the range of 2.67 × 10⁻² to 7.56 × 10⁻² min⁻¹. All the complexes were screened for antifungal and antibacterial activity.     

Photocatalytic Conversion of a FeCl<Subscript>3</Subscript>–CCl<Subscript>4</Subscript>–ROH System

The photocatalytic transformations of carbon tetrachloride and aliphatic primary alcohols in the presence of iron trichloride and a molar ratio of components FeCl₃: CCl₄: ROH = 1: 300: 2550 were studied. CCl₄ is transformed into chloroform and hexachloroethane after exposure to a mercury lamp (250 W) to the FeCl₃–CCl₄–ROH system at 20°C, whereas the primary ROH alcohols are selectively oxidized into acetals (1,1-dialkoxyalkanes). The maximum conversion of CCl₄ reaches 80%. The kinetics and mechanism of the photocatalytic conversion of the FeCl₃–CCl₄–ROH system are considered.     

Thermoanalytical studies of imidazole-substituted coordination compounds

Four manganese(II) coordination compounds with bis(1-methylimidazol-2-yl)ketone (BIK) of general formula Mn(BIK)₂X₂ (X = Cl, Br, NO₃, ClO₄) were synthesized and characterized by elemental analysis, by UV–vis, and FTIR spectroscopies to be compared with the literature data. Following our previous thermoanalytical studies on imidazole-substituted coordination compounds, the thermal behavior of the synthesized Mn(II) complexes was investigated using TG and DTG techniques: the thermal profile is characterized by three substantial consecutive releasing steps for all the three complexes and the releasing supposed behavior is confirmed by EGA analysis performed by coupling the TG analyzer to an MS spectrometer. In particular, the first step is ascribed to the release of the two anions, followed by the loss of four methyl groups (side chains of the ligand) and two bridge-carbonyl groups. The residual tetra-imidazole manganese compound decomposes in a final step to give MnO as the final residue. Both the initial decomposition temperatures and the kinetic rate constants associated to the first decomposition step indicated a higher stability of the Mn(BIK)₂Cl₂ complex, the bromide complex being very close to the chloride one (first-step thermal stability: ClO₄ ⁻ <NO₃ ⁻ ≤Br⁻ <Cl⁻). Finally, the three-dimensional diffusion reaction model (D3) was selected to describe the first decomposition step for all the four complexes examined.     

Kinetics of the borate anion catalyzed oxidation of diethyl sulfide with hydrogen peroxide in an <Emphasis Type="Italic">i</Emphasis>-PrOH–H<Subscript>2</Subscript>O medium

It was found that in a wide range of pH in the presence of boric acid the oxidation of diethyl sulfide (Et₂S) with hydrogen peroxide in an i-PrOH–H₂O medium occurs with the participation of H₂O₂, HOO^–, monoperoxo-(B(OH)₃OOH^–), and diperoxoborates (B(OH)₂(OOH)₂⁻). The stability constants of peroxoborates and the rate constants for the reactions of H₂O₂, HOO⁻, B(OH)₃(OOH)₂⁻, and B(OH)₂(OOH)₂⁻ with Et₂S under these conditions were determined.     

Thermal behavior and thermal safety on 3,3-dinitroazetidinium salt of perchloric acid

3,3-Dinitroazetidinium (DNAZ) salt of perchloric acid (DNAZ·HClO₄) was prepared, it was characterized by the elemental analysis, IR, NMR, and a X-ray diffractometer. The thermal behavior and decomposition reaction kinetics of DNAZ·HClO₄ were investigated under a non-isothermal condition by DSC and TG/DTG techniques. The results show that the thermal decomposition process of DNAZ·HClO₄ has two mass loss stages. The kinetic model function in differential form, the value of apparent activation energy (E _a) and pre-exponential factor (A) of the exothermic decomposition reaction of DNAZ·HClO₄ are f(α) = (1 − α)⁻¹/2, 156.47 kJ mol⁻¹, and 10^15.12 s⁻¹, respectively. The critical temperature of thermal explosion is 188.5 °C. The values of ΔS ^≠, ΔH ^≠, and ΔG ^≠of this reaction are 42.26 J mol⁻¹ K⁻¹, 154.44 kJ mol⁻¹, and 135.42 kJ mol⁻¹, respectively. The specific heat capacity of DNAZ·HClO₄ was determined with a continuous C _p mode of microcalorimeter. Using the relationship between C _p and T and the thermal decomposition parameters, the time of the thermal decomposition from initiation to thermal explosion (adiabatic time-to-explosion) was evaluated as 14.2 s.     

Studies on thermochemical properties of ionic liquids based on transition metal

A brown and transparent ionic liquid (IL), [C₄mim][FeCl₄], was prepared by mixing anhydrous FeCl₃ with 1-butyl-3-methylimidazolium chloride ([C₄mim][Cl]), with molar ratio 1/1 under stirring in a glove box filled with dry argon. The molar enthalpies of solution, Δ_s H _m, of [C₄mim][FeCl₄], in water with various molalities were determined by a solution-reaction isoperibol calorimeter at 298.15 K. Considering the hydrolyzation of anion [FeCl₄]⁻ in dissolution process of the IL, a new method of determining the standard molar enthalpy of solution, Δ_s H _m⁰, was put forward on the bases of Pitzer solution theory of mixed electrolytes. The values of Δ_s H _m⁰ and the sum of Pitzer parameters: and were obtained, respectively. In terms of thermodynamic cycle and the lattice energy of IL calculated by Glasser’s lattice energy theory of ILs, the dissociation enthalpy of anion [FeCl₄]⁻, ΔH _dis≈5650 kJ mol⁻¹, for the reaction: [FeCl₄]⁻(g)→Fe³⁺(g)+4Cl⁻(g), was estimated. It is shown that large hydration enthalpies of ions have been compensated by large the dissociation enthalpy of [FeCl₄]⁻ anion, Δ_d H _m, in dissolution process of the IL.     

Thermal study of mononuclear Pd(II) complexes of the type [Pd(X)<Subscript>2</Subscript>(Rtu)(PPh<Subscript>3</Subscript>)] (X = Cl,SCN; Rtu = <Emphasis Type="Italic">N</Emphasis>-methylthiourea, <Emphasis Type="Italic">N</Emphasis>-phenylthiourea)

The synthesis, spectroscopic characterization, and thermal analysis of the compounds [Pd(X)₂(mtu)(PPh₃)] (X = Cl⁻ (1), SCN⁻ (2); mtu = N-methylthiourea; PPh₃ = triphenylphosphine) and [Pd(X)₂(phtu)(PPh₃)] (X = Cl⁻ (3), SCN⁻ (4); phtu = N-phenylthiourea) are described. The thermal decomposition of the compounds occurs in two, three, or four stages and the final decomposition products were identified as Pd⁰ by X-ray powder diffraction. The thermal stability order of the complexes is 4 > 3>2 > 1.     

Monomeric and polymeric structures derived from 3,3′,4,4′-biphenyltetracarboxylic acid, phenanthroline and metal ions

Under similar hydrothermal synthetic conditions, the reactions of Fe(NO₃)₃/FeCl₂, CuCl₂, NiCl₂, and CdCl₂ with phenanthroline (phen) and 3,3′,4,4′-biphenyltetracarboxylic acid (H₄BPTC) afforded complexes [Fe(phen)₃](H₃BPTC)₂ (1), [Cu(phen)(BPTC)_0.5 · H₂O] · H₂O (2), [Ni₃(phen)₃(BPTC)_1.5(H₂O)₅] · 4H₂O (3) and [Cd(phen)(BPTC)_0.5] · H₂O (4). The short Fe–N distance in the monomeric Fe(phen)₃(H₃ BPTC)₂ (1) shows that the Fe(II) is in a low-spin state. H₃ BPTC⁴⁻ acts as a counter-ion in this complex. In [Cu(phen)(BPTC)_0.5 · H₂O] · H₂O (2), the central Cu(II) is five-coordinated in a square-pyramidal geometry. The ligand BPTC⁴⁻ is centrosymmetric and the four deprotonated carboxylic groups of BPTC⁴⁻ are coordinated to four different copper ions to form a 1D ladder complex indicating a comparatively strong coordination. In [Ni₃(phen)₃(BPTC)_1.5(H₂O)₅] · 4H₂O (3), all nickel(II) atoms are in an octahedral coordination environment. There are two different BPTC⁴⁻ ligands; one is centrosymmetric and the other is asymmetric. Metal ions are linked through fully deprotonated BPTC⁴⁻ ligands to form a 2D metal-organic sheet. [Cd(phen)(BPTC)_0.5] · H₂O (4) has a 3D metal-organic framework. TG, IR, and fluorescence data for the complexes are presented.     

The thermal behavior of triethylenediammonium salts

(trienH₂)[CoCl₄], which contains tetrahedral chlorocobaltate(II) anions, decomposes under argon in two stages via a stepwise deprotonation of the cation. The decomposition starts at 310°C with the liberation of HCl, followed at 400°C by the simultaneous release of a further mole of HCl and triene and/or its cracking products. The second decomposition stage is strongly influenced by the atmosphere. In the lower temperature region (<400°C), increasing oxygen contents of the carrier gas lead to decreasing mass losses. Therefore, the solid residues contain various amounts of C,N-containing products as well as coke. The thermal decomposition of the iron(III) compound, which contains μ-oxalato-bridged FeCl₄ units, begins with the dehydratation followed by the decay of the complex anion to produce CO, CO₂, and HCl. Instead of a binuclear, monooxobridged chloroferrate(III) complex, a [FeCl₄]^? — containing compound is proposed as one of the final products. The third decomposition stage, partially overlaying the preceding one, is the degradation of the organic cation as found for the cobalt compound. The results of thein situ-TA-MS measurements are compared with those obtained from usual TA techniques as well as from the residue characterization by X-ray diffraction, Raman spectroscopy, and chemical analysis.