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.     

Séparation de traces métalliques sur goutte de mercure; application à la préconcentration de Cu(II) et Cu(I)

A method for the rapid separation of copper(II) traces on metallic mercury is proposed. The separation is rendered possible by the reduction of Cu(II) to Cu(I) on mercury in the presence of iodide ions followed by the adsorption of the uncharged complex, Cu(I), on Hg⁰. After a minute of agitation, this adsorption is quantitative (90–100%) for initial concentrations of Cu(II) between 10^?4 to 10^?6 M and iodide cone, of 10^?2 to 10^?3 M at pH 3. The volumes of the aqueous solutions are of the order of 3–10 ml and those of the drops of mercury between 0.5–1 ml. The tests were made using the isotope ⁶⁴Cu (T _1/2 = 12.8 h).     

Dosages Polarographiques du Cobalt et du fer a l'aide de nouvelles solutions de,base au trilon

After stressing the necessity of finding new base solutions for use in polarography, the authors show that Trilon B strongly displaces the reduction potentials of numerous elements.Owing to its ready transformation to the trivalent state cobalt can be determined without preliminary separation, in presence of an excess of most other metals, because it is then reduced at a very much lower negative potential (the step is at about 0.2 v) than in the usual divalent form (for which E$\text{1}\text{2}$, is always greater than I v). The method is applied to the analysis of steels.After complexing by Trilon B small amounts of iron can similarly be determined in the presence of an excess of other metals. The method is applied to the determination of small amounts of iron in brasses and “pure” metals.     

Structure cristalline et expansion thermique de l'iodure de nickel hexahydrate

The structure of NiI₂, 6 H₂O has been determined by X-ray diffraction techniques. The dimensions of the hexagonal unit cell are: a = 7.638 ± 0.005 Å and c = 4.876 ± 0.005 Å, with Z = 1. The space group is $\text{P}\text{3}\text{m1}$. The structure was deduced from Patterson and Fourier syntheses and refined by least-squares method to a final R value of 0.09. It is almost a layer structure, each layer is composed by n complex ions [Ni(H₂O)₆]²⁺ surrounded by 2 n ions I^?; this is in agreement with the good cleavage of crystals and with the marked anisotropy in the thermal expansion. But the structure may also be regarded as a derivation of NiAs structure, with only $\text{1}\text{8}$ of octahedral holes occupied. A structural classification of compounds MX₂, 6 H₂O is proposed.     

Study of complex formation between ��-cyclodextrin and benzene

In this work study of complex formation of ??-cyclodextrin with benzene was performed both experimentally and theoretically. Interaction of benzene with ??-cyclodextrin in aqueous solutions was investigated by means of UV spectroscopy at temperatures in the range 291?C303 K. The stoichiometric composition, stability constant, and thermodynamic parameters of ????-cyclodextrin-benzene?? supramolecular structures formation were calculated from spectroscopic data. It was proved that 1:1 inclusion complex is mainly formed in aqueous solutions. The calculations of a spatial structure, formation energy, and vibration spectra in IR range for the complex of ??-cyclodextrin with benzene were performed by Hartree?CFock?CRoothaan method within PM3 semiempirical approximation with quantum chemistry package GAMESS (version 6.4). The calculated energy parameters for ????-cyclodextrin-benzene?? inclusion complex are in agreement with experimental data.     

Analyse quantitative des hydrocarbures aromatiques polynucleaires par spectrofluorimetrie shpol'skii a 10 k: utilisation de la raie de mercure excitatrice diffusee par la matrice comme intensite lumineuse de reference

(Quantitative analysis by Shpol'skii spectrofluorimetry of polynuclear aromatic hydrocarbons at 10 K with the mercury excitation line scattered by the matrix used as a standard intensity.)High-resolution Shpol'skii spectrometry in a matrix is particularly suitable for the determination of trace polynuclear aromatic hydrocarbons in complex mixtures. In the usual technique, the method of standard additions is backed up by internal calibration, which is tedious. A direct calibration technique is proposed in which the mercury excitation line, scattered by the polycrystalline matrix, serves as the standard intensity. Detection limits vary from 0.3 ng ml^?1 for benzo(a)pyrene to 48 ng ml^?1 for pyrene, with linear response over about 2 orders of magnitude. The dynamics and a statistical analysis of the confidence interval for the results are discussed.     

Dosage titrimétrique du tributylphósphate,de la di-n-hexylsulfoxyde et de l'oxyde de tri-n-butylphosphine par les acides de lewis avec repérage visuel du terme

Tri-n-butylphosphate, tri-n-butylphosphine oxide and di-n-hexylsulfoxide were titrated with SnCl₄, SnBr₄ and TiCl₄ in anhydrous 1,2-dichloroethane with malachite green or crystal violet as indicator. Best results were obtained when SnCl₄ was used with malachite green as indicator. The accuracy of the method is about 1–2% for complex concentrations greater or equal to 0.05 M at the equivalence point.     

Solvatation preferentielle dans les systemes ternaires polyvinylpyrrolidone/solvant halogene/solvant donneur de proton—II: Etude,par spectroscopie infra-rouge,des interactions hydrogene

We have studied, for dilute solutions of polyvinylpyrrolidone in halogenated solvent/protondonor solvent mixtures, the spectroscopic perturbations of the stretching vibration band v(CO) of the polymer and those of the stretching vibration band v(OH) in the particular case of trifluoroethanol. These measurements indicate a hydrogen-bond association polymer/proton-donor solvent, increasing with the proton-donor concentration in the mixture. The interaction with solvents such as trifluoroethanol and phenol is much stronger than that due to ethanol. Hydrogen-bond complexes are of $\text{1}\text{1}$ type. However, study of the v(CO) and v(OH) bands leads, in the case of trifluoroethanol, to the proposal of a complex of $\text{1}\text{2}$ type the structure of which is suggested.     

Dosage de l'americium par coulometrie a potentiel impose

A coulometric determination of americium by reduction of Am(VI) to Am(V) at a potential of + 1.3 V is proposed. The accuracy of the method was evaluated by analyzing ²⁴¹Am solutions prepared by weighing and dissolving AmO₂ of known purity. The results must be corrected by a factor of 1.017, in order to eliminate the systematic error due to autoreduction. After this correction, the relative standard deviation of the method ranged from 0.44% for américium concentrations of 3.125·l0^-3M to 0.96% for those of 1.25·10^-4M.     

Effect of solvent on complexation between Y3+ cation and 4,13-diaza-18-crown-6 in some binary mixed non-aqueous solvents

The complexation reaction of 4,13-diaza-18-crown-6 (DA18C6) with Y³⁺ cation was studied in some binary mixed solvent solutions of acetonitrile (AN) with methanol (MeOH), ethanol (EtOH), 2-propanol (2-PrOH) and methyl acetate (MeOAc) at different temperatures by conductometric method. The obtained data show that in all studied solutions the stoichiometry of the complex formed between DA18C6 and Y³⁺ cation is 1: 1 [ML], but in the case of pure MeOAc, a 2: 1 [ML₂] complex is formed in solution upon addition of the ligand to the metal salt solution, and further addition of the ligand results in formation of a M₂L₂ complex in solution. This results show that the stoichiometry of the composition of the macrocyclic complexes may be affected by the nature of the solvent system. The results obtained in this study show that the stability constant of the resulting 1: 1 [ML] complex in the binary solvent solutions decreases in the order: AN-MeOAc > AN-2PrOH > AN-MeOH > AN-EtOH. A non-linear relationship was observed between the stability constant (logK _f ) of [Y(DA18C6)]³⁺ complex with the composition of the binary mixed solvent solutions. The corresponding standard thermodynamic parameters (H° _c , Δ S° _c ) for 1: 1 [ML] complexation reaction between DA18C6 and Y³⁺ cation were obtained from temperature dependence of the stability constant of the complex. The results show that, in all solvent systems, the (DAI8C6.Y)³⁺ complex is entropy stabilized, but from enthalpy point of view, depending on the solvent system, it is stabilized or destabilized and the result show that the values of both thermodynamic quantities change with the nature and composition of the binary mixed solvent solutions.     

Détermination, à 25°C,du produit ionique des solvants mixtes acétone+eau+perchlorate de sodium

The ionic products of different mixed solvents acetone+water with sodium perchlorate have been determined by a method of standardisation using solutions of “strong” acids and bases.The evolution of pk_i is plotted in function of molar fraction of acetone and concentration of sodium perchlorate.The approximate values of the ionic product of acetone and acetone+sodium perchlorate media (0.5 M, 1 M, 2 M, 3 M) have been achieved easily by graphical extrapolation.     

Enolates de l'acetylacetate d'ethyle. Structure et reactivite du sel de potassium en presence d'ether couronne et de cryptand

It is shown that, through the addition of 18-crown-6 or cryptand (2.2.2) to potassium ethyl acetoacetate enolate solutions in tetrahydrofuran, 1:1 complexes are formed. A single crystal of the 1:1 potassium énolate-18-crown-6 complex has been obtained. Its structure has been determined by X-ray diffraction. The crystal includes entities formed from an enolate anion chelating a potassium cation externally complexed by the crown-ether. The vibrational spectrometry shows that the structure of the entity is kept in solution. In the species formed through the addition of cryptand (2.2.2), the enolate anion has a structure (IR spectroscopy) and a reactivity very close to that of the free anion, observed in a dissociating solvent (DMSO, HMPA). When crown ether is added, a contact ion pair is formed, in which the cation is externally solvated by the crown. On the other hand, the cation encapsulation by the cryptand leads to a released anion with an “ S-trans” or “W” structure. The reactivity and the orientation of the alkylation reactions of these entities have been measured in THF solutions. They are discussed in relation to the structure of the species present in the reaction medium.     

Étude cristallographique et vibrationnelle de complexes metalliques de l'acide aminométhylphosphonique

The crystalline structure of the complex between Zn(II) and aminomethylphosphonic acid [Zn(AMPh)₂· 4H₂O] is described. This complex crystallizes as an orthorhombic system (space group Pca2₁, a = 10.001 ± 0.002, b = 12.140 ± 0.002, c = 10.281 ± 0.002 Å; Z = 4). Zinc is tetrahedral and coordinated with 4 oxygen atoms of 4 phosphonic groups. The IR spectra of this complex and its N-deuterated derivative in the solid state are analysed in relation to its structure. By comparison, a vibrational study of two other complexes showed Mn(II) gives the same type of coordination as Zn(II), but Cu(II) binds with both phosphonic and amino groups.     

Equilibres ioniques obtenus entre un echangeur d'ions et une solution de polyelectrolytes,faibles et de meme signe de charge

When an equilibrium is established between an ion exchange resin and a solution of polyelectrolyte of the same sign of charge (without added salt), there is no co-ion in the resin phase. It is shown that, for a weak acid resin in equilibrium with a solution of a strong acid polyelectrolyte completely neutralized by a monovalent counter-ion M⁺, the graph pH - pM = f(α), where α represents the degree of neutralization of the resin, is independent of the concentration of polyelectrolyte. These results have been verified for a highly swollen ion exchange gel. A weak resin in equilibrium with a solution of a weak polyelectrolyte gives a system in which the counter-ion is distributed between the two phases. The equilibrium partition can be calculated using a set of equations resembling those for buffer solutions. Experimental verifications have been obtained. The possible developments are discussed.     

Détermination de traces de manganèse urinaire après extraction à l'aide de 2,2,6,6-tétraméthylheptane-3,5-dione et dosage par spectrométrie d'absorption atomique

A procedure has been developed for the determination of urinary manganese by flameless atomic absorption spectrometry. The method was checked initially with solutions of manganese(II) before it was applied to mineralized urine (HNO₃—H₂SO₄). Manganese, probably in the trivalent state, is extracted with 0.5 M dipivaloylmethane in methyl isobutyl ketone at pH 10.6 in the presence of n-butylamine. This reagent has good stability and a low limit of detection is obtained. Precision and reproducibility are excellent.     

Spectrophotometric determination of thiocyanate ions in stratal waters

The formation of [FeSCN]²⁺ complex in hydrochloric and sulfuric acid medium was studied by spectrophotometry using iron(III) sulfate and ammonium iron(III) sulfate solutions as reactants. A method for the determination of 10–200 μg SCN^? in 25 mL water solutions containing ammonium iron(III) sulfate in sulfuric acid medium was developed; its determination limit is 2.6 μg (P = 0.99, n = 9). The method was applied for the analysis of model water samples with macro- and micro-component compositions similar to that of water from the Arigol licensed area. Operational control of the accuracy rate was performed by the standard addition method. The developed method can be applied to analyze water samples containing 1–90 mg/L thiocyanate ions.     

Diagramme de phase liquide-solide pour le système binaire sulfolane + 2-méthyl-2-propanol

Solid + liquid phase diagram for sulfolane + 2,methyl-2,propanol mixture has been obtained by thermal analysis.The phase diagram shows the existence of one eutectic at x₁ = 0.772 and T = 278.8 K and the formation of solid solutions in the region 0.93 ? x₁ < 1.The cooling curves of 2,methyl-2,propanol and of solutions at 0.15 ? x₁ ? 0.75 confirm the existence of three crystalline forms for this compound.     

Influence de la tension de vapeur sur une transition de phases et un equilibre peritectoide

The compound As₄Se₃ exhibits two polymorphs, α andβ. The latter undergoes a peritectoid decomposition. The two phenomena require a vapour pressure action. They are both explained on the basis of aT- V- x diagram. Two cases are described. In the first hypothesis, no solid solution exists. The second hypothesis implies two solid solutions for the two forms α andβ. A comparative study of these two cases has been made. The existence of two invariant planes has been shown in the second case, which makes it rather different from the first one.     

Synthèse et propriétés magnétiques de solutions solides entre l'oxyde de chrome CrO2 et l'oxyhydroxyde de cobalt CoOOH

Solid solutions of general formula (1 ? x)CrO₂, xCoOOH have been prepared by hydrothermal synthesis under very high pressure conditions (80 kb). Cr⁶⁺O₃ and CoCr⁶⁺O₄ were used as starting materials. Homogeneous ferromagnetic phases were obtained when 0 ? x ? 0.5. X ray powder patterns clearly demonstrate the isotype with InOOH, an orthorhombic distorted rutile type structure. The results of the magnetic measures performed on samples with different compositions indicate that part of the Cr⁴⁺ cation have been reduced to Cr³⁺ and that the general formula of the solid solutions should be written Cr⁴⁺_1?(x+y)Cr³⁺_yCo²⁺_xO₂H_x+y.     

A new sensitive method of dissociation constants determination based on the isohydric solutions principle

The paper provides a new formulation and analytical proposals based on the isohydric solutions concept. It is particularly stated that a mixture formed, according to titrimetric mode, from a weak acid (HX, C₀ mol/L) and a strong acid (HB, C mol/L) solutions, assumes constant pH, independently on the volumes of the solutions mixed, provided that the relation C₀ = C + C² · 10^pK₁ is valid, where pK₁ = −log K₁, K₁ the dissociation constant for HX. The generalized formulation, referred to the isohydric solutions thus obtained, was extended also to more complex acid-base systems. Particularly in the (HX, HB) system, the titration occurs at constant ionic strength (I) value, not resulting from presence of a basal electrolyte. This very advantageous conjunction of the properties provides, among others, a new, very sensitive method for verification of pK₁ value. The new method is particularly useful for weak acids HX characterized by low pK₁ values. The method was tested experimentally on four acid-base systems (HX, HB), in aqueous and mixed-solvent media and compared with the literature data. Some useful (linear and hyperbolic) correlations were stated and applied for validation of pK₁ values. Finally, some practical applications of analytical interest of the isohydricity (pH constancy) principle as one formulated in this paper were enumerated, proving the usefulness of such a property which has its remote roots in the Arrhenius concept.