Étude quantitative d'équilibres chimiques en solution dans les sels fondus par spectrophotométrie d'absorption: Application au neptunium

The following reactions: NpO₂⁺+4 HCl ? Np⁴⁺ + 2 H₂O + $\text{1}\text{2}$ Cl₂ + 3Cl^- NpO₂⁺+$\text{1}\text{2}$ Cl₂ ? NpO₂²⁺ +Cl^- 2HCl+O^2- ? H₂O +Cl^- have been examined quantitatively. The reactions were studied in fused LiCl-KCl sparged with gas mixtures of definite compositions. The concentrations of the diffrent neptunium species were measured by absorption spectrophotometry. The values of respective equilibrium constants are: K = (9.3±0.4)· 10^-6 atm(^{-$\text{1}\text{2}$}); K₁ = (2.3±0.1)·10^-2 atm(^{-$\text{1}\text{2}$}); k = 10^3.8 1 mol^-1 atm^-1 The standard potential of the system NpO₂²⁺ / NpO₂⁺ was determinedto be E⁰ = 0.220 V (vs.standard chlorine electrode).     

Kinetics of the reaction of aluminum EDTA and cobalt(II) EDTA with calmagite

The reaction of aluminum EDTA with calmagite was found to be first-order in calmagite, half-order in aluminum EDTA, and zero-order in excess EDTA. The three-halves-order apparent rate constant at pH 9.48 and 20°C with ionic strength 0.30 was 0.232 ± 0.0141^{$\text{1}\text{2}$} · mol^{$\text{1}\text{2}$} · s^?1. The activation energy was 3.2 ± 0.3 kcal/mol. The pH dependence was complex between 8 and 10. The mechanism proposed is a rapid dissociation of a dimer of aluminum EDTA to a monomer followed by a rate-determining displacement of the EDTA by calmagite. The reaction of Co(II) EDTA with calmagite was confirmed to be first-order in Co(II) EDTA and first-order in calmagite with an activation energy of 7.5 ± 0.6 kcal/mol.     

Perhalogenmethylmercapto-heterocyclen, (VII) [1] konkurrenzreaktionen elektronenarmer,substituierter aromaten um die halogenmethylmercapto- BZW. Chlorgruppe von Cl3-nFnCSCl in starken saeuren

Electron-deficient aromatics, such as 2,5-bis(trifluoromethylmercapto)thiophene ($\text{1a}$) or (trifluoromethylmercapto)benzene ($\text{8a}$), react with F₃CSCl in the presence of F₃CSO₃ as a catalyst to give mainly 3-chloro-2,5-bis(trifluoromethylmercapto)thiophen ($\text{3a}$) and 1-chloro-4- or 2-(trifluoromethylmercapto)benzene ($\text{10}$, respectively. This reaction competes with the one expected to result in 2,3,5-tris(trifluoromethylmercapto)thiophene ($\text{2a}$) and 1,4- and 1,2-bis(trifluoromethylmercapto)benzene ($\text{9}$,$\text{9′}$), respectively. Further reactions of deactivated aromatics with Cl_3-nF_nCSCl show that the chlorine substitution is in general catalysed by strong acids. Reaction mechanisms are proposed for both Substitutions. The Cl_3-nF_nCS group in aromatics exerts a -M-effect in the case of an attack of a positive ion, e.g. H^⊕, the well-known +M-effect in the case of reactions with positively polarized molecules, e.g. CF₃S^β+Cl^β-.     

Coulometric titration of iodide and iodine with electrolytically generated hypobromite

Conditions for the quantitative coulometric titration of iodide and iodine with electrolytically generated hypobromite in the presence of borax buffer have been established. Iodide and iodine are oxidized to iodate. The method, with biamperometric indication of the equivalence point, was successfully applied for a wide range of iodide concentrations (6.21–2115μg with reliability intervals of ±0.21–±11μg) and iodine concentrations (24.26–3311μg with reliability intervals of ±0.36–±11.7μg). The determinations are accurate and sensitive even in the presence of large amounts of bromides and chlorides ($\text{Br}{}^{\mathrm{?}}\text{I}{}^{\mathrm{?}}$= 1.2·10⁶ and $\text{C}\text{l}$^?I^?=4.0·10^{3), as well as in the presence of oxidizing agents such as IO₃?, BrO₃? and CrO₄2? ($\text{I}\text{O}$₃?/I₂)=3.2·105, $\text{I}\text{O}$₃?/I₂=3.1·103, $\text{Br}\text{O}$-₃/I₂}=1.1·10⁴ and $\text{Cr}\text{O}$^2-₄/I₂=1.0·10⁴, as was confirmed by statistical tests. The oxidation mechanism under the conditions of coulometric titrations is discussed.     

Laser induced photodissociation of C2F5I. Radiative lifetime of the metastable iodine atom (2P12)

Excited iodine atoms I(²P_{$\text{1}\text{2}$}) are formed by laser irradiation of C₂F₅I at 2950 Å. The mean radiative lifetime τ of these metastable atoms and their bimolecular rate constant k₂ for deactivation in collissions with C₂F₅I were measured to be: τ = 108 ± 10 ms; k₂ = (1.8 ± 0.1) × 10^?17 cm³/molec s.     

The preparation and properties of perfluoro-N-heptylbromine(N) tetrafluoride

Reactions of $\text{n}$C₇F₁₅Br with elemental fluorine at 0°C have produced perfluoro-$\text{n}$-heptylbromine(V) tetrafluoride ($\text{n}$-C₇F₁₅BrF₄). This derivative of BrF₅ was characterized by IR, ¹⁹FNMR, mass spectroscopy and elemental analysis. The reactions of $\text{n}$C₇F₁₅BrF₄ with 1,2-dichlorohexafluorocyclopentene-1 (C₅F₆Cl₂) and 1,2-dichlorooctafluorocyclohexene-1 (C₆F₈Cl₂) were used to demonstrate in the fluorinating ability of $\text{n}$C₇F₁₅BrF₄.     

PVC chlorination using fluorine as initiator

The chlorination of PVC has been studied in a fluidized bed reactor, initiating the reaction with elementary fluorine. The reaction has been carried out at temperatures between 20° and 60° for various concentrations of chlorine and fluorine. The rate of reaction is given by the equation:

(1)$\text{x=}\text{k[}\text{Cl}{}_2\text{]}{}^{\mathrm{0·5}}\text{[}\text{F}{}_2\text{]t}\text{1+k[}\text{Cl}{}_2\text{]}{}^{\mathrm{0·5}}\text{[}\text{F}{}_2\text{]t}$

, temperature is given by

$\text{log}\text{k=}\text{3500}\text{4·57}\text{1}\text{T}\text{+0·707}$

.Equation (1) is satisfied also by data obtained from a small scale plant reactor. A reaction mechanism is proposed.     

Absorption and emission spectra in chalcogenide glass of the composition 0.7Ga2S3·0.27La2S3·0.03Nd2S3

Chalcogenide glasses of the composition 0.7Ga₂S₃·0.27La₂S₃·0.03Nd₂S₃ doped by 3 mol% of Nd³⁺ were prepared. The absorption and emission spectra of these glasses were compared to those of commercial ED-2 3.1 wt.% Nd-doped silicate glass. The absorption intensities of Nd³⁺ in chalcogenide glass are higher than in silicate glass due to the increasing covalency of Nd³⁺ in these glasses. Because of the low phonon frequency of the chalcogenide glasses nonradiative relaxations from the ⁴F_{$\text{5}\text{2}$}, ²H_{$\text{9}\text{2}$} to the ⁴F_{$\text{3}\text{2}$} are lower than in other oxide glasses and so fluorescence from this state is observed.     

Thermal investigation of diamine complexes of Zn(II) in the solid state

The complexes [Zn(en)₃]X2·n H₂O, where en = ethylenediamine, X = Cl^?, Br^? or $\text{1}\text{2}$SO^2?₄, n = 1 or 0.5, and [Zn(tn)₂]X₂·n H₂O, where tn=1,3-diaminopropane, X=Cl^?, Br^? or $\text{1}\text{2}$SO^2?₄, n = 0 or 0.25, have been synthesized and their thermal investigations carried out. The complexes were characterized by elemental analysis and IR spectral data. These complexes have been observed to decompose through several isolable as well as non-isolable complex species as intermediates during heating. [Zn(tn)₂]SO₄ undergoes solid-state phase transition in the temperature range 126–145°C. ZnenSO₄ and ZntnX₂ (X = Cl^?, Br^? or $\text{1}\text{2}$SO^2?₄) have been synthesized pyrolytically in the solid state from their corresponding mother diamine complexes. ZnenSO₄ and ZntnX₂ (X = Cl^?, Br^? or $\text{1}\text{2}$SO^2?₄) complexes decompose through non-isolable hemidiamine species. ZnX₂ (X = Cl^? or Br^?) complexes of tn undergo melting after formation of the monodiamine species. In contrast, the corresponding en complexes undergo melting at non-stoichiometric composition. Diamine (en or tn) is found to be bridging in all monodiamine (en or tn) complexes; whilst their mother complexes possess chelated en or tn. The thermal stability sequence of en and tn complexes of Zn(II) is ZnCl₂ < ZnBr₂ < ZnSO₄. ΔH values are reported for some steps of decomposition. Possible mechanistic paths have been reported for each step of decomposition.     

Vibrational study of strong CH · middot; X hydrogen bonds in solid complexes of boron decachlorocarboranes

Solid complexes of boron decachloro-o-carborane and boron decachloro-m-carborane (B₁₀Cl₁₀C₂H₂) with some oxygen and nitrogen bases have been investigated by infrared and Raman spectroscopy. Complexes containing CH · · O hydrogen bonds are characterized by a relative CH stretching frequency shift up to 12% and a halfwidth of the νCH band up to 220 cm^?1. CH · · N hydrogen bonds, with trimethylamine for example, are stronger with a relative shift of about 18% and $\text{ν}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of about 500 cm^?1. Triethylamine complexes, however, form a NH⁺ · · C^? proton transfer hydrogen bond while pyridine can give either CH · · N or C^? · · ⁺HN hydrogen-bonded adducts depending on the solvent and temperature. The CH · · N?c^? · · ⁺HN equilibrium appears to be shifted towards ion-pair formation at considerably smaller enthalpy values compared to the OH · · N?O^? · · ⁺HN system. CH and NH stretching frequencies are correlated with the acidity of the donor and the basicity of acceptor molecules.     

A facile one-pot preparation of 2-methyl-and 2-phenyl-4- fluoro-5-trifluoromethyl-6-methoxypyrimidine from methyl 2-hydryl-2-(F-methyl)-F-propyl ether

The title compounds were readily prepared in one-pot by phase-transfer reaction of a methanol adduct of 2-($\text{F}$-methyl)-$\text{F}$- propene with acetamidine or benzamidine in the presence of aqueous sodium hydroxide in CH₂Cl₂. Various 5-trifluoromethyl- pyrimidines were also synthesized $\text{via}$ nucleophilic substitution of the 4-fluorine of the title compounds.     

H3N·PF5 and H2NPF5−, new compounds in the system H3N/PF5

Phosphorus pentafluoride was reported long ago to give adducts 2 PF₅ ·5 NH₃ (1) and nNH₃·PF₅ (n= 1 ? 4) (2). None of the compounds was characterised in detail. Repeating the reaction of PF₅ and NH₃ we found the adduct H₃N·PF₅, $\text{1}$, in 8% yield besides (H₂N) ₂PF₃ (3) and NH₄PF₆. However, HF and (F₂P=N)₃ gave $\text{1}$ in 41% yield. The ¹H, ¹⁹F, and ³¹P n.m.r. spectra of $\text{1}$ exhibit ¹⁴NH, ¹⁴NPF(cis), and ¹⁴NP coupling. The x-ray structure determination shows almost perfect octahedral geometry at phosphorus with a PN bond length of 1.842 ā. Compound $\text{1}$ is soluble in water without decomposition. Treatment with NH₃ leads to the anion H₂NPF₅^?. Upon heating $\text{1}$ forms in good yield H₂NPF₄ and NH₄PF₆. Without a solvent $\text{1}$ and NH₃ react to give (H₂N) ₂PF₃. A mechanism for the ammonolysis of PF₅ is proposed.     

Composition,properties, stability and thermal dehydration of crystalline caffeine hydrate

It has been shown by gravimetric measurements that caffeine hydrate does not exist as a monohydrate but has a water content corresponding to a $\text{5}\text{6}$ or $\text{4}\text{5}$ hydrate. This result is supported by density determinations of crystals. the stability-point is found to be

_D = 51.5 ± 0.7 °C. The enthalpy of dehydration is determined as well directly by DSC (6.8 ± 0.5 kJ mol^?1) as from the difference of integral enthalpies of solution of anhydrous caffeine and caffeine hydrate (7.06 ± 0.14 kJ mol^?1). The results and their consequences are discussed.     

The crystal structure of polyacrylonitrile

Polyacrylonitrile (PAN) has been prepared by a free-radical mechanism using azobisisobutyronitrile as the initiator. Fibres were produced by extruding a solution of this polymer into dilute sodium thiocyanate. Wide-angle X-ray analysis showed that the resulting fibres exhibited a moderate degree of crystalline order. An orthorhombic unit-cell has been proposed to account for the observed reflections, the cell constants are: $\text{a = 21·48 ± 0·02}\text{A}\text{?}\text{; b = 11·55 ± 0·03}\text{A}\text{?}\text{; c = 7·096 ± 0·003}\text{A}\text{?}$. A helical structure has been proposed for PAN with four monomer units per crystallographic repeat. The probability of a syndiotactic configuration has been suggested to account for the meridional reflections; the calculated density of the proposed cell (1·199 g cm^?3) was found to agree very well with values quoted in the literature.     

Chainlength effects on interactions of polyvinylpyrrolidone with low and high molecular compounds

Very narrow fractions of polyvinylpyrrolidone (PVP) for a range of low molecular weight from 20·10³ to $\text{\&{;10}{}^3$ were prepared by gel filtration using sephadex gel. Interactions between fractions of different M_n and small molecules (iodine and 1-anilinonaphthaline-8-sulphonate) and polymers (polymethacrylic and polyacrylic acids) were studied in aqueous solution. The ability of PVP to form complexes with low molecular weight compounds depends on chainlength. The greatest loss of the ability was observed for PVP with M_n on passing from 5·10³ to $\text{\&{;10}{}^3$. The chainlength effects for PVP are accounted for an unlike dehydration and unlike “local” link concentration near links for these macromolecules in water. For PAA and PMAA. the threshold values of M?_n, below which there is the beginning of weakening of complexation for PVP, are 6·10³ and 2.5·10³ respectively. The difference of the complex formation for these polyacids appears to be related to hydrophobic interactions between the χ-methyl groups of PMAA and nonpolar regions of PVP.     

Détermination par spectrophotométrie d'absorption du potentiel normal du couple Cu(II)/Cu(I) dans les chlorures alcalins fondus

The reaction Cu²⁺ + Cl^? ? Cu⁺ + $\text{1}\text{2}$ Cl₂ has been studied in three different solvents—LiCl—KCl (70–30 % mol), eutectic LiCl–KCl (58–42 % mol) and LiCl–CsCl (55–45 % mol) at different temperatures by visible and near i.r. spectrophotometry. Equilibrium constants are calculated. The standard potential of the couple Cu²⁺/Cu⁺ with reference to the standard potential of Cl₂/2Cl^?, as well as the thermodynamic quantities $\text{Δ}\text{H}$ and $\text{Δ}\text{S}$ in the range 400–600 °C, have been deduced.