Chromium(VI), chromium(V) and chromium(IV) oxidation of 12-tungstocobaltate(II)

The reaction between Cr^VI and 12-tungstocobaltate(II) was carried out in 2.0 mol dm^–3 HCl and followed a simple second order rate law. The reaction was catalysed by hydrogen ion due to the formation of active H₂CrO₄ and was inhibited by chloride ion as, in its presence, conversion of the active species into inactive chlorochromate occurs. Chromium(V) and chromium(IV) were generated in situ by the use of Cr^VI—V^IV or Cr^VI—2-ethyl-2-hydroxybutyric acid and Cr^VI—i-PrOH reactions respectively, and the oxidation of 12-tungstocobaltate(II) by these atypical oxidation states, was also studied. The rate constants for the oxidation of 12-tungstocobaltate(II) by Cr^VI, Cr^V and Cr^IV were found to be in the ratio 1:1.2:5.2 respectively. The ionic strength did not affect the reaction, while decrease in the solvent polarity increased the rate of the reaction. The activation parameters were also determined and the values H , G and S were found to be 52.4 ± 6 kJ mol^–1, 100.8 ± 7 kJ mol^–1, –151.7 ± 10 J K^–1 mol^–1 respectively, supporting the mechanism proposed.     

Spectrochemistry of solutions,part 23. Changes of enthalpy and entropy in the formation of contact ion pairs: A vibrational spectroscopic appraisal using thiocyanate and azide solutions

Summary The vibrational spectra of solutions have been analyzed to assess both qualitatively and quantitatively the changes in enthalpy and entropy for ion pair formation in solutions of LiNCS, Mg(NCS)₂, and LiN₃ in liquid ammonia, dimethylformamide, dimethylsulphoxide and acetonitrile. Contrary to predictions both the H _ass and S _ass terms are all positive in the cases examined, indicating that the driving force in the ion association process derives from solvent-solute restructuring, and not the energy of the interaction between the cation and anion. This characteristic of contact ion pair formation is likely to be found to be applicable over a wide range of solvents. The following specific values of the thermodynamic parameters at 298 K have been obtained: LiNCS/DMF, G=–1.3 (1) kJ mol^–1, H _ass =+1.8 (5) kJ mol^–, S _ass =+10 (2) J mol^–1 K^–1; LiNCS/DMSO, G=+0.9 (2) kJ mol^–1, H _ass =+0.3 (3) kJ mol^–1; Mg(NCS)₂/DMF, G _ass =–4.0 (3) kJ mol^–1, H _ass =+15 (4) kJ mol^–1, S=+64 (17) kJ mol^–1; LiN₃/DMSO, G _ass =–2.5 (3) kJ mol^–1, H _ass =+4.9 (9) kJ mol^–1, S _ass =+25 (10) J K^–1 mol^–1.Submitted to celebrate the 70th Birthday of Professor Viktor Gutmann, and in recognition of his considerable contributions towards the better understanding of Chemistry in the Solution Phase     

Synthetic and kinetic studies on copper(II), nickel(II) and cobalt(III) complexes of 1,4,7,10,13-pentaazacyclohexadecane ([16]aneN5)

Summary The pentadentate macrocycle 1,4,7,10,13-penta-azacyclo-hexadecane [16]aneN₅=(3)=L} has been prepared and a variety of copper(II), nickel(II) and cobalt(III) complexes of the ligand characterised. The copper complex [CuL](ClO₄)₂, on the basis of its d-d spectrum, appears to be square pyramidal, while [NiL(H₂O)](ClO₄)₂ is octahedral. The copper(II) and nickel(II) complexes dissociate readily in acidic solution and these reactions have been studied kinetically. For the copper(II) complex, rate=k_H[complex][H⁺]² with k_H =4.8 dm⁶ mol^–2s^–1 at 25 °C and I=1.0 mol dm^–3 (NaClO₄) with H=43 kJ mol^–1 and S ₂₉₈ =–89 JK^–1 mol^–1. Dissociation rates of the copper(II) complexes increase with ring size in the order: [15]aneN₅ < [16]aneN₅ < [17]aneN₅. For the dissociation of the nickel(II) complex, rate=k_H[Complex][H⁺] with k_H=9.4×10^–3 dm³mol^–1 s^–1 at 25 °C and I =1.0 mol dm^–3 (NaClO₄) with H=71 kJ mol^–1 and S ₂₉₈ =–47 JK^–1mol^–1.The cobalt(III) complexes, [CoLCl](ClO₄)₂, [CoL(H₂O)]-(ClO₄)₃, [CoL(NO₂)](ClO₄)₂, [CoL(DMF)](ClO₄)₃ (DMF=dimethylformamide) and [CoL(O₂CH)](ClO₄)₂ have been characterised. The chloropentamine [CoCl([16]aneN₅)]²⁺ undergoes rapid base hydrolysis with k_OH=1.1× 10⁵dm³ mol^–1s^–1 at 25°C and I=0.1 mol dm^–3 (H=73 kJ mol^–1 and S ₂₉₈ =98 JK^–1 mol^–1). Rapid base hydrolysis of [CoL(NO₂)]²⁺ is also observed and the origins of these effects are considered in detail.     

Multinuclear macromolecule metal complexes 2. Preparation and characterization of Prussian blue and its analogs bonded to pofy(vinylamine hydrochloride)

Prussian blue and its analogs bonded to poly(vinylamine hydrochloride) (PVAm · HCl) containing Fe^II or Fe^III and M²⁺ (M=Fe, Co, Cu) in a 11 molar ratio were obtained by the reaction of [Fe(CN)₆] ^n– (n=3,4) with M²⁺ ion-PVAm · HCl mixture in aqueous solution. Under a limited polymer concentration (T_VAm/T_Fe over 10), these polymer complexes thus obtained were stable and soluble in water. By casting these solutions, colored films can be produced. The formation of Prussian blue and its analogs bonded to PVAm · HCl was also investigated by the Benesi-Hildebrand method. The molar extinction coefficients of intervalence charge transfer (Fe^IIFe^III, Co^IIFe^III, Fe^IICu^II) band for MFe(CN)₆]^(n–2)– bound to PVAm · HCl (M=Fe, Co, Cu) were found to be 10,100–9601 · mol^–1 · cm^–1 at 25 C. The formation constants were found to be in the range of 10⁷ to 10¹⁰ M^–1. The changes of enthalpy (H) and entropy (S) were found to be in the range of –10.4 to –22.5 kJ · mol^–1 and 5.7 to 52.9 J · K^–1 mol^–1 respectively, at 25C.     

Thermogravimetric and differential scanning calorimetric investigations of manganese–glycine interactions

Thermogravimetric (t.g.) and differential scanning calorimetric (d.s.c.) data have been used to study metal–amino acid interactions in adducts of general formula MnCl₂ · ngly (gly = glycine, n = 0.7, 2.0, 4.0 and 5.0). All the prepared adducts exhibit only a one step mass loss associated with the release of glycine molecules, except for the 0.7gly adduct, which exhibits two glycine mass loss steps. From d.s.c. data, the enthalpy values associated with the glycine mass loss can be calculated: MnCl₂ · 0.7gly = 409 and 399 kJ mol^–1, MnCl₂ · 2.0gly = 216 kJ mol^–1, MnCl₂ · 4.0gly = 326 kJ mol^–1 and MnCl₂ · 5.0gly = 423 kJ mol^–1, respectively. The enthalpy associated with the ligand loss, plotted as function of the number of ligands for the n = 2.0, 4.0 and 5.0 adducts, gave a linear correlation, fitting the equation: H (ligand loss)/kJ mol^–1 = 67 × (number of ligands, n) + 76. A similar result was achieved when the enthalpy associated with the ligand loss was plotted as a function of the _a(COO^–) bands associated with the coordination through the carboxylate group, 1571, 1575 and 1577 cm^–1, respectively, for the n = 2.0, 4.0 and 5.0 adducts, giving the equation H (ligand loss) /kJ mol^–1 = 33.5 × _a(COO^–) /cm^–1 – 52418.5. This simple equation provides evidence for the enthalpy associated with the ligand loss being very closely related to the electronic density associated with the metal–amino acid bonds.     

Mechanism of oxidation of DL-methionine by iron(III)-2,2′-bipyridyl in perchloric acid—a kinetic study

Summary The kinetics of oxidation of DL-methionine by iron(III)-2,2-bipyridyl complex in HClO₄ were studied using 20%(v/v) MeOH as solvent. The order with respect to methionine and iron(III) was unity. The rate increased with increased [bipyridyl], but decreased with increased [H⁺]. While the reactive species of the substrate was the zwitterionic form, that of the oxidant was [Fe(bipy)₂-(H₂O)₂]³⁺. At 55 °C E _a and S for the reaction were 50.6 ± 2.5 kJ mol^–1 and –111.4 ± 7.6 JK^–1 mol^–1, respectively.Author to whom all correspondence should be directed.     

étude thermodynamique de certains médicaments

Two compounds of sulphamide type:p-amino-benzene sulphonamide (I) and 3,4-dimethylisoxazol 5-sulphanylamide (II) were studied by combustion calorimetry and by differential scanning calorimetry (DSC).The enthalpies in solid state at 298,15 K of combustion, _c H _m ^o (I)=-2788,5±1,6 kJ mol^–1, _c H _m ^o (II)=-5036±3,8 kJ mol^–1 and of formation, _f H _m ^o (I)=-458,3±1,6 kJ mol^–1, _fH _m ^o (II)=-180,1±3,8 kJ mol^–1 were determined.The thermal effects concerning the melting and phase transition of this compounds were also measured.

     

Selective determination of copper with pyridoin phenylhydrazone as chromogenic extraction reagent

Summary The synthesis, characteristics and analytical applications of pyridoin phenylhydrazone are described. It reacts with copper(I) to produce an orange 11 complex ( _max=450 nm,=2.1×10⁴l· mole^–1·cm^–1) in aqueous ethanolic solution; it behaves as a cuproin type reagent. The orange complex can be extracted into amyl alcohol ( _max=440 nm,=2.0×10⁴l·mole^–1·cm^–1), and used for the spectrophotometric determination of trace amounts of copper. Interferences have been investigated.

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Zusammenfassung Synthese, Eigenschaften und analytische Anwendung von Pyridoin-phenylhydrazon wurden beschrieben. Es reagiert mit Cu(I) unter Bildung eines orange gefärbten 11-Komplexes in wäßrig-alkoholischer Lösung ( _max=450 nm,=2,1×10⁴l·mol^–1·cm^–1); das Reagens verhält sich ähnlich wie Cuproin. Der erwähnte Komplex läßt sich mit Amylalkohol extra-hieren ( _max=440 nm,=2,0×10⁴l·mol^–1·cm^–1) und zur spektrophoto-metrischen Bestimmung von Kupferspuren benützen. Auftretende Störungen wurden angegeben.

     

Mechanism of oxidation of selenium(IV) by cobalt(III) in perchloric acid — a kinetic study

Summary The kinetics of Co^III oxidation of Se^IV have been studied in aqueous HClO₄. The order with respect to Co^m is two the order with respect to Se^IV is one at low concentrations; two at high concentrations. The latter variation is attributed to the greater reactivity of the Se^IV dimier A mechanism involving complexation between oxidant and substrate is proposed. [CoOH]²⁺ is presumed to be the reactive Co^III species and H₂SeO₃ and HSeO ₃ ^– to be those of Se^IV. At 25° C, E_a, H and S for the monomeric path are 125.6±4.0 kJ mol^–1, 122.1±3.8 kJ mol^–1 and 206±12 JK^–1 mol^–1 respectively and those for the dimeric path are 88.6±3.6 kJ mol^–1, 85.9±3.4 kJ mol^–1 and 62.6±11.3 JK^–1 mol^–1 respectively.     

Kinetics of ferrocenoylacetonato substitution from (1,5-cyclooctadiene)(ferrocenoylacetonato)rhodium(I) with 2,2′-dipyridyl and derivatives of 1,10-phenanthroline

Treatment of MeOH solutions of [Rh(cod)(fca)] (cod = 1,5-cyclooctadiene, fca = ferrocenoylacetonato) with seven derivatives of 1,10-phenanthroline (N,N), as well as with the (N,N) ligand 2,2-dipyridyl, gave [Rh(cod)(N,N)]⁺. The kinetics of these reactions follow the rate law: Rate = k[Rh(cod)(fca)[N,N] The temperature dependence of all the studied substitutions resulted in activation entropies, S , more negative than –100 J K^–1 mol^–1 which is indicative of associative mechanisms. The pK _a's of the incoming phenanthroline derivatives were between 3.03 and 6.31 but did not influence the reaction rate to any significant extent. This implies that the rate determining step during the substitution involves Rh—O bond breaking and not Rh—N bond formation. Substitution of fca with 2,2-dipyridyl was slightly faster (k = 118 dm³ mol^–1 s^–1) than with the 1,10-phenanthroline derivatives (k _average = 14.2 dm³ mol^–1 s^–1) and may be attributed to the free rotation capability of the two pyridyl rings about the 1-1 carbon–carbon axis in 2,2-dipyridyl. 1,10-Phenanthroline cannot rotate about the corresponding carbon axis.     

Kinetics and mechanism of the oxidation of acetaldehyde by chromic acid in perchloric acid

Summary The oxidation of MeCHO by chromium(VI) has been studied in HClO₄ medium over a wide range of experimental conditions and has been found to obey the rate law;v=k[MeCHO][HCrO ₄ ^– ][H⁺]. The calculated H and-S values for the reaction are 30±2kJ mol^–1 and 171±7J mol^–1deg^–1, respectively. The mechanism is discussed in terms of carbon-hydrogen bond cleavage.     

Amplification method for the spectrophotometric determination of phosphorus

An amplification method with ion-exchange pre-separation for the spectrophotometric phosphorus determination in various alloys is described. Phosphorus is converted into molybdophosphoric acid, separated by selective extraction and back-extracted into the aqueous phase. The molybdenum is liberated by alkaline decomposition of the heteropoly acid. The spectrophotometric measurement is based on the reaction of molybdenum(VI) with 2,2-biquinoxalyl. High molar absorptivity of 1,1-dihydro-2,2-biquinoxalylene (=3.3 · 10⁴ L mol^–1 cm^–1) and the twelve-fold amplification guarantee high precision and makes the determination of phosphorus in the 1–6 g level possible.     

Heat capacity of indium from 300 to 1000 K

The heat capacity of high-purity indium has been determined by adiabatic-shield calorimetry in the range 300 to 1000 K. Values of thermodynamic functions have been calculated andC _p (1000 K), [H° (1000 K)–H° (298.15 K)], and [S° (1000 K)–S° (298.15 K)] are (27.11±0.15) J K^–1 mole^–1, (22873±70) J mole^–1, and (41.567 ±0.125) J K^–1 mole^–1, respectively. The enthalpy of fusion is (3283±7) J mole^–1 and the melting temperature (429.77±0.01) K. The premelting heat capacity is compatible with the presence of a mole fractionx 1·10^–6 of a liquid-soluble/solidinsoluble impurity in the sample.

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Zusammenfassung Die Wärmekapazität von hochreinem Indium wurde im Bereich von 300 bis 1000 K durch adiabatische Schildkalorimetrie bestimmt. Die Berechnungen der thermodynamischen Funktionen:C _p (1000 K), [H° (1000 K)–H° (298.15 K)] und [S° (1000 K–S° (298.15 K)] ergab 27.11±0.15 J K^–1 Mol^–1, (22 875±70) J Mol^–1, bzw. (41.567±0.125) J K^–1 Mol^–1. Die Schmelzenthalpie beträgt (3283±7) J Mol^–1 und die Schmelztemperatur (429.77±0.01) K. Die Vorschmelz-Wärmekapazität ist mit der Gegenwart einer Molfraktionx1×10^–6 einer flüssig-löslich/fest-unlöslichen Verunreinigung in der Probe vereinbar.

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Résumé La chaleur spécifique de l'indium de haute pureté a été déterminée entre 300 et 1000 K par calorimétrie adiabatique. Les valeurs des fonctions thermodynamiques suivantes ont été calculées:C _p (1000 K)=(27.11±0.15) J K^–1mol^–1, [H° (1000 K)–H° (298.15 K)]= (22 875±70) J mol^–1 et [S° (1000 K)–S° (298.15 K)]=(41.567±0.125) J K^–1 mol^–1. L'enthalpie de fusion est (3283±7) J mol^–1 et la température de fusion (429.77±0.01) K. La chaleur spécifique de pré-fusion est compatible avec la présence d'une fraction molairex1×10^–6 d'une impureté dans l'échantillon, soluble dans le liquide, insoluble dans le solide.

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C - 300 1000 . : _p(1000 ), [ (1000 ) — H (298,15 )] [S (1000 ) — S (298.15 )], : 27.11±0.15 . ^–1. ^–1, 2 2875±70 . ^–1 41.567±0.125 . ^{– 1–1}. 3283±7 .^–1, – 429.77±0,01 . - / 1.10^–6.

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The assistance of Bjørn Lyng Nielsen with the experimental work is recognized with thanks.     

Kinetics of substitution of aqua ligands from cis-diaqua(ethylenediamine)platinum(II) perchlorate by DL-penicillamine in aqueous medium

The kinetics of the interaction of DL-penicillamine with [Pt(en)(H₂O)₂]²⁺ have been studied spectrophotometrically as a function of [Pt(en)(H₂O)₂]²⁺, [DL-penicillamine] and temperature at pH 4.0. The reaction proceeds via rapid outer sphere association complex formation, followed by two slow consecutive steps. The first is the conversion of the aforementioned complex into the inner sphere complex and the second is the slower chelation step whereby another aqua ligand is replaced. The association equilibrium constant (K _E) for the outer sphere complex formation has been evaluated together with rate constants for the two subsequent steps. Activation parameters have been calculated for both steps using the Eyring equation (H ₁ = 46.5 ± 5.0 kJ mol^–1, S ₁ = – 143.0 ± 15.0 J K^–1 mol^–1, H ₂ = 44.3 ± 1.3 kJ mol^–1, S ₂ = –189.0 ± 4.2 J K^–1 mol^–1). The low enthalpy of activation and large negative entropy of activation values indicate an associative mode of activation for both aqua ligand substitution processes.     

State of the structural hydroxyl groups in minerals of the kaolinite group according to infrared spectroscopic data

An interpretation of the IR spectra of kaolinite, dickite, and nacrite is proposed, based on the concept of resonance interaction of two intrasurface hydroxyl groups, and their manifestation in the spectrum as a split doublet 30 cm^–1 and by the individual vibration of a third intrasurface OH-group. The structural identification of each band in the IR spectra of the kaolinite minerals is given. It was demonstrated that thermal dehydroxylation under vacuum of kaolinite occurred in two stages with activation energies of 43 and 84 kJ/mole. The activation energy of proton delocalization of the structural hydroxyl groups of kaolinite has been evaluated (E 13 kJ/mole). The contribution of the energy of the interlayer hydrogen bonds (AH 28 kJ/mole) to the total cohesion energy of adjoining layers of kaolinite (E_c 165 kJ/mole) was calculated.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 1, pp. 73–81, January–February, 1985.     

Molecular mechanics analysis of the conformations of thymidine and implications for the design of anti-AIDS drugs

The steric energies of a number of the conformations of thymidine, derived from appropriate crystal structures, have been determined with the MM2 molecular mechanics force field. With one exception, these have very similar values which are close to 120 kJ mol^–1. The C2-exo/C3-endo conformation has a far higher value of 240 kJ mol^–1. The C3-endo conformation has previously been associated with thymidine derivatives which do not exhibit anti-HIV activity, and it may be that this is due to the relatively low predicted stability.     

Extraction-spectrophotometric determination of iron with 2-(2′-benzothiazolylazo)-4,6-dimethylphenol

An extraction-spectrophotometric method for the determination of trace amounts of iron based on its extraction into chloroform with 2-(2-benzothiazolylazo)-4,6-dimethylphenol (BTADMP) from a pH 6.5 medium has been developed. The extracted 12 FeBTADMP complex species allow the determination of 4–30gmg of iron (=3.92×10⁴1·mol^–1·cm^–1 at 790 nm). The method is highly selective and has been applied to the determination of iron in polymineral-polyvitamin pharmaceutical products.     

Thermal decomposition and kinetic data of Cd(BF4)2·6H2O

The thermal dehydration and decomposition of Cd(BF₄)₂·6H₂O were studied by means of DTA, TG, DSC and X-ray diffraction methods and the end products of the thermal decomposition were identified. The results of thermal analysis show that the compound is fused first, then it is dehydrated until Cd(BF₄)₂·3H₂O is obtained, which has not been described in the literature so far. The enthalpy of phase transition is H _ph.tr.=115.6 kJ mol^–1 Separation of the compound is difficult since it is highly hygroscopic. Then, dehydration and decomposition take place simultaneously until CdF₂ is obtained which is proved by X-ray diffraction. On further increasing the temperature, CdF₂ is oxidized to CdO and the characteristic curve assumes a linear character.Based on TG data, kinetic analyses were carried out separately for both parts of the curve: first until formation of the trihydrate and then — until formation of CdF₂. The formal kinetic parameters are as follows:for the first phase:E ^*=45.3 kJ mol^–1; rate equationF=^2/3; correlation coefficient 0.9858 for the second phase:E ^*=230.1 kJ mol^–1; rate equationF=(1–)^2/3[1-(1–)^1/3]^–1; correlation coefficient 0.9982.     

Magnetic anisotropy of cyclopropane and epoxide rings

MO LCAO results are presented for the interatomic contribution to the anisotropy of the diamagnetic susceptibility; values of _d=–23.5 · 10^–6 and _d=–13.8 · 10^–6 cm³/mole are obtained for the cyclopropane and epoxide ring systems, respectively. The results are used to interpret PMR spectra in terms of the configuration and conformation of the and forms of caran-4-ol and two stereoisomers of caranone.