Effets cinetiques de sels lors de la methanolyse de l'acetate de phenyle par catalyse basique en milieu methanolique: Etude perturbationnelle des effets de sels lors de l'hydrolyse ou de la méthanolyse d'esters aliphatiques ou aromatiques

Methanolysis of phenyl acetate shows a slight rate increase in the presence of NaClO₄ or NaBr or a rather large rate decrease in the presence of LiClO₄ or LiBr. These results are different from those obtained for alkaline hydrolysis of an aliphatic ester. They are interpreted in terms of a frontier orbital controlled reaction. For aliphatic esters, complexation phenomena

is predominant; for aromatic esters, due to a stabilisation of the π^* CO orbital energy level, two opposite effects are possible:

complexation inducing a rate increase, and association of the nucleophile HO^- or CH₃O^- with M⁺ leading to a rate decrease. The relative importance of these two opposite effects depends on the nature of the ester.     

Reaction de metathese des olefines induite photochimiquement en presence d'un complexe de metal de transition. IV.- etude cinetique de l'interconversion catalysee cis-trans du butene-2.

The cis-trans interconversion of olefins in the system W(CO)₆ + CCl₄ + 2-butene is studied, both with initial irradiation of a solution of W(CO)₆ in CCl₄ (photoinduction), and with continuous irradiation of the system, for cis- and trans-butene concentrations between 0.09 and 6.0 M. Analysis of the results of the photoinduction experiments (rate of conversion and kinetic law as a function of the initial concentration of the olefin) allowed us to propose a simple kinetic scheme comprising a cis-trans interconversion of 2-butene and olefin-catalyzed destruction of the catalytic entity (k₂ = (0.62 ± 0.06)x10^?4 M s^?1). In the continuous irradiation experiments the final distribution of the olefin was independent of the initial butene concentration (cis-2-butene/trans-2-butene 3.0) and the reaction kinetics are of first-order (k_obs = (3±1) x10^?4 s^?1. Comparison of the two experiments suggests continuous photochemical regeneration of the catalytically active entity. The first-order reaction kinetics are in agreement with a carbene-metal carbonyl structure of the intermediate     

`Thiobenzophenone S‐Methylide' (=(Diphenylmethylidenesulfonio)methanide), and C,C Multiple Bonds: Cycloadditions and Dipolarophilic Reactivities

Thiobenzophenone and diazomethane afford thiadiazoline 1 at −78°. By elimination of N₂ from 1 at −45° (t_1/2 ca. 1 h), (diphenylmethylidenesulfonio)methanide ( 2 ), which cannot be isolated but is interceptible by dipolarophiles, is set free. The nucleophilic 1,3‐dipole 2 undergoes cycloadditions with electrophilic C,C multiple bonds; the structures of 16 cycloadducts were elucidated. One‐step and two‐step cycloaddition pathways are discussed in the light of the steric course observed for (E)/(Z)‐isomeric ethylene derivatives. Competition experiments with pairs of dipolarophiles at −45° and HPLC analysis of the adducts provided relative rate constants of 26 dipolarophiles, involving 2 C≡C, 13 C=C, 9 C=S, and 2 N=N bonds. In accordance with Sustmann`s reactivity model of concerted cycloadditions, 2 shows the highest selectivity of all known 1,3‐dipoles, i.e., the largest spread of rate constants (k_rel=1 for methyl propiolate and 33×10⁶ for TCNE). As a consequence of low LU energies, thiones are very active dipolarophiles, and fluorene‐9‐thione (k_rel=79×10⁶) stands at the top.     

Polymeres optiquement actifs—IX. Influence de la neutralisation des fonctions ionisables sur l'activite optique des polycondensats formophenoliques de la N-tosyl l-tyrosine

From ORD curves and simultaneous determinations of the phenate-ion molecular absorption coefficient ?, the pH and the rotatory power [a]₄₃₆²⁵, we characterize the neutralization of each of the ionisable functions of N-tostyl l-tyrosine (LTyS) and of its polycondensates with formaldehyde prepared in acidic medium (PaTyS) or in basic medium (PbTyS). The polycondensate PbTyS shows some similarities with the model, but PaTyS is clearly different for all degrees of neutralization. The differences are not conformational as believed previously. They are probably caused by a secondary chemical reaction occurring during the polycondensation in acidic medium. It is underlined that such a combination of techniques may be used for the study of the polyelectrolyte properties of optically active polyelectrolytes.     

Etude par polarisation nucleaire induite chimiquement de la reaction photochimique de l'anthracene avec des tetrahalogenomethanes

The photoreaction of anthracene with CCl₄, CCl₃Br or CBr₄ was studied by CIDNP. The primary products of the reaction (polyhalogeno 9,10-dihydro anthracenes) are thermally unstable, but evidence was shown for their existence. The initiating radical pair of this reaction is: $\text{9-chloro 10-anthryl/trichloromethyl}$^S. This study was extended to 9-methyl and 9,10-dimethyl anthracenes.     

Etude radiocristallographique et calorimetrique des transitions de phase de Ag8GeTe6

Powder and single crystals of the Ag₈GeTe₆ phase have been prepared by direct synthesis and chemical vapor transport reaction (iodine), respectively. The low-temperature phase of this material has been investigated by differential scanning calorimetry analysis and X-ray diffraction. The phase transitions are interpreted as a result of low-temperature ordering of the Ag⁺ ions.     

Substitution électrophile aromatique dans l'anhydride sulfureux liquide. Influence de la concentration en bromure et rôle du solvant sur la réactivité des anisoles au cours de la réaction de bromation

Electrophilic Aromatic Substitution in Liquid Sulfur Dioxide. Kinetic Dependance of Rate on the Bromide Concentration and Influence of the Solvent during the Course of the Reaction On the reported data for bromination of anisole and eleven of its derivatives in liquid SO₂, it was shown that, with a large excess of bromide, the rate of reaction, obeys a first-order law. Rate constants thus obtained do not discriminate between the two different forms of bromide, e.g. Br₂ and Br^?₃ present as the A⁺Br^?₃ form, and corrections were made by use of the apparent equilibrium constant K′ for tribromide formation. The variations of rate constants with initial concentration of bromide has been studied and the effect results in a retardation of the bromination rate. Moreover, the ratio [Br₂] [A⁺Br^?]_T, which is constant during an experiment, varies with initial bromide concentrations, this variation affecting the total rate. To account for the bromide effect on the reactivity, variations of k^o,p_g {1 + K′[A⁺Br^?]_T}VS[A⁺Br^?]_T were studied over a 0.01 to 1M range of bromide concentration. The mechanism proposed shows that liquid SO₂ helps the reactive intermediate to be deprotonated and because of solvation of reactive species this step would probably be rate determining. Bromination by molecular bromine is more sensitive to substituent effects in liquid SO₂ than in water. This result is ascribed to the +M effect of the methoxy group which increase the conjugation of ortho-substituted derivatives (p⁺_p = ?7.83; p⁺_o= ?10.47).     

Photoreduction de la benzophenone par des thioethers etudiee par pnic

CIDNP (Chemically Induced Dynamic Nuclear Polarization) studies of the photoreduction of benzophenone by R-CH₂-S-R' show evidence for the $\text{formation of vinylic}$ deratives and adducts. The central intermediate in the reaction scheme is the radical pair R-CH-S-R' φ₂-C-OH^t. A study with selenides shows a different behaviour for these compounds.     

Stereochimie de l'action des organomagnesiens et des organolithiens sur les dimethyl-1,2 alcoxy-1 silacyclobutanes

The reaction of organomagnesium organolithium compounds (alkyl, aryl, allyl and benzyl derivatives) with 1,2-dimethyl-1-alkoxy-l-silacyclobutanes proceeds with retention of configuration at the silicon atom. Stereochemical results are discussed in terms of the S_N2Si mechanism. The proposed configurations are supported by ¹H and ¹³C NMR data.     

Determination par calorimetrie de dissolution des enthalpies de formation de quelques silicates,aluminates et alumino-silicates de calcium

The enthalpies of formation of 13 calcium silicates, aluminates, alumino-silicates and ferro-alumino-silicates were measured by dissolution calorimetry with the help of a high-temperature Calvet calorimeter. Dissolution experiments were performed in a lead metaborate (2PbO?B₂O₃) baths at 1173 K. The synthesis of the samples was realized by melting together pure silica, alumina, ferric oxide and calcium carbonate in appropriate ratios. The samples obtained in this way were examined by X-ray diffraction and scanning electronic microscopy. The free lime content was also determined by chemical analysis. The enthalpy of formation of silicates and aluminates obeys two different linear relations with respect to the ratio Ca/X (X=Al or/and Si) except for Ca₁₂Al₁₄O₃₃ which does not exist in its pure form but has to be stabilized by anions as OH^? or Cl^?. The data corresponding to the two aluminosilicates are located between these lines. The enthalpy of formation of tricalcium silicate (Ca₃SiO₅ i.e. C₃S according to the Bogue terminology) from dicalcium silicate and lime could be calculated as ?6kJ·mol^?1. This reaction is the most important one in the industrial process of clinkerization.     

Structure des Complexes de Meisenheimer Complexes de Courte Duree de Vie et Complexes Stables Formes par Action des Ions Méthoxydes sur les Dinitro-4,6 Anisoles X-2 Substitues

The NMR study of the reaction of methoxide ions on several substituted 2-X-4,6-dinitroanisoles (X = F, Cl, CF₃, CN) permitted the identification of various Meisenheimer complexes formed by the attack of CH₃O^? ions on the non-substituted 5- and 3-carbons. The shortlived 1,5- and 1,3-complexes undergo a fast conversion to the stable 1,1-complexes. The chemical shifts of anisoles and complexes are dependent on electronic and steric effects of the X-substituent. The influence of the negative charge held by the ring and the geometrical changes of the skeleton are shown by a comparison between the NMR parameters of anisoles and the corresponding complexes. When X = F, a study of the relative signs of the coupling constants shows that ³J(F? H) and ⁵J(F? H) are of opposite signs for the anisole and the 1,1-complex.     

Enthalpies de formation des hydroxynitrates de zinc

The standard enthalpies of reaction of four zinc hydroxide nitrates Zn(OH)(NO₃)-H₂O, Zn₃(OH)₄(NO₃)₂, Zn₅(OH)₈(NO₃)₂·2H₂O et Zn₅(OH)₈(NO₃)₂ and zinc oxide with a solution of nitric acid (2N) were measured in a solution calorimeter. These results, combined with auxiliary thermochemical values from the literature, yielded values of ?429.34, ?442.41, ?897.41 and ?750.70 kcal mol^?1 respectively, for the molar enthalpies of formation of these zinc hydroxide nitrates.     

Etude des réactions pericycliques sous pression—II: Contribution a l'etude du mecanisme de la reaction de Diels-Alder

The kinetics of three Diels-Alder reactions have been investigated under pressures up to 10,000 kg/cm². The determination of the activation volume shows that its value is nearly the same as the total volume change of the reaction. This enables us to elucidate the mechanism as one step concerted characterized by a “quasi-cyclic” transition state with simultaneous formation of two covalent bonds.     

Etude du mecanisme de l'hydrolyse alcaline des N-methyl acetanilides au moyen des effets de milieu

N-methyl acetanilides alkaline hydrolysis mechanism has been studied by means of solvent effect (DMSO and ²H₂O) and of structure-reactivity correlation (log k_obs = f(pK_{B aniline})). Our results are consistent with HO^? rate determining attack only for p-nitro anilide and with a rate determining water assisted decomposition of the tetrahedral intermediate for X  p-CH₃O, H, p-Cl, m-Cl.     

Determination des constantes d'association des paires d'ions et des ions triples au sein de solutions de poly (vinyl-2 pyridine) vivantes

The association constants K_A and k_A for ion-pairs and triple-ions in living polymer solutions of 2-vinyl pyridine have been measured. The values of K_A and k_A in tetrahydrofuran are respectively 4·6 × 10⁸ and 5·2 × 10⁴ with Na' as counter ion, and 6·6 × 10⁸ and 1·6 × 10² with Cs⁺ as counter ion. These values fit in very well with kinetics recently published.In order to evaluate K_A and k_A more accurately, the translation diffusion coefficients of living or dead poly(2-vinyl pyridine) have been measured, monitoring the concentration gradient along an optical cell. In both cases for DP = 8, the value is 0366 cm²/sec. Such a value implies that the equivalent conductance of the poly 2-vinyl pyridine anions is lower than that of polystyrene anions of the same DP.     

Reactions de cycloaddition dipolaire-1,3 des thiazolones mesoioniques avec des composes ethyleniques-1: Etude des problemes de stereochimie poses par l'approache dipole-dipolarophile

The stereochemistry of cycladducts obtained through the reaction of mesoionic thiazolones with ethylenic dipolarophiles is established. The dipole-dipolarophile approach is discussed in terms of interactions between the frontier orbitals. When the dipolarophile is acrylonitrile we note the importance of the destabilising interaction the HOMO orbitals. When the dipolarophile is vinyl ethyl ether we show that the interaction LUMO dipole-HOMO dipolarophile can be dominating.     

Influence de certains ions inorganiques, de l'éthanol et du peroxyde d'hydrogène sur la photominéralisation du β-naphtol en présence de TiO2

TiO₂ photocatalytic mineralization of β-naphthol: influence of some inorganic ions, ethanol, and hydrogen peroxide. In this work, the photocatalytic oxidation of β-naphthol in aqueous suspensions of TiO₂ was investigated at room temperature, by following the formation of CO₂. The disappearance of β-naphthol fits a Langmuir-Hinshelwood kinetic model. The activation energy for the degradation reaction of β-naphthol is estimated at 10.2 kJ/mol. The effects of some additives such as ethanol, H₂O₂, and inorganic ions (Cl⁻, SO₄²⁻, HCO₃⁻, NO₃⁻, Fe³⁺, Cu^2+, and Cr³⁺) on the photomineralization of β-naphthol were examined. The inhibition of the anions for this reaction was in the order : NO₃⁻ < HCO₃⁻ < SO₄²⁻ < Cl⁻. This can be due to a partial blockage of catalyst active sites by these ions or their reaction with an oxidizing radical such as OH. The most photoactive systems for β-naphthol degradation were found in the presence of ferric ions, while the addition of Cr³⁺ strongly inhibited the photocatalytic decomposition of β-naphthol.     

Etude thermodynamique de la décomposition thermique des hydroxynitrates de zinc

The reaction scheme of thermal decomposition for four zinc hydroxynitrates was investigated by means of differential scanning calorimetry, thermogravimetry, mass spectrometry, and radiocrystallography. The thermal transformation of Zn(OH)(NO₃) · H₂O and of Zn₃(OH)₄(NO₃)₂ involves the formation of gaseous water and nitric acid from an actual chemical reaction. This reaction is not observed for Zn₅(OH)₈(NO₃)₂ · 2H₂O and Zn₅(OH)₈(NO₃)₂. These results show that the formation of gaseous nitric acid molecules inside the solids is specific to hydroxynitrates of divalent metals M, whose lamellar crystalline structure is characterized by a stacking of hexagonal close-packed layers of formula MX_2+m, where m = 0 or 1 and X = OH^?, H₂O, or NO^?₃.     

Determination des capacites thermiques d'exces par calorimetrie de reaction directe

Accurate determinations of excess heat capacities,C _p ^E , of liquid and solid phases with respect to composition and temperature are shown to be possible by direct reaction calorimetry. The results are compared with those obtained by heat capacity measurements and departure from the additivity rule. In the case of solutions, the knowledge ofC _p ^E with respect to concentration permits a pertinent analysis of the short-range order. Some results concerning binary alloys, such as In-Te, Cu-Sb and Ag-Te, are given.     

Determination de l'enthalpie de formation du pentalfluorotellurate IV de rubidium RbTeF5 par calorimetrie de reaction

The standard enthalpy of formation of RbTeF₅ has been determined by hydrolysis reaction in a molar aqueous solution of NaOH or KOH as ΔH°₂₉₈f RbTeF_{5 cr} = ?1696 ± 1 kJ.mol^?1