Transferts Protoniques de Sels d'Ammonium Substitues—VII: Deprotonation de Sels de N-Methylpiperidinium en Solution Aqueuse

The deprotonation of N-methylpiperidinium salts BH_a^⊕, observed by means of the coalescence of the N-methyl doublet, is operated either by OH^?, or by the conjugate base B. The action of OH^? is predominant as the steric hindrance increases around H_a and is twice as fast in the axial direction.     

Interpretation Automatique du Spectre de Masse de Complexes Metalliques π Incluant des Derives du Silacyclopentadiene

The programme described previously for the interpretation of mass spectra of heterocyclic derivatives including one group IV element has been extended to -n metallic complexes. Their structure may be determined in few seconds by this method.     

Le formamide,un substitut de l'eau XI: Effet du formamide sur les reactions d'echange chlore-fluor dans les conditions de transfert de phase liquide-solide

The fluoride-chloride exchange reaction RCl + KF → RF + KCl catalysed by ammonium salts takes place in presence of formamide in place of water, faster and qith better yields.     

Mecanisme de la fixation du fer ferrique sur un copolymere non ionisable d'ester carboxylique—III. Reactions de fixation du fer sur le copolymere

Fixation mechanisms for iron(III) on non-ionizable Hycar 4021 copolymer in hydrochloric acid are elucidated by simultaneous analysis of distribution and stoichiometric composition data. Several reactions are proposed depending on the amount of ferric iron in the copolymer and on the ethanol in the liquid phase. These reactions are similar to those dealing with liquid-liquid extraction of iron by organic solvents with carbon-oxygen bonds.     

Interpretation du Spectre RMN de l'Octaacetate de Cellobiose a 250 MHz. Application au Triacetate de Cellulose

Using a 250 MHz NMR spectrometer and double resonance experiments the full identification of the 14 cyclic protons of α octaacetate cellobiose has been performed. The results obtained here are of particular interest as affording an answer to the problem of the existence of particular signals in the NMR spectra of cellulose triacetate. These signals are both due to the anomeric extremity of the polymer.     

Transferts Protoniques de Sels D'ammonium. Substitues—II: Vitesse D'inversion a L'azote Par la Methode de ‘Protonation Competitive’

Nitrogen in version rate of an amine may be brought to within the NMR time-scale by use of an acidic medium of variable pH, in which it is almost completely prevented through protonation. Rigorous equations are derived for computing this rate from the mean lifetime of the ammonium cation determined by NMR spectroscopy. The validity of Saunders and Yamada's approximate formula is discussed: the protonation rate of the amine must be far larger than its nitrogen inversion rate, while the rate at which the salt loses its acidic proton is immaterial. If in version occurs between two different isomers, the equilibrium ratio of the isomeric cations is also derived.     

Effet de la temperature et de la concentration en monomere sur la cinetique de polymerisation du propene par catalyse ziegler-natta

The effects of monomer concentration and temperature on the kinetics of propene polymerization catalysed by δ titanium trichloride (TiCl₃· 1/3 AlCl₃) activated by diethylaluminium chloride have been studied. The study included variation of propene concentration from 0·2 mole/1 to bulk liquid at temperatures between 20 and 80°. Results are in agreement with a mechanism which includes a monomer chemisorption to form a transitory complex (absorption—desorption) and addition of the chemisorbed monomer to the polymer chain. It appears, contrary to the general belief, that addition would be fast compared with the setting up of the chemisorption equilibrium.     

Étude de l'effet de quelques facteurs sur les caractéristiques de fixation du potassium et du rubidium sur l'acide antimonique,en milieu nitrique

Study of the effect of various factors on the retention characteristics of potassium and rubidium by antimonic acid in nitric acid.The effects of the concentration of alkali metal ions, the amount of antimonic acid and the concentration of nitric acid on the retention of potassium and rubidium by antimonic acid have been studied. Different phenomena govern the retention mechanism of potassium and rubidium, under the experimental conditions of this study. The difference between the retention characteristics of the two elements appears from the different shapes of the curves showing their distribution coefficients and their uptake as functions of the various factors studied. Infrared spectroscopy of the antimonic acid and its deuterated compounds showed the presence of several types of OH groups which can be distinguished by the strength of their hydrogen bonds. Rubidium is probably retained on the most accessible exchange sites, forming weak bonds, while potassium could form stronger bonds with the Sb—O groups.     

Action de l'Acide Perpropionique sur le Phosphate de Diphenyle et de p -Nitrophenyle. Destruction et Etude du Mecanisme D'Hydrolyse en Phase Aqueuse Micellaire

L'action de l'acide perpropionique CH 3 CH 2 CO 3 H a été étudiée en milieu micellaire (chlorure de cétyl triméthyl ammonium, CTACl) sur le phosphate de p -nitrophényle et de diphényle (PNPDPP). La destruction est rapide et totale, elle a montré l'intérêt de ce système non agressif. L'utilisation simultanée des spectroscopies UV-visible, IR, et RMN du 31 P a permis de mieux comprendre la réaction et de proposer un mécanisme pour la déphosphorylation du PNPDPP par l'acide perpropionique comportant la formation d'un peranhydride intermédiaire de formule (PhO) 2 P(O)OOC(O)CH 2 CH 3 ; l'évolution de ce dernier a été étudiée en phase aqueuse micellaire (pH ～ 9, CTACl) et par voie radicalaire. The reaction of perpropionic acid CH 3 CH 2 CO 3 H with p -nitrophenyl diphenyl phosphate (PNPDPP) has been carried out in micellar medium (cetyltrimethylammonium chloride, CTACl) providing the fast and complete destruction of PNPDPP. UV-visible, IR, and 31 P NMR spectroscopies allow a better understanding of the reaction. A mechanism for PNPDPP dephosphorylation by peroxyacids is proposed. A peranhydride intermediate, (PhO) 2 P(O)OOC(O)CH 2 CH 3 , is formed; its evolution in buffered micellar medium (pH ～ 9, CTACl) and under organic radical conditions has been studied.     

Spectre raman en phase vapeur du borazene: détermination des constantes de coriolis des espéces E

The gas phase Raman spectrum of borazene has been recorded at medium resolution. The band contours of the E degenerate species have been observed and computer simulation of them has allowed the determination of the ζ_i values. This analysis has given the value of ζ₁₉ and ζ₂₀; ξ₁₈ has been calculated from the “Zeta sum rules”. The gas phase spectrum of borazene is reported for the first time and assigned.     

Reaction de metathese des olefines induite photochimiquement en presence d'un complexe de metal de transition : V. Intervention d'un complexe dinucleaire du tungstene

The photoinduced metathesis [W(CO)₆CCl₄hν] of cis- and trans-RCH=CHMe gives 2-butene in a very high trans but low cis stereoselectivity. Propene behaves like a cis olefin. These results are consistent with the proposal of a dinuclear tungsten intermediate, which requires high steric constraints in the transalkylidenation step.     

Mecanisme de la fixation du fer ferrique sur un copolymere d'ester carboxylique—II. Etude des coefficients de distribution et de la permeation du fer(III)

Experimental determination of distribution coefficients and diffusivity through the Hycar 4021 copolymer of macro-amounts of iron(III) in ethanolic hydrochloric acid lead to the knowledge of the processes involving ethanol. Micro-amounts of iron(III) are fixed on the copolymer by a different process.