Rôle catalytique de l'eau et des sels lors de l'hydrolyse alcaline des esters en milieu hydro-alcoolique: Mise en évidence par spectrométrie ir des associations ester-solvant et ester-cation

Infrared spectra of esters in water-alcohol mixtures, with or without added salts, indicate the formation of 1:1 or 1:2 complexes through hydrogen bonding between the ester carbonyl group and the proton donor molecules of the solvent, as well as the formation of a donor-acceptor complexes with Li⁺ or Ba²⁺. These complexes facilitate nucleophilic attack at the carbon of the carbonyl group by hydroxyl anions. Depending on the water content of the mixture, the addition of LiCIO₄ increases or decreases the rate constant of the reaction. The displacement of equilibria between different entities explains a higher rate constant in water-tert-butanol than in water-methanol mixtures of the alkaline hydrolysis of ethyl acetate.     

Effets de sel sur les mecanismes competitifs de coupure alkyle-oxygene et acyleoxygene lors de l'hydrolyse des esters phenylallyliques en milieu neutre

Salt effects on neutral hydrolysis of α-phenylallyl esters were determined in ethanol-water mixtures. Our results suggest weakening of alkyl-oxygen bond induced by complexation of carbonyl oxygen with the cation and with competition between ester-cation and ester-solvent association. The rate coefficient for hydrolysis of O-alkyl and O-acyl fission depends on water concentration and on cation. When ester-cation association is strong (Ba²⁺ and Li⁺) salt effect is positive; when it is weak, (Na⁺), salt effect is sometimes positive, sometimes negative and changes with the nature of the anion for alkyl-oxygen fission.     

Sur la reactivite des organomagnesiens derivant de l'addition d'organomagnesiens allyliques sur l'isoprene

Contrary to a recent report, it is shown that allylic Grignard reagents prepared by treating allylic Grignard reagents with isoprene and a catalytic amount of Cp₂TiCl₂ react normally with carbon dioxide and carbonyl compounds: a complete allylic rearrangement is observed.     

Mecanisme d'hydrolyse en milieu basique aqueux d'esters allophaniques,modeles de carboxybiotine

This work is dealing with basic hydrolysis in water of allophanic esters as possible models of carboxybiotin. A complex mechanism is involved likely due to competition of nucleophilic attack on the two carbonyl groups of the substrate. The rate of hydrolysis is significantly increased by metallic cation (Mg⁺⁺), a specific effect which allows to consider characterization of selectivity of bond breaking between nitrogen and carboxylate group with other nucleophiles.     

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.     

Effet α. influence de la substitution sur l'exaltation de reactivite d'oximes vis-a-vis de l'acetate de p-nitrophenyle

Kinetic measurements show the relation between the magnitude of the “α effect” exhibited by trifluoromethyloximate anions RR'C=N-O^? and the electron attracting properties of the substituents. Indeed, the reactivity enhancement which is observed for α-trifluoromethyloximes is similar to that found in earlier studies of α-hydroxyiminoketones. This characteristic behaviour is no longer observed for oximes bearing an electron releasing substituent at the α-position of the hydroxyimino group. On the basis of sodium oximate molecular orbital energies the “α effect” induced by electron attracting substituents appears to depend on both the interactions of nitrogen and oxygen lone pairs of electrons and the lowering of the π^* vacant orbital thus favouring a secondary interaction between the π^* anion orbital and the π orbital of p-nitrophenylacetate carbonyl group.     

An Influence of Structure of Ester on Results of Its Macrocyclization Reaction with α,ω-Diamine

Abstract

Sodium methoxide was found to be an excellent catalyst in the reaction of diesters with diamines leading to macrocyclic diamides. Time of reaction was shortened to several hours (in the case of reactive esters) or to several days (in the case of less reactive esters). The template effect of Na⁺ ion was excluded. It was also proposed that the electron density on the carbonyl group in various esters was responsible for different results of amidation reactions. Decrease in electron density increases the reactivity of the carbonyl group. For esters 1–5, the inductive effect of the heteroatom at the α position to the carbonyl group influences reactivity mostly.     

Influence de la solvatation par le tert-butanol sur la structure et la reactivite de l'enolate de potassium de l'acetylacetate d'ethyle en presence de couronne ou de cryptand. etude par spectrometrie infra-rouge et cinetique

The structure and the nucleophilic reactivity of crowned (18-crown-6) or cryptated {cryptand (2.2.2)} potassium ethyl acetoacetate enolate have been compared in tert-butanol and in DME (or THF). In the protic solvent tert-butanol, the crowned and the cryptated potassium enolate species both exist as loose ion pairs in which the enolate anion, strongly hydrogen-bonded to the solvent, is in a “transoid” (non chelating) conformation. Both species show similar reactivities towards alkylating agents but completely different reactivities are observed in aprotic weakly dissociating media (THF, DME). In contrast to what is observed in tert-butanol, the cryptated species and the crowned species have very different nucleophilic reactivities in THF or DME; in those solvents only the cryptated species retains a loose ion pair structure; the crowned species is a contact ion pair in which the enolate anion chelates the potassium cation. The solvation of this crowned chelate species by tert-butanol has been demonstrated in binary mixtures of solvents (C₆D₆-t-BuOH, THF-t-BuOH). The oxygen basicity of the enolate anion is very different in the crowned chelated ion pair compared with the cryptand separated ion pair.     

Alcoylation des enolates de l'acetylacetate d'ethyle dans le dimethoxyethane. Reactivite des formes associee et dissociee

The alkylation of alkali metal and N⁺Bu₄ ethylacetoacetate énolates by means of ethyl iodide, bromide and tosylate has been studied in diméthoxyéthane, in order to measure the reactivity of the associated forms. C/O alkylation ratios, structures of O-alkylated products and rates of alkylation, have been determined. With ethyl tosylate, the amount of O-alkylated products does not increase in the generally observed order Li⁺ < Na⁺ < K⁺ < Cs⁺ but in the order Na⁺ < K⁺ < Li⁺ ≈ Cs⁺. Some aspects of the alkali ethylacetoacetate énolates reactivity in weakly polar medium such as DME are discussed.     

Étude thermodynamique de la complexation de l'argent par la pyridazine,la pyrimidine et la pyrazine

The stability constants of the complexes of Ag⁺ ion with pyridazine, pyrimidine and pyrazine as ligands are determined, at 25°C in KNO₃ 0.1 M, using the corresponding metal-complex electrodes.Enthalpies for the two steps of complexation observed are obtained from direct calorimetric measurements, under the same conditions of temperature and medium.A comparison of these values and of the entropies derived from them forms the basis for a discussion of the effects of the relative position of the nitrogen atoms in each heterocycle on their ability to form coordination compounds.     

Calix[4]pyrrole‐Based Heteroditopic Ion‐Pair Receptor That Displays Anion‐Modulated,Cation‐Binding Behavior

A new ditopic ion‐pair receptor 1 was designed, synthesized, and characterized. Detailed binding studies served to confirm that this receptor binds fluoride and chloride ions (studied as their tetraalkylammonium salts) and forms stable 1:1 complexes in CDCl₃. Treatment of the halide‐ion complexes of 1 with Group I and II metal ions (Li⁺, Na⁺, K⁺, Cs⁺, Mg²⁺, and Ca²⁺; studied as their perchlorate salts in CD₃CN) revealed unique interactions that were found to depend on both the choice of the added cation and the precomplexed anion. In the case of the fluoride complex [ 1? F]^? (preformed as the tetrabutylammonium (TBA⁺) complex), little evidence of interaction with the K⁺ ion was seen. In contrast, when this same complex (i.e., [ 1? F]^? as the TBA⁺ salt) was treated with the Li⁺ or Na⁺ ions, complete decomplexation of the receptor‐bound fluoride ion was observed. In sharp contrast to what was seen with Li⁺, Na⁺, and K⁺, treating complex [ 1? F]^? with the Cs⁺ ion gave rise to a stable, receptor‐bound ion‐pair complex [Cs ?1? F] that contains the Cs⁺ ion complexed within the cup‐like cavity of the calix[4]pyrrole, which in turn was stabilized in its cone conformation. Different complexation behavior was observed in the case of the chloride complex [ 1? Cl]^?. In this case, no appreciable interaction was observed with Na⁺ or K⁺. In addition, treating [ 1? Cl]^? with Li⁺ produces a tightly hydrated dimeric ion‐pair complex [ 1? LiCl(H₂O)]₂ in which two Li⁺ ions are bound to the crown moiety of the two receptors. In analogy to what was seen in the case of [ 1? F]^?, exposure of [ 1? Cl]^? to the Cs⁺ ion gives rise to an ion‐pair complex [Cs ?1? Cl] in which the cation is bound within the cup of the calix[4]pyrrole. Different complexation modes were also observed when the binding of the fluoride ion was studied by using the tetramethylammonium and tetraethylammonium salts.     

Etude cinetique de l'hydrolyse du paranitrophenylphosphate dans l'acetonitrile faiblement aqueux. Processus dissociatif.

Basic hydrolysis of paranitrophenylphosphate in acetonitrile of low water content (0.02 to 0.5 M) is an unimolecular process, with likely a phosphenium cation as intermediate. Comparison with reaction in water - also occuring through an unimolecular process - indicates that the large rate enhancement in CH₃ CN (3.10⁶ for [H₂O] 0.02 M) is entropy controlled.     

Hydrogenation asymetrique de precurseurs d'aminoacides a l'aide de mono- et diphosphines derivees de sucres

Mono- and di-phosphines derived from sugars are synthesized and used as ligands in asymmetric catalysis. In the presence of a base (triethylamine, KOH…) the cationic complex [Rh(COD)dioxop]⁺ClO₄^?, catalyzes reduction of α-amino acid precursors with high optical yields (78–86%). The influence of the base is discussed.     

Induction asymetrique lors de l'addition de Michael d'un ester α-sulfinyle chiral

During the Michael addition of chiral α-sulfinyl eser (+) $\text{1}$$\text{R}$ on αβ-unsaturated esters, an extent of 24% of asymmetric induction was observed. It is shown that the addition products can be transformed into optically active δ-lactones.     

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     

Oligoether‐Strapped Calix[4]pyrrole: An Ion‐Pair Receptor Displaying Cation‐Dependent Chloride Anion Transport

A ditopic ion‐pair receptor ( 1 ), which has tunable cation‐ and anion‐binding sites, has been synthesized and characterized. Spectroscopic analyses provide support for the conclusion that receptor 1 binds fluoride and chloride anions strongly and forms stable 1:1 complexes ([ 1? F]^? and [ 1? Cl]^?) with appropriately chosen salts of these anions in acetonitrile. When the anion complexes of 1 were treated with alkali metal ions (Li⁺, Na⁺, K⁺, Cs⁺, as their perchlorate salts), ion‐dependent interactions were observed that were found to depend on both the choice of added cation and the initially complexed anion. In the case of [ 1? F]^?, no appreciable interaction with the K⁺ ion was seen. On the other hand, when this complex was treated with Li⁺ or Na⁺ ions, decomplexation of the bound fluoride anion was observed. In contrast to what was seen with Li⁺, Na⁺, K⁺, treating [ 1?F ]^? with Cs⁺ ions gave rise to a stable, host‐separated ion‐pair complex, [F ?1? Cs], which contains the Cs⁺ ion bound in the cup‐like portion of the calix[4]pyrrole. Different complexation behavior was seen in the case of the chloride complex, [ 1? Cl]^?. Here, no appreciable interaction was observed with Na⁺ or K⁺. In contrast, treating with Li⁺ produces a tight ion‐pair complex, [ 1? Li ? Cl], in which the cation is bound to the crown moiety. In analogy to what was seen for [ 1? F]^?, treatment of [ 1? Cl]^? with Cs⁺ ions gives rise to a host‐separated ion‐pair complex, [Cl ?1? Cs], in which the cation is bound to the cup of the calix[4]pyrrole. As inferred from liposomal model membrane transport studies, system 1 can act as an effective carrier for several chloride anion salts of Group 1 cations, operating through both symport (chloride+cation co‐transport) and antiport (nitrate‐for‐chloride exchange) mechanisms. This transport behavior stands in contrast to what is seen for simple octamethylcalix[4]pyrrole, which acts as an effective carrier for cesium chloride but does not operates through a nitrate‐for‐chloride anion exchange mechanism.     

Etude de l'hydrogenation de l'α-terpinene et du dihyro-2,3 anisole catalysee par le phenanthrene chrome tricarbonyle

The hydrogenation of α-terpinene and 2,3-dihydroanisole catalysed by phenanthrenechromium tricarbonyl in cyclohexane is described. The catalytic reaction is accelerated when small amounts of ketone are added to the solution. Attempts to induce asymmetric synthesis by adding (+)-3-menthylcyclohexanone or l-carvone to the reaction mixture are discussed. Isomerization of cis-Δ²-methene and α-phellandrene is also presented.     

Synthese,eigenschaften und carbonyl-insertions-reaktionen von tetracarbonyleisen(0)-komplexen para-substituierter styrole

The Fe(CO)₄ η²-complexes of para-substituted styrenes (substituent  H, CH₃, OCH₃, Cl, F) can be obtained in good yields. Complexation changes drastically the chemical shifts and coupling constants of the vinyl protons. Reaction of the complexes with one mole equivalent of bromine in methanol liberates styrenes, but using two equivalents esters and diesters are formed via intermediate complexes of iron(III). For these carbonyl insertion reactions no systematic influence of the substituent on yield and product distribution was observed.     

Effets de micelles cationiques sur l'hydrolyse alcaline d'acetanilides a groupe acyle active par des substituants electro-attracteurs

Micellar effects of CTAB upon the alkaline hydrolysis of CF₃-CO-N(CH₃)C₆H₅, CHCl₂-CO-N(CH₃)C₆H₄X and CH₂Cl-CO-N(CH₃)C₆H₄X, (X=p-OCH₃H,p-Cl) are reported. Variations of k_obs, and of kinetic order of the reaction with respect to HO^? ion, are interpreted as an acceleration of HO^?-catalyzed steps, and a decrease of catalysis by water for decomposition of tetrahedral intermediates; these two effects oppose each other in HO^? and H₂O catalyzed steps. Differences between micellar and DMSO effects suggest a very small local concentration of HO^? ions in micelles.     

Structural Aspects of the Enantioselectivity of Tartrates with α-Amino-alcohol Salts part. I. Crystal structures of eleven tartaric-acid diesters

Enantioselective host-guest complexes of α-amino-alcohol salts with chiral tartaric-acid esters can not be crystallised up to now. To study structural aspects of their enantioselectivity, crystal structures of the components were determined. The structures of eleven diesters with myrtanol, borneol, menthol, neomenthol, and cis-4-(tert-butyl)cyclohexanol in different configurations showed a remarkable rigidity of the tartaric-acid conformation, partly because of intramolecular H-bonding between OH and C=O groups. The conformation of the tartaric-acid part in these diesters is the same as the one observed in optically active tartaric acid (torsion angle OC? C? OH ca. 0°), The binding site for guest molecules is a parallelogram formed by two hydroxy and two carbonyl O-atoms, all lying on the same side of a mean molecular plane. There is one exception: the dimenthyl ester, which is the most enantioselective with a norephedrine guest, has one of the ester groups turned (torsion angle O? C? C? OH ca. 180°), forming a triangle of O-atoms and moving the bulky menthyl group to the vicinity of the binding site.