Etude des pKa et de la protodéboronation des acides furanneboroniques

The pK_a s of the furanboronic acids and their formyl, acetyl and methyl derivatives were determined in order to investigate the influence of electronic and steric effects on the acidity of the boronic group. On the other hand, the protodeboronation kinetic studies of these different acids in perchloric acid may suggest a new mechanism for the electrophilic reaction, in agreement with isotopic effects, substituant effects and the strongly negative activation entropy. Comparison of the reaction rates between the benzene, thiophene and furan series allows one to calculate the specific reaction rate ρ of the protodeboronation.     

Complexes d''addition des metaux halocarbonyle et halonitrosyle avec les acides de lewis

This work deals with the reactions of metal carbonyl-halide adducts with Lewis acids [M(X → Lewis acid)(CO)_aL_b (L = PR₃, π-Cp)]. Results are given regarding electric conductivity measurements in solution and IR spectra, as well as the preparation and study of a new class of metal nitrosyl-halide adducts, [M(X → Lewis acid)(NO)_aL_b]. A classification of Lewis acids is attempted following their electron-acceptor properties.     

Copolymerisation a l'etat cristallise des acides acrylique et methacrylique

Acrylic acid (A Ac) and methacrylic acid (MA Ac) form a eutectic mixture for the equimolecular composition; its melting point is ?30°. Most polymerization experiments were carried out at ?37° with gamma-ray initiation. The irradiation of the eutectic mixture generates a random copolymer with a narrow distribution of compositions and containing 80% MA Ac. In solid mixtures which contain an excess of MA Ac with respect to the eutectic, the reaction product is essentially the same copolymer as generated in the eutectic, the rate of polymerization in MA Ac crystals being negligible as compared with the reaction in the eutectic. When A Ac is in excess, the phenomena are more complex. A pronounced minimum is observed in the rate vs composition curve at ca 20 mole % MA Ac. Fractionation of the reaction product demonstrates the presence of a block copolymer built by sequences of A Ac and of random copolymer. An interpretation is suggested to account for the various results.     

Etude de la pyrolyse a temperature moderee des acides polyacrylique et polymethacrylique

High purity samples of polyacrylic and polymethacrylic acids have been pyrolysed between 160 and 240° in non-oxidative atmospheres. Thermal behaviours of these polymers have been studied by thermogravity, infra-red spectroscopy, acid titration of pyrolysates and particularly by a chromatographic method which allows analysis of products from polymer pyrolysis and specification simultaneously of the kinetics of their formation. In both cases, the kinetics of evolution of light products indicates a competition between dehydration and decarboxylation reactions. These two reactions are not independent. Dehydration is the main reaction and the nearly exclusive one for polymethacrylic acid but its importance decreases as the temperature is raised. Formation of small amounts of monomer has been noticed for polymethacrylic acid.     

Contribution de l'analyse thermique a l'etude des acides humiques et de leurs sels de sodium

Résumé On a étudié le comportement thermique sous oxygène des acides humiques et de leurs sels de sodium. On prépare les humates de sodium, soit par neutralisation des acides humiques, soit par dialyse de leurs pseudo-solutions dans la soude. L'examen des spectres infrarouges et de diffraction X des prélèvements effectués entre les étapes de dissociation (suivie par ATD-TG -TGD) suggère un double mécanisme. Au-dessous de 500°, il s'est formé du carbonate de sodium et du carbone. Dès 600°, débute la dissociation du carbonate. Le carbone restant s'oxyde brutalement à 770°. L'importance de la réaction varie avec la teneur initiale en sodium.

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The thermal behaviour of humic acids and their sodium salts in oxygen has been studied. The sodium humates were prepared by neutralization of humic acids or by dialysis of their pseudosolutions in sodium hydroxide. Infrared and X-ray diffraction spectra of samples taken between the dissociation steps obtained from the DTA-TG-DTG curves suggest a double mechanism. Below 500°, sodium carbonate and carbon are formed. At 600°, the dissociation of carbonate starts. The residual carbon burns at once at 770°. The extent of reaction changes with the amount of sodium initially present.

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Zusammenfassung Es wird über die Untersuchung der thermischen Eigenschaften von Huminsäuren und ihren Natriumsalzen unter Sauerstoff berichtet Letztere wurden entweder durch Neutralisation der entsprechenden Huminsäuren oder durch Dialyse ihrer Pseudolösungen in Natriumhydroxyd erzeugt. Die infrarotspektroskopische und röntgenanalytische Prüfung von zwischen zwei (durch DTA, TG und DTG verfolgte) Dissoziationen entnommenen Proben zeigt zwei Vorgänge. Unter 500° werden Natriumkarbonat und Kohle gebildet. Bei 600° beginnt die Dissoziation des Karbonats. Die zurückbleibende Kohle wird bei 770° plötzlich oxidiert.

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Na- . . - , ( — ), . 500° . 600° . 770°. .

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En l'honneur du 70^e anniversaire du Professeur Clément Duval. Etude entreprise dans le cadre des travaux de l'Equipe de Recherche Associée du C. N. R. S. n 220 (Pédologie des Pays Atlantiques).     

Caracterisation par analyse thermique differentielle des complexes de l'aluminium avec les acides fulviques et humiques

Résumé L'analyse thermique différentielle sous oxygène permet de caractériser divers complexes formés entre l'aluminium et les acides fulviques (ou humiques): en particulier, les complexes pseudo-solubles ne sont pas identiques aux complexes floculés. Les liaisons hydrogènes qui unissent l'alumine hydratée aux acides fulviques (ou humiques) dans la forme floculée rendent l'ensemble beaucoup moins stable thermiquement que les trois formes complexes pseudo-solubles.

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Differential thermal analysis in oxygen renders possible the investigation of various complexes of aluminium with fulvic acid (or humic acid). The pseudo-soluble complexes are not identical with the flocculated complexes. The hydrogen bonds linking hydrated aluminium with fulvic (or humic) acids in the flocculated form reduce the thermal stability of the complexes compared with the three pseudo-soluble forms.

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Zusammenfassung Die Differentialthermoanalyse in Sauerstoff ermöglicht die verschiedenen Komplexe des Aluminiums mit Fulvinsäure (oder Huminsäure) zu charakterisieren. Die pseudo-löslichen Komplexe sind nicht identisch mit den flockulierten Komplexen. Die das hydratierte Aluminium mit den Fulvinsäuren (oder Huminsäuren) in der flockulierten Form verbindenden Wasserstoffbindungen vermindern die thermische Stabilität der Verbindung gegenüber den drei pseudo-löslichen Formen.

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, , . - . , , , - .

     

Synthese et cyclisation electrophile de la bromhydrine de l'acide homogeranique

A new synthesis of 5-bromohexahydro-4,4,7a-trimethyl-2($\text{3H}$)-Benzofuranone (3aα,5β,7aβ)($\text{1}$) was achieved by electrophilic cyclization of the bromohydrin issued from pure homogeranic acid.     

Membranes permselectives obtenues par greffage radiochimique des acides acrylique et methacrylique sur des films de poly(chlorure de vinyle)

Membranes were prepared by subjecting to gamma-rays PVC films swollen in a mixture of acrylic acid and methylene chloride. The kinetics of the reaction were investigated as a function of monomer concentration, temperature and dose-rate. The swelling properties of the resulting membranes were studied as well as those of PVC films grafted with methacrylic acid. It was found that PVC films grafted with methacrylic acid only swell slightly in water even for high grafting ratios and the swelling is very slow. At elevated temperatures the films swell more quickly and reach a higher limiting swelling, but the effect is small. PVC films grafted with acrylic acid swell much more quickly and reach much higher swelling ratios. The extent of swelling markedly increases with temperature but this effect is not reversible: once the membranes have reached a high swelling ratio at elevated temperatures, they keep the same ratio when dipped in water at 20°. The Arrhenius plot of the swelling ratio exhibits a break at 50–60° apparently corresponding to a glass transition temperature. In methanol the swelling is significantly higher for PVC films grafted with methacrylic than with acrylic acid. Swelling of the membranes was also investigated in mixtures of water with methanol and methanol with methylene chloride. The results are interpreted by assuming a strong dipole-dipole interaction between the grafted branches and the trunk polymer resulting in a quasimolecular dispersion of the carboxylic chains in the PVC matrix. The latter acts as a barrier against the penetration of water. Heat treatment favours a segregation of the two polymeric species into microphases and this non-reversible transformation is assumed to be responsible for the unexpected behaviour of PVC films grafted with acrylic acid. The significant differences between the properties of PVC films grafted with either acrylic or methacrylic acid are attributed to the much higher hydrophobic character of the methacrylic chains.     

Transformation d'oxydes d'alkyles et de polyfluoroalkyles par les acides de Lewis. Influence des radicaux alkyles.

The generation of perfluoroalkanoyl fluorides from perfluoroalkyl ethers by Lewis acids R_HOCF₂R_F → FR_H + R_FCOF depends mainly upon the nature of the alkyl R_H radical. It is necessary to use R_H groups with donor character and also electrophilic groups present on the radicals can facilitate the breaking of the R_H-O bond. As examples, ethers with Me₃SiCH₂CH₂ or CH₂=CH-CH₂ groups allowed reactions to occur readily at room temperature or below using common Lewis acids such as ZnCl₂, BF₃-Et₂O, AlCl₃.     

Acidites et complexes des acides (alkyl-et aminoalkyl-) phosphoniques--III Alkylphosphonates substitues de calcium(II) et cuivre(II)

The stability constants of some phosphoric acids RPO(3)H(2) [R = CH(3), C(2)H(5), ClCH(2), Cl(2)CH, Cl(3)C, BrCH(2), Br(2)CH, BrCH(2)CH(2), ICH(2), HOCH(2), (CH(3))(3)N + CH2] and their complexes RPO(3)Ca, RPO(3)Cu, RPO(3)Cu(OH)(-) have been determined by multiparametric refinement of potentiometric titration data obtained at 25 degrees , in a 0.1M potassium nitrate medium. Linear relationships are obtained between stability and acidity constants. Formation of five-membered rings stabilize the hydroxymethylphosphonates. Conversely, cation repulsion by the permanent positive charge reduces the stabilities of complexes with trimethylammoniummethylphosphonic acid.     

Etude comparative de la reactivite des α-aminonitriles secondaires et tertiaires en solution aqueuse entre pH 10 et 14. Hydrolyse des α-aminonitriles secondaires et son importance dans la formation prebiotique des acides amines naturels

A kinetic study of the hydrolysis of secondary α-aminonitrile has been carried out. The results compared to those previously obtained for the decomposition reaction of tertiary α-aminonitriles, show the importance of solvation at the reactivity level of each compound.These results confirm that α-aminonitrile can act as prebiotic precursors of natural α-amino-acids.     

Acidites et complexes des acides (alkyl- et aminoalkyl-) phosphoniques—II: Affinement multiparametrique applique aux complexations suivies par potentiometrie

The determinations are based on potentiometric titration data (volume of reagent, potential). To avoid any systematic error, the acidity constants are refined together with every other significant parameter (initial protolyte concentration, concentration of impurities, electrode chain characteristics …) with the program MUPROT. Comparison of the multiparametrically adjusted results with those obtained by the usual methods reveals noticeable discrepancies. Particular attention is paid to carbonate as impurity; to take it into account, modified expressions for the titrant volume are established. The current of nitrogen used in the classical methods shifts the liquid-gas equilibrium of carbonic acid; in that case, only the approximate equations are to be considered. Working with a closed system is proposed as a more rigorous procedure.     

Synthese de nouveaux acides sulfoniques et de sila-sultones ethyleniques

The sulfonation of 1-sila-3-clopentenes and corresponding silabicyclohexanes by CISO₃SiMe₃ leads to novel ethylenic silasultones which are hydrolyzed to their sulfonic acids. Depending upon the degree of substitution of the double bond or cyclopropane ring, a competition may occur between the usually observed C-Si bond cleavage and the until now more rarely observed CH cleavage. An interpretation of these results is proposed.     

Decomposition thermique des acides peroxybenzoique et peroxydodecanoique en milieu non polaire: role de l'oxygene

A study of the decomposition mechanisms of peroxydodecanoic (RCO₃H) and perbenzoic (φCO₃H) acids in cyclohexane at both reflux temperature and less than reflux temperature (i.e. with and without dissolved oxygene) and comparisons of all the products from these reactions with those obtained from the decomposition of dodecanoyl- and benzoyl-peroxydes under the same conditions, leads to the following conclusions: (a) in both cases there is a radical mechanism, the initiating step being the rupture of the O-O bonds giving RCO₂ and φCO₂, (b) under reflux (i.e. without oxygen) the radical RCO₂ undergoes rapid decomposition and the resulting R- gives rise to a chain reaction leading to the alcohol ROH. The φCO₂ radical undergoes much slower decomposition and through chain transfer with the solvent produces φCO₂H and cyclohexanol. These reactions are fast; (c) at less than reflux temperature (i.e. in presence of dissolved oxygen) R radicals or S (solvent) radicals combine with the oxygen giving peroxy and oxy radicals. These species are electrophilic and therefore do not lead to the breaking of the O-O bond of the peracid. Rather, the acid hydrogen is attacked, giving RCO₃ or φCO₃, radicals. Through a series of reactions involving aldehyde intermediates, the corresponding carboxylic acids are obtained. These reactions are much slower than those at reflux temperature.     

Sur une colorimetrie des acides carboxyliques par hydroxamation directe

Carboxylic acids react with hydroxylamine hydrochloride in the presence of dicyclohexylcarbodi-imide to give the corresponding hydroxamic acid which is developed with iron(III), thus allowing colorimetric determinations on the tenths of a milligram scale. Esters do not react, and acetic acid can be determined in butyl acetate at a concentration of about 0·1%.

Zusammenfassung

Carbonsäuren reagieren mit Hydroxylaminhydrochlorid in Gegenwart von Dicyclohexylcarbodiimid zur entsprechenden Hydroxamsäure, die mit Eisen(III) entwickelt wird. Damit werden colorimetrische Bestimmungen in der Größenordnung von Zehntel Milligrammen möglich. Ester reagieren nicht; etwa 0,1% Essigsäure in Butylacetat können bestimmt werden.