Etude des interferences spectrophotometriques par utilisation d'une matrice d'experiences factorielle

(Use of a factorial design to study interferences in spectrophotometry.) Ozonation of aqueous solutions leads to the formation of hydrogen peroxide and oxalic acid. Hydrogen peroxide is determined spectrophotometrically by the classical method in which TiO·H₂O₂²⁺ is formed, but oxalic acid interferes by forming a complex with titanium. The interference is studied by using a simple factorial design. The results, calculated by linear regression, show the existence of both translational and rotational effects on the absorbance signals.     

Stereochimie et mecanisme de l'ouverture par les amines d'ions N-alcoxypyridinium : Formation competitive d'un ylure endocyclique; application a une nouvelle conversion heterocyclique

The N-alkoxypyridinium salt 1, with pyrrolidine, piperidine and diethylamine, undergoes reversible ring opening in acetonitrile. This competes with irreversible cyclization of an ylide to the bicyclic intermediate 3 which suffers subsequent ring opening to 3-ω-aminobutadienylisoxazol-4 ones in methanol. The different courses of the reaction is tentantively explained by means of HSAB theory. Stereochemistry of the primary open products is consistent with a disrotatory ring opening of cis-dihydropyridine adducts resulting from amine addition to the salt 1 or to the bicyclic ion 3. These primary products are further isomerized and all-trans structures have been isolated in the case of isoxazoline derivatives. Conversion of an N-alkoxypyridinium salt to substituted butadienylisoxazolones exemplifies a new type of heterocyclic ring transformation that can be described by the PARC-ANRO sequence: Proton Abstraction, Ring Closure—Addition of a Nucleophile, and Ring Opening.     

Cis-homo addition-1,4 thiophile d'organomagnesiens avec des composes thiocarbonyles comportant un groupe carbonyle en β: Synthese stereoselective d'alcoylthio-2 et de bis (alcoylthio)-2,2 cyclopropanols

Aliphatic Grignard reagents react stereoselectively with β thioxo carbonyl compounds to give substituted cis 2-alkylthio or 2,2-bis (alkylthio) cyclopropanols with good yields. Two types of non-enethiolisable thiocarbonyl compounds of formulae MeCOC(Me)₂CSR undergo this reaction a thioketone (R = Me) and a number of dithioesters (R = SMe, SEt, S iso Pr). The cis configuration of cyclopropanols has been assigned by ¹H NMR-Eu(fod)₃. The cyclopropane ring closure is a concerted cis-1,4-homo addition.     

Systemes de strecker et apparentes—II : Mécanisme de formation en solution aqueuse des α-alcoylaminoisobutyronitrile à partir d'acétone,d'acide cyanhydrique et d'ammoniaque,methyl ou diméthylamine

The formation of N-substituted tertiary α-aminosobutyronitriles from acetone, alkali, cyanide amine, has been studied in aqueous solutions of pH 8–12. Competition between the cyanide and amine for acetone first favours cyanohydrin formation. The α-aminonitrile is then slowly formed. The kinetic study of the reaction, as a function of cyanide concentration, shows two successive slow steps. In the presence of excess cyanide, the first step, limiting the reaction rate, is formation of intermediate imine. This is catalysed neither by OH^? or H₃O⁺ and depends only on the concentration of amine in basic form. The mechanism of the second step, the imine forming the α-aminonitrile, is discussed in terms of acid catalysed addition of the cyanide ion to the imine.     

Reactivite d'hydrocarbures methylenecyclo-hexaniques—I : Stereochimie de la reaction d'oxymercuration-demercuration

Methylenecyclohexanes, prepared in excellent yield by Corey and Chaykovsky then Cornforth reactions, give on oxymercuration followed by reductive demercuration tertiary alcohols resulting from axial attack by solvent. The attack takes place trans to the substiuent when the latter is at the 2 position. α-Hydroxy or methoxy compounds behave similarly to each other. For acetoxy compounds, the cis alcohols are obtained preferentially, by intramolecular attack of acetoxy group on the mercurinium ion intermediate. The results can be explained satisfactorily on the assumption that the factors inducing stereochemistry are short distance interactions.     

L'extraction des lanthanides et des actinides par les oxydes d'alkylphosphine : L'extraction de L'acide nitrique par les oxydes de tri-n-hexylphosphine,de tri-cyclohexylphosphine et de tri-n-octylphosphine

The distribution of nitric acid between an aqueous phase and a solution of THPO, TcHPO and TOPO in benzene was measured at 25°. The apparent stability constants K₁' were found to be 17.2±1.0 (M)^-2 for THPO.HNO₃, 7.0±0.8 (M)^-2 for TcHPO.HNO₃ and 15.2 ± I.I (M)^-2 for TOPO.HNO3. The stoichionetry of the last complex was confirmed in n-octane solution at constant ionic strength in the aqueous phase.     

Synthèse d'antibiotiques triterpeniques à partir d'acides biliaires—I: Fonctionnalisation en 15 de l'acide apocholique

Allylic oxidation of apocholic acid and some of its derivatives by N-bromosuccinimide in the presence of water and a base is regiospecific leading to 15-keto or 15-hydroxy compounds, depending upon the experimental conditions and the nature of the substrate.     

Dosage du platine par spectrométrie d'absorption atomique: Partie I. Mise au point d'une méthode d'analyse dans les complexes organométalliques et de coordination

A simple fast method for the determination of platinum in complexes in aqueous solution by atomic absorption spectrometry, without previous destruction of complexes, is reported. Several parameters affecting absorbance measurements are discussed. The use of some spectrochemical buffers was necessary in order to prevent interference effects. Lanthanum (20,000 p.p.m. in 0.5 M hydrochloric acid)and phosphate (30,000 p.p.m. in water) were used as buffers. The method requires only standard equipment without scale expansion. The concentration range is 1–100 p.p.m. of platinum.     

Fragmentation des aldehydes cyclopropaniques en spectrometrie de masse: Intervention d'interactions bifonctionnelles

The mass spectra of aliphatic aldehydes which contain a cyclopropane group included in the polymethylenic chain, in some instances, show two intense peaks, called A and B that are not encountered either in other cyclopropane-containing aliphatic compounds or in other aliphatic aldehydes. The intensity of peaks A and B is strictly dependent upon the distance between cyclopropane and aldehyde. When the number x of methylene groups between the two functions is equal to 4 or higher than 10, peaks A and B are intense, but when x is equal to 7, the peaks are small.Specific labelling shows that ion A contains the atoms of the cyclopropane ring, the polymethylenic chain between the two functions and the aldehyde function. Ion B also contains the aldehyde function and results from the expulsion of the polymethylenic interfunctional chain to which a hydrogen atom of the other part of the molecule is added. This hydrogen atom arises, to an extent of about 60%, from the methylene of the cyclopropane ring. A mechanism is proposed in which cyclization of the molecular ion occurs; ion A is obtained by direct α-cleavage to the ether function in the cyclic ion; ion B results from alternative ether-cleavage causing opening of the carbo-ring. One hydrogen from the cyclopropane ring is transferred leading to the elimination of the interfunctional chain.The fact that formulas of ions A and B correspond to [C_nH_2n-3O]⁺ and that their intensities are dependent of x make questionable any structural determination established only by mass spectral examination of cyclopropane aldehydes.     

Synthese de substances macromoleculaires renfermant des motifs monomeres derives de colorants—XIX: Synthese d'oligoethers et d'oligoesters colores par structure

Oligo-oxyethylenes and oligo(oxyethylenes-Co-oxypropylenes) with hydroxy end-groups have been modified by nitration and amination of the end-groups; the modification was partial in some cases and complete in others. Amino end-groups have been diazotized and the oligomers with azo end-groups have been coupled with β oxynaphthic acid and N,N′diethylaniline. Oligomers with chromophoric and hydroxy groups in the chain have been used to prepare polyurethane foams. Structurally coloured polyesters have been synthesized similarly and used to prepare polyurethane elastomers. All these oligomers have been characterized by i.r. and visible spectroscopy, NMR, end-group titration, vapour pressure osmometry and thermal differential analysis.     

L'extraction des lanthanides et des actinides par les oxydes d'alkylphosphine: Tome 1. l'extraction de l'acide nitrique par l'oxyde de tri-n-butylphosphine

The distribution of TBPO, water and nitric acid has been measured between an aqueous phase and various inert diluents at 25°. This study allowed the determination of the apparent stability constants for two molecular complexes, TBPO . HNO₃ (K₁=17.5±1.3 (M/l)^-2 (benzene); 20.1±0.8 (M/l)^-2 (toluene); II±2(M/l)^-2 (n-hexane) and TBPO . 2HNO₃.H₂O (K₂=(2.9±0.3) 10^-3(M/l)^-2 (benzene)).     

Etude des aldimines lithiees : I. Synthese d'aldehydes ω-halogenes et de dialdehydes

Aldimines are conveniently metallated, at a position α to the functional group, by using very powerful bases i.e. activated lithium dialkylamides generated in situ from lithium and a secondary amine in benzene/hexamethylphosphoric triamide. The anions obtained are alkylated with various ω,ω′-dihalogenoalkanes to give, after aqueous acid hydrolysis, good yields of ω-halogenated aldehydes and dialdehydes.     

Alcaloides steroidiques—CLXIV : Isomerisation en presence d'une base ou d'un acide d'oxazirannes steroidiques derives de la conanine

Isomerisation into an imino-carbinol or a nitrone is the first step in the hydrolysis of an oxazirane. This isomerisation, studied on three steroidal compounds lead to the following results: compound 6, bearing cis-oriented 18H and oxazirane ring, gives rise only to the nitrone 13. Compound 1 which bears trans 18H may isomerise either into the imino-carbinol 5 or into the nitrone 11 (11 is quantitatively obtained in acidic conditions with minimum basic catalysis). The case of compound 7 which isomerises whatever the conditions into the α hydroxylated imino-ether 8 shows the influence of structural factors which enhance the mobility of the 18H.     

L'extraction des lanthanides et des actinides par les oxydes d'alkylphosphine : L'extraction del'acide nitrique par quelques dioxydes de diphosphine

The distribution of nitric acid between an aqueous phase of constant or variable ionic strength and a benzene solution of diphosphine dioxide can be explained by the following reactions H⁺_a+ NO_3^-a+ DiPO₀ ? D1PO·HNO₃₀ H⁺_a+ NO_3^-a+ DiPO·HNO₃₀ ? DiPO·2 HNO₃₀ At constant ionic strength, the stability constants K₁″ were determined for the complexes 1,1-DiPO·HNO₃ (98 ± 01 (M)^-1), 1,4-DiPO·HNO₃(44±3 (M)_-1) and 1,5-DiPO·HNO₃ (51 ± 1 (M)^-1). The constants K₁₁″ for the complexes 1,1-DiPO·2 HNO₃ and 1,5-DiPO.2 HNO₃ are respectively 035±001 (M)^-1 and 62 ±0.05 (M)^-1 at 25°. With an aqueous phase of variable ionic strength, values of K₁'=54±7 (M)^-2 for 1,5-D1PO.HNO₃ and K_II'=65 ± 04 (M)^-2 for 1,5-DiPO·2 HN0₃ were obtained     

Étude d'équilibres en solution à l'aide des échangeurs d'ions : I Dissociation du perchlorate d'argent et de l'acide nitrique dans les mélanges eau—acide acétique—acide perchlorique ou acide nitrique

A theoretical relationship postulated between the distribution coefficient of a monovalent element and the parameters upon which it depends (acid concentration in solution, dissociation constants of the acid and the salt, selectivity coefficient of exchanged ions) has been verified for the dissociation of silver perchlorate in water—acetic acid—perchloric acid mixtures. The dissociation constants found have been compared with the experimental values obtained by potentiometric measurements. The relationship established has been employed for the determination of nitric acid dissociation constants in water—acetic acid-nitric acid mixtures containing less than 25 % by weight of water. From the results the pK value for nitric acid in pure acetic acid has been evaluated by extrapolation. The theoretical relationship might be used to determine an acid dissociation constant when the dissociation constant of a salt is known and vice versa.     

Cephalosporines a chaines amino-2 thiazolyl-4 acetyles: Influence de la presence et de la configuration d'un groupe oxyimino sur l'activite antibacterienne

The syntheses of 2-(2-amino-4-thiazolyl) 2-(hydroxy or alkoxy)-imino acetic acid derivatives, with the anti (E) and syn (Z) configurations, are described. By means of these compounds, the acylation of the amino-group of 7β-amino cephalosporanic acid (7-ACA) has been achieved. The two resulting series of cephalosporin derivatives-anti and syn-are markedly different with respect to their antibiotic activity. Some of the syn compounds possess an antibacterial activity which is the highest ever observed.     

Catalyse asymetrique avec des complexes chiraux de rhodium-diop—V: Effets des substituants lors de la reduction d'acides N-acylamino cinnamiques

Asymmetric synthesis of phenylalanine and its derivatives can be accomplished by asymmetric reduction of N-acylamino-cinnamic acid derivatives with CIRh(+)DIOP² as catalyst. The optical yield is influenced by the stereochemistry of the double bond, the para-substituent on the N-benzoyl group and the esterification of the carboxy group. The mechanism of the reduction is discussed.     

Stereochimie d'heterocycles du groupe IVB—II : Syntheses stereoselectives d'hydrogeno-1 et d'alkyl-1 sila-1 cyclobutanes

The reaction between n-butyllithium and 1,2 (or 1,3)-dimethyl-1-t-butoxy-1-silacyclobutanes proceeds with retention of configuration at silicon, and yields 10/90 (or 80/20) Z/E mixture of 1,2 (or 1,3)-dimethyl-1-n-butyl-1-silacyclobutanes. Methylation of 2 (or 3)-methyl-1-t-butoxy-1-silacyclobutanes (Z/E = 15/85 or 65/35) by methylmagnesium iodide gives 15/85 (or 65/35) Z/E mixture of 1,2 (or 1,3)-dimethyl-1-silacyclobutanes. The proposed configurations for substituted silacyclobutanes are supported by spectroscopic data (RMN) and chemical results (correlation of configuration and stereomutation of hydrogenosilacyclobutanes).     

Stereochimie de la des benzoates d'argent sur des diesters iododesoxy ns: I- Action des benzoates d'argent sur des di-o-aroyl-1,2 iododesoxy-3 ns-glycerols

The stereochemistry of the reaction of silver benzoates on chiral di-O-aroyl-1,2 iododeoxy-3-sn-glycerols has been reinvestigated. The reaction proceeds either with or without neighbouring group participation, depending on : - possible electrophilic assistance by the silver ion to the ionisation of the substrate (occuring only with dissociated silver salts), - ability of substituants R¹ and R² on the substrates to stabilize a positive charge. Rearrangements are at minimum with R¹ and R² electronreleasing groups in the substrate, silver salts un-or weakly dissociated and bearing a good nucleophile. For one case, a regio- and stereo specific reaction is observed.     

Recherches en serie azabenzodiazepine—VIII : Hydrazinolyses d'azabenzodiazepinones et d'azabenzodiazepinethiones de type 1,5

The action of hydrazine on several azabenzo-1,5-diazepinones gives 3(5)-methyl-5(3) pyrazole and the corresponding heterocyclic diamines but the reaction with phenylhydrazine is more complicated and depends on the nature of the heterocycle attached to the seven member ring. In this case two reaction centres must be taken into account; the amide group and the carbon atom in the 6 position. According to experimental conditions hydrazinolysis of s-triazolotriazepinethiones and pyrazolodiazepinethiones give either 5-hydrazino s-triazolotriaze-pines or pyrazolylamino-triazole (or pyrazole) or 3-hydrazinopyrazoles and 3,4-diamino triazole. The mechanism suggested is addition of molecules of hydrazine in the 5 position followed by a transannular reaction to the 7 position.