Kinetic Study on Models of the Tetrabutqxyzirconium-Catalyzed Reaction Between α, ω -Dicarboxypolyamide-11 and α, ω -Dihydroxypolyoxyethylene

The kinetics of the tetrabutoxyzirconium-catalyzed esterifications between 11-dodecylamideundecanoic acid and 1-dodecanol, 2-tridecanol, a-dodecyl-ω-hydroxypolyoxyethylene are studied and compared to that of α, ω-dicarboxypolyamide-l 1 and α, ω-dihydroxypolyoxyethylene. The reaction with 2-tridecanol is characterized by an autoacceleration phenomenon. In the other cases the reaction rate is not greatly affected by catalyst concentration. An explanation involving the formation of catalyst condensates at the very beginning of the reaction is put forward.     

Synthèse d'homologues de la (–)--(1R,2S)-norephedrine

Synthesis of (–)-(1R,2S)-Norephedrine Homologues The amino function of esters of some simple natural amino acids I is blocked in the form of a cyanoenamine by means of 2-oxocyclopentanecarbonitrile, so that the corresponding cyanoenamino esters II are obtained. The reaction of a disubstituted lithium amide with II leeds to the cyanoenamino-amides VI . The amide function present in VI is then transformed into an aromatic ketone by means of phenyllithium, to give the (benzoylalkyl)aminocyclopentenecarbonitriles VII . Reduction of Compounds VII with NaBH₄ in EtOH ?80° affects only the keto function and leads to the [(α-hydroxybenzyl)alkyl]amino-cyclopentenecarbonitriles VIII . The amino function is then deprotected by acid hydrolysis to give the amino-alcohols IX with yields close to 50%; in every amino-alcohol IX , the erythro isomer, homologous to natural (–)-(1R,2S)-norephedrine is the more abundant or the single product. All the polyfunctional compounds prepared conserve optical activity; it has been demonstrated that the amino-alcohols IX are pure enantiomers and that no racemisation lakes place at any step of their synthesis.     

Causes and remediation of reduced efficiency in micellar liquid chromatography

Broad peaks are obtained when purely aqueous micellar phases are used in micellar liquid chromatography (MLC). The causes of reduced efficiency in MLC are investigated. Slow solute mass-transfer kinetics between micelles, the aqueous phase and the surfactant covered stationary phase are the origins of the efficiency loss. Knox plots show that the reduced efficiency comes from A term increase and, for lipophilic solutes, A and C terms increases. Surfactant adsorption reduces the pore volume and surface area of the stationary phase changing the flow anisotropy (A term). The surfactant adsorbed layer slows down the mass transfer (C term). Three ways for efficiency loss remediation are known: flow-rate reduction, temperature increase and alcohol addition. Alcohols are known to change the micelle structure and to increase the kinetics of micelle formation-destruction. It is shown that the ratio of the alcohol chain length to surfactant alkyl chain length, C_{n, OH}/C_{nm surf}, should be equal or higher than 1/3 to produce the best efficiency enhancements in MLC. Also, the volume of alcohol to be added is not absolute but relative to the surfactant concentration. The alcohol to surfactant concentration ratio should be kept constant. Temperature increases and especially alcohol additions reduce the retention factors. Thermodynamic and kinetics of the micellar exchanges in MLC cannot be dissociated.     

Reverse hydrolysis reaction in aqueous medium without any cosolvent

The synthesis of L-tyrosine fructosyl ester, from fructose and L-tyrosine methyl ester, was carried out by a transesterification reaction catalyzed by α-chymotrypsin in water without cosolvent. The effect of fructose concentration and temperature for the transesterification reaction were determined on both specific activities and product yield. The influence of the presence of fructose has been studied regarding α-chymotrypsin and L-tyrosine fructosyl ester stabilities. It appeared that an increase of temperature enhanced enzyme activity but slumped the product yield because of the very weak stability of tyrosine fructosyl ester.     

Use of sulfur derivatives as an ortho directing group for the metalation of diazines. Metalation of diazines. XVIII

The metalation of thioethers, methyl and phenyl sulfoxides and sulfones of pyrazine and pyridazine has been performed. Methyl sulfoxides and sulfones were first metalated on the methyl group. The ortho directing effect of thioethers, sulfoxides and sulfones have been compared with the methoxy group. The sulfoxides were shown to be very good ortho directing groups.     

Cationic polymerization of 1,3-pentadiene I. infrared, 1H-NMR and 13C-NMR investigations on the microstructure of poly(1,3-pentadiene) synthesized with cationic catalysts

This study deals with cationic polymerization of the cis- and trans-isomers of 1,3-pentadiene. The microstructure of the polymer chains is studied by ¹H-NMR, ¹³C-NMR and IR spectroscopies. It is shown that the trans-diene gives strictly trans-1,4 and trans-1,2 residual linear insaturations, whereas the cis-isomer yields also cis-1,4, cis-1,2 and 3,4-units whose overall content can reach 10 mol-%. According to the cyclization degree of the macromolecules, ranging from 30 to 70 mol-%, the number of trans-(1,2+1,4) units varies between 33 to 65 mol-% and that of trans-1,2 units between 4 and 20 mol-%. An analytical method is proposed to evaluate the average number of rings present in the polycyclic sequences. It is found that the cyclic fragments of the polymer chains consist of bi- or tri-cyclohexane fused rings containing α tetrasubstituted double bond.     

Melt grafting of polymethyl methacrylate onto poly(ethylene‐co‐1‐octene) by reactive extrusion: Model compound approach

The grafting of poly(methylmethacrylate) onto poly(ethylene‐co‐1‐octene) by in situ radical polymerization of methyl methacrylate is a process where the side reactions are difficult to characterize. To increase the understanding of both the nature and the extent of such reactions, products resulting from the same chemical system, where polymer is replaced by squalane and/or pentadecane, are analyzed. The influence of the temperature, the nature of peroxides (used as radicals generators) and the monomer concentration are investigated toward the chain length of the grafts. The resulting grafted PMMA and PMMA homopolymer are qualitatively analyzed by MALDI‐TOF spectroscopy and size exclusion chromatography. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5215–5226, 2007     

Effect of microemulsion-like polysoap on the catalysed esterolysis of hydrophobic p-nitrophenyl esters

The esterolytic activity of metal ion complexes of n-alkyl-2-hydroxymethylbenzimidazoles/Zn²⁺ towards p-nitrophenyl esters (picolinates and alkanoates) was investigated in the presence of an amphiphilic polymer, poly(1-hexadecyl-3-vinylpyridinium bromide), as a macromolecular matrix. The reaction rate constants obtained for the polymer hydrophobic microdomains were compared with those observed for the new conventional surfactant, 3-ethyl-1-hexadecylpyridinium bromide, chosen as the model of the repeat unit of the homopolymer. In both cases, the kinetic analysis indicated that the esterolysis reaction proceeds through the formation of an initial binary complex Ligand–Zn²⁺, the stoichiometry of which is 2/1 type.