Les systèmes biphasiques. 3. Alkylation des purines en catalyse par transfert de phase

The phase transfer catalysed methylation of adenine gave selectively 9-methyladenine (98%), while benzylation yields 9-benzyladenine as the major product accompanied by very small amounts of the 3-isomer. Alkylation of xanthine, theobromine and theophylline by the same technique gave also the corresponding N-alkyl derivatives in high yields, with no other O-alkylated regioisomer. These alkylation procedures, owing to their simplicity and selectivity, constitute a considerable improvement upon the classical techniques.     

Reactivité de composés carbonylés avec des cétènes en présence d'alkoxydes de titane ou de zirconium. 3e communication

Reactivity of Carbonyl Compounds with Ketenes in the Presence of Titanium or Zirconium Alkoxides The reaction of ketene or dimethylketene with aldehydes or ketones in the presence of titanium or zirconium alkoxides gives essentially β-hydroxyesters. By polyinsertion of ketene and aldehydes in the Ti? O bond, di- tri- and tetraesters are formed. An excess of ketene produces acetyl derivatives of esters and 6-alkyl-3,4,5,6-tetrahydro-2,4-pyrandiones.     

Synthèse et polymérisation de monomères chlorofluorés allyliques vinyliques et acryliques

Synthesis, polymerization and copolymerization of allylic, vinylic and acrylic monomers containing chlorinated or chlorofluorinated substituents were studied. The reactivity of terminal alcohols or acids is influenced by their neighbouring group. By products and their mechanism of formation were studied.La synthèse et la polymérisation d'acrylates fluorés, a donné lieu à de nombreux travaux. Une première méthode d'obtention de ces composés consiste à faire réagir un alcool fluoré avec un chlorure d'acide insaturé. Les acrylates obtenus sont de la forme :

     

Caractère séquencé des polyacroléines préparées par voie anionique

Several independent studies confirm that anionic polyacroleins are block polymers. Chemical analysis, thermogravimetric studies, and variations of the refractive index increment and sequences lengths all support this hypothesis.     

Synthèse de copolymères greffés à base de polyéthylène—1

Polyethylene macromolecular free radical initiators, obtained by ozonization, are used to prepare graft copolymers with methyl methacrylate, styrene and vinyl chloride. The reactions parameters are the number of initiator groups (found by DPPH), peroxide and hydroperoxide proportions (respectively 36 and 64%), decomposition rate (K_d at 90° 10⁻¹sec⁻¹) and monomer concentration. The molecular structure of these copolymers is defined.     

Etude de l'acylation de l'acétyl-3 acétoxy-8 indolizine par action de chlorures d'acide en présence de chlorure d'aluminium

Study of acylation of 3-acetyl-8-acetoxyindolizine by miscellaneous acid chlorides in the presence of aluminium chloride shows that this reaction is either limited to a transesterification (in the case of benzoyl chloride) or leads to introduction of an acyl group in position 1 with simultaneous liberation of the phenol function in position 8. When acylation takes place, acetyl chloride resulting from the cleavage of the acetoxy group competes with the acid chloride used in the reaction. Predominant acylation by the latter is observed when the reaction is performed with ethoxalyl chloride or with non branched aliphatic acid chlorides; by contrast solely acetylation takes place when pivaloyl or phenylacetyl chloride is used. These results are tentatively explained by a process related to the Fries rearrangement. The hypothesis of intramolecular transfer of an acyl group from the ester function in position 8 can be discarded by the observed results.     

Isomérisation de 2,3‐époxypinanes fonctionnels en présence d'acides de Lewis

Isomerization of Functionalized 2,3‐Epoxypinanes in the Presence of Lewis Acids The functionalized 2,3‐epoxypinanes 1b – i were submitted to isomerization in the presence of ZnBr₂ at 110° (Table 1) or of BF₃⋅Et₂O at different temperatures (Table 2), and their behavior was compared with that of the non‐functionalized parent 1a and with similar known transpositions. The produced campholenals 2 , pinocamphones 3 , and in some cases, fencholenals 4 were isolated and characterized. A mechanism involving a concerted oxirane ring opening is proposed (Scheme 4).     

Synthèse de l'analogue sélénié de la sérotonine

Starting from 2-bromo-5-methoxyacetophenone, an unambiguous synthesis of the selenium analog of serotonine is described with a 25% overall yield. Application of the Wittig reaction to selenoindoxyls appears to be a successful pathway to products of this nature.     

Etude de copolymères ABS (acrylonitrile–butadiène–styrène): Solvatation préférentielle du polybutadiène par les promoteurs

ABS resins formed by copolymerization of styrene and acrylonitrile (AN) in presence of polybutadiene, consist of a mixture of SAN graft copolymer on polybutadiene (PBut) and of ungrafted SAN copolymer (styrene-co-acrylonitrile). The kinetic study was completed by showing a preferential solvation of polybutadiene by the initiator. This solvation effect was studied as a function of the concentration ratio SAN/PBut and in relation with the type of initiator. The adsorption of initiator appeared to be maximum when its solubility parameter (σ) is close to that of polybutadiene. As a function of the polybutadiene characteristics, this selective adsorption can be given by where I₁ is the quantity of initiator in the polybutadiene medium, I is the total amount of peroxide, [PBut] is the concentration of polybutadiene, and M?_n its molecular weight. It has been shown furthermore that the preferential solvation of polybutadiene by the benzoyl peroxide can be increased by addition of SAN or acrylonitrile. The consequences of this solvation effect on the characteristics of the grafting reaction, more precisely on the molecular weight of grafted and ungrafted SAN and on the rate of polymerization, were examined.     

Coefficient seebeck et méanismes de conduction dans les polymères (PPP) electroactifs dopés par implantation ionique

A study of the Seebeck coefficient has shown that doping of polyparaphenylene by ion implantation makes it possible to obtain an electronically doped semiconductor at low energy: n-type with alkali metal ions and p-type with halide ions. At the highest energies (E > 100 keV) the p-type conductivity is due to the creation of defects by irradiation. Generally the semiconductor obtained is degenerate with a Seebeck coefficient close to that obtained by chemical doping. Study of the mechanisms of conduction suggests plots of log σ = (T^?l/n); the greater n is, the better is the agreement between the experimental curve and theory. Representation of the conductivity is proposed according to Mott's theories, which are applicable to amorphous semiconductors and involve several conduction processes in the temperature space. For the variable-range-hopping (VRH) mechanism at low temperature, two parameters, α^?1 (representing the spatial separation of hopping sites) and N(E_F) (the density of states at the Fermi Level) are obtained.