Poly(vinyl chloride) stabilization with organo-tin compounds: Part VI—The behavior of dibutyltin dilaurate

The reaction between dibutyltin dilaurate (DBTL) and chloro-4-hexene-2 (containing its isomer chloro-2-hexene-3) as a model compound for the allylic chlorine atom in poly(vinyl chloride) has been studied in dichlorobutane solution at 80°C. The reactions observed—elimination of HCl to give hexadiene and substitution of the laurate group to give hexenyl laurate—are believed to obey E2 and SN2 mechanisms through a common intermediate carbocation, with a rather low selectivity towards the substitution owing to the associated structure of the DBTL. The kinetics are complex because of the complex nature of the exchange reaction between DBTL and Bu₂SnCl₂. A reverse reaction between the hexenyl laurate and the organo-tin chloride is proposed to explain the limitation of the substitution reaction.     

Synthese de N-(tetrazol-5-yl) azetidin-2-ones

The title compounds were obtained by addition of a glycine enolate to a N-(tetrazol-5-yl) imine followed by cyclisation. This route provided both the $\text{cis}$ and the $\text{trans}$ substituted azetidinones. The $\text{cis}$ compounds possessed improved antibiotic activity as compared to the $\text{trans}$ counterparts.     

Intrinsic reactivity of active species in Ziegler–Natta polymerization of ethylene initiated with Li/Ti-based macromolecular complexes

Polymerization of ethylene was initiated with soluble polystyrene₁₀₀-butadiene₃-Li/TiCI₄ complexes in toluene leading to block copolymers. The activity of the system was measured at a constant ratio r = [Li]/[Ti] and for different concentrations in active centers and in monomer. Measurement of the amount of the block copolymers formed led to the direct determination of the efficiency of the catalytic system. This efficiency is defined with respect to the number of potentially active centers and is close to 90%. From both measured values of activity of the catalytic system and of its efficiency, the rate constants of propagation were deduced. The kinetic behavior of the system is fully consistent with that of a living system. The rate is first order towards both ethylene and active centers concentrations. So, the rate constant of propagation is an absolute rate constant, measuring the intrinsic reactivity of active sites. Determination of the absolute rate constant at different temperatures, led to thermodynamic parameters of the propagation reaction. The chemical composition of the complex and the absence of polymeric aggregation, leads to propose a structure of the active species: a bioctahedral binuclear structure is consistent with kinetic, thermodynamic results, and structural determinations.     

Synthesis of some 4H,10H[1]benzoxepino[3,4-c]pyrazol-4-one derivatives

1H(or 2H)4H10H[1]Benzoxepino[3,4-c]pyrazol-4-ones were prepared from phenoxymethylpyrazolecarboxylic acids which in turn were synthesized from simple starting materials. Different pathways to allow the predominant formation of the N-1 or N-2 substituted derivatives are described. The isomeric 1 or 2-substituted structures were supported by ¹³C-nmr.     

Mécanisme de la réaction de cyclisation en milieu aqueux de carbanilates de propargyle en méthylène-4 oxazolidinones-2

The alkaline hydrolysis of propargyl 3-chlorocarbanilates was investigated kinetically using uv spectropotometry. The cyclization to 4-methoylene-2-oxazolisinones proceeds via the numcleophilic attack of the substrate anion concomitantly with that of the hydroxide ion on the triple bond. The nucleophilic attack leads directly to the heterocycle whereas the hydroxide ion attack gives rise to a ketocarbamate which is then cyclized to the oxazolidione.     

TWO NEW METHODS OF ACTINOMETRY FOR EPR-MEASUREMENTS

Abstract— Two methods to perform actinometry in an EPR-cavity are described. One method is based on the observation that photoproduced anion radicals of hematoporphyrin react with the stable free radical 2,2,6,6-tetramethyl-4-piperidone-N-oxyl to eliminate the spin. The other method is based on the dye sensitized photoproduction of nitroxyl radicals resulting from the reaction of singlet oxygen with sterically hindered amines.     

Photo- and radiation-produced H-atoms in acid low temperature glasses containing Fe2+ ions

Frozen solutions of H₂SO₄ and acid 7 M NaClO₄ containing Fe²⁺ ions have been exposed to X rays and UV light and examined by EPR methods. It is concluded that the H atoms formed in UV-irradiated acid perchlorate matrices do not have mobile electrons as precursors. Thus no trapped electrons are found after UV irradiation even though these matrices provide efficient traps for electrons. The effect of the electron scavenger NO^?₃ is identical in UV- and X-irradiated matrices and largest in the H₂SO₄ matrix. Thus it seems that NO^?₃ acts on a similar H-atom precursor in the two cases, and that this precursor may be an excited CTTS state, rather than a mobile electron. The absence of allyl alcohol scavening effect on H atoms produced by UV light in the perchlorate matrix indicates that this H-atom scavenger does not interact with the CTTS state, and that the H atom is trapped in the vicinity of the Fe²⁺ ion where it was formed. The presence of small amounts of Fe²⁺ ions (< 10^?3 M) in the matrices causes a marked decrease in the spin—lattice relaxation time of the trapped hydrogen atoms as well as a decrease in the intensities of the satellite lines relative to the main hydrogen lines.     

Automatic apparatus for the determination of carbon and hydrogen in organic compounds

A microanalytical determination of carbon and hydrogen in organic compounds is achieved by an original technique of coulometric titration in a nonaqueous medium. The apparatus, designed for the purpose, wholly automatic and monitored by a computer, makes possible the analysis of 23 samples without any intervention from the operator. Each analysis takes about 10 min and the precision of the method results in relative standard deviations of about 0.1 and 1% for carbon and hydrogen, respectively.     

The dichlorovinylation of enolates

The condensation of certain ketone and ester enolates with trichloroethylene proceeds with surprising ease to yield dichlorovinylation products. The $\text{trans}$ stereochemistry for one such product is established by X-ray, and subsequent transformations of these initial products to ethinyl or ω-chloroethinyl derivatives is described.     

Sterols with Cyclopropane-Containing Side Chains: Synthesis and Acid Isomerization

To test the eventual involvement of sterols with a cyclopropane containing side chain in bio-methylation processes, 24,25-methanocholest-5-en-3β-ol ( 5 ) and 24,25-methano-26-methylcholest-5-en-3β-ol ( 6 ) were synthesized. Together with the naturally occurring cyclopropane petrosterol ( 1 ), they were submitted to acid isomerization to provide chemical models for some of their potential metabolites.