Kinetic modelling of the thermal oxidation of polyisoprene elastomers. Part 1: Unvulcanized unstabilized polyisoprene

The thermal oxidation of an unvulcanized, unstabilized polyisoprene rubber (IR) has been studied in the 40-140 °C temperature range. Ageing was monitored by FTIR determination of double bonds and carbonyl groups, mass uptake measurement, and weight average molar mass determination. A mechanistic scheme based on the standard scheme for radical chain oxidation, but taking into account the diversity of initiation processes and the existence of inter- and intramolecular radical additions to double bonds, was built. The kinetic model derived from this scheme is composed of seven differential equations to be solved in discrete thickness layers to take into account the kinetic control by oxygen diffusion. This system was numerically solved using a Matlab program dedicated to stiff systems of differential equations. The elementary rate constants and other kinetic parameters were then determined from experimental data, using an inverse approach. A set of physically reasonable parameter values was obtained, thus allowing us to envisage lifetime predictions at low temperature (long term). The results led to observations difficult to make from classical analytical studies, for instance the predominance of bimolecular hydroperoxide decomposition among other initiation modes or the competition between intermolecular hydrogen abstraction and intramolecular addition of peroxy radicals to double bonds.     

Über den Nachweis und die Bestimmung des Schädlingsbekämpfungsmittels E 605 in der gerichtlichen Chemie

Zusammenfassung Es wird gezeigt, daß sich Insektizide auf der Basis der Ester der Thiophosphorsäure (E 605) aus biologischem Material mittels Wasser-dampfdestillation auf verhältnismäßig einfache Weise abscheiden lassen. Im Destillat erfolgt die Bestimmung nach Ausäthern und Lösen des Rückstandes in Äthanol durch Messen der Lichtabsorption im UV. Hierbei zeigt sich, daß die rechnerische Eliminierung der Störstoffe bei geringeren Konzentrationen der Ester leichter ist als bei hohen.Durch Messung der Lichtabsorption im IR läßt sich, genügende Konzentration vorausgesetzt, entscheiden, welcher Ester vorliegt.

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Summary It was shown that insecticides based on the ester of thiophosphoric acid (E 605) can be separated in relatively simple fashion from biological material by means of steam distillation. The distillate is shaken out with ether and the residue dissolved in ethanol and the determination is accomplished by measuring the absorption in ultraviolet light. It was found that the computational elimination of the interfering materials is easier at lower concentrations of the ester than when higher concentrations are present. By measuring the light absorption in infrared, it is possible to decide which ester is present, provided the concentration is high enough.

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Résumé On montre que les insecticides se séparent d'une manière relativement simple de l'élément biologique par un entraînement à la vapeur d'eau sur la base de l'ester de l'acide thiophosphorique (E 605). Le dosage s'effectue sur le distillat d'après l'épuisement à l'éther et la solubilité du résidu dans l'éthanol et la mesure de l'absorption lumineuse dans l'ultraviolet. On en déduit que l'élimination calculée de la substance gênante est plus facile pour les faibles concentrations de l'ester que pour les grandes. En mesurant l'absorption de la lumière dans l'infrarouge, on peut savoir de quel ester il s'agit pour des concentrations supposées suffisantes.

     

Sterically demanding diporphyrin ligands and rhodium(II) porphyrin bimetalloradical complexes

A series of sterically demanding diporphyrins H2(por)-X-(por)H2 ligands that contain spacers (X) with different degrees of flexibility were synthesized from the trimesitylporphyrin derivatives 5-(4-hydroxyphenyl)-10,15,20-trimesitylporphyrin (TMP-OH)H2 (1a) and 5-(2,6-dimethyl-4-hydroxyphenyl)-10,15,20-trimesityl-porphyrin, (DMTMP-OH)H2 (1b). The monomeric porphyrins 1a,b, which have steric demands similar to that of tetramesitylporphyrin, (TMP)H2, and carry a hydroxyl functional group at the para position of one of the mesophenyl substituents, were constructed from reaction of pyrrole with two aromatic aldehydes by a mixed aldehyde condensation approach. The diporphyrins with alkyl diether tethers were obtained stepwise from reactions of the hydroxy functionalized porphyrins 1a,b with dibromides Br(CH2)nBr. The diporphyrin which contains a more rigid m-xylylene spacer, was made directly from reaction of 1b with alpha,alpha'-dibromo-m-xylene. Rhodium was inserted into the porphyrins using Rh2(CO)2Cl2 and converted to dimethyl complexes Me-Rh(Por)-X-(Por)Rh-Me. The dirhodium(II) derivatives .Rh(por)-X-(por)Rh.) were generated by photolysis of the dimethyl complexes and observed to occur as stable bimetalloradicals because the ligand steric demands prohibit Rh(II)-Rh(II) bonding. EPR spectra of the dirhodium(II) derivatives, triphenyl phospine adducts, and dioxygen complexes are reported. The kinetic advantage of bimetalloradical complexes for substrate reactions that have two metal-centered radicals in the transition state is demonstrated by reactions of dihydrogen with dirhodium(II) bimetalloradical complexes.     

The Baylis-Hillman condensation of alpha,beta-conjugate cycloketones with aldehydes using diethylaluminum iodide alone as the promoter

The Baylis-Hillman condensation of three types of alpha,beta-conjugate cycloketones with aldehydes was successfully performed by using diethylaluminum iodide as the Lewis acid promoter alone without the direct use of a Lewis base. The reaction proceeded to completion at 0 degree C in CH2Cl2 within 24 h to give modest to good yields (53-72%).     

Influence of extended π-conjugation units on carrier mobilities in conducting polymers

Carrier mobilities in thin films of copolymers with repeat units consisting of oligothiophenes bridged by Si atoms are measured over a range of doping levels, where the numbers of thienylenes in the repeat unit are 7, 8, 10, 12, and 14. The mobilities for these polymer films increased with the increase in doping level and the mobility enhancement followed an increasing order of the π-conjugation length. The magnitude of the mobility increase for the Si polymer comprising 14 thiophene units reached ca. 10⁴, implying that this π-conjugation length is almost sufficient to reproduce transport properties of polythiophenes.     

The Studies of Lanthanide Shift Reagents in NMR Spectroscopy

The action of a series of lanthanide chelate complexes LnL₃, where Lu=La, Pr, Nd, Sm, Eu, Dy, Ho, Er and Yb; L= dbm (dibenzoylmethanato), dpm (dipivaloylmethanato), and acac acetylactonato), on nmr spectra of 2-butanol has been studied. The origin of shifting abilities and shifting sign of various lanthanide ions are explained by means of Bleaney's theory.     

Adsorption, desorption and activities of acid phosphatase on various colloidal particles from an Ultisol

Adsorption, desorption and activity of acid phosphatase on various soil colloidal particles and pure clay minerals were studied. Higher adsorption amounts and low percentage of desorption of acid phosphatase were found on fine soil clays (<0.2 μm). Electrostatic force and ligand exchange are the major driving forces that are involved in the adsorption of enzymes on soil clays. More enzyme molecules were adsorbed on soil clays in the presence of organic components. However, enzymes on organic clays were more easily released. One-third of the enzyme on goethite was adsorbed via ligand exchange process. Some other interactions, such as van der Waals force, hydrophobic force and hydrogen bonding may be more important in the adsorption of enzyme on kaolinite and the enzyme in this system cannot be easily removed. Coarse clays (0.2–2 μm) and inorganic soil clays had higher affinities for enzyme molecules than fine clays and organic clays, respectively. The activity of enzyme bound on soil clays was inhibited and the thermal stability was increased in the presence of organic matter. Data obtained in this study are helpful for a better understanding of the interactions of enzymes with inorganic and organic constituents in soil and associated environments.     

Migration of 99Tc in a Weak Loess Aquifer: A Field Column Experiment

The migration of ⁹⁹Tc in a weak loess aquifer was investigated in-situ with undisturbed aquifer medium columns. The columns were obtained horizontally at a depth of 3236 m in an Underground Research Facility (URF). Quartz containing ³H (HTO) and ⁹⁹Tc (in the form of ⁹⁹TcO₄ ^-) was introduced into one end of the columns and the columns were covered tightly. Aquifer water was introduced into the columns directly from an experimental shaft in the UFR. Effluents from the columns were collected and the activity of ³H and ⁹⁹Tc were determined with a liquid scintillation analyzer. The breakthrough curves of ³H and ⁹⁹Tc indicate that ⁹⁹Tc migrates a little faster than that ³H does in the aquifer.     

A ferrocene based palladacyclic precatalyst for the Suzuki cross-coupling of aryl chlorides

Addition of palladium acetate to 2-(dicyclohexylphosphino)-phenylferrocene gave palladacycle 16 that is a very effective precatalyst for the Suzuki cross-coupling of aryl chlorides at room temperature (1 mol% 16) or 60 degrees C (> or = 0.01 mol% 16).