Volume and heat capacity of model non-aqueous self-assembly systems

Blends of immiscible polymers are often stabilized by block copolymers which can form non-aqueous micelles and microemulsions in the liquid polymers. The phase diagrans, apparent volumes and apparent heat capacities of model non-aqueous binary and ternary systems were studied in order to investigate the conditions under which such self-assembly systems could form. 1,2-Hexanediol, which can cosolubilize hexane and ethyleneglycol, forms inverse micelles in hexane and weak microaggregates in ethyleneglycol. Genapol X-060, a commercial alcoholic surfactant containing on the average an aliphatic chain of 13 carbons and 6 oxyethylenes (C₁₃E₆), forms microaggregates in poly(ethyleneglycol) 400. These self-assembly systems are strengthen in the presence of a third component which has an affinity for the inner phase.Presented at the Symposium, 76^th CSC Congress, Sherbrooke, Quebec, May 30–June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65^th birthday.     

The additivity principle in pyrolysis—gas chromatography of brown coal

Pyrolysis—gas chromatography of brown coal exhibits additive properties and it is therefore possible to construct the pyrogram of the original coal from the individual pyrograms of the bitumen, humic acids, lignin and humin fractions. The contents of phenols in the pyrograms are typical for all of the above classes except bitumen and are in agreement with the contents of the individual groups in the original coal. The results suggest that the separation does not bring about significant chemical changes in individual brown coal fractions.     

Analyse theoretique des lois cinetiques couramment utilisees en thermoanalyse pour l'etude des reactions solid-gaz. III. proposition d'une nouvelle methode d'approche en regime dynamique

Résumé Dans la première partie de ce travail, les auteurs mettent en évidence que la vitesse d'une réaction en régime non isotherme dépend d'un facteur supplémentaire: le régime de montée en température. Cette assertion est basée sur le fait que le taux de réactionx est une fonction de trois variables: températureT, tempst, et vitesse de chauffeT, variable qui n'avait pas été prise en considération jusqu'ici par les autres auteurs travaillant sur ce problème.Puis, se basant sur les deux hypothèses suivantes: a) l'équation de vitesse en régime isotherme est la forme limite de l'équation de vitesse en régime dynamique, b) la variation de température en régime dynamique affecte la fréquence d'apparition des germes de la nouvelle phase, une formulation théorique des loisg(x) est proposée pour le régime non-isotherme. Cette formulation est explicitée en fonction de l'écart, à une température donnée, entre les valeurs de Lnk _i (isotherme) et Lnk _d (dynamique) dans le diagramme Lnk = f(1/T).L'étude, par thermogravimétrie, de la décomposition du gypse, du sulfate de calcium semihydraté, et de l'oxalate de calcium monohydraté, réalisée en montée linéaire de température, permet de vérifier expérimentalement la formulation théorique proposée.Pour obtenir une bonne interprétation cinétique d'une réaction chimique en régime dynamique, la vitesse de chauffe ne doit pas excéder 20°/heure.

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In the first part of this paper, the authors point out that the rate of reaction with non-isothermal kinetics depends on a supplementary factor: the heating rate. This assertion is based on the fact that the degreex of reaction is a function of three variables:T (temperature),t (time) andT (heating rate); this was not taken into account by other authors concerned with the subject.Then from the two following hypotheses: a) the rate equation for isothermal conditions is the limit form of the rate equation for non-isothermal conditions, b) the temperature change under dynamic conditions affects the frequency of nucleus formation of the new phase, a theoretical formulation of non-isothermalg(x) laws is proposed. This formulation involves the value of the difference, at constant temperature, between Ink _i (isothermal) and In k_d (dynamic) in the Ink=f(1/T) diagram.The thermogravimetric study of the dehydration of gypsum, of calcium sulfate hemihydrate, and of calcium oxalate monohydrate, under non-isothermal conditions, allows experimental verification of the theoretical formulation proposed.For a good kinetic approach of a chemical reaction under dynamic conditions, the heating rate must not exceed 20°/hour.

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Zusammenfassung Im ersten Teil dieser Arbeit wird von den Autoren bewiesen, daß die Geschwindigkeit einer Reaktion unter nicht-isothermen Bedingungen von einem zusätzlichen Faktor, den Bedingungen des Temperaturenstiegs, abhängt. Diese Behauptung beruht auf der Tatsache, daß der Reaktionsverlauf eine Funktion dreier Variablen ist: der TemperaturT, der Zeitt und der AufheizungsgeschwindigkeitT, wobei letztere Variable bisher von den auf diesem Gebiet arbeitenden Autoren außer Acht gelassen worden ist.Nachfolgend wird an Hand der zwei Voraussetzungen, daß a) die Geschwindigkeitsgleichung unter isothermen Bedingungen die Grenzform der Geschwindigkeitsgleichung unter dynamischen Bedingungen ist und b) die Temperaturänderung unter dynamischen Bedingungen sich auf die Erscheinungsfrequenz der Keime der neuen Phase auswirkt, eine theoretische Formulierung der Gesetzeg(x) für nicht-isotherme Bedingungen vorgeschlagen. Diese Formulierung wird als Funktion der Abweichung ausgedrückt, welche bei einer gegebenen Temperatur zwischen den Werten von Lnk _i (isotherm) und Lnk _d (dynamisch) im Diagramm Lnk=f(1/T) besteht.Die bei linearem Temperaturanstieg thermogravimetrisch durchgeführte Untersuchung der Zersetzung von Gips, von Calciumsulfat Semihydrat und von Calciumoxalat Monohydrat ermöglicht die vorgeschlagene theoretische Formulierung experimentell zu bestätigen.Um unter dynamischen Bedingungen eine gute kinetische Interpretation einer chemischen Reaktion zu erhalten, darf die Aufheizungsgeschwindigkeit den Wert von 20° pro Stunde nicht überschreiten.

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, : . , : (),t () ' ( ), , . : ) ) t(x) . Lnk _j () Lnk _d ( ) Lnk=f(1/T) . , , . , 20° .

     

Expedient synthesis of cyclopropane alpha-amino acids by the catalytic asymmetric cyclopropanation of alkenes using iodonium ylides derived from methyl nitroacetate

A highly enantioselective (up to 97.5% ee) and diastereoselective (95:5 dr trans/cis) Cu(I)-catalyzed cyclopropanation of alkenes using phenyliodonium ylide generated in situ from iodosobenzene and methyl nitroacetate is reported. The cyclopropanation took place with high enantioselectivity for a wide range of alkenes, and the reaction was performed at room temperature. 1-Nitrocyclopropyl esters are versatile building blocks to access the corresponding cyclopropane amino esters and aminocyclopropanes in two and three steps, respectively, from commercially available products.     

Kinetic parameters obtained from TG and DTG curves of acrylamide-maleic anhydride copolymers

The thermal behaviour of acrylamide-maleic anhydride copolymers was studied by thermogravimetric (TG and DTG) analysis. The obtained data permitted the calculation of activation energies and reaction orders of the decomposition steps by the Coats-Redfern and Freeman-Carroll methods.Thermal analysis shows four distinct peaks in the case of polyacrylamide and AAMA (71) copolymer and only three for AAMA (11) copolymer.In AA:MA (11) copolymers intermolecular imidization occurs only and thermal degradation is influenced more by the anhydride groups which are equal in number with the amide ones.

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Zusammenfassung Das thermische Verhalten von Acrylamid-Maleinsäureanhydrid-Kopolymeren wurde durch thermogravimetrische Analyse (TG und DTG) untersucht. Aus den erhaltenen Daten wurden die Aktivierungsenergien und Reaktionsordnungen der Zersetzungsschritte nach den Methoden von Coats-Redfern und Freeman-Carroll berechnet. Durch thermische Analyse können im Falle von Polyacrylamid und AAMA (71 (-Kopolymeren 4 Peaks und bei AA:MA (11) -Kopolymeren nur 3 Peaks unterschieden werden. Bei AAMA (1 1)-Kopolymeren verläuft nur eine intermolekulare Imidisierung und der thermische Abbau wird mehr durch die in gleicher Zahl wie die Amidgruppen vorliegenden Anhydridgruppen beeinflußt.

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T () — (). , - -, . : ( 71) , : 11 — . : 11 , , .

     

Simple, rapid and selective method using high-performance liquid chromatography for the determination of bretylium in plasma.

A high-performance liquid chromatographic method with ultraviolet detection has been developed for the determination of bretylium in plasma. Following a single-step solid-phase extraction procedure, bretylium is selectively isolated and well recovered from plasma. The assay sensitivity is 0.156 micrograms/ml from 250-microliters plasma samples and its linearity was assessed up to 40 micrograms/ml. The method is accurate (101.0 +/- 5.4%) and precise (maximum coefficient of variation of 8%). It provides a simple and time-saving alternative to existing methods and is particularly suitable for pharmacokinetic studies.     

Possible Mechanisms of Intercalation

Recent knowledge of the kinetics and intercalation mechanisms are summarized and accompanied by examples of intercalation reactions of water and ethanol into anhydrous vanadyl phosphate and redox intercalation of alkali metal cations into vanadyl phosphate dihydrate. Three possible mechanisms of intercalation are presented which are based on: (i) a concept of exfoliation of layers; (ii) the formation of stages and randomly stacked layers; (iii) co-existence of intercalated and non-intercalated parts of crystals of the host separated by an advancing phase boundary. The corresponding kinetic curves are ascribed to mechanisms (ii) and (iii).     

H-quadrupolar coupling-based analysis of stereochemical and regiochemical memory in the Pd-catalysed allylic alkylation of iso-cinnamyl type substrates employing the chiral monophosphine ligands ‘MOP’ and ‘MAP’

The reaction of iso-cinnamyl acetate with NaC(Me)(CO₂Me)₂, catalysed by Pd-‘MOP’ (MOP=2-methoxy-2′-diphenylphosphino-1,1′-binaphthalene) is known to proceed with a regiochemical memory effect that results in the predominant generation of the branched alkylation product. The analogous reaction employing ‘MAP’ as ligand (MAP=2-N,N-dimethylamino-2′-diphenylphosphino-1,1′-binaphthalene) proceeds with ‘normal’ regioselectivity to generate predominantly the linear isomer of product. A ²H-NMR based analysis, employing quadrupolar coupling in a chiral liquid crystal matrix, has been developed to facilitate the simultaneous study of the regiochemical and stereochemical outcome of the reaction of both enantiomers of iso-cinnamyl ester substrates in ²H-labelled but racemic samples. The analysis allows the comparison of relative rates of two competing isomerisation processes occurring in the π-allyl intermediates in the Pd-catalysed reaction, one of which facilitates asymmetric induction, the other resulting in loss of regiochemical memory. It is demonstrated that the two processes are partially coupled and that this then limits the attainment of high global enantiomeric excess in the branched product to reactions that proceed with low regiochemical retention. A key factor for the observation of high regiochemical memory is found to be the nucleophilicity of the malonate anion and the electrophilicity of the Pd-π-allyl intermediate with reduction in the reactivity of either partner resulting in the onset of substantial loss of memory.     

Modelisation of the Electric Field Linear Response of an Infinite Aggregate of All-Trans Hexatriene Chains by Electrostatic Interaction Model

A classical electrostatic polarization scheme using the additive distribution procedure has been applied to determine the longitudinal polarizability of an all-trans hexatriene molecule in an infinite stretched fiber. The parameters have been derived from ab initio CPHF/6-31G calculations and the electrostatic scheme has been validated via comparison with ab initio results on small clusters. Upon packing the polarizability of all-trans hexatriene increases by 7%. This small increase results from the balance between the enhancement of the polarizability due to collinear packing and the reduction associated with lateral packing.