Reaction of 5-phenylpenta-2,4-dienoic acid with benzene in trifluoromethanesulfonic acid

The reaction of 5-phenylpenta-2,4-dienoic acid with benzene in CF₃SO₃H, depending on the reaction conditions, gives three products, namely, 5,5-diphenylpent-2-enoic acid and tetralone and indanone derivatives. These carbocyclic compounds are formed through the addition of two benzene molecules to the starting diene acid and subsequent intramolecular acylation.

     

Nucleophilic Addition to Carbonyl Compounds. Competition Between Hard (Amine) and Soft (Phosphite) Nucleophile

Abstract

In the reaction mixture of carbonyl compound, amine and diethyl phosphite several different reactions are observed. The formation of aminophosphonate (Kabachnik- Fields reaction) is frequently accompanied with the formation of hydroxyphosphonate (Pudovik reaction) or product of its rearrangement. ^1–3 This is due to the presence of one electrophile (carbonyl compound) and two nucleophiles (amine and phosphite) in the reaction mixture, which may compete for the electrophilic center.     

Stereochemie und Mechanismus derPrins-Reaktion bei ausgeprägter Ladungsdelokalisierung im intermediären Carbeniumion

A detailed investigation of the reaction of 2.6-dimethyl-4-propenylphenol with formaldehyde showed thatPrins reactions of hydroxystyrenes in alkaline medium in most cases are kinetically controlled. By attack of formaldehyde, the same intermediate is generated from eithercis ortrans olefin. On further reaction by two independent pathways a 1.3-diol is formed by attack of a hydroxyl ion, or a 1.3-dioxane by reaction with additional formaldehyde via a hemiacetal. The steric course of the reaction is deduced from a discussion of the conformations of transition states.Prins reactions of arylolefins carrying strong +M-substituents proceed analogously under acylating conditions (e.g. in acetic acid) in weak acidic medium.

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Column Liquid Chromatography of Reducing Carbohydrates by Fluorometric Reaction Detection with a Pressurized Reactor Outlet

Abstract

The use of reaction detection In column liquid chromatography Is not always precluded by the limitation of the reaction time to one or two minutes. A closed pressurized reactor allows heating of the reaction mixture to temperatures that exceed the boiling point of the mixture to enhance reaction speed.     

Semi-synthesis of a novel hybrid isoxazolidino withaferin via chemoselective and diastereoselective 1,3-dipolar nitrone cycloaddition reaction

Abstract

A facile, atom-economic synthesis of isoxazilidino withaferin, a novel hybrid of withaferin A, has been accomplished via two-step reaction of nitrone synthesis followed by nitrone 1,3-dipolar cycloaddition. The reaction is highly chemoselective (preferential reaction only on one of the two double bonds present on withaferin A) and diastereoselective affording exclusively the cis-fused products. The structure was determined by detailed analysis of 1D, 2D NMR and mass spectral data.     

Kinetic study of the multistep thermal behaviour of barium titanyl oxalate prepared via chemical precipitation method

This study describes the physico-geometrical mechanism and overall kinetics for the multistep thermal dehydration of barium titanyl oxalate tetrahydrate (BTO). The thermal dehydration kinetics of BTO was studied at four different linear heating rates under non-isothermal conditions. The reaction kinetics was performed using differential scanning calorimetry (DSC) and the curves obtained were analysed using different isoconversional model-free equations and the values are found to be compatible with each other. The kinetic deconvolution principle is used for identifying the partially overlapped kinetic processes of the thermal dehydration of BTO, and it occurs in two stages. The overall reaction kinetics parameters calculated via kinetic deconvolution of the sample indicate the multistep nature of the process and the kinetic analysis of the non-isothermal data of this reaction model shows that the reaction is best described by Sestak–Berggren (m, n) empirical kinetic model. The prepared sample was identified and characterized by means of FT-IR, XRD, SEM, and TEM.

     

A New Heterocycle from the Reaction of N,N′-Dimethylthiourea with Diamino Phosphinoalkines

Abstract

The reaction of N,N′-dimethylthiourea with bis(dialkylamino)phosphinoalkines proceeds in two steps: 1) a transamination reaction, 2) ring closure by the nucleophilic attack of the sulfur atom at the C°C triple bond.     

The adequacy of the observed kinetic order in catalyst and the differential selectivity patterns to the hypothesis of the cooperative mechanism of catalysis of the Suzuki—Miyaura reaction

The generally accepted mechanism of the Suzuki—Miyaura reaction suggests a sequential activation of the substrate (aryl halide) and the reagent (arylboronic acid) by a palladium catalyst with the formation of unsymmetric biaryl as a result of a single turnover of the catalytic cycle, i.e., it is linear from the kinetic point of view. At the same time, the use of an unconventional kinetic approach based on the analysis of the differential selectivity of the reaction, rather than the regularities of catalytic activity, indicates the inadequacy of the linear mechanism, that is consistent with the hypothesis of a nonlinear (the so-called cooperative) mechanism of catalysis, in which the product is formed as a result of the substrate and reagent activation by two different palladium-containing intermediates in two parallel catalytic cycles. The experimentally observed low kinetic orders of the Suzuki—Miyaura reaction with respect to the concentration of the palladium catalyst precursor under the ligand-free conditions of catalysis are also consistent with the cooperative mechanism and can be due to the changes in the relative amount of the catalyst in two parallel catalytic cycles and/or to the process of catalyst deactivation.

     

The effect of a chemical reaction on the damping of the hydrodynamic modes and the spectrum of scattered light

Abstract

The roots of the hydrodynamic matrix for a two species chemically reactive system are obtained under assumptions for which the pressure fluctuations are decoupled from those in entropy and concentration. All roots are affected by the chemical reaction and attention is directed to the implications of the resulting dependence of the roots for the determination of chemical reaction rates from light scattering spectra     

Synthesis of 5-arylazo-2,4-dithiohydantoins

It was shown that during the interaction between 2-thiohydantoin and P₂S₅ in dioxane 2,4-dithiohydantoin (I) is formed, and without isolation from the reaction solution this compound forms 5-arylazo-2,4-dithiohydantoins (II–XI) with salts of diazone. The structure of two of these compounds has been determined by countersynthesis. When 5-arylazo-2,4-dithiohydantoins interact with amines the corresponding 4-substituted derivatives are formed.

     

Preparation,Crystal Structure and Properties of Spirophosphoranes Derived from Hydroxycarboxylic Acid Azides

Abstract

Spirophosphoranes are produced by reaction of 2–phenyl–1,3,2–dioxaphospholane with both 2- and 3–hydroxycarboxylic acid azides, whereas 1–phenyl–phospholane yields spirophosphoranes only upon reaction with the former. The structures of two spirophosphoranes have been determined by X-ray analysis.     

The Reaction of Phosphonyl Radicals with Hindered Carbonyl Compounds

Abstract

The reaction between phosphonyl radicals and substituted o-and p-benzoquinone has been studied by ESR. The addition of phosphonyl radicals to benzoquinone occurs at two sites, either at carbonyl oxygen or at double bond of the cycle. The reaction of phosphonyl radicals with p-benzoquinone and methylenquinones proceeds in a similar fashion.     

ETUDE DE QUELQUES REACTIONS DE LA TRIS(TERT-BUTYL)PHENYLPHOSPHINE

Abstract

The reaction of tris(tert-butyl)phenylphosphine with some hydrogen acceptors has been investigated. Triphenylcarbenium hexafluorophosphate allows to obtain a phosphonium salt: the possibility of preliminary formation of phosphenium with a P[sbnd]H bond during this reaction is discussed. With methyltrifluoromethanesulfonate, two pentacoordinated phosphorus compounds are isolated. Diethylazodicarboxylate gives rise to a σ³, λ⁵-phosphorane. The transient formation of phosphinidene and of 1,2-bis(ethylcarboxylate) 3-tris(tert-butyl)phenyldiazaphosphirine is discussed.     

Simple voltammetric approach for characterization of two-step surface electrode mechanism in protein-film voltammetry

Many enzymes embedding multivalent metal ions or quinone moieties as redox-active centres undergo electrochemical transformation via two successive electron transfer steps. If electrochemical features of such redox enzymes are analyzed with “protein-film voltammetry”, one frequently meets a challenging reaction scenario where the two electron transfers take place at the same formal potential. Under such conditions, one observes voltammogram with a single oxidation-reduction pattern hiding voltammetric features of both redox reactions. By exploring some aspects of the two-step surface EECrev mechanism one can develop simple methodology under conditions of square-wave voltammetry to enable recognizing and characterizing each electron transfer step. The method relies on the voltammetric features of the second electron transfer, which is coupled to a follow-up chemical reaction. The response of the second electron transfer step shifts to more positive potentials by increasing the rate of the chemical reaction. The proposed methodology can be experimentally applied by modifying the concentration of an electrochemically inactive substrate, which affects the rate of the follow-up chemical reaction. The final voltammetric output is represented by two well-separated square-wave voltammetric peaks that can be further exploited for complete thermodynamic and kinetic analysis of the EECrev mechanism.

     

Preliminary Evaluation of Luminescent Techniques for the Determination of Bleomycin

Abstract

The luminescence characteristics of the reaction between bleomycin and fluorescamine have been investigated with respect to the optimum pH for fluorophor formation and stability. Thin-layer chromatography separates the reaction product into two species. Direct phosphorescence properties of bleomycin have also been studied. The results confirm the potential of luminescence methods for the determination of bleomycin.     

OXIDATIVE ADDITION REACTIONS OF d8 COMPLEXES. I. CHLORINE OXIDATION OF TETRACHOLOROPALLADATE (II)

Abstract

The reaction of Na₂PdCl₄ with chlorine in aqueous acid solution proceeds in two stages: oxidation of the complex to a Pd(IV) species followed by a slower substitution reaction. The oxidation reaction is first order in complex and first order in chlorine. At high chloride concentration, a six-coordinate palladium(II) intermediate is formed, which is oxidised via an outer-sphere type mechanism. Oxidation of the chloroaquopalladium(II) species present at low chloride concentration occurs via a different mechanism, probably involving coordination of the oxidant in a ‘quasiinner-sphere’ mechanism.     

Darstellung und thermische Zersetzung von Lithiumcyanuraten Eine einfache Methode zur Gewinnung von wasserfreiem Lithiumcyanat

Zusammenfassung Die Darstellung von Mono-, Di- und Tri-Lithiumcyanurat durch Umsetzung von Cyanursäure mit LiOH bzw. Li₂CO₃ in hochsiedenden Alkoholen und durch lösungsmittelfreie Festkörperreaktion wird beschrieben. Die Festkörperreaktionen werden mit Hilfe thermoanalytischer Methoden untersucht. Die Reaktion mit LiOH erfolgt in zwei Schritten und ergibt bei 400°C. Trilithium-cyanurat. Unter denselben Bedingungen wird mit Li₂CO₃ nur Dilithium-cyanurat gebildet. Die Thermolyse von Trilithium-cyanurat bei 550°C liefert in hoher Ausbeute Lithiumcyanat und stellt somit eine einfache Methode zur Darstellung dieser Verbindung in wasserfreier Form dar.

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Formation and thermolysis of lithium cyanurates (a simple preparation of anhydrous lithium cyanate)

The formation of mono-, di- and tri-lithium cyanurate by reaction of LiOH or Li₂CO₃ with cyanuric acid has been investigated as a solid state reaction and by using high boiling alcohols as reaction medium. For investigating the solid state reactions thermoanalytical methods were used. The reaction with LiOH proceeds in two steps yielding trilithium cyanurate at 400°C. Under the same conditions only dilithium cyanurate is formed by reaction with Li₂CO₃. Lithium cyanate is obtained in high yields by thermolysis of trilithium cyanurate at 550°C. This procedure is therefore a simple method in synthesizing pure anhydrous lithium cyanate.

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Herrn Univ.-Prof. Dr.O. Kratky zum 70. Geburtstag gewidmet.     

Zum Abbau von polycyclischen aromatischen Kohlenwasserstoffen

Summary Eight further polycyclic aromatic compounds (PCA), chosen as model substances, were submitted to ozonolysis in dilute aqueous systems. The products were derivatized, separated by capillary gas-chromatography, and identified mass-spectrometrically. Aromatic carboxy acids and oxalic acid, derivatives of indane and fluorene as well as sulfones and sulfonic acids occur as reaction products. With one exception the degradation reactions of the PCA are very fast and the composition of the reaction products is largely independent of the ozonation time. The influence of ultra-sound on the reaction path has been investigated.

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Herrn Prof. Dr. W. Fresenius zum 75. Geburtstag gewidmet

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Teil II: Fresenius Z Anal Chem (1978) 293:205–207     

Testosterone Heptafluorobutyrates: Derivatives for Gas Chromatography

Abstract

The reaction of testosterone with heptafluorobutyric anhydride, in the presence of pyridine or collidine, leads to two diheptafluorobutyrate (HFB) derivatives. These compounds are believed to be the di-HFB esters of 2,4-androstadien-3, 17β-diol (A) and 3, 5-androstadien-3, 17β-diol (B), with A as the major product. This is similar to the reaction with silylating reagents which leads to two isomeric enol ethers. In benzene or acetone solution, and in the absence of an organic base, the same two isomers are formed, but with B as the major product. Although the latter reaction has been recommended for quantitative work, the formation of isomeric enol esters has not been noted. Since the products are not stable in the reaction medium, the method is not entirely satisfactory. The reaction in pyridine solution should be suitable for quantitative work; the products are stable in solution and can be detected in subnanogram amounts.