Zinc reaction with diphenylantimony and diphenylbismuth chlorides in aprotic solvents

Products of zinc oxidation with diphenylantimony and diphenylbismuth chlorides in aprotic solvents are established. The effective adsorption constants of the reagents on the metal surface and the rate constants and activation energies of the processes under study are calculated.     

Effect of polar aprotic solvents and organometallic catalysts on the reaction of alcohols with isocyanates

DMF and DMSO catalyse the reaction of butanol with PhNCO but inhibit that with aliphatic isocyanates, due to formation of an active 1:1 charge transfer complex with the aromatic isocyanate. Similarity was found in the mode of catalysis of the urethane reaction with these solvents to that with tert, amines. Various organometallic compounds were tested as catalysts for urethane formation with aliphatic isocyanates. Those that gave fast addition to the NCO group, such as tributyltin oxide, Zr(OBu)₄ and Zr(acac)₄, were the strongest catalysts. In the presence of organometallic catalysts, urethane formation was the sole reaction and trimerization of the isocyanate was suppressed.     

Kinetics of the reaction of malachite green and crystal violet with formally aprotic solvents

The stability of malachite green and crystal violet has been studied spectrophotometrically in 17 formally aprotic media. The cations of these compounds react with solvents that are Lewis bases; the pseudo-first order rate constant values (k') are dependent on Gutmann's donor numbers. The sensitivity of the two dyes to the solvent effect correlates with the net charge on their central carbon atoms.     

Kinetics of reaction of copper with substituted benzyl chlorides in dipolar aprotic solvents

The reaction of copper with benzyl chlorides in dipolar aprotic solvents has been investigated. The kinetic and thermodynamic parameters of the reaction of copper with benzyl chloride in dimethyl sulfoxide, dimethylacetamide, and hexamethylphosphoramide have been obtained. Hammett plots of log (k/k°) versus the substituent constant σ gave good correlation. The structure of the organic group has little effect on the rate of reaction of benzyl chloride with copper. The kinetic and thermodynamic parameters were correlated with donor number of solvent (DN). The ratio k_RBr/k_RCl and Hammett ρ values provide evidence in favor of the halogen atom transfer mechanism. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 547–555, 2007     

The kinetics of reaction of copper with substituted benzyl bromides in dipolar aprotic solvents

The reaction of copper with benzyl bromides in dipolar aprotic solvents has been studied. There are no linear or other simple relations between ε, 1/ε, Y, P, n, and the rate of reaction. The activity of the solvent is determined by donor number (DN) in reaction under consideration. The kinetic and thermodynamic parameters of the reaction of copper with benzyl bromide in dimethyl sulfoxide (DMSO) have been clarified. Hammett plots of log (k/k°) vs. the substituent constant σ gave good correlations (ρ = 0.18, S_ρ = 0.02, r = 0.961 in dimethyl sulfoxide and ρ = 0.21, S_ρ = 0.02, r = 0.947 in dimethylacetamide (DMAA)). The structure of the organic group has little effect on the rate of reaction of benzyl bromide with copper. The Hammett ρ value also depends on DN. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 496–501, 2005     

The effect of the medium polarity on the mechanism of the reaction of hydroxybenzenes with hydrazyl radical in aprotic solvents

Mechanisms of the reaction of di- and trihydroxybenzenes with 2,2′-diphenyl-1-picrylhydrazyl (stable radical) in aprotic media of different polarity have been elucidated by experimental and quantum-chemical methods. Kinetic, stoichiometric, and activation parameters of the reaction have been determined. In benzene (nonpolar solvent), the studied reaction occurs via the hydrogen atom transfer mechanism; in the polar solvent with weak ionizing ability (i.e. DMSO), the reaction predominantly occurs via the faster mechanism of coupled electron and proton transfer.     

Reaction of metals with benzenediazonium tetrafluoroborate in aprotic solvents

The reaction of metals and glassy carbon with benzenediazonium tetrafluoroborate (BDFB) in aprotic solvents has been studied. During contact of Pt, Au, Ag, Pd, or V with glassy carbon in concentrated diazonium salt solution no change of color was observed. For Al, Ca, Cr, Cu, Fe, Ga, In, Mg, Li, Na, or Zn the process was accompanied by a rapid solution color change, rapid N₂ release and the loss of metal sample mass. The copper metal ionization-dissolution was studied by ultraviolet and visible absorption spectroscopy, along with gravimetric and volumetric measurements. A dissolution mechanism was proposed based on kinetic, infrared, and X-ray diffraction data. The 432 nm absorption band appearing after Cu-BDFB reaction indicates formation of the mixed complex [Cu(N₂C₆H₅·(N≡C-CH₃)₃]⁺ where the copper atom is covalently bonded to the azophenyl radical and coordinated to acetonitrile (ACN). This complex is thermodynamically unstable and decomposes slowly to a colorless crystalline and a black amorphous phase. The crystalline phase was identified as [Cu(NC-CH₃)₄]BF₄. The amorphous phase is a mixture of products formed by azophenyl and phenyl radical condensation.      

Oxidation of magnesium with carbon tetrachloride in aprotic solvents

Formal kinetic regularities and the end products of oxidation of magnesium with carbon tetrachloride in the environment of dipolar aprotic solvents were revealed. The effective equilibrium constant, enthalpy and entropy of adsorption of carbon tetrachloride and N,N-dimethylformamide at a metal surface, the rate constant and activation energy of the investigated reaction were determined. The effect of temperature on the dependence of the process on the donor properties of the used coordinating solvents was established and justified. A probable scheme of the process was suggested.     

Proton solvation in protic and aprotic solvents

Protonation pattern strongly affects the properties of molecular systems. To determine protonation equilibria, proton solvation free energy, which is a central quantity in solution chemistry, needs to be known. In this study, proton affinities (PAs), electrostatic energies of solvation, and pK_A values were computed in protic and aprotic solvents. The proton solvation energy in acetonitrile (MeCN), methanol (MeOH), water, and dimethyl sulfoxide (DMSO) was determined from computed and measured pK_A values for a specially selected set of organic compounds. pK_A values were computed with high accuracy using a combination of quantum chemical and electrostatic approaches. Quantum chemical density functional theory computations were performed evaluating PA in the gas‐phase. The electrostatic contributions of solvation were computed solving the Poisson equation. The computations yield proton solvation free energies with high accuracy, which are in MeCN, MeOH, water, and DMSO ?255.1, ?265.9, ?266.3, and ?266.4 kcal/mol, respectively, where the value for water is close to the consensus value of ?265.9 kcal/mol. The pK_A values of MeCN, MeOH, and DMSO in water correlates well with the corresponding proton solvation energies in these liquids, indicating that the solvated proton was attached to a single solvent molecule. © 2016 Wiley Periodicals, Inc.     

Rotational diffusion in aprotic and protic solvents

We present the orientational relaxation times in protic and aprotic solvents for rose bengal in its lowest excited singlet state. The method uses a mode locked dye laser for polarized excitation, and time correlated single photon counting for determination of the time resolved polarized fluorescence. The observed orientational decay for the dipolar aprotic solvents and the alcohols are in agreement with the values predicted by the Stokes-Einstein diffusion equation. In the latter solvents, volume and shape corrections must be made for attachment of the alcohol to the two anion sites of the dye molecule. The solvent N-methylformamide, however, shows rose bengal reorienting much faster than the alcohols. Our interpretation of this data suggests that agreement with the Stokes-Einstein equation (stick boundary conditions) is coincidental. We propose a solvent torque model in which the solvent interaction at each anion site of rose bengal controls the deviations from an expected slip boundary condition. This qualitative model is used to correlate our data as well as relevant data in the literature. The values in picoseconds for the observed orientational relaxation times are given in parenthesis; acetone (70), DMF (160), DMSO (420), MeOH (190), EtOH (450), isopropanol (840), NMF (500).     

Complexes of acid amides with aprotic polar solvents IV. Complexes of poly(acid amides) with aprotic solvents

The process of solid-phase cyclodehydration of films cast from solutions of poly(acid amides) (PAA) in dimethylformamide, dimethylacetamide and N-methyl-2-pyrrolidone has been investigated by mass-spectrometric thermal analysis (MTA). It is shown that MTA is a structure-sensitive method making it possible to follow the appearance and changes in the character of ordered structures formed in PAA films. The authors relate these structures to the process of crystallization of complexes of PAA with aprotic polar solvents.     

Complexes of acid amides with polar aprotic solvents

A study was made of the effects of organic carbonyl-containing compounds and inorganic acids on the character of complex formation of the solvent with polyacid amides, and in particular on the frequency of three-dimensional networks formed by hydrogen-bonds in solid polyacid amide films. It was found that the characteristics of the solid-phase cyclodehydration process can be varied within a wide range by means of active additives.

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Zusammenfassung Die Wirkung von organichen carbonyl-enthaltenden Verbindungen und anorganischen Säuren auf den Charakter der Komplexbildung von Lösungsmitteln mit Polysäureamiden wurde untersucht, inbesondere was die Häufigkeit von dreidimensionalen, durch Wasserstoffbindungen in den festen Polysäureamidfilmen zustande kommenden Vernetzungen betrifft. Es wurde festgestellt, daß die Kennwerte des Cyclodehydratisierungsprozesses in fester Phase innerhalb weiter Grenzen durch aktive Additive variiert werden können.

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Complexes of amic acids with polar aprotic solvents

The polymer-polymer interactions of a polyamic acid (PAA) with polybases (polyvinylpyrrolidone, polyacrylonitrile and polyvinylpyridine) were studied by means of massspectrometric thermal analysis (MTA), TG, DTA and IR-spectroscopic methods in solution and in the solid state. The polybases were shown to substitute the solvent from its complex with PAA, forming H-bonds or salt-type polycomplexes with PAA. The MTA method proved to be very informative for the investigation of interpolymer interactions in the solid state.

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Zusammenfassung Mittels MS-Thermoanalyse (MTA), TG, DTA und IR-Spektroskopie wurden sowohl in Lösung als auch im festen Aggregatzustand die Polymer-Polymer-Wechselwirkungen zwischen Polyamicsäure (PAA) und Polybasen (Polyvinylpyrrolidon, Polyacrylnitril und Polyvinyl-pyridin) untersucht. Polybasen ersetzen das Lösungsmittel in seinem Komplex mit PAA und bilden dabei mit PAA Wasserstoffbindungen oder salzähnliche Polykomplexe. Die MTA-Methode erwies sich bei der Untersuchung von interpolymeren Wechselwirkungen im festen Aggregatzustand als sehr informativ.

     

Complexes of amic acids with polar aprotic solvents

The nonisothermal kinetics of solid-phase cyclodehydration of poly(4,4'-oxydiphenylene) pyromellitamic acid has been investigated with the aid of mass-spectrometric thermal analysis. It was established that depending on the method of preparation of the samples, the kinetics of cyclization vary from the polychromatic (film) to the monochromatic (fiber) kinetics. The possibility of the catalysis of the process as a result of the formation of complexes between the polymer and imidazole and its substituents is shown.

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Zusammenfassung Mittels massenspektrometrischer Thermoanalyse wurde die nichtisotherme Kinetik der Cyclodehydratation von Poly(4,4'-Oxydiphenylen)pyromellithsäure im festen Zustand untersucht. Es wurde festgestellt, daß die Cyclisationskinetik in Abhängigkeit vom Herstellungsverfahren der Proben von polychromatisch (Film) bis monochromatisch (Fiber) variiert. Die Möglichkeit der Katalyse des Vorganges infolge von Komplexbildung zwischen Polymer und Imidazol und seiner Substituenten wird gezeigt.

     

Complexes of acid amides with polar aprotic solvents

Solid complexes of bis(N-phenyl)-pyromellitic acid amide with equimolar binary mixtures of dimethylformamide, dimethylacetamide, dimethylsulfoxide and N-methylpyrrolidone were prepared and studied by evolved gas analysis using mass spectrometry. The activity sequence of these compounds in forming complexes with bis(N-phenyl)-pyromellitic acid amide was established.