Acid and complex-forming properties of tetrapyrazinoporphyrazines

The reactions of octaethyl- and octaphenyltetrapyrazinoporphyrazines with dimethyl sulfoxide were studied. The compositions of the resulting complexes with proton-transfer were determined. The reaction of the formation of a magnesium(II) octaethyltetrapyrazinoporphyrazine complex in pyridine was studied. Kinetic parameters of the reaction were determined and assumptions on the reaction mechanism were made.     

Thermal stability of substituted poly-xylylenes

The insertion of meta units in the chain of poly-p-xylylene decreases both the onset temperature of oxidative degradation and the rate of decomposition.Functionalization of the polymer with chlorine and sulphonic groups makes the chain more resistant to high temperature treatments, notwithstanding the low stability of the substituent groups.

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Zusammenfassung Die Einführung von Metaeinheiten in die Kette von Poly-p-xylen setzt sowohl die Einsetztemperatur des oxydativen Abbaues als auch die Zersetzungsgeschwindigkeit herab. Die Einführung von Chlor und Sulfogruppen erhöht trotz der geringen Stabilität der Substituenten die Temperaturbeständigkeit der Kette.

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取代苄基瞵酸脂与取代苯甲醛反应的动力学研究

本文报导几种中等活性的瞵酸脂与各种取代苯甲醛反应的动力学研究, 并考查了中等活性的瞵酸脂组分及中等活性的醛组分上不同取代对反应速度的影响。     

Kinetic studies of some substituted hexarhodium carbonyl clusters

Reactions of the halides X- (X- = chloride, bromide or iodide) with the substituted cluster Rh6(CO)15(PPh3) in oxygen-free chloroform lead to [Rh5(CO)14(PPh3)]-, Rh(CO)2(PPh3)2X and [Rh(CO)2X2]- in the molar ratios 2:1: approximately 13. Oxidation by the solvent is assumed to lead to most of the Rh(I) product, and the stoichiometry for reactions with I- can be defined as 4Rh6(CO)15(PPh3) + 27I- + 12CHCl3 --> 2[Rh5(CO)14(PPh3)]- + Rh(CO)2(PPh3)2I + 13[Rh(CO)2I2]- + 6C2H2Cl4 + 4CO + 12Cl-. This can be rationalized quite simply with the aid of a few generally justifiable assumptions. Rate constants for reactions with bromide increase to a limiting value with increasing [Br-] in a way that shows that breaking of one Rh-Rh bond, with an unusual closo to nido structural change, is rate determining. This opening of the cluster might be spontaneous or solvent induced. To complete the reaction, the bromide has to compete with the reverse nido to closo change. The same closo to nido change is also a major rate determining step for reactions with P(OPh)3 in oxygen-free solutions, and for reactions with bromide in oxygenated solutions in the presence of trifluoroacetic and some other acids. The limiting rates increase slightly with increasing basicity of the ligands P(p-XC6H4)3 along the series X = F3C, Cl, F, H and MeO. Activation parameters for these reactions are reported.     

Kinetic stability of 1,1,1-Trifluoroethane

1,1,1-Trifluoroethane has been decomposed in comparative rate single-pulse shock-tube experiments. The rate expression for elimination at ca. 2.5 bar and in the temperature range of 1050 to 1200 K has been found to be The experimental conditions appear to be such that the unimolecular reaction is at the beginning of the fall-off region and we find that for step sizes down between 500 and 1000 cm⁻¹ the high-pressure rate expression is in the range where the smaller rate parameters refer to the larger step size down. The results are compared with those from an earlier study and the anomalously high A-factor is noted. It is suggested that the existing rate expressions for the fluorinated ethanes may need to be reevaluated. © 1998 John Wiley & Sons, Inc., Int J Chem Kinet: 30: 621–628, 1998     

Hydroxypropyl substituted nitrogen bridgehead fused cyanopyridines

The reaction of 2-hetaryl-2-(tetrahydro-2-furanyliden)acetonitriles with substituted acetonitriles as C-nucleophiles has been investigated and the mechanism of the reaction has been suggested. A base promoted Michael addition of the substituted acetonitriles to 2-hetaryl-2-(tetrahydro-2-furanyliden)acetonitriles followed by ring transformations has provided novel convenient synthetic methods to nitrogen bridgehead fused cyanopyridines bearing hydroxypropyl side chain. The structures of obtained compounds have been established based on NMR spectroscopy investigation and X-ray diffraction data.     

Mass spectra of substituted 4-aminopiperidines with a shielded nitrogen atom

The principal fragmentation pathway of 4-aminopiperidines under the influence of electron impact are determined by charge localization on the nitrogen atom of the piperidine ring or on the nitrogen atom of the substituent in the 4 position. In the case of electron-donor substituents in the 4 position and in the absence of a substituent attached to the nitrogen atom of the polysubstituted piperidine ring the charge is primarily localized on the nitrogen atom of the substituent; this is expressed in the specific fragmentation pathways. The principles found in this research make it possible to establish the structures of nitrogen-containing compounds that are similar to the investigated compounds.Communication 10 in the series Application of mass spectrometry in structural and stereochemical studies. See [1] for Communication 9.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 72–77, January, 1981.     

Kinetic stability of tetra(1,2,5-thiadiazolo)porphyrazine in the system nitrogen-containing base-dimethyl sulfoxide

The behavior of tetra(1,2,5-thiadiazolo)porphyrazine in dimethyl sulfoxide has been studied, and fairly high stability of the resulting proton-transfer complex has been revealed. The complex is kinetically unstable in strongly basic media. The effects of the nitrogen-containing base and NH acidity of the porphyrazine macrocycle on the rate and activation parameters of decomposition of the proton-transfer complex have been estimated.     

Kinetic stability of complex molecular clusters

This investigation is concerned with modeling the evaporation, or decay, of n-nonane molecular clusters. We use a unique cluster decay model that was first developed to estimate the decay time scale of argon clusters using molecular-dynamics simulations. In this study we seek to enhance the model so that it represents a more complex cluster decay dynamic, suitable for n-nonane clusters. Experimental measurements of nucleation rates of n-nonane droplets have been used to deduce the rate at which a molecule escapes from the cluster. Typically for an n-nonane cluster containing 40 molecules, at an experimental temperature of 225 K, the empirical decay time, which is the inverse of the decay rate, is estimated to be 50 ns. For this time scale, the direct observation of n-nonane cluster decay from a molecular-dynamics trajectory is not feasible, since decay events are so rare. However, the cluster decay model uses a combination of molecular dynamics and stochastic dynamics in order to resolve the problem associated with long decay time scales. The model is based on a Langevin treatment that views cluster decay as single-particle escape from a confining potential of mean force. It is used to predict kinetic decay times of n-nonane clusters. We discover this result differs significantly from a classically derived decay time scale determined from a continuum thermodynamic treatment of the population balance equations of clusters. However, the dynamically generated results obtained from the kinetic decay model compare more favorably than the classical results with the empirical decay times that are deduced from experimental measurements of n-nonane clusters.     

Kinetic stability of water-dispersed oil droplets encapsulated in a polyelectrolyte multilayer shell

The original theoretical model of polyelectrolyte adsorption onto water-dispersed colloid particles is extended to the system of polydisperse droplets of sunflower oil. Polycation (poly(allylamine hydrochloride)) and polyanion (poly(sodium 4-styrenesulfonate)) are taken in the theoretically projected concentrations to perform Layer-by-Layer assembly of a multilayer shell on the surface of oil droplets preliminary stabilized with a protein emulsifier (bovine serum albumin). The velocity of gravitational separation in suspension of encapsulated oil droplets is theoretically predicted and experimentally measured depending on the coating shell's thickness, aiming to clarify the mechanism to control over the separation process. Combining the theory and experimental data, the mass density of a polyelectrolyte multilayer shell assembled in a Layer-by-Layer fashion is obtained. Polyelectrolyte multilayer coated oil droplets are characterized by means of ζ-potential, and particle size measurements, and visualized by scanning electron microscopy.     

The thermal stability of two substituted thioamides

A derivatographic investigation was performed on the thermal behaviour of three thioamides and the nonisothermal kinetic parameters for the liquid-phase decomposition of N-acetylthiobenzamide were determined.     

Kinetic stability of complexes of conjugated macroheterocycles with metals in a proton-donor medium

The rate of decomposition of conjugated macroheterocyclic ligands containing isoindole and 1,2,4-thiadiazole residues has been studied together with the rate of dissociation of their complexes with copper, cobalt, and zinc in a proton-donor medium at three temperatures. Rate constants and activation parameters have been determined for the decomposition of the macrocyclic ligands and the dissociation of their complexes.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 268–271, February, 1990.     

EPR study of protonation of substituted three-member nitrogen heterocycles

The kinetics of fast proton transfer from 4-triphenylmethyl-6-tert-butyl-3-chloro-2-hydroxyphenoxyl to some three-member nitrogen heterocycles (1,2-dimethylaziridine, 1,2,3-trimethyldiaziridine, and 2-methoxymethyl-3-methyl-3-ethylhydroxyaziridine) were investigated by EPR and their kinetic basicity was estimated in comparison to proton acceptors with known pK. A comparison of the thermodynamic parameters of protolysis of the radical used in toluene solutions of the three-member heterocycles studied and known bases allowed estimating the pK of these heterocycles (7-5).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 60–65, January, 1991.     

On the stability of substituted 1,2-diazaallyl radicals

The heats of formation of fully optimized methyl-ethyl-and 2-propyl-substituted 1,2-diazaallyl radicals and their parent compounds have been calculated at the level of semiempirical quantum-chemical methods (MNDO-HE, AM1-HE). The resonance energies and the stabilization energies were found to be 30–60 kJ mol^–1 and around 60 kJ mol^–1, respectively. From AM1-HE calculations, the group values _fH^°[C–(N_A)(H₂)]=90.4 kj mol^–1, _fH^°[C–(N_A)(C)(H)]=94.8 kj mol^–1 were obtained.

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-, - 2- 1,2- - (MNDO-HE, AM1-HE). 30–60 /, 60 /. AM1-HE _fH^°[C–(N_A)(H₂)]=90,4 ͆/, _fH^°[C–(N_A)(C)(H)]=94,8 ͆/.

     

N,N-二甲基甲酰胺吸收氮氧化物对1,2-二芳基肼的氧化

报道了将NO~X废气吸收在N,N-二甲基甲酰胺(DMF)中氧化1,2-二取代芳基肼制备对称的偶氮化合物。结果表明,DMF-NO~X是一种优良的氧化体系,在温和的条件下,高产率地将8个1,2-二取代芳基肼氧化为相应的偶氮化合物。     

Kinetic barriers in the isomerization of substituted ureas: implications for computer-aided drug design

Urea derivatives are ubiquitously found in many chemical disciplines. N,N′-substituted ureas may show different conformational preferences depending on their substitution pattern. The high energetic barrier for isomerization of the cis and trans state poses additional challenges on computational simulation techniques aiming at a reproduction of the biological properties of urea derivatives. Herein, we investigate energetics of urea conformations and their interconversion using a broad spectrum of methodologies ranging from data mining, via quantum chemistry to molecular dynamics simulation and free energy calculations. We find that the inversion of urea conformations is inherently slow and beyond the time scale of typical simulation protocols. Therefore, extra care needs to be taken by computational chemists to work with appropriate model systems. We find that both knowledge-driven approaches as well as physics-based methods may guide molecular modelers towards accurate starting structures for expensive calculations to ensure that conformations of urea derivatives are modeled as adequately as possible.     

Metal complexes of tetrapyrazinoporphyrazines — effective catalysts of the oxidation of mercaptans

The catalytic activity of the tetrapyrazinoporphyrazine complexes of cobalt and iron have been studied in the oxidation of aliphatic mercaptans by molecular oxygen. n-Butyl mercaptan was used as the model compound. The metallotetrapyrazinoporphyrazines tested exhibited a considerably higher catalytic activity than cobalt phthalocyanine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1257–1259, September, 1984.