Molecular structure and mechanisms of unimonomolecular decomposition of primary <Emphasis Type="Italic">N</Emphasis>-nitramines

By means of nonempirical and the density functional methods the geometrical parameters, the enthalpies of formation of the compounds and radicals, and the dissociation energies of the N-NO₂ bond in primary and secondary N-nitramines were evaluated. The tendencies to the variation of spatial arrangement, of the formation enthalpies, and of the dissociation energies in the series of simplest N-nitramines were analyzed. Alternative mechanisms of the initial stage of the gas phase unimolecular decomposition were considered. It is noted that among all the processes of unimolecular decomposition the formation and destruction of aci-form according to the complex multy-stage mechanism was the most energetically favored.     

Energy barriers to gas-phase unimolecular decomposition of mono- and dinitrotoluenes

Alternative paths of gas-phase unimolecular decomposition of three nitrotoluenes and six dinitrotoluenes, in particular homolytic dissociation of the C–N bond, nitro–nitrite rearrangement, intramolecular hydrogen transfer from the methyl to nitro group with formation of isomeric aci-nitrotoluenes, and various paths involving formation of bicyclic intermediates, have been studied at the DFT B3LYP/6-31+G(2df,p) level of theory using GAUSSIAN 09 software package. The most energetically favorable path for o-nitrotoluene and 2,3-, 2,4-, 2,5-, and 2,6-dinitrotoluenes is the formation of aci-nitrotoluenes. The effect of the substrate structure on the competition between different mechanisms of these reactions has been analyzed.     

Study of the reaction of 3,6-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-<Emphasis Type="Italic">о</Emphasis>-benzoquinone with organozinc and organocadmium compounds

The effect of substituents in the reactions of 3,6-di-tert-butyl-о-benzoquinone with organozinc and organocadmium compounds, leading to three types of products: 3-alkyl-6-tert-butyl-о-benzoquinones, 4-alkyl-3,6-di-tert-butyl-о-benzoquinones, and 2-alkoxy-(or 2-phenoxy)-3,6-di-tert-butylphenols. Correlation analysis gave evidence to show that the first- and second-type products are formed by nucleophilic 1,2- and 1,4-addition, while substituted phenols result from single-electron transfer.     

Diastereoselective 1,3-Dipolar Cycloaddition of Nitrones to 1<Emphasis Type="Italic">H</Emphasis>-Pyrrole-2,3-diones. Synthesis of pyrrolo[3,2-<Emphasis Type="Italic">d</Emphasis>]isoxazoles

1H-pyrrol-2,3-diones react with nitrones affording substituted pyrrolо[3,2-d]isoxazoles. The structures of ethyl (3R*,3aR*,6aR*)-6-benzyl-3-(4-bromophenyl)-4,5-dioxo-2,6a-diphenylhexahydro-3aHpyrrolo[ 3,2-d]isoxazole-3a-carboxylate and dimethyl (3R*,3aR*,6aS*)-3-(4-bromophenyl)-4,5-dioxo-2,6-diphenyltetrahydro-3aH-pyrrolo[3,2-d]isoxazole-3a,6a(4H)-dicarboxylate were proved by single-crystal X-ray analysis.     

Electrophilically activated nitroalkanes in the synthesis of 6,7-dihydro-1<Emphasis Type="Italic">H</Emphasis>-cyclopenta[<Emphasis Type="Italic">g</Emphasis>]perimidines

A highly efficient synthetic route to 6,7-dihydro-1H-cyclopenta[gh]perimidines has been proposed on the basis of a novel reaction of nitroalkanes with 4,5-diaminoacenaphthene in the presence of polyphosphoric acid. The reaction involves phosphorylation of the aci-nitro compound, followed by intramolecular cyclization.     

DMT [(−)-(2<Emphasis Type="Italic">R</Emphasis>,3<Emphasis Type="Italic">R</Emphasis>)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol], a highly efficient host compound for nitroaromatic guests: selectivity,X-ray and thermal analyses

In this work, we reveal that the compound (?)-(2R,3R)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol (DMT) is a highly efficient host material for nitroaromatics o-nitrotoluene (o-NT), m-nitrotoluene (m-NT), p-nitrotoluene (p-NT) and nitrobenzene (NB). Each of these guests was included with a 2:1 host:guest ratio. The host displayed selectivity for p-NT and NB when these guests were mixed in equimolar proportions with any one of the other guest solvents, and the host recrystallized from this binary mixture. A selectivity order for the host in these conditions was thus noted to be NB?≈?p-NT?>?o-NT?>?m-NT. Furthermore, guests were also mixed in non-equimolar proportions and the host behaviour analysed, the results of which were in accordance with observations from the equimolar studies. Additionally, an equimolar quaternary experiment of all four guests provided a somewhat adjusted host selectivity order [p-NT (39.9%)?>?NB (30.2%)?>?m-NT (17.1%)?>?o-NT (12.8%)]. Single crystal diffraction analyses of all four complexes showed the crystals to share the same host packing, and comparable host–guest interactions were observed in each. However, thermal analyses, both DSC and TG, showed that the preferred guests p-NT and NB formed complexes with increased relative thermal stabilities, and this observation correlated with the selective behaviour of the host in competition experiments.     

Effect of donor and acceptor properties of solvents on the kinetics of photoreduction of sterically hindered <Emphasis Type="Italic">о</Emphasis>-benzoquinones

Effect of the solvent nature on the kinetics of photoreduction of 3,6-di-tert-butyl-1,2-benzoquinone and its six derivatives in the presence of N,N-dimethylaniline and 4-(N,N-dimethylamino)benzaldehyde has been investigated. It has been found that for the о-quinone—amine pair, for which the free energy change of electron transfer is ΔG_e > +0.11 eV, the rate constant of о-quinone photoreduction k_H decreases proportionally to the increase in the acceptor number of the solvent. For the о-quinone—amine pair with ΔG_e < +0.11 eV, the k_H value decreases proportionally to the increase in the donor number of the solvent. It has been established that the enhancement of the electron-acceptor properties of the solvent leads to the emergence of kinetic isotope effect for the reactant pairs of 3,6-di-tert-butyl-1,2-benzoquinone and 4,5-dimethoxy-3,6-di-tert-butyl-1,2-benzoquinone with N,N-di-methylaniline (ΔG_e = +0.11 and +0.22 eV, respectively).     

Stereodirected reactions of salicilaldehyde derivatives with <Emphasis Type="Italic">tert</Emphasis>-butyl 3(4)-hydroxy-2(3)-(3-methylbut-2-enyl)- piperidine-1-carboxylates as an efficient preparation procedure of tetrahydropyran derivatives fused with a piperidine ring

Reaction of salicilaldehyde and its derivatives with unsaturated cis-, trans-alcohols of the piperidine series in the presence of methyl orthoformate and p-toluenesulfonic acid led to the formation of a new heterocyclic system connecting four fuzed rings (two tetrahydropyrans, a piperidine, and an aromatic ring), 6,6-dimethyl-6а,7,7а,8(9),10,11,11а,12а-octahydrochromeno[3′,4′:5,6]pyranо[3,2-с(b)]pyridine.     

Die thermische Zersetzung von Bariumazid-Einkristallen, 5. Mitt.: Der Einfluß der Korngröße auf die thermische Zersetzung von Bariumazid

Decomposition studies on ground samples of anhydrous Ba(N₃)₂ with defined particle size are described. The kinetic equations derived for single crystals hold for the decomposition of powders too. The far faster decomposition of powders is caused both by the increased numberN ₀ of potential nuclei forming sites and the larger specific surfaceF ₀/V ₀, whereas the rate constantsk ₁ andk ₂ for nucleation and linear nucleus growth, resp., and their respective activation energies coincide with the data for single crystals. The proportionality between the rate of decomposition and the specific surface is confirmed experimentally and thereby a further proof of the geometric decomposition model is established. Independent of particle size and temperture always 75% of the azide are transformed into nitride during thermal decomposition, this value corresponding exactly to the theoretical one. It is shown experimentally that with decomposition conditions no reaction takes place between metallic Ba and N₂ in its electronic ground state and therefore the mechanism proposed for nitride formation is confirmed.     

Thermooxidative decomposition of heterocyclic <Emphasis Type="Italic">N</Emphasis>-oxides

Thermooxidative decomposition of pyridine N-oxide, 4-(4-dimethylaminostyryl)pyridine N-oxide, 4-(4-methoxystyryl)pyridine N-oxide, quinoline N-oxide, 2-methylquinoline N-oxide, 4-chloroquinoline N-oxide, 2-styrylquinoline N-oxide, and 2-(4-dimethylaminostyryl)quinoline N-oxide was studied. The kinetic parameters of the thermooxidative processes were calculated according to three independent procedures. The relation between the nature of heterocyclic N-oxide and its stability to thermal oxidation was analyzed.     

Kinetics of thermal decomposition of sulfur-containing amino acids

Rates of thermal decomposition of sulfur-containing amino acids such as D,L-methionine, L-cysteine, and L-cystine are studied. It is established that the amino acids decompose at 190–240°C to give the gaseous and liquid decomposition products in the polyphasic system formed. The rate of summary process is described by the first order kinetic equation up to 30–50% conversion. In spite of close values of the effective activation energies of thermal decomposition of D,L-methionine, L-cysteine, and L-cystine (195, 193, and 184 kJ mol^?1 respectively) the effective rate constants at one and the the same temperature differ by one or two orders of magnitude in the above-mentioned series. Sulfur-containing compounds prevail in the gaseous decomposition products, while in the liquid phase the nitrogen-containing ones are accumulated.     

Structural and kinetic regularities of thermal decomposition of <Emphasis Type="Italic">gem</Emphasis>-trinitromethylazoles in the liquid phase

Kinetics of liquid-phase thermal decomposition of a series of triazoles and tetrazoles containing a gem-trinitromethyl group were studied by manometry and photoelectrocolorimetry, and the mechanism of the thermal decomposition was established. The activation parameters of the rate-limiting stage of the process were evaluated. It was shown that the thermal stability of the gem-trinitromethyl group varies over a broad range, depending on the steric effect of the azole. The rate constant and activation energy correlate with the steric effect of the azole. The thermal decomposition of β-trinitroethylaminotetrazoles proceeds heterolytically with initial dissociation of the C-C bond to give a carbocation and the nitroform anion.     

One-Pot Synthesis of Secondary Amines from Nitroarenes and Aldehydes on Supported Copper Catalysts in a Flow Reactor: The Effect of the Support

The effect of the support on the properties of copper catalysts supported on γ-Al₂O₃, SiO₂, and TiO₂–SiO₂ with a ~5 wt % Cu content was studied in the one-pot synthesis of N-heptyl-p-toluidine from p-nitrotoluene and n-heptanal. The catalysts were characterized by elemental analysis, X-ray diffraction analysis, transmission electron microscopy, temperature-programmed reduction, and low-temperature nitrogen adsorption. The reaction was carried out in a flow reactor with the use of molecular hydrogen as a reducing agent. It was established that the nature of the support exerts a profound effect on the yield of the target secondary amine; in this case, 5%Cu/Al₂O₃ was found the most active catalyst. A combination of high catalyst activity in the hydrogenation of a nitro group to an amino group with the presence of acid sites, which facilitate imine formation as a result of the interaction of n-heptanal with p-toluidine, on the catalyst surface is necessary for reaching the greatest yield of N-heptyl-p-toluidine. The study of reaction mechanism on the 5%Cu/Al₂O₃ catalyst showed that p-nitrotoluene inhibits the hydrogenation of n-heptanal, and aldehyde hydrogenation into alcohol begins only after the conversion of the major portion of p-nitrotoluene as a result of the selective adsorption of the nitroarene under the conditions of the simultaneous presence of p-nitrotoluene and n-heptanal in the reaction mixture.     

Synthesis of novel carborane-containing terminal alkynes

Lithiation of 1-bromomethyl-o-carborane with lithium diisopropylamide (LDA) in THF results in the in situ formation of 1-lithio-2-bromomethyl-o-carborane, the reaction of which with 3-trimethylsilylprop-2-ynal gives 2-(2-trimethylsilylethynyl)-3,4-(о-carborano)-2,5-dihydrofuran. Subsequent base-catalyzed desilylation furnishes new terminal alkynes of closoand nido-carborane series.     

Thermal stability of chlorophyll <Emphasis Type="Italic">a</Emphasis> derivatives containing hydrophilic groups

Trends in thermal stability of aromatic macroheterocycles based of pheophorbide a and chlorin e ₆ containing hydrophilic groups have been revealed by means of thermogravimetric analysis at 298–1223 K under inert atmosphere. Methylpheophorbide a and 13(1)-N-methylamide of chlorin e ₆ are the most stable, the decomposition onset temperature being t _o 351 and 333°С. Their functional substitution leads t _o the reduction in thermal stability. Depending on the macrocycle structure the decrease in t _o can reach 20–200°С.     

Kinetics and mechanism of <Emphasis Type="Italic">N</Emphasis>-chloromethylamine decomposition in solutions

Kinetics of N-chloromethylamine decomposition in an aqueous base medium and chloroform at different temperatures is studied. The decomposition of N-chloromethylamine is found to obey a second order equation in an aqueous base medium at an equimolar ratio of the reagents and a first order equation in chloroform with excess base. The activation energy of N-chloromethylamine decomposition in the both solvents is determined. A mechanism for the reaction is proposed. N-Chloromethylamine is shown to have approximately equal stability in these solvents within the studied temperature range.     

Thermochemistry of С<Subscript>60</Subscript> fullerene solutions in benzene,toluene, <Emphasis Type="Italic">о</Emphasis>-xylene,and <Emphasis Type="Italic">о</Emphasis>-dichlorobenzene at 298.15 K

The enthalpies of dissolution of С₆₀ in benzene, toluene, о-xylene and о-dichlorobenzene are measured in a sealed high-sensitivity calorimeter at 298.15 K and at different concentrations of the solute. The standard enthalpies of dissolution of С₆₀ in these solvents are determined.     

Two directions of heterocyclization in the reactions of dimethyl bicyclo[2.2.2]oct-5-ene-<Emphasis Type="Italic">endo</Emphasis>-2,<Emphasis Type="Italic">endo</Emphasis>-3-dicarboxylate with hetarenesulfenyl chlorides

A reaction of dimethyl bicyclo[2.2.2]oct-5-ene-endo-2,endo-3-dicarboxylate with 1,3-benzо- thiazole-2- and 3-methoxycarbonylpyridine-2-sulfenyl chlorides leads to two types of heterocyclization products, which are formed through the ring closure by the oxygen atom of the carbоmethoxy group and/or by the nitrogen atom of the hetaryl fragment of the sulfenylating agent. The product ratio is affected by the medium nature and structural features of sulfenyl chlorides.     

Influence of octadecylammonium, <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylhexadecylammonium,and 1-hexadecyltrimethylammonium chloride upon the fractionated montmorillonite

The thermal degradation of thermally cured vinyl ester resin systems is studied for different heating rates. The kinetic triplets, the activation energy, pre-exponential factor and the reaction model f(α) for the different reaction extent of conversions (α) are estimated using advanced isoconversional methods. Although the thermal degradation curves show the degradation occurs as a single stage, the kinetic parameters suggest the otherwise. The activation energy remains constant for α?=?0.3–0.575 but varies during the initial and final stages of conversion. Similarly, the pre-exponential factor shows considerable variation between the lower and higher reaction extent (α) values. This shows the complexity in the reaction. The probable reaction mechanism that the degradation follows has been explained. The complexity of the thermal degradation and the changes in reaction model f(α) over different reaction extent has been related. The appropriate working temperature for different thermal lifetime of the cured vinyl ester resin system for the failure of conversion α?=?0.2 has been predicted under the nitrogen atmosphere.     

Synthesis and properties of 1-aroyl-5,5-dialkyl-2,3,5,6-tetrahydropyrrolo[ 2,1-<Emphasis Type="Italic">a</Emphasis>]isoquinoline-2,3-diones

Acylation of 1-methyl-3,3-dialkyl-3,4-dihydroisoquinolines with acid chlorides afforded enaminoketones. Enaminophenylketones from the obtained series were reacted with oxalyl chloride to provide 1-benzoyl-5,5-dialkyl-2,3,5,6- tetrahydropyrrolo[2,1-a]isoquinoline- 2,3-diones. The reaction of the latter with binucleophiles leads to the opening of the pyrrole ring and to the heterocyclization: Under the effect of o-phenyldiamine qinoxaline is formed, 1,2-cyclohexanediamine provides the hexahydro-benzimidazole system, о-aminophenol gives benzoxazole, 3-hydroxy-2-amino-pyridine furnishes oxazolo[4,5-b]pyridine. In the reaction with hydrazine hydrate the acylation occurs with hydrazide formation.