Theoretical study of nonrigid rotation of the tetrahedral cation and anion in NH4BH4

Segments of the potential energy surface of NH₄BH₄ corresponding to nonrigid rotations of the NH₄ ⁺ cation and BH₄ ^– anion relative to each other were calculated using the SCF/3–21G approximation with complete geometrical optimization and MP3/6–31G^* approximation for special points. The barriers for these motions are only several kcal/mole and the molecule is very nonrigid relative to several types of intramolecular rotations (rotation about the B-N bond, rotations with change in the dentation of the cation and anion, and rotations of the cation and anion facilitating the formation of some H₃N-N..H-BH₃ bonds and the cleavage of other such bonds). The strong geometric deformation of the NH₄ ⁺ and BH₄ ^– ions, the polarization of the electron density in these ions, and the H-H interaction between the hydrogen atoms belonging to different ions were discussed. The structural nonrigidity of NH₄BH₄ is closely related to its stability relative to decomposition.Institute of New Chemical Products, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 5, pp. 27–34, September–October, 1989.     

Isomorphous substitution effects on the thermally induced interlayer reaction inN-hexylammonium layered aluminosilicates

It was found that the variation in the thermally evolved gases obtained by decomposition ofn-hexylammonium layered aluminosilicates is mainly due to the difference between octahedral and tetrahedral coordination of aluminium in the lattice and also to the contribution of the excess negative layer charges.ESCA, TG-DSC, GC and MS results indicate that the layer charge originated from the octahedral substitution induces only desintercalation ofn-hexylamine around 250–360°C, whereas that from the tetrahedral substitution induces the catalytic decomposition reaction involving the cleavage of C–N and C–C bonds at 350–450°C with the evolution of ammonia, ethylene, pentene and hexene.It is therefore concluded that the former reaction step is a simple desintercalation, but for the latter one a Brönsted acid catalytic mechanism is proposed.Presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986.     

Thermal decomposition of benzotrifuroxane

The thermal decomposition of benzotrifuroxane proceeds through cleavage of the C-C and O-N(O) bonds of the furoxane ring with formation of dinitriloxodifuroxanyl.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1914–1915, August, 1991.     

Thermal decomposition of dicyanofuroxane

The thermal decomposition of dicyanofuroxane (DCFO) proceeds through cleavage of the O-N(O) and C-C bonds of the furoxane ring with formation of dicyanogen N-oxide. The autocatalytic reactions of this N-oxide with DCFO lead to a pentamer, most likely, with 1,2,4-oxadiazole structure.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1916–1918, August, 1991.     

Catalytic and thermal transformations of methyl- and isopropylcyclobutanes

Conclusions The thermal decomposition of the methyl- and isopropylcyclobutanes in the presence of quartz powder proceeds only with cleavage of the ring at two bonds, while in the presence of amorphous aluminosilicate and zeolite NM the additional reactions of ring opening, cleavage of groups containing one carbon atom, and hydrogen redistribution take place.Translated from Izvestya Akademii Nauk SSSR, Seriya Khimieheskaya, No. 1, pp. 170–172, January, 1973.     

On the Existence and Hydrolytic Stability of Titanosiloxane Bonds in the System: Glycidoxypropyltrimethoxysilane-Water-Titaniumtetraethoxide

Heterometal materials based on glycidoxypropyltrialkoxysilane and titaniumalkoxide are used for optical applications and require a high homogeneity on the molecular level. The presence of heterometal titanosiloxanes, their distribution and hydrolytic stability should influence the homogeneity of these materials. 29Si and 17O NMR spectroscopy has been used to investigate sols with molar ratios Si : Ti = 1 and H2O : OR (H) = 0.5 – 2.0 and their gels after heat treatment at 130°C. The presence of Si—O—Ti bonds in sols with a low water content (H < 0.2) and in the corresponding gels was identified by the high-field shift of the 29Si NMR signals of T1 and T2 units of up to 2–3 ppm compared to corresponding signals of homo-condensed Si—O—Si bonds. The existence of Si—O—Ti bonds in the sols is supported by 17O NMR spectra which show a characteristic signal around 340 ppm. A cleavage of the Si—O—Ti bonds occurs with increasing water/OR ratio in the sols. The cleavage of the heterometal bonds and the building up of homo-condensed species leads to a separation into areas with predominantly Ti—O—Ti and Si—O—Si bonds resulting in a decreased molecular homogeneity of the materials.     

Accelerated and Natural Aging of Cellulose-Based Paper: Py-GC/MS Method

Samples of papers artificially (2 to 60 days) and naturally (10, 45, and 56 years) aged were studied by the Py-GC/MS method to identify decomposition products. Possible reaction scenarios for cellulose degradation were developed. One of the degradation products is acetic acid, which can (auto)catalyze the cleavage of cellulose β(1→4)-glycosidic bonds of cellulose polymer chains. However, during 20 s of Py-GC/MS analysis, temperatures of up to 300 °C did not significantly increase or modify the formation of decomposition products of paper components. At 300 °C, the amount of several cellulose decomposition products increased regularly depending on the number of days of artificial aging and natural aging, demonstrated mainly by the generation of 2-furancarboxaldehyde, 5-hydroxymethylfurfural, and levoglucosan and its consecutive dehydration products. No correlation between the amount of lignin decomposition products and the time of aging was found when the pyrolysis was performed at 300 °C and 500 °C. Compounds present in the products of decomposition at 500 °C bear the imprint of the chemical composition of the sampled paper. Pyrograms taken at 300 °C using the Py-GC/MS method can give additional information on the changes in the chemical structure of paper during natural or artificial aging, mainly about the cleavage of β(1→4)-glycosidic bonds during aging.     

Secondary ionization of neutral products by field dissociation of molecular ions

An analysis of the data obtained herein and literature data on the field-ionization mass spectra of simple compounds has permitted advancement of the hypothesis that the free radicals formed upon cleavage of bonds in the molecular ions in a strong electric field undergo secondary field ionization when the following conditions are fulfilled: a) the ionization potentials of the neutral dissociation products do not exceed the ionization potentials of the original molecules; b) dissociation of the molecular ions occurs so rapidly that these ions and their decomposition products do not manage to leave the zone of the strong field during the dissociation process.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 6, pp. 733–737, November–December, 1986.     

Quantum-Chemical Study of Various Pathways to Carbenium Ions from Olefins and Alkyl Fluorides in the Medium of Hydrofluoric Acid

Elementary reactions of carbenium ion generation from olefins and alkyl fluorides in the medium of hydrofluoric acid are studied by the Hartree–Fock method taking into account electron correlation at the MP2 level and by the DFT (B3LYP) method in the 6-31++G** basis set. Based on enthalpies calculated for these reactions, possible pathways to carbenium ions in the olefin–HF system are determined. A conclusion is drawn that carbenium ions can be formed from olefins by protonation and from the corresponding alkyl fluorides and their protonated forms. It is shown that the heterolytic decomposition of alkyl fluoride in the medium of liquid HF is possible due to the stabilization of carbenium and fluoride ions by hydrogen bonds with HF molecules. The discrete model of microsolvation and the polarizable continuum model (PCM) are used to estimate a decrease in the activation barrier of the heterolytic decomposition of alkyl fluorides due to solvation in the medium of liquid hydrofluoric acid.     

Estimation of Enthalpies of Alkoxy Radical Formation and Bond Strengths in Alcohols and Ether

Kinetic data on the thermal decomposition of peroxides were analyzed, and energies of the O–O bond dissociation were calculated. Enthalpies of formation of various alkoxy radicals and peroxides were determined. The dissociation energies for the O–H bonds in alcohols and C–O bonds in ethers were estimated. Comparative analysis of literature and obtained data was performed.     

Chemical transformations of organic sulfides during hydrogenolysis in the presence of metal chloride complexes

Desulfurization of organic sulfides in hydrocarbon solvents in the presence of aqua complexes of metal chlorides H[MAlCl₄OH] that exhibit lower acidity as compared to AlCl₃ proceeds under mild conditions (450–525 K, atmospheric pressure) without external introduction of hydrogen. The process occurs with cleavage of C-S bonds and through intermediate formation of mercaptans to give H₂S and the corresponding hydrocarbons. The reaction is accompanied by cleavage of C-C bonds in the groups surrounding the organosulfur moiety, in thiacyclane rings, as well as in hydrocarbon solvent molecules, resulting in the formation of a wide spectrum of gaseous and liquid products.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1998–2002, October, 1995.     

The mechanism of the formation of quinonic acids in the oxidation of the bark of the Siberian larch. I

Summary 1. It has been established that in the reaction of Siberian larch bark with atmospheric oxygen in nitric acid, the hemicelluloses and the phenolic complex are oxidized most readily.2. The phenolic acids are decomposed almost completely. The considerable yield of oxalic acid shows a degradation of their aromatic nucleus during oxidation.3. In the oxidation of the bark lignin the cleavage of the lignin macromolecule to the final products does not take place directly. During oxidation an intermediate product with a quinoid system of bonds is formed in considerable amounts, and this then undergoes fragmentation as the result of the oxidative-hydrolytic action of the medium.Siberian Technological Institute, Krasnoyarsk. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 403–409, May–June, 1977.     

Dissociation and rearrangements of the molecular ions of sulfides,sulfoxides, and sulfones generated by a strong electric field

The field mass spectra of 18 sulfides, sulfoxides, and sulfones were investigated, and the principles of charge localization in the dissociation and rearrangements of the molecular ions of these compounds were established. A new type of fragmentation leading to the elimination of S^+., SO^+., and SO₂. was observed. A new mechanism, according to which cleavage of two C-S bonds and the formation of one new C-C bond due to radical recombination cocur in the cyclic transition complex, is proposed. Prior migration of alkyl radicals from sulfur to oxygen with subsequent cleavage of the S-O and C-S bonds via the above-mentioned mechanism may also occur in the molecular ions of sulfoxides and sulfones.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 2, pp. 172–181, March–April, 1987.     

Primary structure of subunit B of the 11S globulin of cotton seeds of variety 108-F. IV. High-molecular-weight peptides from the complete tryptic hydrolysis and from tryptic hydrolysis at the arginine residues of subunit B

The high-molecular-weight peptides from the complete tryptic hydrolysis and tryptic hydrolysis at arginine residues of subunit B, which contained uncleaved bonds of the basic amino acids, have been studied. In the investigation of these peptides, use was made of additional cleavage by trypsin at lysine residues and of cyanogen bromide cleavage.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 227–230, March–April, 1984.     

Application of Microwave Energy to Cleavage of Sulfur Bonds in the S8Ring in the Simplest Amide Solvents

Microwave energy has been employed for cleavage of sulfur bonds in the S₈ring. Cleavage of S–S bonds was carried out in extraction of elemental sulfur in simple amide solvents. Due to the use of microwave energy and the polarity of amides, up to, 100 times lower concentration of a nucleophilic reducer, such as azide or nitrite, may be used to cleave the sulfur bonds. The time needed for cleavage of sulfur bonds at sulfur concentration higher than 0.1 mg S/100 mg solvent was reduced from hours to minutes. This cleavage was quantitative when carried out in a Teflon container in a microwave oven with continuous or pulsed heating. UV spectra show from which value of absorption there will be a sulfur sol at different sulfur concentrations. This allows us to adjust the microwave exposure power and time to avoid sulfur sol formation and not destroy the sample.     

Effect of intramolecular hydrogen bonds on the kinetics of proton exchange of thiocarboxylic acids with phenols

The kinetics and mechanism of proton exchange between thiocarboxylic acids and o-substituted phenols with intramolecular hydrogen bonds (IMHB) were studied by dynamic PMR spectroscopy. Fast uncatalyzed exchange in cyclic binary complexes is observed for phenols with weak IMHB. In systems with strong IMHB fast exchange occurs only in the presence of an alkaline catalyst, the reaction of which with the phenol leads to cleavage of the IMHB. Concerted transfer of two protons and a cation is realized in the final step of the reaction. According to the proposed mechanism, the measured energy of activation of proton exchange is the sum of the energies of activation of the steps involving cleavage of the IMHB and strictly proton transfer.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 24, No. 1, pp. 49–56, January–February, 1988.     

Cleavage of the peptide bonds in pepsin with cyanogen bromide

Summary 1. Conditions for the cyanogen bromide cleavage of the peptide bonds of pepsin formed by methionine have been found.2. Pepsin contains a methionyl-valine bond and two methionyl-aspartic acid (or methionyl-asparagine) bonds.Khimiya Prirodnykh Soedinenii, Vol. 2, No. 2, pp. 138–141, 1966     

Decomposition of Chlorinated Hydrocarbons on Iron-Group Metals

The decomposition of 1,2-dichloroethane and chlorobenzene on nickel–alumina, cobalt–alumina, and iron–alumina catalysts at 400–600°C was studied. Thermodynamic calculations demonstrated that the susceptibility of metals to chlorination under exposure to HCl increases in the order Ni < Co < Fe. The addition of hydrogen to the reaction mixture was found to dramatically decrease the rate of carbon deposition in the decomposition of 1,2-dichloroethane because of the intense hydrogenation of intermediates that are graphite precursors. Two fundamentally different reaction paths were found in the degradation of 1,2-dichloroethane: decomposition via a carbide-cycle mechanism with the formation of carbon as the main product (under conditions of a deficiency of hydrogen) and 1,2-dichloroethane hydrodechlorination accompanied by methanation of the formed carbon (under conditions of an excess of hydrogen). The degradation of chlorobenzene diluted with hydrogen in a molar ratio of 1 : 50 was not accompanied by carbon formation on the catalyst. A comparison between the selectivity for reaction products on nickel–alumina and cobalt–alumina catalysts indicated that the former catalyst is more active in the rupture of C–C bonds and in the methanation reaction of deposited carbon, whereas the latter is more favorable for hydrodechlorination. The optimum conditions and thermal regime for efficient and stable operation of the catalysts were found.     

Acyl Iodides in Organic Synthesis: VI. Reactions with Vinyl Ethers

Reactions of acetyl iodide with butyl vinyl ether, 1,2-divinyloxyethane, phenyl vinyl ether, 1,4-di-vinyloxybenzene, and divinyl ether were studied. Vinyl ethers derived from aliphatic alcohols (butyl vinyl ether and 1,2-divinyloxyethane) react with acetyl iodide in a way similar to ethyl vinyl ether, i.e., with cleavage of both O–Csp2 and Alk–O ether bonds. From butyl vinyl ether, a mixture of vinyl iodide, butyl acetate, vinyl acetate, and butyl iodide is formed, while 1,2-divinyloxyethane gives rise to vinyl iodide, vinyl acetate, and 2-iodoethyl acetate. The reaction of acetyl iodide with divinyl ether involves cleavage of only one O–Csp2 bond, yielding vinyl acetate and vinyl iodide. In the reactions of acetyl iodide with phenyl vinyl ether and 1,4-divinyloxybenzene, only the O–CVin bond is cleaved, whereas the O–CAr bond remains intact.     

Gamma-radiolysis of solid zirconium nitrate and its binary mixtures with potassium halides

Gamma-radiolytic decomposition of zirconium nitrate and its binary mixtures with potassium halides viz. KCl, KBr and KI has been studied at different compositions up to an absorbed dose of 550 kGy. Radiolytic decomposition has been found to decrease with the absorbed dose. It also varies with the concentration of zirconium nitrate in the binary mixtures. G(NO ₂ ^– ) values are enhanced by the addition of halides but only at 75% composition. It is not affected so significantly by KI. A plot of G(NO ₂ ^– ) vs. composition of the binary mixtures of the nitrates shows a somewhat parabolic curve with a minimum at 75% Zr(NO₃)₄+25% KX composition. A part of the energy absorbed by the system is being taken up by the halides depending upon their nature and concentration. Thermal decomposition shows slow decomposition, finally yielding an oxynitrate of indefinite composition.