Computational study of reaction pathways in the course of interaction of deactivated silylenes with buta-1,3-diene

The PESs of systems including deactivated silylenes (SiHHal, SiHal₂, Hal = F, Cl, and 2-silaimidazol-2-ylidene, SiN₂H₂C₂H₂) and buta-1,3-diene have been studied using G3(MP2)//B3LYP method. Two major reaction channels, (2 + 1) and (4 + 1) cycloaddition reactions, leading to 2-vinylsiliranes and silacyclopent-3-enes, respectively, as well as [1,3]-sigmatropic rearrangements between 2-vinylsiliranes and the corresponding silacyclopent-3-enes, have been considered in detail. Reactivity of silylenes toward buta-1,3-diene decreases in the following series: SiHHal > SiHal₂ > SiN₂H₂C₂H₂, which is reflected in increase of the reaction barriers for both cycloaddition reactions and in decrease of exothermicity of the formation of the corresponding products. The (4 + 1) cycloaddition is preferable for SiHal₂ and SiN₂H₂C₂H₂ and can compete with (2 + 1) cycloaddition for SiHHal. [1,3]-Sigmatropic rearrangement is important for isomerization of 2-vinylsiliranes to the corresponding silacyclopent-3-enes for all systems studied, except the SiCl₂ system.     

Kinetics of decomposition of alkylammonium salts

The thermogravimetric curves of di-n-propylammonium, di-iso-propylammonium, di-n-butylammonium and di-iso-butylammonium chlorides showed similar profiles, characterized by mass loss in only one stage, corresponding to decomposition of compounds. The following thermal stability order was obtained: [Bu₂ ⁿNH₂]Cl>[Pr₂ ⁿNH₂]Cl>[Pr₂ ⁱNH₂]Cl>[Bu₂ ⁱNH₂]Cl. The values of activation energy for non-isothermal data obtained by Ozawa and Coats-Redfern integral methods were in agreement and stability order obtained by thermogravimetry were reproduced in both methods. The decomposition reactions of [Pr₂ ⁿNH₂]Cl, [Pr₂ ⁱNH₂]Cl and [Bu₂ ⁱNH₂]Cl were better described by A3 model and [Bu₂ ⁿNH₂]Cl by A2 model. This revised version was published online in August 2006 with corrections to the Cover Date.     

Stages of thermal decomposition of sodium oxo-salts of sulphur

Thermal behaviour of sodium oxo-salts of sulphur: Na₂SO₄, Na₂S₂O₇, Na₂S₂O₆, Na₂SO₃, Na₂S₂O₅, Na₂S₂O₄, Na₂S₂O₃, Na₂S₃O₆ and of sulphides Na₂S and Na₂S₂ was studied on heating up to 1000°C. The experiments were performed with anhydrous compounds obtained from commercial products by recrystallisation and dehydration. The stage mechanisms of decomposition of anionic sub-lattices of the salts have been proposed basing on the Górski’s morphological classification of simple species. The thermal stability and the stage decomposition mechanisms were correlated with the structure and the potential chemical properties of the salt anions. The thermal decomposition processes were studied by means of thermal analysis, and the decomposition products were identified by means of X-ray phase analysis.     

钛硅分子筛催化环己酮液相氨肟化固定床工艺

采用固定床模式,研究了钛硅分子筛催化环己酮制环己酮肟液相氨肟化反应.结果表明,该工艺模式具有可行性与普适性.优化的反应条件为:温度333K,体系氨浓度>2%,酮/H₂O₂摩尔比=5,H₂O₂空速0.083h^-1.此时环己酮转化率、环己酮肟选择性、H₂O₂转化率及其有效利用率分别达18.7%,99.5%,94.7%和98.7%.进一步研究了H₂O₂在该过程中的反应行为,发现固定床工艺模式能有效提高H₂O₂的有效利用率,其主要原因是该模式有利于羟胺的生成及其进一步与酮反应生成肟.适当的空速与氨和酮的浓度是实现H₂O₂高效利用的关键因素.     

A study of the selenites of cerium

The solubilities of the systems CeO₂-SeO₂-H₂O and Ce₂O₃-SeO₂-H₂O were studied at 100°C. The field of crystallization of Ce(SeO₃)₂ was established in the system CeO₂-SeO₂-H₂O, and fields of crystallization of Ce₂(SeO₃)₃ and Ce₂(SeO₃)₃H₂SeO₃ were established in the system Ce₂O₃-SeO₂-H₂O. The compound obtained were identified by means of chemical, X-ray and derivatograph analysis. The mechanism of thermal dissociation of Ce(SeO₃)₂, Ce₂(SeO₃)₃ and Ce₂(SeO₃)₃·H₂SeO₃ was studied. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study of the pyrolysis of H2O2 in the presence of H2and CO by use of UV absorption of HO2

In dissociation experiments of H₂O₂ under shock wave conditions, the spectra of H₂O₂ and HO₂ have been observed in the UV at 2200 ≤ 2800 Å. By the use of these spectra the H₂O₂ decomposition in the presence of H₂ and CO at 870 ≤ T ≤ 1000°K has been analyzed. It was found that in this temperature range, in contrast to low temperature behavior, reactions of H atoms with H₂O₂ and with HO₂ are equally important. The rate of the reaction H + H₂O₂ ← HO₂ + H₂ was estimated in comparison with the rate of the reaction between H and HO₂. Good agreement between calculated and measured concentration profiles of HO₂ and H₂O₂ was obtained.     

Synthesis and Application of New Salan Titanium Complexes in the Catalytic Reduction of Aldehydes

Complexes of formula [(H₂N₂O₂)TiCl₂] and [(H₂N₂O₂)Ti(OⁱPr)₂] (H₂N₂O₂H₂ = HOPh’CH₂NH(CH₂)₂NHCH₂Ph’OH, where Ph’ = 2,4-(CMe₂Ph)C₆H₂) were synthesized by the reaction of the salan ligand precursor H₂N₂O₂H₂ with TiCl₄ and Ti(OⁱPr)₄, respectively, in high yields. The dichlorido complex [(H₂N₂O₂)TiCl₂] revealed to be an efficient catalyst for the reduction of benzaldehyde in toluene. Full conversion was observed after 24 h at 55 °C in THF. The same catalyst also converted phenylacetaldehyde and hydrocinnamaldehyde into the corresponding alkanes quantitatively.     

Kinetic Analysis of Dissociation of Smithsonite from a Set of Non-isothermal Data Obtained at Different Heating Rates

The heats of hydration reactions for MgCl₂⋅4H₂O and MgCl₂⋅2H₂O include two parts, reaction enthalpy and adsorption heat of aqueous vapor on the surfaces of magnesium chloride hydrates. The hydration heat for the reactions MgCl₂⋅4H₂O+2H₂O→MgCl₂⋅6H₂O and MgCl₂⋅2H₂O+2H₂O→MgCl₂⋅4H₂O, measured by DSC-111, is –30.36 and –133.94 kJ mol^–1,respectively. The adsorption heat of these hydration processes, measured by head-on chromatography method, is –13.06 and –16.11 kJ mol^–1, respectively. The molar enthalpy change for the above two reactions is –16.64 and –118.09 kJ mol^–1, respectively. The comparison between the experimental data and the theoretical values for these hydration processes indicates that the results obtained in this study are quite reliable. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inactivation of Bacillus subtilis Spores Using Various Combinations of Ultraviolet Treatment with Addition of Hydrogen Peroxide

This study aims at comparing the inactivation of Bacillus subtilis spores by various combinations of UV treatment and hydrogen peroxide (H₂O₂) addition. The combinations included sequential (UV–H₂O₂, H₂O₂–UV) and simultaneous (UV/H₂O₂) processes. Results showed that B. subtilis spores achieved a certain inactivation effect through UV treatment. However, hardly any inactivation effect by H₂O₂ alone was observed. H₂O₂ had a significant synergetic effect when combined with UV treatment, while high irradiance and H₂O₂ concentration both favored the reaction. When treated with 0.60 mm H₂O₂ and 113.0 μW/cm² UV irradiance for 6 min, the simultaneous UV/H₂O₂ treatment showed significantly improved disinfection effect (4.13 log) compared to that of UV–H₂O₂ (3.03 log) and H₂O₂–UV (2.88 log). The relationship between the inactivation effect and the exposure time followed a typical pseudo‐first‐order kinetics model. The pseudo‐first‐order rate constants were 0.478, 0.447 and 0.634 min^?1, for the UV‐H₂O₂, H₂O₂–UV and UV/H₂O₂ processes, respectively, further confirming the optimal disinfection effect of the UV/H₂O₂ process. The disinfection could be ascribed to the OH radicals, as verified by the level of para‐chlorobenzoic acid (pCBA).     

Synthesis and properties of amino acid esters of hydroxypropyl cellulose

The amino acid esters of hydroxypropyl cellulose (HPC) [R′ = H ( 2a ), CH₃ ( 2b ), CH₂CH(CH₃)₂ ( 2c ), CH₂CONH₂ ( 2d ), CH₂CH₂CONH₂ ( 2e ), CH₂CH₂CH₂CH₂ NHOCOC(CH₃)₃ ( 2f )] were synthesized in good yield by the reaction of t‐butoxycarbonyl (t‐Boc)‐protected amino acids with hydroxy groups of HPC ( 1 ; molar substitution (MS), 4.61). The amino acid functionalities displaying varied chemical nature, shape, and bulk were utilized and the bulk of the substituent on the α‐carbon of amino acids was elucidated to be of vital significance for the observed degree of incorporation (DS_Est). The ¹H NMR spectra and elemental analysis were employed to determine the degree of incorporation of amino acid moiety (DS_Est) and almost complete substitution of the hydroxy protons was revealed for 2a , 2b , and 2f . The presence of the peaks characteristic of the carbonyl group in the FTIR spectra furnished further evidence for the successful esterification of HPC. The starting as well as the resulting polymers ( 1 and 2a – f ) were soluble in polar organic solvents; however, the esterification of 1 with bulky organic moieties resulted in an increased hydrophobicity as all of the amino acid‐functionalized polymers ( 2a – f ) were insoluble in water. The onset temperatures of weight loss of 2a – f were 175–230 °C, indicating fair thermal stability. The amino acid functionalization led to the enhanced polymer chain stiffness, and the glass transition temperatures of the derivatized polymers were 30–40 °C higher than that of 1 (T_g 3.9 °C; cf. T_g of 2a – f , 35.1–43.3 °C). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2326–2334, 2008     

Synthesis and1H NMR study of some organotin derivatives of diethanolamines

A number of organotin derivatives of diethanolamines (stannocanes) R₂Sn(OCH₂CH₂)₂NR', O(SiMe₂CH₂)₂Sn(OCH₂CH₂)₂NR', and Sn[(OCH₂CH₂)₂NR']₂ (R = Ph,cyclo-Hex; R' = H, Me, Ph) were synthesized and studied by¹H NMR spectroscopy. The effect of steric factors on the ability of molecules of stannocanes to form associates in solutions is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp.714–718, April, 1994.     

An ab initio and density functional study of microsolvation of carbon dioxide in water clusters and formation of carbonic acid

Geometry of the CO₂–H₂O complex and reaction barriers leading to the formation of H₂CO₃were studied at the RHF/6-311++G**, MP2/6-311++G**, B3LYP/AUG-cc-pVDZ, B3LYP/AUG-cc-pVTZ, MP2/AUG-cc-pVDZ and CCD/AUG-cc-pVDZ levels of theory. The rotational barrier of the CO₂–H₂O complex and the reaction barrier leading to the formation of H₂CO₃–H₂O from CO₂–(H₂O)₂ were studied using the first three of the above-mentioned methods. Microsolvation of CO₂ in water clusters having upto eight water molecules was studied using the B3LYP/AUG-cc-pVDZ method. Various methods except MP2/AUG-cc-pVDZ predict the equilibrium structure of the CO₂–H₂O complex to be symmetric while the MP2/AUG-cc-pVDZ method predicts it to be unsymmetric. Formation of H₂CO₃ from CO₂–H₂O is strongly catalyzed by the presence of a second water molecule. Atomic orbitals are strongly rehybridized in going from the equilibrium structures of the CO₂–H₂O and CO₂–(H₂O)₂ complexes to the transition states involved in the formation of H₂CO₃ and H₂CO₃–H₂O, respectively, as shown by hybridization displacement charges.     

Kinetics of the thermal decomposition of dinitramide

The kinetic regularities of the heat release during the thermal decomposition of liquid NH₄N(NO₂)₂ at 102.4–138.9 °C were studied. Kinetic data for decomposition of different forms of dinitramide and the influence of water on the rate of decomposition of NH₄N(NO₂)₂ show that the contributions of the decomposition of N(NO₂)₂ ⁻ and HN(NO₂)₂ to the initial decomposition rate of the reaction at temperatures about 100 °C are approximately equal. The decomposition has an autocatalytic character. The analysis of the effect of additives of HNO₃ solutions and the dependence of the autocatalytic reaction rate constant on the gas volume in the system shows that the self-acceleration is due to an increase in the acidity of the NH₄N(NO₂)₂ melt owing to the accumulation of HNO₃ and the corresponding increase in the contribution of the HN(NO₂)₂ decomposition to the overall rate. The self-acceleration ceases due to the accumulation of NO₃ ⁻ ions decreasing the equilibrium concentration of HN(NO₂)₂ in the melt. For Part 2, see Ref. 1. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 395–401 March 1998.     

Comment on the assignments of some vibrational bands of oxalyl fluoride

In view of existing contradictory assignments of the symmetrical stretching vibrations associated with the formal C-C and C-F bonds of trans/cis oxalyl fluoride, an additional theoretical analysis of the corresponding calculated wavenumbers was preformed on trans-C₂O₂F₂ and cis-C₂O₂F₂ based on previously calculated ab initio scaled force fields at the HF/6-31G computational level and new force fields calculated at the MP2/aug-cc-pVTZ level. This novel analysis included computational data from the isotopic shifts brought about by incorporating ¹³C and ¹⁴C atoms into the structure. A detailed examination of the calculated wavenumbers made it possible to validate the assignments of the ν₂ and ν₃ wavenumbers in the trans-C₂O₂F₂ and cis-C₂O₂F₂ molecules as the formal C-C bond stretching and the formal C-F bond symmetrical stretching vibrations, respectively.     

Complexation of Ketoconazole by Native and Modified Cyclodextrins

Complexation of ketoconazole (KET), a broad-spectrum antifungal drug, with β- and γ-cyclodextrins (CDs), heptakis (2,6-di-O-methyl)-β-CD (2,6-DM-β-CD), heptakis (2,3,6-tri-O-methyl)-β-CD (TM-β-CD), 2-hydroxypropyl-β-CD (2HP-β-CD) and carboxymethyl-β-CD (CM-β-CD) was studied. The stability constants were determined by the solubility method at pH = 6 and for 2,6-DM-β-CD and CM-β-CD at pH = 5. At pH = 6, the stability constants increased in the order: TM-β-D < γ-CD < 2HP-β-CD < β-CD < CM-β-CD < 2,6-DM-β-CD. At pH = 5, due to the increased ionization of KET, the stability constant with CM-β-CD increased and with 2,6-DM-β-CD decreased. For complexes of KET with 2HP-β-CD and 2,6-DM-β-CD, the thermodynamic parameters of complexation were determined from the temperature dependence of the corresponding stability constants. For β–γ and TM-β-CD complexes, calculations using HyperChem 6 software by the Amber force field were carried out to gain some insight into the host–guest geometry.     

Influence of the texture of chromia catalysts on their activity in synthesis of 2-methylthiophene

The texture of Cr₂O₃-K₂O/Al₂O₃catalysts containing oxides of rare earth elements (REE) was studied. The catalysts are used for the synthesis of 2-methylthiophene by the reaction of H₂S with n-pentane or piperilene. The heterocyclization of n-pentane is a consecutive reaction involving a step of dehydrogenation of initial hydrocarbon. At this step the texture of the catalyst affects the yield of 2-methylthiophene. The yield of 2-methylthiophene obtained from piperilene and I₂S is independent of the catalyst texture.     

Syntheses and spectroscopic studies of diphenylphosphinato derivatives of boron

Summary 2-Diphenylphosphinato-1,3,2-dioxaborolanes and -borinanes of the type (whereG = -CH₂CHMe-, -CH₂CH₂CH₂-, -CH₂CH₂CHMe-,-CMe₂CMe₂-, -CMe₂CH₂CHMe-,-CH₂CMe₂CH₂-, -CH₂CEt₂CH₂-, and -C₆H₄-) are obtained by the reaction of diphenylphosphinic acid with the corresponding 2,2-oxo-bis-1,3,2-dioxaborolanes and-borinanes. The products are white crystalline solids, which have sharp melting points and are hydrolytically stable. They have been characterized by elemental analysis, IR and multinuclear NMR (¹¹B,³¹P, and¹¹⁹Sn) studies. The data suggest structures with monodentate phosphinato moieties and 3-coordinated boron atoms.

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Synthesen und spektroskopische Untersuchungen von Diphenylphosphinatoderivaten von Bor

Zusammenfassung 2-Diphenylphosphinato-1,3,2-dioxaborolane und -borinane des Typs (mitG = -CH₂CHMe-, -CH₂CH₂CH₂-,-CH₂CH₂CHMe-, -CMe₂CMe₂-,-CMe₂CH₂CHMe-, -CH₂CMe₂CH₂-, -CH₂CEt₂CH₂- und C₆H₄) erhält man durch Reaktion von Diphenylphosphinsäure mit den entsprechenden 2,2-Oxo-bis-1,3,2-dioxaborolanen und -borinanen. Die Produkte sind weiße, kristalline, hydrolyseunempfindliche Festkörper. Sie wurden mittels Elementaranalyse, IR-Spektroskopie und multinuklearer NMR-Spektroskopie (¹¹B,³¹P und¹¹⁹Sn) charakterisiert. Die Resultate legen Strukturen mit monodentaten Phosphinatoeinheiten und dreifach koordinierten Boratomen nahe.

     

NHC-Adducts of Cyclopentadienyl-Substituted Alanes

The mono- and bis-iodo-substituted NHC-stabilized alanes (NHC) ⋅ AlH₂I and (NHC) ⋅ AlHI₂ offer a convenient entry for further substitution reactions at aluminum. Reactions of (NHC) ⋅ AlH₂I 1 – 4 with one equivalent of NaCp afforded the adducts (NHC) ⋅ AlH₂Cp 9 – 12 (NHC=Me₂Im^Me ( 9 ), iPr₂Im^Me ( 10 ), iPr₂Im ( 11 ), Dipp₂Im ( 12 )). Alane adducts with two Cp substituents (NHC) ⋅ AlHCp₂ 13 – 16 (NHC=Me₂Im^Me ( 13 ), iPr₂Im^Me ( 14 ), iPr₂Im ( 15 ), Dipp₂Im ( 16 )) were prepared by the analogous reaction of (NHC) ⋅ AlHI₂ 5 – 8 using two equivalents of NaCp. The unusual dimeric adducts ((NHC) ⋅ AlH₂Cp ⋅ CpMgI)₂ 17 – 19 (NHC=Me₂Im^Me ( 17 ), iPr₂Im^Me ( 18 ), iPr₂Im ( 19 )) were obtained from the reaction of 1 – 3 with MgCp₂.     

Regularities of formation of nanocrystalline particles in titanium subgroup dioxides

Trends in formation and evolution of nanocrystalline phases in TiO₂, ZrO₂, and HfO₂ powders were studied. The stability of metastable phases increases in the order of HfO₂ > ZrO₂ > TiO₂, and the probability of formation of thermodynamically stable phases increases in the order of TiO₂ > ZrO₂ > HfO₂. The enthalpies of formation were determined for TiO₂, ZrO₂, and HfO₂ nanocrystallites, as well as the activation energies of their subsequent growth. For TiO₂ and ZrO₂, a phenomenological model was advanced to describe nanocrystallite formation and subsequent polymorphic transformations.     

Tentative Identification of the Reactive Species in the Reaction of Cp2 TiCl2 with Salts of Diacids

The tentative identification of the reactive species in the condensation of Cp₂ TiCl₂ with salts of diacids to form titanium polysters is made. The reactive species are believed to be the same for both aqueous solution and interfacial systems, i.e., R -CO₂ ^? and Cp₂ Ti²⁺ with reaction occurring in the aqueous phase. The condensation of Cp₂ TiCl₂ with disodium terephthalate in interfacial systems occurs via a pseudo-first-order reaction:

Rate = K[Cp₂ TiCl₂] The rate-determining step (s) is believed to be diffusion of CP₂ TiCl₂ into the aqueous layer and/or hydrolysis of Cp₂ TiCl₂