Synthesis of pyrazolide-bridged heterometallic binuclear complexes

A convenient synthetic procedure is described for the synthesis of heteronuclear bimetallic complexes involving platinum and one other group VIII metal with a single bridging pyrazolide group. The reagent used is the nucleophilic anion, trans-[Pt(Cl₂)(pz)(C₂H₄)]^-, (pz  C₃H₃N₂^-) generated in situ by deprotonation of the Zeise's adduct of pyrazole which will react with reasonably labile substrates to yield binuclear products. Spectroscopic and chemical properties of the products are discussed.     

Pyrolysis and Oxidation of Methane in a RF Plasma Reactor

The chemical kinetic effects of RF plasma on the pyrolysis and oxidation of methane were studied experimentally and computationally in a laminar flow reactor at 100 Torr and 373 K with and without oxygen addition into He/CH₄ mixtures. The formation of excited species as well as intermediate species and products in the RF plasma reactor was measured with optical emission spectrometer and Gas Chromatography and the data were used to validate the kinetic model. The kinetic analysis was performed to understand the key reaction pathways. The experimental results showed that H₂, C₂ and C₃ hydrocarbon formation was the major pathways for plasma assisted pyrolysis of methane. In contrast, with oxygen addition, C₂ and C₃ formation dramatically decreased, and syngas (H₂ and CO) became the major products. The above results revealed oxygen addition significantly modified the chemistry of plasma assisted fuel pyrolysis in a RF discharge. Moreover, an increase of E/n was found to be more beneficial for the formation of higher hydrocarbons while a small amount of oxygen was presented in a He/CH₄ mixture. A reaction path flux analysis showed that in a RF plasma, the formation of active species such as CH₃, CH₂, CH, H, O and O (¹D) via the electron impact dissociation reactions played a critical role in the subsequent processes of radical chain propagating and products formation. The results showed that the electronically excitation, ionization, and dissociation processes as well as the products formation were selective and strongly dependent on the reduced electric field.     

Kinetic study of n-heptane oxidation

The oxidation of n-heptane has been studied in a jet-stirred flow reactor in the temperature range 950–1200 K at atmospheric pressure for a wide range of fuel-oxygen equivalence ratios (0.2 to 2.0). A chemical kinetic reaction mechanism developed from previous studies on smaller hydrocarbons and extended to C₆ and C₇ species was used to reproduce the experimental data. Good agreement between computed and measured concentrations of major chemical species was obtained for the entire range of experimental conditions. Sensitivity analyses were carried out to identify the reactions having the greatest influence on the modeling results. The major reaction paths for n-heptane consumption and for the formation of the main products have been identified. In addition n-heptane ignition delays behind a reflected shock wave measured by other investigators were used to validate the present reaction mechanism at higher temperature and pressure.     

Reaction gas chromatography: Study of the photodecomposition of selected substances

Summary A simple apparatus that permits to carry out photolytic reactions in direct connection with a gas chromatograph has been designed. The photodecomposition of C₅–C₇ aliphatic alkanes, C₁–C₅ primary, secondary and tertiary aliphatic alcohols and of some other substances was studied using this apparatus. The degradation products are characteristic of the individual types of alcohols. The identification of the individual types of alcohols. The identification of the degradation products confirms the proposed schemes for the photodegradation reactions. The apparatus described can also be used for the study of photolysis kinetics, as it permits the easy and rapid variation of the reaction conditions.     

Iridium-catalyzed ring-opening reactions of unsymmetrical oxabenzonorbornadienes with water and alcohol nucleophiles

The iridium-catalyzed ring-opening reaction of unsymmetrical oxabenzonorbornadienes (OBD) with water and alcohol nucleophiles is reported, with the effects of various C₁-substituents explored. Electron-donating alkyl groups lead entirely to the substituted naphthol derivatives in excellent yields while substitution of the C₁ position for electron-withdrawing groups afforded ring-opened products in fair to excellent yields with excellent regioselectivity. The reaction was demonstrated to be highly regioselective for the C₂ position with no C₃ regioisomer observed in all cases. A proposed mechanism for the formation of C₂ regioisomeric ring-opened products has been included.     

Deamination of protonated amines to yield protonated imines

Primary and secondary amines, when examined in atmospheric pressure chemical ionization, electrospray ionization, or chemical ionization, display protonated imines in their mass spectra. These products arise formally by nucleophilic substitution at the α-carbon with loss of both ammonia and molecular hydrogen. Collision-induced dissociation (CID) is used to characterize the product ions by comparison with authentic protonated imines. Gas-phase ion/molecule reactions of protonated amines with neutral amines also yield products that correspond to protonated imines (deamination and dehydrogenation), as well as providing simple deamination products. The reaction mechanism was investigated further by reacting the deamination product, the alkyl cation, with a neutral amine. The observed dehydrogenation of the nascent protonated secondary amine indicates that the reaction sequence is loss of ammonia followed by dehydrogenation even though the isolated protonated secondary amines did not undergo dehydrogenation upon CID. Formation of the deamination products in the protonated amine/amine reaction is competitive with proton-bound dimer formation. The proton-bound dimers do not yield deamination products under CID conditions in the ion trap or in experiments performed using a pentaquadrupole instrument. This demonstrates that the geometry of the proton-bound dimer, in which the α-carbons of the alkylamines are well separated [C _a -N-H-N-C _a ], is an unsuitable entry point on the potential energy hypersurface for formation of the imine [C _a -N-C _a ]. Isolation of the proton-bound dimers in the quadrupole ion trap is achieved with low efficiency and this characteristic can be used to distinguish them from their covalently bound isomers.     

Theoretical investigation into structures and magnetic properties of smaller fullerenes and their heteroanalogues

The smaller fullerenes, C₂₀, C₂₄, C₂₈, C₃₂, C_36, C₄₀ and C₅₀, their hydrogenation products and selected B-, N- and P-doped analogues have been investigated systematically at the B3LYP/6-31G* density functional level of theory. The degree of spherical electron delocalization is evaluated by using the computed nucleus-independent chemical shifts ( NICS) at the cage center and the individual ring centers of interest. The calculated NMR chemical shifts and the NICS values at the cage center, which can be accessed by endohedral ³He chemical shifts, should provide a basis for further experimental characterization of these compounds. Received: 26 March 2001 / Accepted: 10 May 2001 / Published online: 11 October 2001     

五羰基乙酰基锰的深度氢硅烷化

采用两步法合成(CO)₅MnCOCH₃ (1), 然后对1与Me₂PhSiH的深度氢硅烷化反应做9 h的¹H NMR连续监控, 通过将反应物和衍生物的特征峰与内标物C₆H₅(CH₂)₂C₆H₅的特征峰对照直接积分定量, 得到适时含量(mmol)随反应时间改变(h)的变化规律。期间共得到了9种中间体或最终产物, 通过核磁波谱对比, 确定了这些化合物的分子结构。除了对其中6种化合物的特征峰积分直接定量外, 对另外3个化合物采用化学计量结合特征峰积分间接定量, 并对其反应机理做出了合理的解释。最后提出了深度氢硅烷化的多步反应与双通道机理, 并且对反应原料1和Me₂PhSiH中Mn和Si进行了全程跟踪, 结果发现, 在9 h时, Mn总含量高达90.7%, 而Si总含量高达91.4%。     

Packed Bed DBD Discharge Experiments in Admixtures of N<Subscript>2</Subscript> and CH<Subscript>4</Subscript>

The physical, chemical and electrical properties of a coaxial Dielectric Barrier Discharge (DBD) fed by various mixtures of N₂ and CH₄ at atmospheric pressure and ambient temperature has been studied. FTIR spectral measurements of the products formed in the discharge have shown that the main chemical products are C₂H_2, HCN and C₂H₆ produced by dissociation of CH₄, with small but significant traces of NH₃.such a chemical transformation may provide some insight into the chemical processes prevalent in the atmosphere of Titan. During operation of the discharge a solid brown-yellowish deposit was formed on the central rod electrode and the dielectric pellets. Such a deposit is similar to that observed in other N₂:CH₄ discharges and is believed to be an analogue of the aerosol and dust observed in Titan’s atmosphere being composed of chemical species commonly known as ‘tholins’.     

Composition of aromatic products in the catalytic degradation of the mixture of waste polystyrene and high-density polyethylene using spent FCC catalyst

In this chemical recycling process, spent FCC catalyst used had an advantage with an economical and environment aspect, such as a low catalyst price in liquid-phase reaction and a reuse of waste catalyst. The characteristics of oil product and its aromatic product distribution, as a function of reaction time in the reactor and also proportion of HDPE and PS in the mixture, were compared. Main products obtained were light hydrocarbons within the gasoline range that were mainly produced during initial reaction time. The formation of aromatic products such as styrene and ethylbenzene as major components depended appreciably on the reaction time, as well as the composition of HDPE and PS in the mixture used for degradation. For the distribution of C₉-C₁₂ alkylaromatic components as by-products, methylstyrene (C₁-styrene) and isopropylbenzene (C₃-benzene) components were the main products formed by β-scission and hydrogen transfer of PS, while the rest of alkylaromatic products showed very low fraction being 1% or less.     

Investigation of the fragmentation and oxygen reactivity of endohedral metallofullerenes M@C60

The stability, fragmentation, and chemical reactivity of endohedral metallofullerenes M@C₆₀ (M = Ca, Sr, La, and Gd) were examined with laser desorption/ionization mass spectroscopy. A laser ablation/sublimation procedure was used to generate and purify M@C₆₀ samples, which were then characterized by both time-of-flight and Fourier transform ion cyclotron resonance mass spectrometries. Collisional dissociation of the ionized endohedral fullerenes listed above revealed multiple C₂ loss (either as sequential C₂ loss or larger C_2n eliminations) to generate similar terminal fragmentation products (i.e. MC_44,46), which might be predicted due to the similar ionic radii of the encapsulated metals. The reactivity of the endohedral compounds with oxygenated compounds was found to be dependent on the charge state of the metallofullerene. Singly charged cations of the metallofullerenes (M@C_n⁺) were completely unreactive in the gas phase with oxygenated compounds such as ethylene oxide; however, the corresponding neutral species appear to react readily with oxygenated species. This point was demonstrated in that exposure of solid phase M@C₆₀ to ambient conditions (laboratory air at room temperature) leads to the ultimate destruction of the metallofullerenes concomitant with the formation of metal oxides and carbonates.     

Molecule/radical reactions prior to ionization under negative chemical ionization conditions

It is shown that alkyl radical species present in CH₄ or iso-C₄H₁₀ plasma can react with substrate molecules to give [M+C_nH_2n] species. These species become evident especially in negative chemical ionization as [M+C_nH_2n]^?˙ and, less obviously, in positive chemical ionization as [M+C_nH_2n+1]⁺ ions which, for example in natural products chemistry, may be mistaken for a series of homologous compounds present in the sample.     

五羰基乙酰基锰的深度氢硅烷化

采用两步法合成(CO)₅MnCOCH₃ (1), 然后对1与Me₂PhSiH的深度氢硅烷化反应做9 h的¹H NMR连续监控, 通过将反应物和衍生物的特征峰与内标物C₆H₅(CH₂)₂C₆H₅的特征峰对照直接积分定量, 得到适时含量(mmol)随反应时间改变(h)的变化规律。期间共得到了9种中间体或最终产物, 通过核磁波谱对比, 确定了这些化合物的分子结构。除了对其中6种化合物的特征峰积分直接定量外, 对另外3个化合物采用化学计量结合特征峰积分间接定量, 并对其反应机理做出了合理的解释。最后提出了深度氢硅烷化的多步反应与双通道机理, 并且对反应原料1和Me₂PhSiH中Mn和Si进行了全程跟踪, 结果发现, 在9 h时, Mn总含量高达90.7%, 而Si总含量高达91.4%。     

Gas‐Phase Oxidation of Methyl‐10‐undecenoate in a Jet‐Stirred Reactor

To better understand the chemistry of biodiesel surrogates, the gas‐phase oxidation of a C₁₂ unsaturated methyl ester, methyl‐10‐undecenoate, has been studied in a jet‐stirred reactor in the temperature range 500–1100 K. These experiments were performed using neat fuel synthesized in the laboratory, with an initial fuel mole fraction set as 0.0021, at quasi‐atmospheric pressure (1.07 bar), at a residence time of 1.5 s with dilute mixtures in helium of equivalence ratios of 0.5, 1.0, and 2.0. The maximum obtained conversion was shown to be more than twice lower than that of methyl decanoate under the same conditions. This difference cannot be reproduced by the only published model for an unsaturated ester with a close number of carbon atoms (methyl‐9‐decenoate). A large range of products was quantified in addition to common oxidation products: saturated and unsaturated aldehydes, saturated and unsaturated methyl esters with a second carbonyl function, C₂–C₁₀ alkenes, C₄–C₁₀ dienes, C₄–C₁₀ unsaturated methyl esters, C₈–C₉ saturated methyl esters, and saturated, unsaturated, and hydroxyl methyl esters involving a cyclic ether. Pathways of formation for the products specific to unsaturated ester oxidation were proposed, and possible model improvements were discussed.     

Electronic Structure and Chemical Bonds in Titanium Dicarbide with Disordered C2Dimers

A quantum–chemical zone and cluster approaches were used to model the electronic energy spectrum and to study the chemical bond in a hypothetical phase of titanium dicarbide (TiC₂) composed of C₂dimers as structural units. The effect of orientational disorder of the C₂dimers on the electronic structure and chemical stability of the dicarbide was investigated.     

Molecular states formed by ion beam neutralization of [C2H2]+ and [C2H3]+ on metal targets

A combination of charge-stripping and beam-scattering techniques has been used to study the molecular states formed when a fast beam of [C₂H₂]⁺ and [C₂H₃]⁺ in several isotopic forms are neutralized by electron transfer from metal target atoms (K, Na, Mg and Zn). For [C₂H₃]⁺ the isotopic compositions and relative abundances of product states were found to be insensitive to the method of ion preparation (electron impact and chemical ionization). Ground state neutrals are formed in partial abundance when Mg or Zn is used as a target atom. With low ionization potential targets (K and Na) excitel dissociative states of C₂H₂ and C₂H₃ are formed as major beam constituents. For these states decomposition products have been identified and fragmentation energies measured. The excited states of C₂H₂ and C₂H₃ lie alout 6.8 eV and 2.9 eV, respectively, above their stable ground states. The discussion focuses on the possible identity of the excited states and their structural relations to the precursor ions.     

Effect of aerosol chemical vapor deposition on characteristics of MoS<Subscript>2</Subscript> particles

Influence exerted by the main technological parameters in the process in which nano- and microparticles of molybdenum disulfide are formed by the aerosol chemical vapor deposition method from a gas phase containing aerosol particles of (NH₄)₂MoS₄?C₃H₇NO solutions on the dimension characteristics, structure, and composition of the products being formed was studied. It was shown that the shape, size, and structure of the particles being formed are determined by the processes occurring in the first, streamwise, reactor zone. The temperature of this zone is the most important technological parameter. The concentration of ammonium thiomolybdate in solution makes it possible to gradually vary the size of disulfide particles in a wide range (from tens of nanometers to micrometers). In the conditions under study, the technological conditions have no effect on the chemical composition of the products being synthesized, which is always described by the formula MoS₂. The results obtained can be used in development of industrial apparatus and technology for synthesis of molybdenum disulfide nano- and microparticles to be used as the antifriction component of lubricating materials.     

Synthesis and Characterization of UV-Curable Poly(dimethylsiloxane) Dimethacrylate

This paper presents a new route to the synthesis of UV-curable poly(dimethylsiloxane) dimethacrylate (PDMSDMA). PDMSDMA was essentially prepared by modification of poly(dimethylsiloxane), bis(3-aminopropyl) terminated (PDMS-NH₂) with methacrylic anhydride (MAA). The synthesized products were cured under UV in the presence of camphorquinone (CQ) used as a photoinitiator. The chemical structure of PDMSDMA samples was analyzed by FT-IR and ¹H-NMR spectroscopy. The ¹H-NMR spectrum of PDMSDMA revealed new peaks at 3.20 ppm, corresponding to methylene protons in  CH₂ NH , and 5.25 and 5.65 ppm, corresponding to vinylic protons in  NH CO CCH₃CH₂. The chemical structure of the cured products and the degree of curing were determined by solid state ¹³C CP/MAS NMR and FT-IR (Micro-ATR) spectroscopy. Various parameters, such as concentration of methacrylic anhydride, amount of camphorquinone, and curing time, were studied.     

Polyadducts of fullerene C60 with tert-butyl groups

New soluble fullerene derivatives Bu^t _n C₆₀ were synthesized by the reaction of C₆₀M _n (THF) _x (M = Li, Na; n = 4, 6, 8, 10, 12) with tert-butyl bromide ButBr. The thus obtained compounds were characterized by spectroscopic methods (IR and NMR spectroscopy), mass spectrometry (MALDI), elemental analysis, and quantum chemical calculations. HPLC was used for chromatographic separation of the products of the reaction of C₆₀Na _n (THF) _x (n = 4, 6, 8, 12) with Bu^tBr. It was found that Bu^t ₄C₆₀ and Bu_t ⁶C₆₀ decompose on the column. A complex of physicochemical methods of analysis was used for establishing compositions of individual fractions of chromatographic separation of Bu^t ₄C₆₀. The structure of one of the components was determined as 1-tert-butyl-1,2-dihydrofullerene 1,2-Bu^tC₆₀H.     

Ionic liquid 1-ethyl-3-methylimidazolium acetate: an attractive solvent for native chemical ligation of peptides

The ionic liquid 1-ethyl-3-methylimidazolium acetate ([C₂mim][OAc]) was successfully used as alternative solvent for native chemical ligation of peptide fragments to produce model peptide LYRAXCRANK (X = G, A, L, N, Q, K, and F). The commonly used buffer system including thiol additives such as thiophenol and benzyl mercaptan can be replaced by the nontoxic ionic liquid [C₂mim][OAc]. In addition to improving the solubility of the peptides in [C₂mim][OAc], yields and rates of the ligation reactions were found to be efficiently enhanced.