ReOx/ZrO2催化甲醇一步合成二甲氧基甲烷的研究

利用负载型ReOxZrO2催化剂,将甲醇选择性氧化并一步合成二甲氧基甲烷。考察了反应时间、反应温度以及铼负载量对反应的影响。并利用N2吸附/脱附、X射线光电子能谱、氨程序升温脱附(NH3-TPD)和氢程序升温还原(H2-TPR)等手段对催化剂进行了表征。结果表明,较高的反应温度有利于提高甲醇的转化率,但对二甲氧基甲烷的选择性不利;催化剂上所负载铼的质量分数对甲醇转化率影响较大,在铼的质量分数为1.64%时转化率达到最大值25.1%;负载于ZrO2上的ReOx 具有双功能催化性质：它既可作为氧化中心氧化甲醇,在还原后又可作为酸中心催化醇醛缩合。     

Kinetic studies of polyamide-imide synthesis

To understand the kinetic of synthesis of polyamide-imide (PAI) via p-chlorophenol-(PCP) blocked 4,4′-diphenyl methane diisocyanate (MDI) with trimellitic anhydride (TMA), a series of reactions of blocked MDI with excess phthalic anhydride (PA) and benzoic acid are designed. PCP-blocked phenyl isocyanate (BPI) which also released isocyanate at higher temperatures was used as a model compound for BMDI. The dissociation constants of BPI and BMDI in the presence of excess PA or BA was measured by collecting the evolved CO₂. The effect of the catalyst concentration and temperatures were combined by a Hostettler equation. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1703–1710, 1997     

Kinetic relationships of the formation of antimony sulfide

The kinetics of deposition of antimony sulfide from solutions of sodium thiosulfate was studied. The reaction orders with respect to the components and the activation energy of the process were determined. Original Russian Text A.A. Uritskaya, T.P. Bol’shchikova, N.S. Kozhevnikova, 2007, published in Zhurnal Obshchei Khimii, 2007, Vol. 77, No. 5, pp. 717–720.     

Effect of crystallinity in HZSM-5-amorphous alumosilica systems on their catalytic properties in the synthesis of dimethoxymethane

Granulated catalysts with 3–5% H-ZSM-5 phase were obtained from a highly dispersed alumosilica and were used for the synthesis of dimethoxymethane (DMM) from methanol and formaldehyde. The activity of these catalysts is greater than the activity of pure zeolite. A linear correlation was found between the yield of DMM and the content of Brönsted acid sites in the catalysts.     

甲醇制备甲酸甲酯、甲缩醛和聚甲醛二甲醚的催化反应研究进展

由甲醇向下游衍生合成甲酸甲酯、甲缩醛和聚甲醛二甲醚等反应过程,不仅可以有效延伸甲醇产业链,消化业已形成的甲醇过剩产能,而且还可以带来巨大的经济和环境保护方面的效益,近年来受到研究者的广泛关注,与之相关的催化研究和开发也已取得长足的进步和发展。述评概述了近年来由甲醇出发制备甲酸甲酯、甲缩醛以及聚甲醛二甲醚等过程在催化剂制备和反应机理探索方面的研究进展,侧重介绍了贵金属催化剂上甲醇选择氧化制甲酸甲酯、钒基催化剂上甲醇选择氧化制甲缩醛以及分子筛催化剂上甲醇或甲缩醛与三聚甲醛合成聚甲醛二甲醚等催化反应过程。最后,对甲醇催化转化利用的未来发展方向进行了展望。     

Kinetic relationships of hexachlorocyclotriphosphazatriene hydrolysis in aqueous acetonitrile in the presence of triethylamine

The kinetic and thermodynamic relationships of hexachlorocyclophosphazatriene hydrolysis in aqueous acetonitrile in the presence of triethylamine were determined. The hydrolysis mechanism involving base catalysis with triethylamine is described. The halogen substitution in hexachlorocyclotriphosphazatriene occurs by the mechanism of bimolecular nucleophilic substitution.     

Kinetic characterization of the synthesis of cotton cellulose

The influence of the temperature, pH, and inhibitors on the synthesis of cellulose from cottonplant shoots has been investigated. The maximum activity of glucan synthetase was exhibited at 27°C, pH 8. O. The greatest inhibition of the formation of cellulose was shown by EDTA.A. S. Sadykov Institute of Bioorganic Chemistry, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 62 70 71. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 300–302, March–April, 1995. Original article submitted October 24, 1994.     

Ambident electrophilicity of 4-nitrobenzochalcogenadiazoles: Kinetic studies and structure-reactivity relationships

The kinetics of the reactions of 4-nitrobenzofurazane 1a , 4-nitrobenzothiadiazole 1b , and 4-nitrobenzoselenadiazole 1c with a series of 4-Y-substituted phenoxide anions 2a-e (Y = OMe, Me, H, Cl, and CN) in aqueous solution at 20°C were investigated photometrically. The derived second-order rate constants (k₂) have been combined with the nucleophilicity parameters values of these series of anions 2a-e to determine the electrophilicity parameters E of electrophiles 1a-c according to the linear free-energy relationship (log k₂)/s versus N. General reactivity of these electrophiles 1a-c is found to be fairly similar with E values ranging in −10.77 ± 0.61 < E < −7.53 ± 0.29. The comparison with structurally related neutral electron-deficient heteroaromatic and aromatic compounds revealed that 1a - c are more reactive than 1,3,5-trinitrobenzene, as benchmark aromatic electrophile used in nucleophilic addition or substitution processes. The rate constants for the reactions of 4-nitrobenzochalcogenadiazoles 1a-c with some other nucleophiles were measured and found to agree with those calculated from Mayr's equation. Finally, analysis of the rate data in terms of the Brønsted approach reveals that 1a-c exhibits especially low intrinsic reactivity in σ-adducts 3 forming reactions.     

Kinetic relationships and mechanism of ozone reaction with polystyrene in CCl4 solution

In this work a study is made of the degradation on ozonation of unfractionated polystyrene (PS) in CCl₄ solution. It was found that the ozone attack of PS molecules is accompanied by hydrogen abstraction from tertiary CH bonds and by the formation of ozonides due to the reaction of ozone with the aromatic rings. A scheme of PS degradation in solution is suggested; several kinetic parameters are evaluated.     

Two-dimensional oligoarylenes: synthesis and structure-properties relationships

A novel series of two-dimensional π-conjugated oligoarylenes has been synthesized by a divergent approach using Pd-catalysed Suzuki cross-coupling of tetraiodophenylbenzene and arylboronic acid as a key step. It has been shown that the ‘X-branched’ structure can provide a useful platform to construct amorphous molecular materials as it can enhance the morphological and thermal stability as well as to facilitate solubility and processibility of a material when compared to those of the corresponding linear oligomers. The diphenylamino end-capped two-dimensional oligoarylenes were found useful as a hole transporting/emitting layer for light emitting applications.     

Kinetic relationships of metal filling of epoxy resin by in situ reduction of silver nitrate

The kinetics of metal filling of ED-20 epoxy oligomer by its action on AgNO₃ in the temperature interval 50–90°C was studied.     

Conformations of dimethoxymethane: matrix isolation infrared and ab initio studies

Conformations of dimethoxymethane (DMM) were studied using matrix isolation infrared spectroscopy. DMM was trapped in an argon matrix using an effusive source at 298, 388 and 430 K. Experiments were also done using a supersonic jet source to look for conformational cooling in the expansion process. As a result of these experiments, spectrally resolved infrared features of the ground and first higher energy conformer of DMM have been recorded, for the first time. The experimental studies were supported by ab initio computations performed at HF and B3LYP levels, using a 6-31++G** basis set. Computationally, four minima were identified corresponding to conformers with GG, TG, G+G- and TT structures. The computed frequencies at the B3LYP level were found to compare well with the experimental matrix isolation frequencies, leading to a definitive assignment of the infrared features of DMM, for the GG and TG conformers. At the B3LYP/6-31++G** level, the energy difference between the GG and TG conformers was computed to be 2.30 kcal mol(-1). The barrier for conformation interconversion, TG-->GG level was calculated to be 0.95 kcal mol(-1). This value is consistent with the experimental observation that the spectral features due to the TG conformer disappeared in the matrix on annealing.     

Kinetic regularities of synthesis of alkali silicates from silica hydrosols

The method of colorimetric analysis based on the formation of colored β-silicon-molybdenum complex was used to study the formation kinetics of solutions of alkali metal silicates in the course of sol depolimerization.     

Kinetic modelling of synthesis of N-aminopiperidine from hydroxylamine-O-sulfonique acid and piperidine

A new route to synthesize N-aminopiperidine (NAPP) from hydroxylamine-O-sulfonique acid (HOSA) and piperidine was described. Kinetics of the reaction was investigated to optimize the conditions of the synthesis. Since the reaction is fast, this study was carried out in a diluted medium (10⁻³ to 10⁻² mol/l). To determine the concentration of the reaction product, NAPP was allowed to react with formaldehyde and the product was analysed by UV and HPLC techniques. The formation of NAPP is consistent with the first-order reaction to two reagents, governed by the nucleophilic substitution via SN2 mechanism. Oxidation of NAPP by HOSA was identified as the main secondary reaction which consistently reduced the yield of NAPP. A number of differential equations were elaborated and solution of these equations serves to predict the behavior of the system as a function of the reagent concentrations, pH and temperature. From the corresponding mathematical treatment a unique implicit expression was derived that characterizes the reaction medium. It was found that the [PP]₀/[HOSA]₀ molar ratio (p), the initial concentrations of [PP]₀ and [HOSA]₀, the ratio of rate constants k ₂/k ₁ and temperature are the only parameters that affect the yield of NAPP from HOSA. The results calculated from this model are in good agreement with the experimental data and they can be used to determine the optimal conditions of the reaction.     

Kinetic control and thermodynamic selection in the synthesis of atomically precise gold nanoclusters

This work presents a combined approach of kinetic control and thermodynamic selection for the synthesis of monodisperse 19 gold atom nanoclusters protected by thiolate groups. The step of kinetic control allows the formation of a proper size distribution of initial size-mixed Au(n)(SR)(m) nanoclusters following the reduction of a gold precursor. Unlike the synthesis of Au(25)(SR)(18) nanoclusters, which involves rapid reduction of the gold precursor by NaBH(4) followed by size focusing, the synthesis of 19-atom nanoclusters requires slow reduction effected by a weaker reducing agent, borane-tert-butylamine complex. The initially formed mixture of nanoclusters then undergoes size convergence into a monodisperse product by means of a prolonged aging process. The nanocluster formula was determined to be Au(19)(SC(2)H(4)Ph)(13). This work demonstrates the importance of both kinetic control of the initial size distribution of nanoclusters prior to size focusing and subsequent thermodynamic selection of stable nanoclusters as the final product.     

Air-breathing fuel cells fed with dimethoxymethane (DMM) vapor

The dimethoxymethane vapor-fed fuel cell (V-DMMFC) described in this paper is an innovative design for passive water management without the need for a complex micro-fluidic subsystem. DMM is a promising fuel for vapor-fed fuel cells because it has high energy density, an absence of C–C bonds, and lower toxicity as well as high vapor pressure. In a polarization measurement, the V-DMMFC showed an open circuit voltage of around 0.55 V and a high power density of 34.7 mW cm^?2 at 0.315 V, which is higher than that of a fuel cell with MeOH vapor. The V-DMMFC achieved a fast response in fuel feeding and a higher Faradic efficiency (76.1%) than that of fuel cells fed with MeOH vapor (53.7%); these improvements result from a higher vapor pressure and a lower fuel crossover of DMM. For constant voltage (CV) mode, the V-DMMFC provided evidence for the long-term stability of the device and for the sustainability of humidity within the self-humidified MEA without any additional provision of water.     

Kinetic aspects of non-linear effects in asymmetric synthesis,catalysis, and autocatalysis

The Kagan ML_n models developed for rationalizing non-linear effects of catalyst enantiopurity have become a valuable mechanistic tool for probing complex asymmetric catalytic reactions. This work demonstrates how these models also provide clues about reactivity that may be used for further evidence to test a mechanistic hypothesis. Special considerations for probing non-linear effects in asymmetric synthesis using stoichiometric chiral auxiliaries and in asymmetric autocatalysis are highlighted in comparison with asymmetric catalysis.