Numerical study of the kinetics of unimolecular heterogeneous reactions onto planar surfaces

In this paper we investigate two-dimensional in space mathematical models of the kinetics of unimolecular heterogeneous reactions proceeding onto planar surfaces. The models are based on Langmuir-type kinetics of the adsorption, desorption, and reaction including the surface diffusion of the adsorbate, surface diffusion of the product before its desorption, and slow desorption of the product from the adsorbent. It is also assumed that the reactant diffuses towards an adsorbent from a bounded vessel and the product diffuses from the adsorbent into the same vessel. Diffusivity of all species and kinetic coefficients are constants. The numerical simulation was carried out using the finite difference technique for four models: one model neglects the surface diffusion of the adsorbate and product, the second one includes the surface diffusion of the adsorbate and product, the third of them includes the surface diffusion of the adsorbate and neglects diffusion of the product along the surface, and the last one neglects the surface diffusion of the adsorbate and includes diffusion of the product along the adsorbent. By changing input parameters effects of the surface diffusion of the adsorbate and product and the slow desorption of the product are studied numerically.     

钒酸铋颜料制备实验的改进——pH优化

使用改进的实验装置研究钒酸铋颜料制备实验中p H对产物的影响。X射线衍射分析结果表明,在选定实验条件下,产物为四方相为主的四方、单斜两相混合物。p H对钒酸铋颜色有重要影响。酸性条件下颜色偏深,为土黄色;碱性条件下为亮黄色,且p H越大,颜色越淡。推荐反应p H为9,此时产物颜色呈色调较好的亮黄色。     

Approximate Mathematical Model of Heat Exchange in a Complex Thermal Engineering System of Several Product Pipelines Carrying a Motionless Isothermal Product within a Single Insulating Jacket

An approximate mathematical model was developed to describe the heat exchange in a complex thermal engineering system of several parallel product pipelines carrying an motionless isothermal product within a single insulating jacket. The model is distinguished by using a simplified mathematical model of the steady-state heat conduction on a circle (motionless product) and in an annulus (product pipeline wall) under the Robin boundary conditions using various “approximating” effective heat-transfer coefficients in different parts of the boundary of a heated product pipeline carrying the isothermal product with the air space and the insulation.     

Effect exerted on properties of rubber blends and vulcanizates by modification of the silicic acid filler with the product of the reaction of methacrylic acid with trimethylolpropane triglycidyl ether

The product of the reaction of methacrylic acid with trimethylolpropane triglycidyl ether was prepared. The interaction of the epoxy groups of this product with silanol groups on the surface of silicic acid filler was confirmed and studied by IR spectroscopy. Properties of vulcanized rubbers prepared using the filler modified with the product obtained were studied. This product appreciably decreases the viscosity of rubber blends with the silicic acid filler.     

Correlation of product ion profiles with molecular structures of androgenic and anabolic steroids in ESI MS/MS

Androgenic and anabolic steroids (AASs) are a class of chemical substances closely related to testosterone in molecular structure. They can be abused to enhance performances in human and equine athletes, and are banned by the sports authorities. To assist with method development for doping analyses of AASs, investigations were conducted to correlate their product ion profiles with the molecular structures. Although very similar in chemical structure, AASs generated noticeably different product ion profiles from collision‐induced dissociation (CID). On the basis of both outlines of the product ion profiles and molecular structures, AASs studied were classified into six subclasses. In each subclass, the product ion profiles were identical or similar. However, the product ion profiles in one subclass were remarkably different from those in another. The classification reveals that the position and number of double bond(s) in conjugation with the 3‐carbonyl group in the molecular structure of an AAS have significant effects on product ion profile. The presence or absence of the 19‐methyl group in an AAS also has a remarkable influence on its product ion profile. A substitution in the A‐, B‐ or D‐ring of an AAS may cause a shift in mass value of the product ions. The correlation of product ion profiles with molecular structures of AASs has the implication that each AAS can be characterized by a combination of its [M + H]⁺ ion and product ion profile and as a result be identified with specificity. The classified product ion pattern may be useful in the identification of unknown AASs. Copyright © 2010 John Wiley & Sons, Ltd.     

An Improved Synthesis of the Natural Product Isorhapontigenin

lsorhapontigenin (I ) is a natural product with many biological activities. M. Linel a/ first isolated it from the traditional Chinese herb, G.parvdoliunl 1. The totalsynthesis of (I ) has been reported' using miting reaction and TMS as the protectinggroup. the reaction gives both E and Z-stilbene, In an attempt to obtain enough sample of(I ) for screening its bioactivities, we have developed an alternative synthetic route toprepare isorhapontigenin through a 7 steps reaction sequence 3. H…     

Synthesis of aluminum oxides from the products of the rapid thermal decomposition of hydrargillite in a centrifugal flash reactor: II. Structural and textural properties of aluminum hydroxide and oxide obtained from the product of the centrifugal thermal activation of hydrargillite (CTA product)

The basic properties of aluminum hydroxide compounds, namely, the flash product and the centrifugal thermal activation (CTA) product both before and after heat treatment at 400–1100°C are considered. The hydration conditions for obtaining 100% pseudoboehmite from the CTA product are determined. The structure, morphology, and texture of pseudoboehmite aluminum hydroxide synthesized from the CTA product and of the aluminum oxides obtained from this hydroxide in the temperature range 600–1100°C are described.     

Total Synthesis of the Natural Product-Pinosylvin and its Analog

Polyhydroxy stilbenes were proved to have many biological activitiesl'2. 'We havereported the total synthesis of tWo natural products-resveratrol (3,5,4'-tTihydroxylstilbene) and isorhapontigenin 3'4 which were first found in a traditional Chinese herb,G.Parvghlium by M. Lins et al. Herein,we want to present the total synthesis of anothernatural hydroxyl stilbene, pinosylvin (3,5-dihydroxy stilbene,10) isolated from this plantand its analog (3,5,3',5'-tetfahydroxy stilbene,9 ). In the synth…     

Non-isothermal Kinetics of Consecutive Reactions

Theoretical consideration has been made of the non-isothermal kinetics of consecutive reactions based on the superposition principle. In the model the first reaction product reacts to form the final product and the two reactions proceed independently. The amount of the first reaction product and the production rate of the final product have been obtained as a function of time for isothermal cases and as a function of the reduced times for non-isothermal cases. This revised version was published online in August 2006 with corrections to the Cover Date.     

Prediction of the phosphorus pentoxide content in the product as a function of raw material composition in phosphate beneficiation by calcination

A linear model is discussed to describe the phosphorus pentoxide content in the product of phosphate beneficiated by calcination, as a function of the impurities in the product. Relationships were found between the concentrations of the impurity variables in the raw material and in the product. These relationships were used to amend the model permitting prediction of the phosphorus pentoxide content in the product as a function of the composition of the raw material.     

Colorimetric method for the quantitative determination of the antibilharzial drug praziquantel and its application to pharmaceutical preparations.

A method for the colorimetric assay of praziquantel has been developed. For the colorimetric assay, it was necessary to hydrolyse praziquantel with 3 mol dm-3 NaOH, 6 mol dm-3 HCl and 85% phosphoric acid separately. 4-Chloro-7-nitro-2,1,3-benzoxadiazole (NBD-Cl) reacts with the basic hydrolysis product in methanolic aqueous phosphate buffer (pH 7.4), resulting in the formation of an orange product with a characteristic absorption maximum at 478 nm. The red-orange product of the interaction between the hydrochloric acid hydrolysis product and NBD-Cl showed an absorption maximum at 486 nm. The colours obtained were stable for 24 h. The colour system obeyed Beer's law in the concentration range 2-15 and 2-18 micrograms ml-1 for the basic hydrolysis product and the acid hydrolysis product, respectively. The results obtained showed good recoveries with relative standard deviations of 0.378 and 0.47% for the basic and the acid hydrolysis product, respectively. The determination limit was found to be 0.124 and 0.150 micrograms ml-1 for the praziquantel basic hydrolysis product and the acid hydrolysis product, respectively. The coloured reaction products obtained with the proposed method were synthesized. The structures of these products were studied and the compounds identified.     

DNA的滚环扩增合成研究

滚环扩增(RCA)反应作为一种简单高效的等温酶促反应,现已发展为核酸扩增领域的新技术,其产物在组装体搭建和多功能材料的制备方面有着广泛的应用。本文采用琼脂糖凝胶、紫外和透射电镜(TEM)等手段,探究了时间、三磷酸脱氧核糖核苷(dNTPs)、酶以及引物的浓度等因素对脱氧核糖核酸(DNA)滚环扩增产物的影响。结果表明:在反应开始的前30 min,RCA产物的长度受时间的影响比较明显;随着dNTPs浓度的提高,RCA产物的链长增长,浓度也不断提高;酶和引物的浓度对滚环扩增产物的长度没有明显影响,但对RCA产物浓度的影响较大,过量的酶致使RCA产物的含量显著下降。     

Studying of silane thermal decomposition mechanism

The mechanism of silane thermal decomposition is investigated in a flow reactor. The time dependencies of silane consumption and disilane formation were compared with those parameters of solid product (aerosol particles) such as concentration, total hydrogen content in solid product, and fraction of hydrogen contained in solid product as polyhydride groups (SiH₂)_n. Silane loss and gaseous product formation were analyzed using a mass spectrometer. The hydrogen content in solid product was analyzed by the methods of IR-spectroscopy and hydrogen evolution. Based on a simple kinetic scheme we qualitatively explained the experimental dependencies of silane conversion and disilane formation, the effective activation energy of the decomposition process, and the amount of polyhydride groups in the solid product on reaction time and initial silane concentration. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 99–110, 1998.     

Synthesis of aluminum oxides from the products of the rapid thermal decomposition of hydrargillite in a centrifugal flash reactor: II. Physicochemical properties of the products obtained by the centrifugal thermal activation of hydrargillite

A variety of physicochemical methods were used to characterize the product of the rapid thermal decomposition of hydrargillite in a centrifugal flash reactor under the following conditions: the average particle size of the reactant, 80–120 μm; the temperature of the solid heating surface (plate or cylinder), 300–700°C; hot-zone residence time, ～1 s; transfer of the product to the cooled zone of the reactor. The composition of the product and the extent of decomposition of hydrargillite were determined as a function of the processing temperature. The centrifugal thermal activation (CTA) of hydrargillite affords an X-ray-amorphous, highly reactive product with a developed surface and a disordered and inhomogeneous porous structure. This structure is capable of forming different modifications of aluminum hydroxide and oxide. The properties of the CTA product are compared with the properties of the earlier reported hydrargillite rapid decomposition products obtained using a gaseous heat-transfer agent (thermochemical activation product) or a fluidized bed of a granular heat-transfer agent (thermal dispersion product).     

双单体固相共聚改性聚丙烯技术及其机理研究

在马来酸酐(MAH)固相接枝改性聚丙烯(PP)的过程中加入合适比例的异氰脲酸三烯丙酯(TAIC)作为共聚单体,可以大大提高MAH在PP上的接枝率,同时可以有效抑制在普通固相接枝过程中PP的严重降解,得到了性能较好的高极性PP.与普通固相接枝法与熔体接枝法对比,双单体固相共聚接枝改性PP是一种得到高极性PP的有效方法.本文同时对双单体在固相接枝反应中的作用机理进行了探讨.     

离子热法合成沸石咪唑骨架材料及其溶解-结晶机理研究

基于沸石咪唑骨架材料在离子液体和低共熔溶剂中冷却结晶的析出方式,开发了一种离子热法合成沸石咪唑骨架材料的新途径,采用X射线衍射、扫描电镜、核磁共振光谱、红外光谱以及热重分析等方法对制备的产物进行了表征,研究了合成条件对产物结晶度、尺寸和形貌的影响,探讨了沸石咪唑骨架材料在离子热合成体系中的溶解-结晶析出机理.研究发现,冷却速率能够影响产物形貌,急速冷却时,sod(RCSR代码)型产物的形貌为球形,zni(RCSR代码)型产物为棒状或平板状;程序控制冷却时,sod型产物的形貌为多面体,zni型产物呈团簇状.     

Uses and analyses of curtin-hammett/winstein-holness systems involving second order reactions

The Curtin-Hammett (C-H) principle and the Winstein-Holness (W-H) equation approximate the product ratio and overall rate constant of reaction for systems involving a starting material which exists in two forms, each of which reacts via first-order kinetics to give a different product. The C-H/W-H approximations are valid when the rates of isomer interconversion are significantly faster than the rates of product formation. The present treatment encompasses non-first-order reactions to product. A numerical predictor-corrector technique is used to show (1) that relative reagent concentration can affect both the product ratio and the observed rates of product formation; (2) that the absolute concentration of reagent and substrate can affect the kinetics; and (3) that factors (1) and (2) above can affect the validity of the C-H/W-H approximations for non-first-order C-H/W-H schemes.     

The photoinitiated substitution reactions of 2-pyridinecarbonitrile with benzophenone in aqueous 2-propanol

The photoinitiated reaction of 2-pyridinecarbonitrile and benzophenone in acidic 4:1 2-propanol-water yields substitution product 3 and bicyclic product 4 . In nonacidic solution 3 is the principal product in addition to small amounts of a bipyridyl compound 5 .     

Amine-catalyzed Michael reactions of an aminoaldehyde derivative to nitroolefins

Catalytic enantioselective Michael addition reactions of α-amino functionalized aldehydes to nitroolefins have been developed. The Michael product was obtained in up to 98% ee, but the enantiomeric purity of the Michael product was decreased during isolation of the product.     

Chemistry of the phenoxathiins and isosterically related heterocycles. XVII. First synthesis of a benzoxathiinopyridazine and the determination of structure by 13C-NMR: 1-Methoxy-3,4-diazaphenoxathiin

The reaction of 5-methoxy-3,4-dichloropyridazine with the disodium salt of o-mercaptophenol leads to the formation of 1-methoxy-3,4-diazaphenoxathiin as the sole product of the reaction. The structure of the isolated product was confirmed by ¹³C-nmr spectroscopy, with the development of arguments to discriminate the isolated compound from 4-methoxy-1,2-diazaphenoxathiin, the other product possible in this reaction. Mechanistic considerations in the formation of the isolated product are discussed.