The decomposition of surface methoxy on clean and oxygen post dosed Fe(100); control of reaction selectivity

Pure methoxy overlayers on the Fe(l00) surface were prepared and characterized by high resolution electron energy loss spectroscopy (HREELS). Reactions of the methoxy overlayer on the clean surface and in the presence of coadsorbed oxygen have been studied using temperature programmed reaction spectroscopy (TPRS). Post-dosed oxygen alters dramatically the selectivity of methoxy decomposition. Carbon monoxide and hydrogen are the major decomposition products from a pure methoxy overlayer, while formaldehyde is the major decomposition product from an oxygen coadsorbed methoxy overlayer. Clear evidence for production of formaldehyde via a disproportionation of methoxy is presented. Coadsorbed oxygen raises the decomposition temperature of methoxy by 200 K.     

The origin of the support effect in supported metal oxide catalysts: in situ infrared and kinetic studies during methanol oxidation

The strong influence of the oxide support upon the turn-over frequency (TOF) of methanol oxidation over supported metal oxide catalysts has been well documented in recent years. However, the mechanistic origins (adsorption equilibrium of methanol to methoxy species, rate-determining methoxy surface decomposition, or product desorption equilibrium) of this interesting phenomenon are not completely understood. In order to obtain additional insight, the steady-state surface concentrations of adsorbed methoxy intermediates on monolayer catalysts (8 V atoms nm⁻²) of V₂O₅/(TiO₂, CeO₂, Al₂O₃ and ZrO₂) have been quantified with in situ transmission infrared spectroscopy/mass spectrometry. Calculations of the adsorption equilibrium constant, K_ads, show a six times increase for vanadia on oxide supports of Al < Ti < Zr < Ce, whereas the methoxy surface decomposition rate constant, k_rds (rds = rate-determining step), shows a 22 times increase in value over these same catalysts. Thus, changes in both the adsorption equilibrium and the methoxy decomposition properties of supported metal oxide catalysts appear to be responsible for the support effect, although the methoxy decomposition is clearly the reaction step that is more sensitive to the specific metal oxide support. More fundamentally, the support effect appears to correlate with the electronegativity of the support cation, which is proposed to have influence upon the rate of methoxy decomposition through hydride abstraction and on the steady-state equilibrium adsorption capacity of methanol to surface methoxy intermediates through the basicity of the bridging V–O–support bond (the adsorption site).     

The importance of diffusion in surface reactions demonstrated with STM

We have used STM to observe directly a process which can be described as two-dimensional, surface-mediated Ostwald ripening, occurring during the decomposition of methoxy intermediates on a Cu(l10) surface. Some islands get bigger during the course of the reaction, at the expense of smaller ones, and it is shown that this diffusion is important for dictating the rate of methanol decomposition. This is proposed to occur from the dilute phase of methoxy existing in the inter-island region and the methoxy maintains a pseudo steady state there, supplied by diffusion from, and between, islands of adsorbate on the surface.     

不同结构二苯胺重氮盐及重氮树脂的光，热分解

对二苯胺－4－重氮盐（DS），邻－甲氧基二苯胺－4－重氮盐（MDS）和N－甲基－间硝基二苯胺－4重氮盐（NDS）及它们的重氮树脂（DR，MDR，NDR）在水溶液中的光，热分解研究表明，这些重氮盐和树脂的光分解性质，即感光灵敏性差别不大，而热分解性质，即热稳定性差别很大，MDS的热稳定性最好，固相膜中3种树脂的光分解亦差别不大，但N－甲基－间硝基二苯胺－4－重氮树脂（NDR）固相膜的热稳定性出乎预料地好，从疏水性的角度对NDR固相膜突出的热稳定性作了初步解释。     

聚[2-甲氧基-5-(3′-甲基)丁氧基]对苯乙炔的合成及性能研究

以对甲氧基苯酚和溴代异戊烷为原料,经过三步反应制备了大π共轭高分子聚[2 甲氧基 5 (3′ 甲基)丁氧基]对苯乙炔(MMB PPV),摩尔产率为48%。聚合反应投料比为n(双氯苄)∶n(叔丁醇钾)=1∶5。利用1H NMR、FT IR和元素分析等对产物及中间体的结构进行了表征。UV Vis光谱表明,MMB PPV在波长450～550nm具有显著的吸收。TG曲线显示,MMB PPV的失重主要由两个部分组成,245℃对应于聚合物的分解温度。分别用H2SO4、FeCl3和I2对MMB PPV粉末进行掺杂,掺杂后MMB PPV的电导率依次为0 34、8 5×10-2和4 7×10-3S/cm。此外,采用分光光度计对MMB PPV的光学禁带宽度(Eg)进行测量,线性拟合的结果分别为2 02eV及2 07eV。     

A comparative study of the catalytic decomposition of methanol on rhodium and nickel

Pulsed field desorption mass spectrometry shows that decomposition of methanol on Rh and Ni occurs via step-wise hydrogen abstraction from an adsorbed methoxy. Contrary to previous suggestions, an alternative mechanism through adsorbed methyl was not observed on Ni for pressures up to 3×10^–3 Pa and temperatures up to the desorption of CO.     

烯丙基化二苯醚低聚物的合成及其与BMI的共聚合

本文从甲氧基二苯醚出发,合成了一种新型的烯丙基化合物,采用现代分析方法,如IR,UV/VIS,H~1NMR和元素分析等手段对其进行表征。表明,这是一个主链为芳香结构,链端带有烯丙基的低聚物。该低聚物与BMI的固化反应由一个低温下的烯基加成反应和一个高温下的Diels-Alder反应构成。热重分析表明,该低聚物与BMI的固化物具有极高的热稳定性,在氮气氛中,起始热分解温度可达560℃,分解速率最高时的温度可达600℃、800℃时的碳残留率接近45％。     

Oxidation of methanol at copper surfaces

The role of preadsorbed oxygen present at Cu(111), Cu(110) and polycrystalline surfaces in the oxidation of methanol has been investigated by X-ray and electron energy loss spectroscopies. In addition to the well established formation of methoxy species and its subsequent decomposition and desorption as formaldehyde, a second reaction pathway to surface formate is present. The latter is temperature dependent being undetectable at 260 K at a polycrystalline surface but occurs at a significant rate at 295 K and above. The limitations of experimental data for methanol oxidation by temperature programmed desorption and molecular beam techniques are discussed.     

新型耐热树脂ANDPO/E-44共聚物的研究

本文研制了一种新型的氨基二苯醚树脂（ＡＮＤＰＯ）,并利用其与环氧树脂共聚,研究了共聚机理,考察了共聚物的耐热性,结果表明共聚物热分解温度可达３０８℃,耐热指数为１８９℃。     

Hydrolytic,reductive and pyrolytic decomposition of selected ozonolysis products. Water as an ozonization medium

Hydrolytic, reductive and pyrolytic decompositions of ozonolysis products formed in water were surveyed as potential preparative routes to aldehydes. Water is an effective ozonolysis medium and reacts with the transient zwitterion formed during ozonolysis in the same manner as participating solvents. Reductive decomposition proved to be superior to either hydrolytic or pyrolytic decomposition for the preparation of aldehydes. Pyrolytic decomposition, as carried out in the injection port of a gas chromatograph, gave varying amounts and types of products depending upon the type of ozonolysis product used. Interconversion of the various types of ozonolysis products, including ozonides, methoxy hydroperoxides, acetoxy hydroperoxides and hydroxy hydroperoxides, does not occur except under acid catalysis. Presented in part at the AOCS Meeting, Philadelphia, October, 1966. No. Utiliz. Res. Dev. Div., ABS, USDA.     

Improved atom efficiency via an appreciation of the surface activity of alumina catalysts: Methyl chloride synthesis

The hydrochlorination of methanol over a commercial grade η-alumina catalyst has been investigated via temperature-programmed reaction (TPR). Experiments were conducted over a temperature range of 295–1000 K using: (i) a methanol-only feed stream and (ii) a methanol/HCl mixed feed stream in a 1:1 mole ratio. Methanol-only studies showed activity for the formation of dimethyl ether (DME) above 450 K, consistent with temperature-programmed desorption studies. A rapid decline in DME activity and consumption of methanol at higher temperatures were observed and are attributed to a deactivation pathway, involving the conversion of methoxy species to surface formate species. At elevated temperatures these processes lead to the deposition of carbon on the substrate. The introduction of HCl to the reaction stream resulted in the formation of methyl chloride (MC) over a temperature range of 400–750 K. Relatively small quantities of DME by-product were also observed over a similar temperature range. The coincidence of the reaction profiles of both MC and DME imply that the same reactive methoxy species are involved in both processes. The rate of reaction for the formation of both products declines rapidly above 700 K. This is attributed to the methoxy decomposition pathway to formate and, ultimately, to carbon retention by the catalyst.

The effect of carbon deposition was also investigated via a subsequent cooling process carried out immediately after TPR experiments. Reaction profiles showed comparable activity for the formation of both products with respect to initial TPR experiments. Taken together, these results indicate an optimum reaction temperature for the formation of methyl chloride from the hydrochlorination of methanol. At such temperatures, carbon deposition is minimized and high conversion is maintained.     

Methanol oxidation on Au/TiO2 catalysts

We have investigated the adsorption and reaction of methanol with Au/TiO₂ catalysts using a pulsed flow reactor, DRIFTS and TPD. The TiO₂ (P25) surface adsorbed a full monolayer of methanol, much of it in a dissociative manner, forming methoxy groups associated with the cationic sites, and hydroxyl groups at the anions. The methoxy is relatively stable until 250 °C, at which point decomposition occurs, producing mainly dimethyl ether by a bimolecular surface reaction. As the concentration of methoxy on the surface diminishes, so the mechanism reverts to a de-oxygenation pathway, producing mainly methane and water (at ~330 °C in TPD), but also with some coincident CO and hydrogen. Au catalysts were prepared by the deposition-precipitation method to give Au loadings between 0.5–3 wt %. The effect of low levels of Au on the reactivity is marked. The pathway which gives methane, which is characteristic of titania, remains, but a new feature of the reaction is the evolution of CO₂ and H₂ at lower temperature (a peak is seen in TPD at 220 °C), and the elimination of the DME-producing state. Clearly this is associated with the presence of Au and appears to be due to the production of a formate species on the surface of the Au component. This formate species is mainly involved in the reaction of methanol with the Au/TiO₂ catalysts which results in a combustion pathway being followed, with complete conversion occurring by ~130 °C.     

Synthesis and Characterization of Poly(o-anisidine) Doped with Polymeric Acids

ABSTRACT

Conducting poly(o-anisidine) doped with polymeric acids [viz, poly(styrene sulphonic acid) (PSSA), poly(vinyl sulphonic acid) (PVSA) and poly(acrylic acid) (PAA)] was synthesized by in-situ chemical polymerization method using ammonium persulphate as an oxidizing agent. This is a single-step polymerization process for the direct synthesis of emeraldine salt phase of the polymer. The polymers were characterized by using UV-Vis., FT-IR spectroscopy, thermal analysis, and conductivity measurements. Formation of mixed phases of polymer together with conducting emeraldine salt phase are confirmed by spectroscopic techniques. Thermal analysis shows that PAA doped poly(o-anisidine) undergoes three stage decomposition pattern similar to unsubstituted polyaniline. While, in PSSA and PVSA, doped sample splitting up of the second weight loss stage is observed leading to a four-step decomposition pattern. Room temperature conductivity measurements show less conductivity in poly(o-anisidine) than in polyaniline, due to the cumulative steric as well as electronic effects of the bulky methoxy substituent present at ortho position on the benzene ring. Increase in conductivity with increase in temperature is observed by high temperature conductivity measurements, showing “thermally activated behavior.”     

檀香醚的绿色合成

目前工业上合成檀香醚的工艺存在对设备要求高、腐蚀性强、污染环境、产物不易分离等问题,本实验通过改进传统工艺中的环氧化和催化氢化反应,实现了标题化合物的绿色合成.实验所得的中间体和檀香醚结构经1HNMR、13CNMR确定.     

Palladium-catalysed direct regioselective C5-arylation of a thiophene bearing a cyclopropyl ketone group at C2

A thiophene bearing a cyclopropyl ketone group at C2 was successfully employed in palladium-catalysed direct arylation. The reaction proceeds regioselectively at C5 without decomposition of the cyclopropyl ketone substituent. These couplings were performed employing as little as 0.5 mol% of ligand-free Pd(OAc)₂ catalyst with electron-deficient aryl bromides. A wide variety of functional groups on the aryl bromide such as nitrile, nitro, acetyl, formyl, benzoyl, ester, trifluoromethyl, fluoro or methoxy was tolerated. © 2013 Elsevier Science. All rights reserved.     

Microstructure and tacticity in radical copolymerization I.

The NMR spectra of styrene-methyl methacrylate copolymers were found to exhibit a multiplicity in the 2.0–3.6δ region characteristic for methoxy protons. The methoxy pattern is explained by taking into account the degree of shielding of methoxy protons, in relation to both number and configuration of the neighbouring styrene units along the chain. The relative areas of the methoxy peaks are compared with results of the statistical analysis of monomer sequence probabilities.     

Pendent polyimides using mellitic acid dianhydride. III. The effect of pendent group functionality on polymer properties

Methyl, methoxy, and nitrile (cyano) functional groups were incorporated into the metal–organic pendent group of a co‐polyamic acid, co‐PAA[(3,4′‐ODA/ODPA)_0.9(3,4′‐ODA/{MADA‐p‐Zr(adsp)(Rdsp)})_0.1], in various locations to investigate their effects on polymer chain interactions and film quality. Proton nuclear magnetic resonance and gel permeation chromatography (GPC) performed on solutions of these products were consistent with the expected 10% (mol) functionalized pendent polymeric structures. Thermogravimetric analysis performed on ether‐precipitated samples revealed little functional group effect on imidization temperature (decreases of 5–8°C), but showed a somewhat‐greater effect on decomposition temperature (decreases of 6°C for the 3‐methoxy derivative to 28°C for the methyl derivative). Differential scanning calorimetry performed on imidized powder samples showed that glass transition temperatures increased with the addition of the functional groups from 2°C for the methyl derivative to 19°C for the 3‐methoxy derivative. Imidized films were solvent resistant, transparent, and flexible, with the nitrile derivative least susceptible to crack formation. Light scattering results revealed that the nitrile derivative had the lowest second virial coefficient of the functional groups tested and formed aggregates at room temperature in NMP with n = 2, thus rationalizing its superior film forming properties. Results of contact angle measurements and atomic oxygen exposure of functionalized pendent co‐PI films are included. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Convenient determination of methoxy groups of methylated melamine-formaldehyde resins by IR spectroscopy

The content of methoxy groups of methylated melamine-formaldehyde resins was determined by infrared spectroscopy. The correlation between the area ratio (S) of 815 cm^?1 band to 913 cm^?1 band, which are the characteristic absorption bands of triazine and methoxy residue, respectively, and methoxy groups values (OMe) determined by gas liquid chromatography analysis was expressed as S = 1.08 × OMe + 0.24. The correlation coefficient was found to be 0.997.     

Electrochemical performances of lithium ion battery using alkoxides of group 13 as electrolyte solvent

Tris(methoxy polyethylenglycol) borate ester (B-PEG) and aluminum tris(polyethylenglycoxide) (Al-PEG) were used as electrolyte solvent for lithium ion battery, and the electrochemical property of these electrolytes were investigated. These electrolytes, especially B-PEG, showed poor electrochemical stability, leading to insufficient discharge capacity and rapid degradation with cycling. These observations would be ascribed to the decomposition of electrolyte, causing formation of unstable passive layer on the surface of electrode in lithium ion battery at high voltage. However, significant improvement was observed by the addition of aluminum phosphate (AlPO₄) powder into electrolyte solvent. AC impedance technique revealed that the increase of interfacial resistance of electrode/electrolyte during cycling was suppressed by adding AlPO₄, and this suppression could enhance the cell capabilities. We infer that dissolved AlPO₄ components formed electrochemically stable layer on the surface of electrode.     

Biodegradable nanoparticles of methoxy poly(ethylene glycol)-b-poly( d, l-lactide)/methoxy poly(ethylene glycol)- b-poly(ϵ-caprolactone) blends for drug delivery

The effects of blend weight ratio and polyester block length of methoxy poly(ethylene glycol)-b-poly( d, l-lactide) (MPEG- b-PDLL)/methoxy poly(ethylene glycol)- b-poly(ϵ-caprolactone) (MPEG- b-PCL) blends on nanoparticle characteristics and drug release behaviors were evaluated. The blend nanoparticles were prepared by nanoprecipitation method for controlled release of a poorly water-soluble model drug, indomethacin. The drug-loaded nanoparticles were nearly spherical in shape. The particle size and drug loading efficiency slightly decreased with increasing MPEG- b-PCL blend weight ratio. Two distinct thermal decomposition steps from thermogravimetric analysis suggested different blend weight ratios. Thermal transition changes from differential scanning calorimetry revealed miscible blending between MPEG- b-PDLL and MPEG- b-PCL in an amorphous phase. An in vitro drug release study demonstrated that the drug release behaviors depended upon the PDLL block length and the blend weight ratios but not on PCL block length.