Solvenseffekte bei der Photoinduzierten Elektronenübertragung von ungeladenen Donatoren auf Arendiazoniumsalze

Solvent Effects in the Photoinduced Electron Transfer Reaction of Uncharged Donors with Arenediazonium Salts In the photochemical electron transfer reactions to arene diazonium salts no strong Coulomb forces arise but the rate constants possibly vary in dependence on the state of the diazonium salt (tight ion pair in nonpolar solvents or free diazonium cations). This problem is studied in the present work using anthracene and tetracene, respectively, as electron donors. They react in their S₁ states diffusion-controlled with ion pairs ArN₂^⊖ BF₄^⊖, whereas the respective triplet reactions proceed up to 10³ times more slowly. These rates are not significantly influenced by the dielectric properties of the solvent. Thus, ion pairing of the diazonium salts in solvents of low polarity has no screening effect on the electron transfer. This behavior is explained including electrostatic effects into the MARCUS theory of outer sphere electron transfer processes. No indication of a Marcus inverted region was found.     

Oxidation of alkenes with use of phase transfer catalysis

The use of phase transfer catalysis (PTC) as an aid in the oxidation of long chain olefins with aqueous potassium permanganate (KMnO₄) in neutral and alkaline media and with aqueous ruthenium tetroxide (RuO₄) is reported. The phase transfer catalysts (PTCT) were either quaternary ammonium halides or crown ethers. The long chain olefins studied were 1-pentadecene, 9-octadecene, and methyl oleate. PTC not only increases the rate of these reactions but also gives good yields of reaction products. For example,cis-9-octadecene in methylene chloride reacted with aqueous KMnO₄ to give either dihydroxyoctadecane (80%) or pelargonic, acid (80%) depending upon pH, when tetrabutylammonium bromide was used as the PTCT. When RuO₄ in conjunction with a PTCT was used as the oxidant, a quantitative yield of myristic acid was obtained from 1-pentadecene. The RuO₄ oxidant was conveniently regenerated in situ from RuO₂ and sodium hypochlorite. This regeneration is facilitated with a PTCT.     

Photoinduzierte Elektronenübertragungsreaktionen zwischen aromatischen Diazoniumkationen und Anionen

Photoinduced Electron Transfer between Arenediazonium Cations and Anions Anions X^⊖ can act as donors in electron transfer reactions to photoexcited arenediazonium ions. The yield of the arene formed in this reaction increases with decreasing electrochemical oxidation potential E of X^⊖ (X^⊖ = BPh₄^⊖, Br^⊖, HOOC COO^⊖, Cl^⊖, BF₄^⊖). The oxidized donor X· (Cl·, ·COO^⊖) and aryl radicals Ar· benig intermediates of the reductive dediazoniation of ArN₂^⊖ can be detected by spin trapping with nitrosodurene (ND) and phenyl-tert-butylnitrone (PBN). A solvent effect in the electron transfer reaction is interpreted in terms of ion pairing, where the electron transfer is favored by preorientation and a short distance between the electron donor and the acceptor previous to excitation of ArN₂^⊖ by light.     

Synthesis of polystyrenes having 2-pyridylthio group and their use as phase transfer catalysts for the reduction of carbonyl compounds by sodium borohydride

p-(2-Pyridylthiomethyl)styrene (PTMS) and p-(2-pyridylthioethyl)styrene (PTES) were prepared from the reactions of 2-pyridinethiol with p-chloromethylstyrene and with p-bromoethylstyrene, respectively. These monomers are readily polymerized in the presence of AIBN. From the copolymerization of PTMS with styrene, Q_PTMS = 1.19 and e_PTMS = 0.24 were obtained. The resulting polymers can extract alkali metal ions such as sodium and potassium cations. The extraction ability increases with increasing the density of active sites in polymers. Further these polymers serve as phase transfer catalysts for the reduction of carbonyl compounds by sodium borohydride.     

Perkin反应合成肉桂酸工艺的改进

采用PEG400为相转移催化剂,以无水碳酸钾和氟化钾为催化剂,对肉桂酸的Perkin合成工艺进行了改进,通过考察催化剂配比、反应时间得到最佳的反应条件,产率可达64.86%。     

普拉洛芬的合成研究改进

以2-氯烟酸为原料,在强碱环境下与苯酚缩合,然后通过多聚磷酸脱水,硼氢化钾还原,再经过酸性水解,最后与氯乙酰氯进行酰化反应后,在碱性条件下发生水解反应,经磺酰氯酰化,最终通过重排得到普拉洛芬。此工艺不仅避免使用氯化锌和氰化钾,同时也减少了副反应,总收率23．7％,工艺稳定可行。     

The N2O–carbon reaction: The influence of CO and potassium on reactivity and populations of oxygen surface complexes

N₂O reduction on two different chars promoted with potassium was investigated using temperature programmed reaction, as well as isothermal reaction followed by temperature programmed desorption. It was found that potassium promotion significantly increased the N₂O reduction activity of the phenolic resin char, but not for the Wyodak coal char. Additional CO in the reactor feed gas had no discernible effect on the N₂O reduction rate of the phenolic resin char, but it did significantly increase the reactivity of the promoted, demineralized Wyodak coal char. The latter is attributed to residual mineral matter impurities in the coal that are not removed by the demineralization process used.     

Ionenpaareffekte bei der Photolyse und Thermolyse von Aryldiazonium-tetrafluoroboraten

Ion Pair-Effects in the Photolysis and Thermolysis of Arenediazonium Tetrafluoroborates Fluoroarenes produced by Schiemann-reaction of p-methyl- and p-tert.-butyl-benzenediazonium tetrafluoroborates in solution are formed mainly from ArN₂⁺/BF₄⁻-ion pairs. The ratio of product yields formed from the reaction of arene cations with the solvent to the yields of fluoroarenes increases with increasing K_D/α; K_D is the conductometrically determined dissociation constant, and α the dissociation degree of ion pairs. The photochemical and thermal dediazoniation gives the same product ratios, indicating, that both sorts of reactions proceed via the same intermediate — the arene cation.     

A KINETIC STUDY OF PHASE TRANSFER CATALYZED BENZYLATION OF 2,4,6-TRIBROMOPHENOL IN LIQUID-LIQUID TWO-PHASE SOLUTION

Phase-transfer catalytic reactions of the derivatives of benzyl halide and 2,4,6-tribromophenol have been successfully carried out in an organic solvent/alkaline solution of KOH two-phase medium. The main purpose of this work is to study the effects of the leaving groups, orientations, and functional groups of the derivatives of benzyl halide on the reaction rate and the product yield. To identify the reaction rate in the organic phase, 2,4,6-tribromophenol is employed as the nucleophilic reagent under phase-transfer catalytic reaction. Reactions of aqueous phase and organic phase can be separately carried out to determine the reaction rate constants. Results obtained from the single organic-phase reaction are compared with those obtained from the two-phase phase transfer catalytic reaction. According to the experimental data, simplified models for representing the single-phase reaction and the two-phase reactions were proposed and derived. The reaction rate constants for the single-phase model (k_s) and the two-phase model (k_T) were compared to show their consistency. The kinetics of the reactions of the derivatives of benzyl halide and 2,4,6-tribromophenol were also studied. The effects of the leaving group, orientation, and functional group of the organic substrate on the reaction rate constant were also investigated in detail. A satisfactory explanation was arrived at to account for the experimental evidence.     

Cyclone flow cell for the investigation of gas-diffusion electrodes

Electrochemical gas–liquid reactions can be efficiently carried out at porous gas diffusion electrodes (GDE). These electrodes are simultaneously in contact with a gas phase and a liquid phase. For the design and scale-up of electrochemical reactors based on these GDE their macrokinetic behaviour (i.e., the interaction of reaction and internal mass transport phenomena) must be investigated under well defined external mass transfer conditions and controlled wetting conditions. To meet these requirements, a novel cyclone cell has been designed in which two vortex flow fields are realised on either side of a horizontally positioned GDE. The external mass transfer coefficients in this cell are determined from limiting current measurements for the oxidation of Fe(CN₆)^4–.     

Phase Transfer Oxidations with Hypochlorite: Scope and Mechanism

The use of phase transfer catalysis (PTC), with catalytic amounts of lipophilic quaternary ammonium salts for the transfer of hypochlorite ion from aqueous to organic media, has been found to be an extremely effective and convenient method for the oxidation of many alcohols and amines. An interesting and unexpected specific solvent effect has also been discovered with the use of ethyl acetate which greatly expands the synthetic utility of this method. Both the synthetic scope and mechanistic aspects of these reactions are reported.     

The reductive alkylation of Illinois No. 6 coal. Factors governing the reductive alkylation reaction in ethereal solvents

The reductive alkylation of Illinois No. 6 coal has been investigated to determine the experimental conditions that are most suitable for the conversion of the coal to an alkylated product that is soluble in tetrahydrofuran. Thermodynamic and kinetic factors influence the reactivity of the reducing agent; potassium is the most effective alkali metal. The reduction potentials of the aromatic hydrocarbons used as electron transfer agents dictate the effectiveness of these reagents; biphenyl and naphthalene are more suitable reagents than anthracene. The alkylation reaction is a kinetically controlled S_N2 process and reactive reagents such as primary alkyl iodides and sulphonates are necessary for complete alkylation reactions. Under the most suitable conditions, potassium, naphthalene, and straight-chain butyl iodide allow the conversion of almost 90 wt% of Illinois No. 6 coal to products that are soluble in tetrahydrofuran.     

Polymerization of Butyl Acrylate using Potassium Peroxy Disulfate as Initiator in the Presence of Phase Transfer Catalyst—A Kinetic Study

The kinetics and mechanism of free radical polymerization of butyl acrylate (BA), using potassium peroxydisulfate (K₂S₂O₈) as initiator in the presence of propiophenonebenzyldimethylammonium chloride (PPBDMAC) as phase transfer catalyst (PTC) has been studied. The reactions were carried out under inert, unstirred conditions and at a constant temperature of 60°C in cyclohexanone/water biphase media. The dependence of the rate of polymerization (R_p) on various experimental conditions such as different concentrations of monomer, initiator, phase transfer catalyst, varying acid and ionic strength, temperature, and volume fraction of aqueous phase were studied. The order with respect to monomer, initiator, and the phase transfer catalyst were found to be 1.5, 0.5, and 0.5, respectively. The rate of polymerization was independent of acid and ionic strength. Based on the results, a mechanism has been proposed for the polymerization reaction.     

Use of potassium conductors in the electrochemical promotion of environmental catalysis

This study summarizes the effect of the electrochemical promotion of catalysis (EPOC) by using potassium conductors in environmental catalytic reactions applied to the removal of several automotive pollutants, such us CO, C₃H₆ and nitrogen oxides (N₂O and NO_x). It has been shown the extraordinarily potential of using Pt/K–βAl₂O₃ in a wide variety of environmental reactions (oxidation, reduction), activating the catalyst at lower reaction temperatures and decreasing the inhibitory effect of poisons such as water in the reaction atmosphere. In addition, a new application of potassium conductors-based electrochemical catalysts has been developed for the NO_x storage/reduction process (NSR). The idea of coupling catalysis and solid-state electrochemistry on this process would allow to improve and simplify the current NSR technology. Finally, the results have been obtained under reaction conditions compatible with the treatment of automotive exhaust emissions. This demonstrates the potential for the practical use of the phenomenon of electrochemical promotion by using potassium conductors on this kind of process.     

Design of mixed conducting ceramic membranes/reactors for the partial oxidation of methane to syngas

The performance of mixed conducting ceramic membrane reactors for the partial oxidation of methane (POM) to syngas has been analyzed through a two‐dimensional mathematical model, in which the material balance, the heat balance and the momentum balance for both the shell and the tube phase are taken into account. The modeling results indicate that the membrane reactors have many advantages over the conventional fixed bed reactors such as the higher CO selectivity and yield, the lower heating point and the lower pressure drop as well. When the methane feed is converted completely into product in the membrane reactors, temperature flying can take place, which may be restrained by increasing the feed flow rate or by lowering the operation temperature. The reaction capacity of the membrane reactor is mainly determined by the oxygen permeation rate rather than by the POM reaction rate on the catalyst. In order to improve the membrane reactor performance, reduction of mass transfer resistance in the catalyst bed is necessary. Using the smaller membrane tubes is an effective way to achieve a higher reaction capacity, but the pressure drop is a severe problem to be faced. The methane feed velocity for the operation of mixed conducting membrane reactors should be carefully regulated so as to obtain the maximum syngas yield, which can be estimated from their oxygen permeability. The mathematical model and the kinetic parameters have been validated by comparing modeling results with the experimental data for the La_0.6Sr_0.4Co_0.2Fe_0.8O_3‐α (LSCF) membrane reactor. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Effect of laminar flow on the rate of mass transfer inside cubical cavities

An electrochemical technique which involved measuring the limiting current of the cathodic reduction of potassium ferricyanide was used to study the rate of mass transfer inside a cubical cavity machined in the wall of a vertical rectangular duct. Variables studied were side length, physical properties of the solution and flow rate of the solution. The mass transfer coefficient was found to decrease with increasing cavity size; in all cases, the mass transfer coefficient inside the cavity was less than that at the duct wall. Mass transfer data inside the cavity were correlated by the equation Sh_c = 0.525 (Sc Re d_e/L)^0.33. Comparison of the present results with the results obtained using other cavity geometries shows that cavity geometry plays an important role in determining the rate of mass transfer inside the cavity.     

Influence of potassium loading at different reaction temperatures on the NOx reduction process by potassium-containing coal pellets☆

The activity of potassium-containing coal pellets and the corresponding free-metal char for NO_x reduction in an oxygen-rich environment has been investigated by temperature-programmed reactions (TPRs) up to 750 °C, 2 h isothermal reactions in the range of 250-475 °C and lifetime tests, (until the samples were completely consumed), for selected samples and temperatures. An interesting ‘reactivity window’, where NO_x reduction is observed, but carbon conversion is negligible, was found from TPRs experiment for a high potassium content sample, at moderate temperatures. This interval was not observed for the char. The catalytic effect of potassium is more dramatic at high temperatures, therefore, metal loading and reaction temperature are very much interrelated. Lifetime tests provide a very valuable information (average selectivity, profitable use of samples for NO_x reduction, etc.), allowing us to check the whole efficiency of the samples. The progressive addition of potassium to the pellets makes samples more effective in terms of: (i) capacity to reduce higher NO_x amounts; (ii) maximum NO_x conversion values and (iii) higher values of average selectivity. In general, the samples studied, exhibit a maximum temperature, very much dependent on their potassium contents, that must not be exceeded with a view to practical applications.     

Poly(styrene)s with oligo(ethylene oxide) side chains as catalysts for phase transfer reactions

Summary A very interesting part within the wide field of chemical reactions are-catalyzed reactions. To find an effective low cost catalyst for various applications is a primary goal of many workers. Polymer chemistry is able to provide systems with qualities not known for monomeric catalysts. Especially in heterogenic systems the use of polymeric catalysts has many advantages such as easy separation for reuse or low toxicity. A special type of heterogenic catalysis is the phase transfer catalysis. Comb polymers of poly(styrene) with oligo(ethylene oxide) side chains were investigated for their ability as phase transfer catalysts.     

6-苯甲酰基-2,2-二甲基-7-羟基色满的合成研究

以间苯二酚、3-甲基-2-丁烯酸为原料经过环合反应,锌汞齐还原,与酰氯反应成酯,Fries重排得到6-苯甲酰基-2,2-二甲基-7-羟基色满,总收率49.6%。该路线原料廉价易得、操作简单、副反应少、收率较高,具有工业化应用前景。     

Hydrothermal processing of microalgae using alkali and organic acids

Aquatic organisms such as microalgae have been identified as a potential source of third generation biofuels due to their fast growth rate, ability to sequester CO₂ and their potential for producing lipids. Conversion by hydrothermal liquefaction is ideally suited to high moisture content feedstocks such as microalgae and involves the processing of biomass in hot compressed water with or without the presence of a catalyst. This study aims to investigate the conditions for producing high quality, low molecular weight bio-crude from microalgae and cyanobacteria containing low lipid contents including Chlorella vulgaris and Spirulina. Liquefaction experiments have been performed in a high pressure batch reactor at 300 °C and 350 °C. The influence of process variables such as temperature and catalyst type has been studied. Catalysts employed include the alkali, potassium hydroxide and sodium carbonate and the organic acids, acetic acid and formic acid. Liquefaction yields have been determined and the bio-crude has been analysed for CHNOS content and calorific value. The bio-crude has been analysed by GC/MS to examine composition and thermal gravimetric analysis (TGA) to estimate its boiling point range. The aqueous fraction has been analysed for typical cations and anions by ion exchange chromatography and for total organic carbon (TOC). The yields of bio-crude are higher using an organic acid catalyst, have a lower boiling point and improved flow properties. The bio-crude contains a carbon content of typically 70-75% and an oxygen content of 10-16%. The nitrogen content in the bio-crude typically ranges from 4% to 6%. The higher heating values (HHV) range from 33.4 to 39.9 MJ kg⁻¹. Analysis by GC/MS indicates that the bio-crude contains aromatic hydrocarbons, nitrogen heterocycles and long chain fatty acids and alcohols. A nitrogen balance indicates that a large proportion of the fuel nitrogen (up to 50%) is transferred to the aqueous phase in the form of ammonium. The remainder is distributed between the bio-crude and the gaseous phase the latter containing HCN, NH₃ and N₂O depending upon catalyst conditions. The addition of organic acids results in a reduction of nitrogen in the aqueous phase and a corresponding increase of NH₃ and HCN in the gas phase. The addition of organic acids has a beneficial effect on the yield and boiling point distribution of the bio-crude produced.