Kinetic investigation of propene polymerization with stopped‐flow method

The stopped‐flow technique, by which a quasi‐living polymerization process can be performed within an extremely short period (ca. 0.2s), is a powerful method for kinetic investigation in Ziegler catalysis. Significant understanding of many controversial problems was achieved, such as arguments concerning the nonuniformity of the active sites, the accurate kinetic parameters, the active sites formed in the different stages, the role of cocatalyst, the effects of hydrogen and electron donors, etc..     

Palladium‐catalyzed carbonylation of primary amines in supercritical carbon dioxide

The chemoselectivity of the palladium‐catalyzed carbonylation of amines was affected by the addition of MeOH in supercritical carbon dioxide. The results show different selectivity in supercritical carbon dioxide CO₂(sc) from that in alcohol. Methyl carbamate and its derivatives were obtained in high yields in CO₂(sc).     

Analysis of xylene in aqueous media using needle‐trap microextraction with a carbon nanotube sorbent

This paper describes a new extraction technique with needles and a sorbent based on carbon nanotubes to analyze trace amounts of three isomers of xylenes in aqueous samples. In this research, results have been compared with one commercial sorbent. The synthesized sorbent was prepared using sol–gel technology and was packed into 20 gauge needles, and the same size needle was used for packing the commercial sorbent. In the extraction process, a purge and trap sampling methodology is developed, so purging and trapping cycles were performed by a sampling pump. Optimized conditions for standard xylene samples have been obtained, and eight urine samples from workers that were exposed to xylene in the workplace were collected and analyzed. Experimental parameters such as limits of detection and quantification were investigated, and these two parameters were <1 μg/L.     

Palladium‐catalyzed Suzuki reaction using 1,3‐dialkylbenzimidazol‐2‐ylidene ligands in aqueous media

From readily available starting compounds, six functionalized 1,3‐dialkylbenzimidazolium salts ( 2a–c and 4a–c ) have been prepared and characterized by conventional spectroscopic methods and elemental analyses. A highly effective, easy to handle, and environmentally benign process for palladium‐mediated Suzuki cross‐coupling was developed. The in situ prepared three‐component systems Pd(OAc)₂/1,3‐dialkylbenzimidazolium chlorides and Cs₂CO₃ catalyze quantitatively the Suzuki cross‐coupling of deactivated aryl chlorides. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:419–423, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20034     

Kinetics of the reaction of pure CO2 with N‐methyldiethanolamine in aqueous solutions

The process of pure carbon dioxide absorption is analyzed in aqueous solutions of N‐methyldiethanolamine (MDEA). The experiments were made in a stirred tank reactor with a plane and known interface area. The variables considered were the MDEA concentration within the range 0.1–3.0 M and the temperature in the interval 288–313 K. From the results, we deduce that the process takes place under isothermal conditions and moderately fast regime, with second‐order kinetics. We determined a reaction order of one with respect to the amine, and an expression for the kinetic constant valid throughout the entire range of temperatures and concentrations assayed ln k = 22.4 ? 6243.5/T. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 204–214, 2009     

Kinetics and mechanism of diethanolamine degradation in aqueous solutions containing carbon dioxide

The problem of diethanolamine (DEA) degradation in gas-treating processes was quantified through a detailed kinetic study. This reaction was found to be catalyzed by CO₂, and degradation occurs in a successive manner to 3-(2-hydroxyethyl)oxazolidone-2, to N,N,N′-tris(2-hydroxyethyl)ethylenediamine and then to N,N′-bis(2-hydroxyethyl)piperazine. A reaction mechanism consistent with these observations was proposed and tested through kinetic analyses. A satisfactory kinetic model which can be of practical use was derived.     

Palladium‐catalysed Suzuki reaction of aryl chlorides in aqueous media using 1,3‐dialkylimidazolidin‐2‐ylidene ligands

A highly effective, easy to handle and environmentally benign process for palladium‐mediated Suzuki cross‐coupling is developed. The in situ prepared three‐component system Pd(OAc)₂–1,3‐bis(alkyl)imidazolinium chlorides (2a–f) and Cs₂CO₃ catalyses quantitatively the Suzuki cross‐coupling of deactivated aryl chlorides. Copyright © 2005 John Wiley & Sons, Ltd.     

Kinetics of chemical absorption of carbon dioxide into aqueous calcium acetate solution

Increasing energy demand in the world leads to more electricity generation mainly at fossil fuel power plants. Greenhouse gases are thus produced and mostly emitted to the atmosphere directly, resulting in global warming and climate change. Carbon dioxide is believed to be a main pollutant among greenhouse gases responsible from global warming. Conventional systems using mostly amine solutions to capture carbon dioxide at the source have some disadvantages, and alternatives are constantly being searched. In this work, a benign system of aqueous calcium acetate solution was investigated for this purpose. Calcium acetate is easy to produce, relatively cheap, environmentally friendly, nonhazardous, and noncorrosive. These properties make it a great alternative for use in capturing carbon dioxide. This absorption process is accompanied by chemical reaction. Therefore, the reaction kinetics needs to be investigated before its use in absorbers. A stirred cell reactor was used in the experiments using aqueous calcium acetate solution of different concentrations (2-20% w/w) and different carbon dioxide concentrations in gas mixtures (4.5-100% v/v dry carbon dioxide) at temperatures ranging from 286 to 352 K. The Gibbs free energy change for the overall reaction between carbon dioxide and aqueous calcium acetate solution was found to be –2.75 kJ/mol that shows the reaction is exergonic and occurs spontaneously. It was also found out that the reaction is pseudo–first order with respect to carbon dioxide which was also proven by calculating the Hatta number. Activation energy and Arrhenius (frequency) constant were also determined experimentally.     

Kinetics and mechanism of the reaction of aquachromium(III) with l-ascorbic acid in aqueous media

The kinetics of the reaction of l-ascorbic acid (H2A) with aquachromium(III) has been studied over the range 0.04 [H2A]T 0.16 mol dm–3, 3.5 pH 6.0, 25.0 t 50.0C, 0.03 I 1.0 mol dm–3 (KNO3) and 0% [MeOH] 20% (v/v). The reaction takes place via an outer-sphere association between Cr3+/CrOH2+ and H2A, followed by transformation of the outer- into an inner-sphere complex by slow interchange. The anation rate constants for Cr3+ and CrOH2+ species (k1 and k2) at 25C and I=1.0moldm–3 (KNO3) are 1.68×10–4 and 2.14×10–4s–1, respectively. H and S for the k1 and k2 paths are 27.0±2kJmol–1, –227±5J K–1mol–1 and 57.2± 4kJmol–1, –123±14JK–1mol–1, respectively. Anation of Cr(H2O)3+6 and Cr(H2O)5OH2+ follow an Ia path.     

Direct asymmetric aldol reaction in aqueous media using polymer-supported peptide

PEG-PS resin-supported tripeptide/zinc chloride catalyst system has been developed for use in the direct asymmetric aldol reaction of acetone with aldehydes in aqueous media. The peptide catalyst could be separated from the reaction mixture by filtration, and was reusable at least five times without significant change in its activity and selectivity.     

The reaction of p-benzenediols with Co(III) in aqueous perchlorate media. Kinetics of oxidation

The kinetics of redox reactions between Co(III) and a series of 1,4-benzenediol derivatives has been investigated in aqueous perchlorate media by means of a stopped-flow technique. Reaction rates dependences on oxidant, organic substrate (S), and acidity, were found to conform with: $\text{rate}\text{= (k + k′[}\text{H}{}^{\mathrm{+}}\text{]}{}^{\mathrm{-1}}\text{)[}\text{Co(III)}\text{][S]}$ for all the investigated compounds. Substituents effects on the rate of the single reaction pathways are discussed with reference to Co(III) reactive species and reaction mechanisms.     

Catalytic reaction of methane with carbon dioxide

High activities and selectivities of Ni on SiO₂ catalysts producing CO in the reaction of CH₄ with CO₂, have been obtained at relatively low temperatures. These aspects are considerably different from the activities or selectivities of other catalysts, and have been explained by assuming that the Ni on SiO₂ catalyst markedly suppresses carbon deposition.

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CO Ni SiO₂ CH₄ CO₂. , Ni SiO₂.

     

Miscibility and hydrogen‐bonding interactions in blends of carbon dioxide/epoxy propane copolymer with poly(p‐vinylphenol)

The miscibility and hydrogen‐bonding interactions of carbon dioxide and epoxy propane copolymer to poly(propylene carbonate) (PPC)/poly(p‐vinylphenol) (PVPh) blends were investigated with differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy and X‐ray photoelectron spectroscopy (XPS). The single glass‐transition temperature for each composition showed miscibility over the entire composition range. FTIR indicates the presence of strong hydrogen‐bonding interassociation between the hydroxyl groups of PVPh and the oxygen functional groups of PPC as a function of composition and temperature. XPS results testify to intermolecular hydrogen‐bonding interactions between the oxygen atoms of carbon–oxygen single bonds and carbon–oxygen double bonds in carbonate groups of PPC and the hydroxyl groups of PVPh by the shift of C_1s peaks and the evolution of three novel O_1s peaks in the blends, which supports the suggestion from FTIR analyses. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1957–1964, 2002     

Selectivity of gas‐phase ion/molecule reaction of carbon dioxide with phenide ions

On contrary to the widely accepted conviction that the m/z 93 ion derived from phenol does not react with CO₂, we demonstrate that it makes an adduct with CO₂ to a small but demonstrable extent. For example, the product‐ion mass spectrum recorded for the m/z 98 ion derived from [²H₆]phenol showed a small peak at m/z 142 when CO₂ was used as the collision gas. The formation of an m/z 137 adduct ion from the m/z 93 ion (generated either directly from phenol, or indirectly from salicylic acid by in‐source decarboxylation) was demonstrated also by multiple‐reaction‐monitoring tandem mass spectrometric experiments. According to literature, the m/z 93 ion derived from salicylic acid does not undergo CO₂ addition because it is deemed to exist only in the phenoxide form. This reaction has been previously proposed as a method for differentiating phenoxide ion from its isomeric hydroxyphenide ions. We propose that the m/z 93 ion, albeit small, exists also as the phenide form together with the predominant phenoxide ion. Copyright © 2014 John Wiley & Sons, Ltd.