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Dendrimers in Supramolecular Catalysis
Published in Jubaraj Bikash Baruah, Principles and Advances in Supramolecular Catalysis, 2019
Gels have found extensive application in supramolecular catalysis.23–25 The compounds listed in Figure 5.20 are examples of some that form gels under specific conditions. These gels act as catalysts of different types of reactions. The compounds in 5.20a and 5.20b, in the presence of cadmium sulphate and copper (I) salt, respectively, form gel in water; the compound 5.20c forms a gel in the presence of palladium acetate in dimethylsulphoxide. The gel of 5.20a, with cadmium sulphate, is a catalyst for carbon—carbon bond formation between active hydrogens containing nitrile with aldehydes. The combination of the copper (I) salt and gel of the compound 5.20bis useful in the click reaction between acetylic compounds with azide to form five-membered heterocyclic compounds. The compound 5.20c with palladium acetate in dimethylsulpoxide is utilised in the catalytic oxidation reaction of benzyl alcohol to benzaldehyde. The palladium complex 5.20d itself forms a gel and catalyses the Michael addition reaction between ethylcyanoacetate and methyl-vinyl ketone. This catalytic reaction proceeds at room temperature in dichloromethane in the presence of a catalytic amount of the gel but requires isopropyl amine as the base in the reaction. This gel-catalysed reaction is superior to a reaction where the soluble palladium complex of a similar skeleton is used. The compound 5.20d forms a gel upon heating followed by cooling; this gel is a catalyst for aldol-type reactions under sonicating conditions.
Molecular Reactions: The Diels-Alder and other reactions
Published in Richard A. Larson, Eric J. Weber, Reaction Mechanisms in Environmental Organic Chemistry, 2018
Richard A. Larson, Eric J. Weber
montmorillonite to give a 77% yield of the cycloadducts, whereas after it was heated at 200° C for 20 hr in the absence of the clay, only a 30% yield was achieved (Laszlo and Lucchetti, 1984). Similar yield improvements were observed for reactions in which acrolein (CH2 = CHO) was used as the dienophile (Laszlo and Moison, 1989). In the above experiments, use of a phenol as a co-catalyst was found to improve yields significantly. Apparently, the phenol engages in electron-transfer processes on the iron-doped surface, giving radical cations which are said to promote cycloaddition reactions. In keeping with the proposed Lewis acid mechanism for the clay-catalyzed Diels-Alder reaction, some studies have shown that the presence of water is inhibitory (Collet and Laszlo, 1991); dried kaolinite was an effective catalyst for the cyclopentadiene-methyl vinyl ketone condensation, but moist air diminished the rate and stereoselectivity of the reaction.
Chemical Characterization of Silica Powders and Fibers: Application to Surface Modification Procedures
Published in Michel Nardin, Eugène Papirer, Powders and Fibers, 2006
The papers [127–129] describe surface grafting of hyperbranched dendritic polyamidoamine onto glass fiber, or disperse silica having surface amino groups (prepared by treatment of surface with 3-aminopropyltriethoxysilane or by introduction of polymer with terminal NH2-groups). Grafting reaction was executed by repeating Michael addition of methyl acrylate to surface amino groups, followed by amidation of end groups (reaction of the resulting ester surface compounds with ethylenediamine or hexamethylenediamine). In a case of silica, the amino group content increased from 0.40 to 8.30 mmol/g after 10th generation [128]. Obtained by this means, modified glass fibers [127] were applied for postgrafting of poly(isobutyl vinyl ether) and poly(2-methyl-2-oxazoline). A somewhat different route for preparation of grafting of polyamidoamine dendrimer hybrids was proposed in the paper [130]. Michael addition reaction was also used [131] for surface fuctionalization of aminated glass, silicon crystals, and silica microspheres with vinylic monomers (methyl vinyl ketone, methyl acrylate, methacrolein, and acrolein). In a case of aldehydes, Schiff base bond formation was also observed.
Atmospheric degradation mechanisms and kinetics for OH-initiated oxidation of trans-β-ocimene
Published in Molecular Physics, 2023
In 1999 and 2002, by using gas chromatography (GC) with flame ionisation detection (GC-FID), GC-mass spectrometry (GC-MS) and GC-Fourier transform infrared (GC-FTIR), the gas-phase reaction products for the title reaction have been investigated twice in the NO concentration of 2.4 × 1014 molecule cm−3 at 298 ± 2 K and 740 Torr total pressure of purified air [22,23]. The formation yield of acetone was measured to be ∼18% [22,23], and the formation of 4-methyl-3,5-hexadienal was found to be less than 2% [23]. Furthermore, Gaona-Colmán et al. also investigated the β-ocimene + OH reaction products at (298 ± 2) K and 760 Torr of synthetic air in the absence and presence of NOx [21]. In the presence of NO (initial concentration of 7.38 × 1013 molecule cm−3), the determined molar products were formaldehyde (24.3 ± 1.5)%, acetone (58.3 ± 3.4)%, methyl vinyl ketone (<5%) and glycolaldehyde (<5%). Very recently, Morales et al. reported a laboratory study of OH-initiated oxidation of β-ocimene and quantified the total (gas- and particle-phase) organic nitrates RONO2 yield of 38(±9) % in the presence of NO [24].
A perspective on the development of gas-phase chemical mechanisms for Eulerian air quality models
Published in Journal of the Air & Waste Management Association, 2020
William R. Stockwell, Emily Saunders, Wendy S. Goliff, Rosa M. Fitzgerald
Early versions of the GEOS-Chem included inorganic chemistry to simulate H2O2 and other products that are produced at low NOx concentrations. It also included inorganic species for NOx, HNO3, three peroxyacyl nitrates, and two different organic nitrate compounds were included because of their importance in simulating O3 formation and the long-range transport of nitrogen oxides (Horowitz et al. 1998). GEOS-Chem treated less reactive alkanes, methane, ethane, and propane while extensive use was made of surrogate species to represent other alkane chemistry (Horowitz et al. 1998). Propene represented all alkenes with three or more carbon atoms while butane was used to represent all VOCs with four or more carbon atoms. VOCs were summed into butane or propene according to class and the number of carbon atoms of the aggregated VOC species. Many of VOCs emitted in highly polluted urban areas, such as aromatic hydrocarbons, were ignored because the mechanism developers’ focus was on the simulation of global ozone concentrations. The version of GEOS-Chem developed by Horowitz et al. (1998) includes isoprene but not terpenes to represent biologically emitted compounds. The isoprene scheme is rather extensive. There are some emissions of aldehydes and ketones which are also oxidation products of hydrocarbons. These compounds are represented in the GEOS-Chem mechanism by formaldehyde, acetaldehyde, methacrolein, higher aldehydes (RCHO), acetone, methyl vinyl ketone and higher ketones (MEK). GEOS-Chem includes an extensive scheme for the reactions of HO2 and organic peroxy radicals which is necessary for modeling low NOx conditions.
Updating the SAPRC Maximum Incremental Reactivity (MIR) scale for the United States from 1988 to 2010
Published in Journal of the Air & Waste Management Association, 2018
Melissa A. Venecek, William P.L. Carter, Michael J. Kleeman
Figures 4b and 4d illustrate the 2010 base and aloft VOC composition by functional group, averaged across all cities. Functional groups were used to illustrate the broad classification changes. Profiles developed by compound for each represented city are provided in the Supporting Information, Table S2. These VOC composition profiles can be compared to the 1988 base and aloft average VOC composition (Carter 1994a) in Figures 4a and 4c. Ketones, alcohols, and “other” species were not available in the original 1988 aloft chemical composition profile (Carter 1994a), but these compounds are included in the updated inputs since they are expected to influence atmospheric reactivity. Ketones are a combination of the following SAPRC11 species: “MEK,” defined as ketones and other non-aldehyde oxygenated products that react with OH radicals more quickly than 5 × 10−13 but more slowly than 5 × 10−12 cm6 molecules−2 sec−1, “PROD2,” defined as ketones and other non-aldehyde oxygenated products that react with OH radicals more quickly than 5 × 10−12 cm6 molecules−2 sec−1,”MVK,” defined as methyl vinyl ketone, and “ACET,” defined as acetone. The 2010 scenario also included two other lumped species groups, alcohols and “others.” The alcohol species group is a combination of ethanol and methanol, while the “others” group is a combination of biacetyl, formic acid, and acetic acid. Figure 4 illustrates that the 2010 composition has a reduced proportion of alkanes, alkenes, and aromatic species due to a reduction in anthropogenic emissions. The 2010 composition has an increased proportion of ketones and aldehydes due to the increased proportion of biogenic emissions relative to conditions in 1988. This trend is reflected in the order of magnitude decrease in median NMOC emissions between 1988 and 2010 (Figure 3a) and the smaller changes to median isoprene emissions over the same time period (Figure 3d).