Catalyst additive 353 - ionic

Consideration of reasonable mechanisms for producing formic acid from an aldose led to the hypothesis that the sugar forms an addition product with the hydroperoxide anion, comparable with an aldehyde sulfite or the addition product of aldoses with chlorous acid (52). The intermediate product (12) could decompose by a free-radical or an ionic mechanism. In the absence of a free-radical catalyst, the ionic mechanism of Scheme VIII seems probable. By either mechanism the products are formic acid and the next lower sugar. The lower sugar then repeats the process, with the result that the aldose is degraded stepwise to formic acid. Addition of the hydroperoxide anion to the carbonyl carbon is in accord with its strong nucleophilic character (53) and with certain reaction mechanisms suggested in the literature (54) for related substances. 

Catalyst for Ionic Ring-Opening Addition Polyesterification Initiator for Free-Radical Styrene/Maleic Ester Copolymerization (Cross-linking Reaction)... 

Quaternary phosphonium salts are organophosphorous compounds used as Wittig olefination reagents, phase transfer catalysts, electrolytes, ionic liquids, and as surface active reagents. Their preparation involves the C-P bond formation in tertiary phosphines. We envisaged that addition of phosphines to unsaturated compounds should be preferable as compared to the conventional method using a substitution reaction of organohalogen compounds (Scheme 1). In this chapter, we describe our recent study on this subject. 

Polyetheriflcation means formation of an ether bond or sequence of ether bonds by (poly)addition of epoxy groups which is released by proton donors (like the OH group formed in the amine-epoxy addition), ionic catalysts or other initiators... 

Micelles are used in many applications. Their largest industrial use is in emulsion polymerization, as detailed in Section 5.9 below. On the other hand, micelles made of ionic surfactants can trap hydrocarbon wastes in polluted water, since these hydrocarbon molecules prefer to be in the hydrocarbon interior of the micelle in an aqueous environment. In addition, ionic wastes dissolved in water adsorb onto the polar heads of these micelles. The resulting waste-filled micelles may be removed by simple ultrafiltration. As an example of another application, micelles can affect the rate of several chemical reactions and are used in micellar catalysis, similar to enzyme catalysis, in biochemistry. The rate of the chemical reaction increases with increasing micelle concentration, eventually leveling off. Nevertheless, micellar catalysts are less specific than enzymes. 

Chlorination and bromination in the side chain of alkylaromatic compounds requires exclusion of the catalysts of ionic halogenation, i.e., above all of metal salts. Thus it is recommended to add substances that form stable complexes with metal salts, e.g., ethylenedinitrilotetraacetic acid (EDTA).417 Side-chain halogenation requires conditions under which radicals can be formed, illumination (100-200 household lamps or UV), high temperatures, and addition of radical formers. Discoloration occurring during side-chain chlorination, which inhibits light absorption, can be avoided by adding 0.1-5% of benzamide.418... 

For the addition polymers the thermo-oxidative and mechano-chemical degradations are most important. These processes are mostly radical, but in the presence of specific catalysts addition polymers also decompose ionically. During storage, PO chains slowly react with ambient oxygen forming peroxy, hydroperoxy, or peroxy-acid groups (the auto-oxidation). When heated, the peroxides decompose into free radicals that... 

The enantioselective addition of alkynes to imines using a 2,6-bis(4-phenyloxazolino)pyridine catalyst was carried out by Rosa et al. to give a chiral amino aUcyne (Scheme 5.2-97) [227]. The reaction gave similar yields and selectiv-ities to the reaction in toluene, but the catalyst and ionic liquids could be recycled and reused. 

Ionic liquids can efficiently immobilize transition metal complexes used as catalysts for epoxidation. This phenomenon is encountered not only when specially designed, polar ligands are used, but also for unmodified catalysts. For instance, several unsuccessful attempts have been made to immobilize Jacobsen s chiral Mn(iii)salen epoxidation catalyst 81. Ionic liquids are the first medium to immobilize this complex efficiently without requiring additional modification of the ligand. 

The Mizoroki-Heck reaction is usually performed in polar solvents, and salt additives such as tetrabutylammonium chloride have been shown to activate and stabihze the catalytically active palladium species [19]. Furthermore, the reactions in ionic hquids perform differently in terms of thermodynamic and kinetic properties of the reaction system. Additionally, ionic liquids allow a facile recovery of catalyst and substrates, as well as an easy product separation. Here, another beneficial effect might be used by combination of solvent mixtures for example, of ionic liquids and SCFs. SCFs and ionic liquids have a mixing gap which allows working in two-phase systems, and results in a straightforward phase separation [20]. 

In addition, the activated hydride form of a cymene ruthenium complex was shown to be elfective as a racemising catalyst in ionic liquids such as... 

Catalytic hydrogenation by H2, like hydroformylation, is almost ideally suited for the application of phase-separation techniques, as it involves only two reagents (the substrate and hydrogen), requires no additional ionic or non-ionic components and, most importantly, produces only the single target product without any by-products that may accumulate in the reaction system and poison the catalyst. 

The concept of supported ionic liquid catalysis involves the surface of a support material that is modified with a monolayer of covalently attached ionic liquid fragments. Treating this surface with additional ionic liquid results in the formation of multiple layers of free ionic liquid on the support material. These layers serve as the reaction phase in which a homogeneous hydroformylation catalyst was dissolved. The concept of supported ionic liquid catalysis has successfully been used for hydroformylation reactions ]81]. 

The initiators which are used in addition polymerizations are sometimes called catalysts, although strictly speaking this is a misnomer. A true catalyst is recoverable at the end of the reaction, chemically unchanged. Tliis is not true of the initiator molecules in addition polymerizations. Monomer and polymer are the initial and final states of the polymerization process, and these govern the thermodynamics of the reaction the nature and concentration of the intermediates in the process, on the other hand, determine the rate. This makes initiator and catalyst synonyms for the same material The former term stresses the effect of the reagent on the intermediate, and the latter its effect on the rate. The term catalyst is particularly common in the language of ionic polymerizations, but this terminology should not obscure the importance of the initiation step in the overall polymerization mechanism. 

Common catalyst compositions contain oxides or ionic forms of platinum, nickel, copper, cobalt, or palladium which are often present as mixtures of more than one metal. Metal hydrides, such as lithium aluminum hydride [16853-85-3] or sodium borohydride [16940-66-2] can also be used to reduce aldehydes. Depending on additional functionahties that may be present in the aldehyde molecule, specialized reducing reagents such as trimethoxyalurninum hydride or alkylboranes (less reactive and more selective) may be used. Other less industrially significant reduction procedures such as the Clemmensen reduction or the modified Wolff-Kishner reduction exist as well. 

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