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Reactive carbonyl species

Aldini, G., Facino, R. M.. Beretta, G., Carini, M. Carnosine and related dipeptides as quenchers of reactive carbonyl species from structural studies to therapeutic perspectives. Eiofactors 2005, 24, 77-87. [Pg.22]

Methylglyoxal (MG), also called pyruvaldehyde, is one of the reactive carbonyl species. It is present in three forms in aqueous solution in rapid equilibrium, as shown below. Among these, monohydrate is the most abundant (71%), followed by dihydrate (28%), and the unhydrated form is present at only about 1%. [Pg.246]

Enzyme deactivation is frequently encountered when highly reactive carbonyl species such as acetaldehyde or cyclohexenone are involved in the recycling process. [Pg.141]

High yields of a single desired product are possible in base if the more reactive carbonyl (usually an aldehyde) has no a-hydrogens, so that only the less reactive carbonyl species (usually a ketone) can form the enolate anion. [Pg.839]

Lo Ch.-Y., Li S., Tan D. Pan M.-H., Sang S., Ho Ch.-T. Trapping reactions of reactive carbonyl species with tea polyphenols in simulated physiological conditions. Molecular Nutrition and Food Research, 50 1118-1128 (2006). [Pg.1072]

Phosgenation. Reaction of phosgene with arylamines to form ureas, and with reactive aryl species to form substituted hen zophen ones, are special cases of acylation. They are dealt with separately siace a more specialized plant is required than for other acylations. Urea formation takes place readily with water-soluble arylamines by simply passiag phosgeae through a slightly alkaline solutioa. An important example is carbonyl-J-acid from J-acid. [Pg.293]

The irradiation is usually carried out with light of the near UV region, in order to activate only ihc n n transition of the carbonyl function," thus generating excited carbonyl species. Depending on the substrate, it can be a singlet or triplet excited state. With aromatic carbonyl compounds, the reactive species are usually in a Ti-state, while with aliphatic carbonyl compounds the reactive species are in a Si-state. An excited carbonyl species reacts with a ground state alkene molecule to form an exciplex, from which in turn diradical species can be formed—e.g. 4 and 5 in the following example ... [Pg.221]

The commercially available (tj5-cyclopentadienyl)iron dicarbonyl dimer 1 is the source of the carbonyl(//5-cyclopentadienyl)iron(L) moiety. Reductive or oxidative cleavage of 1 provides reactive monomeric species that may be converted into iron-acyl complexes as described in the following sections (see also Houben-Weyl, Vol. 13/9a, p208). [Pg.518]

The presence of a site with a low metal-metal coordination is compatible with the non-crystalline nature of the cobalt deposits [64]. It is to be expected that these sites exhibit different chemical reactivity than the usual adsorption sites. This can be verified by subsequent deposition of a small amount (0.1 A) of Pd atoms, which are known to nucleate exclusively on the cobalt particles [64]. The corresponding IR spectrum is shown as the bottom trace in Fig. 6. It is seen that an additional peak appears at 2105 cm which is readily assigned to CO bound terminally to Pd. More importantly, the growth of this Pd feature is completely at the expense of the carbonyl species, indicating that Pd nucleates almost exclusively at these low coordinated sites and prevents the formation of the carbonyl species. [Pg.129]

Rates of addition to carbonyls (or expulsion to regenerate a carbonyl) can be estimated by appropriate forms of Marcus Theory. " These reactions are often subject to general acid/base catalysis, so that it is commonly necessary to use Multidimensional Marcus Theory (MMT) - to allow for the variable importance of different proton transfer modes. This approach treats a concerted reaction as the result of several orthogonal processes, each of which has its own reaction coordinate and its own intrinsic barrier independent of the other coordinates. If an intrinsic barrier for the simple addition process is available then this is a satisfactory procedure. Intrinsic barriers are generally insensitive to the reactivity of the species, although for very reactive carbonyl compounds one finds that the intrinsic barrier becomes variable. ... [Pg.19]

The possible mechanisms which one might invoke for the activation of these transition metal slurries include (1) creation of extremely reactive dispersions, (2) improved mass transport between solution and surface, (3) generation of surface hot-spots due to cavitational micro-jets, and (4) direct trapping with CO of reactive metallic species formed during the reduction of the metal halide. The first three mechanisms can be eliminated, since complete reduction of transition metal halides by Na with ultrasonic irradiation under Ar, followed by exposure to CO in the absence or presence of ultrasound, yielded no metal carbonyl. In the case of the reduction of WClfc, sonication under CO showed the initial formation of tungsten carbonyl halides, followed by conversion of W(C0) , and finally its further reduction to W2(CO)io Thus, the reduction process appears to be sequential reactive species formed upon partial reduction are trapped by CO. [Pg.206]

One approach to enantioselective reduction of prochiral carbonyl compounds is to utilize chiral ligand-modified metal hydride reagents. In these reagents, the number of reactive hydride species is minimized in order to get high chemo-selectivity. Enantiofacial differentiation is due to the introduced chiral ligand. [Pg.356]

Intermolecular nucleophilic acyl substitution is a fundamental carbon—carbon bondforming reaction. In spite of its high synthetic potential, however, its intramolecular version, that is, intramolecular nucleophilic acyl substitution (INAS) is rather rare because of the intrinsic difficulties involved in carrying it out. One difficulty associated with the INAS reaction is that a reactive nucleophilic species must be generated in the presence of carbonyl functionality, and at the same time this nucleophile is expected to react only with... [Pg.337]

Thus it has been shown that some metal-carbonyl compounds can be activated by electrochemical reduction generating reactive anionic species. Without going into details, it is worth pointing out that the synthesis of aldehydes can be obtained by electrolyzing a stoichiometric mixture of alkyl halides and ironpentacarbonyls (Eq. 17) [124, 125] ... [Pg.167]

Surface reactive hydroxo or silanolate Os(II) carbonyl species are initially formed, their nature depending on the basicity given to the siUca surface. With a low basicity (molar ratio Na2C03 Os = 2 1), neutral surface species such as [Os(CO)3(OR)2] ... [Pg.663]

Radical-anions of carbonyl compounds are basic and undergo protonation at the oxygen centre generating highly reactive radical species. [Pg.331]

Nickel carbonyl charged, or formed in the carbonylation reaction mixture, can catalyze the carbonylation of methanol (11). To maintain the activity of the nickel carbonyl catalyst high temperature and pressure are required (12-14). However, certain promoters can maintain an active, soluble, nickel carbonyl species under much milder conditions. The most reactive promoters are phosphines, alkali metal salts, tin compounds, and 2-hydroxypyridine. Reaction rates of 2 to 7 X 10-3(mol/1.sec) can be achieved without the use of high concentration of iodine (Table II). in addition, high reaction rates... [Pg.63]


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See also in sourсe #XX -- [ Pg.24 ]




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Reactive species

Reactive species reactivity

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