Atom-economic oxidation

FIGURE 3.2. Atom-economical oxidation of secondary alcohol. 

We synthesized uniform CU2O coated Cu nanoparticles from the thermal decomposition of copper acetylacetonate, followed by air oxidation. We successfully used these nanoparticles for the catalysts for Ullmann type amination coupling reactions of aryl chlorides. We synthesized core/shell-like Ni/Pd bimetallic nanoparticles from the consecutive thermal decomposition of metal-surfactant complexes. The nanoparticle catalyst was atom-economically applied for various Sonogashira coupling reactions. 

The hydration of C-C triple bonds represents one of the most atom economical and environmentally friendly oxidation reactions [37], Recently, Nolan and co-workers reported the cationic [Au(lPr)][SbF ] system, which was generated in situ from [AuCl(lPr)] and AgSbF. The catalyst system showed remarkable activity in the hydration of a large range of alkynes, at An loadings as low as 10 ppm (typically 50-100 ppm), under acid-free conditions (Table 10.6) [38],... 

Redox-type reactions show by far the worst performance in meeting the golden atom economical threshold. Three reductions meet this criterion with (AE)min values of 1 hydrogenation of olefins using the Lindlar catalyst (1952), Noyori stereoselective hydrogenation reaction (1985), and Zincke disulphide cleavage reaction (1911) whereas, oxidations... 

Once the major cause of the waste has been recognized, the solution to the waste problem is evident the general replacement of classical syntheses that use stoichiometric amounts of inorganic (or organic) reagents by cleaner, catalytic alternatives. If the solution is so simple, why are catalytic processes not as widely used in fine and specialty chemicals manufacture as they are in bulk chemicals. One reason is that the volumes involved are much smaller, and thus the need to minimize waste is less acute than in bulk chemicals manufacture. Secondly, the economics of bulk chemicals manufacture dictate the use of the least expensive reagent, which was generally the most atom economical, for example O2 for oxidation H 2 for reduction, and CO for C-C bond formation. 

The Feng group showed that organic molecules without an imine bond also seem to be able to catalyze the cyanation of imines [14]. In the presence of (stoichiometric) amount of a chiral N-oxide, 19, addition of trimethylsilylcyanide to several types of aldimine gave the desired a-amino nitriles with enantioselectivity up to 73% ee [14]. For example, (S)-4a is obtained in 95% yield and with 58% ee (Scheme 5.10). In addition to medium enantioselectivity, a drawback of this method is the need for stoichiometric amounts of the chiral N-oxide. The use of trimethylsilylcyanide is also less recommendable than HCN from both atom-economical and industrial considerations. 

The hydroacylation of olefins with aldehydes is one of the most promising transformations using a transition metal-catalyzed C-H bond activation process [1-4]. It is, furthermore, a potentially environmentally-friendly reaction because the resulting ketones are made from the whole atoms of reactants (aldehydes and olefins), i.e. it is atom-economic [5]. A key intermediate in hydroacylation is a acyl metal hydride generated from the oxidative addition of a transition metal into the C-H bond of the aldehyde. This intermediate can undergo the hydrometalation ofthe olefin followed by reductive elimination to give a ketone or the undesired decarbonyla-tion, driven by the stability of a metal carbonyl complex as outlined in Scheme 1. 

Hydrosilylation, the addition of a Si-H bond across an unsaturated carbon-carbon linkage, is a facile and atom-economical route to organosilanes, which can be functionalized further, for example, using the Tamao or Fleming oxidation protocol [33],... 

In short, we expect that the synthetic utility of both biocatalytic and biomimetic copper-based systems will be further improved in the future. This will provide economically viable catalytic methodologies for the green, atom efficient oxidations of alcohols employing molecular oxygen as the primary oxidant, and affording water as the sole byproduct. 

Another concern in an atom-economic design of oxidations involves the use of dioxygen for the selective monoxidation of a substrate S according to... 

The search for atom-economical epoxidation of olefins led to the recent discovery of efficient titanium catalysis using aqueous hydrogen peroxide as the oxidant.From the viewpoint of green chemistry, aqueous hydrogen peroxide is the oxidant of choice, since it is inexpensive, with a high active hydrogen content (47%) and the only byproduct is water. 

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