Metal alcohol oxidation

Catalysts used for preparing amines from alcohols iaclude cobalt promoted with tirconium, lanthanum, cerium, or uranium (52) the metals and oxides of nickel, cobalt, and/or copper (53,54,56,60,61) metal oxides of antimony, tin, and manganese on alumina support (55) copper, nickel, and a metal belonging to the platinum group 8—10 (57) copper formate (58) nickel promoted with chromium and/or iron on alumina support (53,59) and cobalt, copper, and either iron, 2iac, or zirconium (62). 

Cobalt(II) chloride hexahydrate [7791-13-1], C0CI2 6H20 is a deep red monoclinic crystalline material that deflquesces. It is prepared by reaction of hydrochloric acid with the metal, simple oxide, mixed valence oxides, carbonate, or hydroxide. A high purity cobalt chloride has also been prepared electrolyticaHy (4). The chloride is very soluble in water and alcohols. The dehydration of the hexahydrate occurs stepwise ... 

In contrast to the asymmetric procedures discussed above, the metal-catalyzed oxidation of alkyl aryl sulphides by t-butylhydroperoxide carried out in a chiral alcohol gives rise to chiral sulphoxides of low optical purity290 (e.e. 0.6 9.8%). Similarly, a very low asymmetric induction was noted when prochiral sulphides were oxidized by sodium metaperiodate in chiral alcohols as solvents291. 

The complex Pd-(-)-sparteine was also used as catalyst in an important reaction. Two groups have simultaneously and independently reported a closely related aerobic oxidative kinetic resolution of secondary alcohols. The oxidation of secondary alcohols is one of the most common and well-studied reactions in chemistry. Although excellent catalytic enantioselective methods exist for a variety of oxidation processes, such as epoxidation, dihydroxy-lation, and aziridination, there are relatively few catalytic enantioselective examples of alcohol oxidation. The two research teams were interested in the metal-catalyzed aerobic oxidation of alcohols to aldehydes and ketones and became involved in extending the scopes of these oxidations to asymmetric catalysis. 

Besides Wacker oxidation, other transition-metal catalyzed oxidations have also been carried out in aqueous medium. For example, methyl groups can be selectively hydroxylated by platinum salts in water.88 In this way, p-toluenesulfonic acid was oxidized to benzy-lic alcohol, which was subsequently oxidized into the aldehyde (Eq. 3.19).89... 

SEGPHOS [271, 272]. Using this complex as a precatalyst, transfer hydrogenation of 1,1-dimethylallene in the presence of diverse aldehydes mediated by isopropanol delivers products of ferf-prenylation in good to excellent yield and with excellent levels of enantioselectivity. In the absence of isopropanol, enantio-selective carbonyl reverse prenylation is achieved directly from the alcohol oxidation level to furnish an equivalent set of adducts. Notably, enantioselective ferf-prenylation is achieved under mild conditions (30-50°C) in the absence of stoichiometric metallic reagents. Indeed, for reactions conducted from the alcohol oxidation level, stoichiometric byproducts are completely absent (Scheme 13). 

Two different mechanisms have been proposed for the ROP of (di)lactones depending on the nature of the organometalhc derivatives. Metal halides, oxides, and carboxylates would act as Lewis acid catalysts in an ROP actually initiated with a hydroxyl-containing compound, such as water, alcohol, or co-hydroxy acid the later would result more hkely from the in-situ hydrolysis of the (di)lac-tone [11]. Polymerization is assumed to proceed through an insertion mechanism, the details of which depends on the metal compound (Scheme la). The most frequently encountered Lewis acid catalyst is undoubtedly the stannous 2-ethylhexanoate, currently referred to as stannous octoate (Sn(Oct)2). On the other hand, when metal alkoxides containing free p-, d-, or f- orbitals of a favo-... 

Oxidation of alcohols to carbonyl compounds is an important reaction. Stoichiometric oxidants such as chromates, permanganates and MO4 (M = Ru, Os) are the commonly used reagents [19a,59,60]. However, they are going out of favour increasingly because they create heavy metal wastes . In view of this, development of environmentally friendly heterogeneous catalysts for alcohol oxidation is very important. In the use of catalytic amounts of transition metal salts or complexes as homogeneous catalysts for the oxidation of alcohols [61-64], separation of the catalyst from the reaction mixture and its subsequent recovery in active form is cumbersome. Heterogeneous catalysts for this kind of reaction are therefore necessary [65]. Clearly, encapsulation and/or immobilization of known... 

Transition metal compounds, such as organic macrocycles, are known to be good electrocatalysts for oxygen reduction. Furthermore, they are inactive for alcohol oxidation. Different phthalocyanines and porphyrins of iron and cobalt were thus dispersed in an electron-conducting polymer (polyaniline, polypyrrole) acting as a conducting matrix, either in the form of a tetrasulfonated counter anion or linked to... 

Common alcohol oxidation methods employ stoichiometric amounts of toxic and reactive oxidants like Cr03, hypervalent iodine reagents (Dess-Martin) and peracids that pose severe safety and environmental hazards in large-scale industrial reactions. Therefore, a variety of catalytic methods for the oxidation of alcohols to aldehydes, ketones or carboxylic acids have been developed employing hydrogen peroxide or alkyl hydroperoxides as stoichiometric oxygen sources in the presence of catalytic amounts of a metal catalyst. The commonly used catalysts for alcohol oxidation are different MoAV(VI), Mn(II), Cr(VI), Re(Vn), Fe(II) and Ru complexes . A selection of published known alcohol oxidations with different catalysts will be presented here. 

TABLE 30. Comparison of the results of metal-catalyzed alcohol oxidation to ketones, carboxylic acids or aldehydes using H2O2 or TBHP... 

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