Catalytic hydroxylations

Synthesis of optically pure compounds via transition metal mediated chiral catalysis is very useful from an industrial point of view. We can produce large amounts of chiral compounds with the use of very small quantities of a chiral source. The advantage of transition metal catalysed asymmetric transformation is that there is a possibility of improving the catalyst by modification of the ligands. Recently, olefinic compounds have been transformed into the corresponding optically active alcohols (ee 94-97%) by a catalytic hydroxylation-oxidation procedure. 

In the M. capsulatus (Bath) system, all three components are necessary to obtain turnover with NADH as the reductant (57). With the M. trichosporium OB3b system, protein B is apparently not required (27). Instead, in this latter system, protein B increases the initial rates of the catalytic hydroxylation reaction (27). Catalysis can be achieved by means of a shunt pathway with hydrogen peroxide and Hox alone from both organisms (58-60). The efficiency of the shunt pathway, however, varies significantly. With M. trichosporium OB3b, alcohol yields greater than those obtained with the completely reconstituted system have been observed (58). Furthermore, upon addition of protein... 

Catalytic hydroxyl radicals dominate the chemistry of the troposphere. These are formed by the following processes ... 

Glycerol, used for the production of alkyds, is produced by the catalytic hydroxylation or the hypochlorination of allyl alcohol. Allyl alcohol is produced by the reduction of acrolein, which is in turn obtained by the oxidation of propylene. 

Table 11. Catalytic hydroxylation of n-octane, 1-hexene and phenol with aqueous H2O2...

Stack and co-workers recently reported a related jx-rf / -peroxodi-copper(II) complex 28 with a bulky bidentate amine ligand capable of hydroxylating phenolates at - 80 °C. At - 120 °C, a bis(yu,-oxo)dicopper(III) phenolate complex 29 with a fully cleaved 0-0 bond was spectroscopically detected (Scheme 13) [190]. These observations imply an alternative mechanism for the catalytic hydroxylation of phenols, as carried out by the tyrosinase metalloenzyme, in which 0-0 bond scission precedes C - 0 bond formation. Hence, the hydroxylation of 2,4-di-tert-butylphenolate would proceed via an electrophilic aromatic substitution reaction. 

The first useful asymmetric synthesis with a-halo boronic esters utilized (S)-pinanediol [1S-(la,2/1.3//,5a)]-2,6,6-trimethylbicyclo[3.1.1]heptane-2,3-diol as the chiral director39,40. This diol is easily prepared from ( + )-a-pinene by a catalytic hydroxylation with osmium tetroxide, and its enantiomer (i )-pinanediol is available from (-)-(a)-pinene41,42. Pinanediol esters remain useful in view of their excellent stability as well as the ease of preparation of the diol. and their stereoselectivity is very high even though it is no longer the state of the art. 

Notes Oxidizing agent. See also THP with 0s04 for catalytic hydroxylation reactions. 

These complexes (205) were found to be good models for the reactive intermediates involved in the catalytic decomposition of alkyl hydroperoxides (Haber Weiss mechanism), and in the catalytic hydroxylation of hydrocarbons by ROOH. 

The catalytic hydroxylation of methane [39, 95], ethane [136, 137], propane [138-141], cyclohexane [68] and cyclododecane [142] has been tested using the Fe-contain-ing zeolites. In most cases the selectivity was low or even zero. With ethane and propane, instead of their hydroxylation to alcohols, oxidehydrogenation (ODH) takes place, yielding ethylene and propylene, respectively, in yields of up to 25-30%. According to Bulanek et al. [140] the ODH of propane proceeds via intermediate formation of propanol, which further is subjected to dehydration. 

Complex (2) is an effective catalyst for the asymmetric hydroxylation of aromatic hydrocarbons with 2,6-dichloropyridine IV-oxide as terminal oxidant. Up to 76% ee was achieved for the catalytic hydroxylation of 4-ethyltoluene, 1,1-diethylindane, and benzylcyclopropane. Both electron-donating and -withdrawing substituents were found to accelerate the catalytic oxidation reaction. A large primary kinetic isotope effect (kH/kD = 11 at 298 K) was observed for the catalytic ethylbenzene-dio oxidation. A... 

The works devoted to catalytic hydroxylation of aromatic and heterocyclic compounds with hydrogen peroxide under soft conditions should be mentioned [34], The authors showed that the main experiments were performed in the Fenton system and the process can be described by the following generalized mechanism ... 

In our catalytic hydroxylations described above we added some pyridine to the solution to coordinate with one face of the manganese porphyrin, so as to direct an oxygen atom and the bound substrate to the same face. To avoid this, we synthesized catalyst... 

Maurer, S. C., Kuhnel, K., Kaysser, L. A., Eiben, S., Schmid, R. D., and Urlacher, V. B. 2005. Catalytic hydroxylation in biphasic systems using CYP102A1 mutants. Adv. Synth. Catalys.,347,1090-1098. 

WiA osmium tetroxide, considerable diastereoselectivity may be achieved in the stoichiometric and catalytic hydroxylation of allylic alcohol systems in which the oxygen-containing groiq> forms part of a chirai center (equation 4). " ... 

Siqtpott for the enmitical rule has beat obtained, subsequently, during synthetic studies in carbohydrate chemistry For example, catalytic hydroxylation wifo osmium tetroxide of ( )-allylic alco-... 

This method of finding the concentration of ions near the surface was applied by Davies (49,21) to the hydrolysis of ionized films of the ester monocetyl succinate. Table IX shows that the rate constant for this hydrolysis, which increased 300% if calculated using bulk concentrations of the catalytic hydroxyl ion, varied by not more than 36% when evaluated using the surface concentrations deduced from (xxv) and (xxvi). Figure 19 shows a similar effect for the addition of neutral salt, the marked catalysis by which is thus demonstrated to be due entirely to electrostatic effects. The acceleration in the rate of hydrolysis of a film cholesterol formate if the surface bears a negative charge can be predicted on the basis of the Donnan equations (xxv) and (xxvi). Values of 5 of 6 A. and 8 A. have been used, the results being compared with experiment in Fig. 21a. The calculated retardation is shown in Fig. 21b. 

B. H. Brodsky, J. Du Bois, Oxaziridine-mediated catalytic hydroxylation of unactivated 3°C-H- bonds using hydrogen peroxide, J. Am. Chem. Soc. 127,15391-15393 (2005). 

The mechanism of the catalytic hydroxylation of aromatic hydrocarbons by hydrogen peroxide has been reviewed (ref.8). The hydroxylation of benzene or toluene by peroxydiphosphate (ref.9) and peroxydisulphate, (more comnronly termed persulphate) (ref. 10) in aqueous (0.05-1.OM) acid in the presence of Cu(ll) has been found to be similar. Phenol (15.6%), diphenyl (5.2%), and 2-and 4-nitrophenols (11.7% and 5.6% respectively) resulted from a mixture of benzene and nitrobenzene in water at 80 C with peroxydisulphate. 

Scheme 1.15. Fast catalytic hydroxylation with a fluorophenylruthenium porphyrin.

The catalytic hydroxylation of olefins with was first reported by Milas in 1936 [3, 4] and studied in more detail by Mugdan and Young a few years later... 

Catalytic hydroxylation of phenol by hydrogen peroxide. Kinetic study and comparison between solid acids and titanosilicates. 

Table 4.Catalytic hydroxylation of phenol over iM(lt)Al binary hydrotalcites...

Allian, M.. Germain. A., Cseri, T. and Figueras, F. (1993). Catalytic hydroxylation of phenol by hydrogen peroxide. Kinetic study and comparison between solid acids and litanosilicatcs. Stud. Surf. Sci. Catal., 78. 455-462. 

Rives, V., Dubey, A. and Kannan, S. (2001). Synthesis, characterization and catalytic hydroxylation of phenol over CuCoAl ternary hydrotalcites. Phys. Chem. Chem Phys., 3,4826-36. 

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