Catalytic oxidation transfer conditions

KRs based on the oxidation of a chiral secondary alcohol to a prochiral ketone has been of considerable interest as the later can be usually recycled into the racemic starting material by simple hydride reduction [2d, 55]. The first broadly applicable method for this purpose was reported by Noyori et al. [56], under catalytic hydride transfer conditions similar to those employed for the asymmetric hydrogenation of ketones. For example, excellent results (s>50) have been reported for the KR of benzyhc alcohols by using a chiral diamine-ruthenium complex in the... 

Ketones are resistant to oxidation by dioxygen in aqueous solutions at T= 300-350 K. Transition metal ions and complexes catalyze their oxidation under mild conditions. The detailed kinetic study of butanone-2 oxidation catalyzed by ferric, cupric, and manganese complexes proved the important role of ketone enolization and one-electron transfer reactions with metal ions in the catalytic oxidation of ketones [190-194],... 

The use of cerium(IV) salts as catalytic oxidation mediator is restricted by their insolubility in non-aqueous media. Cerium(IV) ammonium nitrate (CAN) may be used in organic solvents upon the addition of quaternary ammonium salts, but cerium(IV) sulphate is not transferred under analogous conditions. Bis(tetra-/t-butyl-ammonium) hexanitratocerate(IV) is obtained in a solid form by metathesis of CAN... 

Preliminary efforts to examine the mechanism of C-H amination proved inconclusive with respect to the intermediacy of carbamoyl iminoiodinane 12. Control experiments in which carbamate 11 and PhI(OAc)2 were heated in CD2CI2 at 40°C with and without MgO gave no indication of a reaction between substrate and oxidant by NMR. In Hne with these observations, synthesis of a carbamate-derived iodinane has remained elusive. The inability to prepare iminoiodinane reagents from carbamate esters precluded their evaluation in catalytic nitrene transfer chemistry. By employing the PhI(OAc)2/MgO conditions, however, 1° carbamates can now serve as effective N-atom sources. The synthetic scope of metal-catalyzed C-H amination processes is thus expanded considerably as a result of this invention. Details of the reaction mechanism for this rhodium-mediated intramolecular oxidation are presented in Section 17.8. 

Oxidative decyanation (6, 430). This reaction can be conducted under phase-transfer conditions with 50% NaOH in DMSO with catalytic amounts of benzyl-triethylammonium chloride (TEBA). The method fails with purely aliphatic nitriles. The highest yields (85-90%) are obtained with aromatic secondary nitriles. 

As cataluminescence (CTL) is emitted from the excited species produced in the course of the catalytic oxidation of gas, the CTL intensity is limited by the total reaction rate. As we described in the previous section, the total reaction rate is limited by the rate of the slower process between the surface reaction and the transfer of gases from the gas phase to the catalyst surface. The rate of diffusion is characteristics of the gas itself, so that the maximum gas sensitivity is limited by the flow-dynamical condition and not by the activity of... 

Under reaction-controlled conditions, the total rate of catalytic oxidation is governed by the rate of surface reaction and is independent of the gas transfer rate from the gas phase to the catalyst surface, so that the CTL intensity is also independent of the flow velocity of sample gas around the sensor. Under diffusion-controlled conditions, the rate of catalytic oxidation is independent of the catalytic activity, but depends on the transfer rate of combustible gas in the gas phase, so that the CTL intensity depends on the flow rate of the gas... 

H202 oxidizes S02 to sulfate, H2S to sulfate and sulfur, RSH and RSSR to sulfonic acid and sulfate and RSR to sulfoxides and sulfones. The products of oxidation are all odorless. Hence, H202 may provide an economic effective means for odor and wastewater quality control in kraft mills. For the case of RSSR which are resistant to complete oxidation, catalytic oxidation by a peroxide in acidic medium can be employed. The fact that H202 is a liquid completely miscible with water and does not give solubility (or mass transfer) problems under any conditions, makes it an attractive choice for pollution control. 

Oxygen transfer to the metal site of several organometallics is also possible in some instances this occurred under ultrasonic conditions. In this way its polymeric oxide was obtained from triphenylbismuthine, whereas triphenylstibine afforded its crystalline dimeric oxide [57], Several metalloporphyrins are also oxygenated at the metal site by IOB. Some of the oxo species formed have been isolated but normally they are non-isolable. These systems have been used in some catalytic oxidations. 

Fig. 1.26 Catalytic oxidations with hydrogen peroxide under phase transfer conditions.

In 2005, Cho and Bolm (152) used the previously discussed [Ag2(f-Bu3tpy)2] system to catalyze the imination of sulfoxides. Good to excellent yields could be achieved with various sulfoximines under mild conditions. If a chiral sulfoxide is employed, the corresponding sulfoximine can be prepared after oxidation and deprotection with retention of ee. This reaction further highlights the versatility of the disilver(I) system in catalytic nitrene-transfer chemistry (111,112). The silver-bathophenanthroline system was not employed in this chemistry, however, it may give interesting results as well (Fig. 38) (120). 

A related reaction involves a-substituted aryl nitriles having a sufficiently acidic a hydrogen, which can be converted to ketones by oxidation with air under phase transfer conditions. The nitrile is added to NaOH in benzene or DMSO containing a catalytic amount of triethylbenzylammonium chloride (TEBA). " This reaction could not be applied to aliphatic nitriles, but an indirect method for achieving this conversion is given in 19-60. a-Dialkylamino nitriles can be converted to ketones, R2C(NMe2)CN —> R2C=0, by hydrolysis with Q1SO4 in aqueous methanol or by autoxidation in the presence of r-BuOK. ... 

In the oxidative decyanation of dialkylaminophenylacetonitriles under phase transfer conditions the generated a-carbanion is oxidized by a stream of oxygen (equation 21) Catalytically, a direct conversion occurs with the system consisting of Pd(OAc)2, benzyl bromide and potassium carbonate. ... 

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