Aldehydes, catalytic oxidation

Ca.ta.lysis, The mechanism of hydrogen abstraction from alcohols to form aldehydes (qv) over silver has been elucidated (11). Silver is the principal catalyst for the production of formaldehyde (qv), the U.S. production of which was 4 x 10 metric tons in 1993. The catalytic oxidation of... 

In the chemical industry, simple aldehydes and ketones are produced in large quantities for use as solvents and as starting materials to prepare a host of other compounds. For example, more than 1.9 million tons per year of formaldehyde, H2C=0, is produced in the United States for use in building insulation materials and in the adhesive resins that bind particle hoard and plywood. Acetone, (CH.3)2C"0, is widely used as an industrial solvent approximately 1.2 million tons per year is produced in the United States. Formaldehyde is synthesized industrial ) by catalytic oxidation of methanol, and one method of acetone preparation involves oxidation of 2-propanol. 

One of the exciting results to come out of heterogeneous catalysis research since the early 1980s is the discovery and development of catalysts that employ hydrogen peroxide to selectively oxidize organic compounds at low temperatures in the liquid phase. These catalysts are based on titanium, and the important discovery was a way to isolate titanium in framework locations of the inner cavities of zeolites (molecular sieves). Thus, mild oxidations may be run in water or water-soluble solvents. Practicing organic chemists now have a way to catalytically oxidize benzene to phenols alkanes to alcohols and ketones primary alcohols to aldehydes, acids, esters, and acetals secondary alcohols to ketones primary amines to oximes secondary amines to hydroxyl-amines and tertiary amines to amine oxides. 

Catalysis is demonstrated by the process that the radicals are generated by the oxidized form of the catalyst in the reaction with aldehyde, and the reduced form of the catalyst is rapidly oxidized by perbenzoic acid formed in the chain reaction. Data on the catalytic oxidation of aldehydes of different structures are found in Refs. [50,51]. 

CATALYTIC OXIDATION OF OLEFINS TO ALDEHYDES 10.6.1 Catalysis by Palladium Salts... 

James An early process for making mixed oxygenated organic compounds by the catalytic oxidation of petroleum fractions. The products were aldehydes, alcohols, and carboxylic acids. Developed by J. H. James at the Carnegie Institute of Technology, Pittsburgh. 

Catalytic oxidant.1 In combination with N-methylmorpholine N-oxide (7,244) as the stoichiometric oxidant, this ruthenium compound can be used as a catalytic oxidant for oxidation of alcohols to aldehydes or ketones in high yield in CH2C12 at 25°. Addition of 4A molecular sieves is generally beneficial. Racemization is not a problem in oxidation of alcohols with an adjacent chiral center. Tetrabutylammonium perruthenate can also be used as a catalytic oxidant, but the preparation is less convenient. 

Micro)titer plate in a pressure vessel Selective catalytic oxidation of alcohols to aldehydes and ketones9... 

Perhaps the most important recent discovery in catalytic oxidation of alcohols is the use of a catalyst prepared from [Pd(OAc)2] and sulfonated batophenanthroline (see Scheme 8.1 above). This catalyst was found to oxidize primary and secondary, as well as benzylic and allylic alcohols with close to quantitative yields and 90-100 % select vities to the corresponding aldehydes or ketones (Scheme 8.4) [18]. The easy oxidation of non-activated secondary alcohols is particularly noteworthy since in general these are rather unreactive towards O2. 

The catalytic preparation of esters and amides under mild and waste free reaction conditions using readily available starting materials is a desirable goal. The first redox process of this type using heterocyclic carbenes was reported by Castells and co-workers in 1977 in which aldehydes were oxidized to esters in one-pot in the presence of nitrobenzene [104], Furfural 169 is converted into methyl 2-furoate 170 in 79% yield Eq. 15. Nitrobenzene is the presumed stoichiometric oxidant for the oxidation of the nucleophilic alkene XXX to the acyl azolium XXXI by successive electron transfer events. The authors observe nitrosobenzene as a stoichiometric byproduct. This type of reactivity is also observed when cyanide is used as the catalyst. Miyashita has expanded the scope of this transformation using imida-zolylidene carbenes [105-107]. 

The system (4- Bu-pyH)3[Ru(0)3Cl ]/NM0/PMS/CH2Cl3 catalysed the oxidation of primary alcohols to aldehydes and of secondary alcohols to ketones like TRAP (Tables 2.1 and 2.2), such oxidations did not attack double bonds. As stoich. trans-(PPh )2[Ru(0)2Cl ] -/CH3CN it is a two electron oxidant for alcohols [561]. For tran -[Ru(0)2Cy - in solution the effective oxidant or oxidant precursor is [Ru(0)2Cl3]", and this species is coordinatively unsaturated. That this is the case is suggested by the observation that addition of extra Cl" (as (PPh )Cl) to the green [Ru(0)2Cl3]" in solution (Eq. 1.4) generating the red franx-[Ru(0)3Cl ] ", a markedly less effective catalytic oxidant for alcohols than [Ru(0) Cl ]" [561]. 

Catalytic oxidation of ozonides over platinum appears to be accompanied by the same ester by-product disadvantage found in the thermal process. Chain degradation by other reactions is less serious, however, and transesterification does not occur. The method can therefore be used to prepare a half-ester of a dicarboxylic acid from an ester of a suitable unsaturated acid. If ozonide autoxidation occurs by the route, ozonide — aldehyde — peracid, with the latter acting as precursor of both acid and ester products (20-24), it is interesting to compare reaction rates observed in the present study with the rate of uptake of oxygen by... 

Catalytic Epoxidation of Olefins by Hydroperoxides Catalytic Oxidation of Olefins to Aldehydes... 

Catalytic oxidation and ammoxidation of lower olefins to produce a,/3-unsaturated aldehyde or nitrile are widely industrialized as the fundamental unit process of petrochemistry. Propylene is oxidized to acrolein, most of which is further oxidized to acrylic acid. Recently, the reaction was extended to isobutylene to form methacrylic acid via methacrolein. Ammoxidation of propylene to produce acrylonitrile has also grown into a worldwide industry. 

The influence of substituents on the catalytic oxidation of toluene was investigated by Trimm and Irshad [330]. Toluene, chlorotoluenes and xylenes were oxidized over a M0O3 catalyst at 350—500° C. Partial oxidation products are aldehydes, acids and phthalic anhydride (in the case of o-xylene). Unexpectedly, both xylenes and chlorotoluenes are oxidized faster than toluene. The authors conclude that apparently the electromeric effect of the chlorosubstituent is more important than its inductive (—I) effect. The activation energies of the xylenes and chlorotoluenes all fall in the same range (17—18 kcal mol"1), while a much higher value is reported for toluene (27 kcal mol 1). 

In experiments (i) and (iv), no oxidation was observed after 50 h, in toluene / oxygen at 80 °C implying that a perruthenate derived species was responsible for the catalysis and not Ru02. In experiments (i) and (iii), approximately 10% and 70% oxidation respectively, to the aldehyde was observed after 3 days under the same conditions and complete leaching of potassium perruthenate was observed in both cases. The used solid material from experiments (ii) and (iii) showed no catalytic oxidative activity when reused.. 

Reaction of aldehydes with hydrazine followed by catalytic oxidation of the hexahydro-... 

Fig. 60. Correlations between catalytic activity and oxidizing ability for (a) oxidation of acetaldehyde (surface reaction) and (b) oxidative dehydrogenation of cyclohexene (bulk-type 11 reaction). (From Ref. 327.) r(aldehyde) and r(hexene) show the rates of catalytic oxidation of acetaldehyde and oxidative dehydrogenation of cyclohexene, respectively. (From Ref. 337.) r( CO) is the rate of reduction of catalysts by CO r(H2) is the rate of reduction of catalysts by H2. M, denotes M,H3-,PMO 2O40. Na2-1, 2, 3, and 4 are Na2HPMoi2O40 of different lots, of which the surface areas are 2.8, 2.2, 1.7, and 1.2 m2 g, respectively.

The aerobic oxidation of alcohol under neutral or acidic conditions to produce the corresponding adds, which can avoid the neutralization of the carboxylate salts, is also an important R D issue. In Au-catalyzed alcohol oxidation in methanol, the corresponding methyl esters are obtained with high seledivity instead of carboxylic acids by using metal oxide supported Au NPs [157, 160], In this case, base is not necessary, or only a catalytic amount of base is required to promote the readion. However, in water, it was demonstrated that alcohols were not oxidized under acidic conditions [161] and only aldehydes were oxidized to carboxylic adds [162]. Even under solvent-free conditions or in organic solvents, alcohols were converted into aldehydes without base however, the alcohols were not fully oxidized to carboxylic acid under acidic conditions [163-166]. 

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