Selective oxidation of alcohols

Interestingly, free nano-iron oxide particles are active catalysts for the selective oxidation of alcohols to yield the corresponding aldehydes/ketones [72, 73]. Different aromatic alcohols and secondary aliphatic alcohols were oxidized with high selectivity, but at low conversion. Here, further improvement should be possible (Scheme 25). 

Scheme 25 Selective oxidation of alcohols to aldehydes and ketones...

The reaction is carried out using a titanium silicalite-1 (TS-1) zeolite catalyst [30, 122]. This type of catalyst is known to accelerate the selective oxidation of alcohols, epoxidation of alkenes and hydroxylation of aromatics. These reactions have importance for fine-chemical production. 

Desrosiers, P., Guram, A., Hagemeyer, A. et al. (2001) Selective oxidation of alcohols by combinatorial catalysis. Catal. Today, 67, 397. 

The Effect of Bismuth Promotion on the Selective Oxidation of Alcohols Using... 

Pillai, U.R. and Sahle-Demessie, E. (2002) Selective oxidation of alcohols in gas phase using light-activated titanium dioxide. Journal of Catalysis, 211 (2), 434—444. 

Scheme 6.30 Solvent-free selective oxidation of alcohols with clayfen.

R. Ciriminna, C. Bolm, T. Fey and M. Pagliaro, Sol-Gel Ormosils Doped with TEMPO as Recyclable Catalysts for the Selective Oxidation of Alcohols, Adv. Synth. Catal., 2002, 344, 159. 

M. Besson, and P. Gallezot, Selective oxidation of alcohols and aldehydes on metal catalysts, Catal. Today 57(1-2), 127-141 (2000). 

S. Venkatesan, A. S. Kumar, J.-M. Zen, A Rugged Lead-ruthenate pyrochlore Membrane Catalyst for Highly Selective Oxidation of Alcohols, J. Mol. Catal. A Chem. 250 (2006) 87-93. 

G. Barak, J. Dakka, Y. Sasson, Selective Oxidation Of Alcohols by a H2O2-RUCI3 System under Phase-Transfer Conditions, J. Org. Chem. 53 (1988)3553—3554. 

Various solid-supported perruthenate reagents have been designed for the oxidation of alcohols.Solid-supported NMO has also been used. A number of perruthenate systems employing O2 as the terminal oxidant have also been reported. The use of ionic liquids based upon substituted imidazolium cations as alternative solvent media for the selective oxidation of alcohols to aldehydes and ketones has also been investigated. ... 

SCHEME 119. Selective oxidation of alcohols using a chromium-piUared montmoriUonite catalyst and TBHP... 

The selective oxidation of alcohols to the corresponding aldehydes and ketones is of prime importance for organic synthesis, and various types of reagents have been described that achieve this transformation selectively and efficiently [141,142]. However, the number of sub-stoichiometric, nontoxic, non-hazardous oxidation systems has been relatively Umited. As copper enzymes such as galactose oxidase are known to catalyze this oxidation reaction, bioinspired homogeneous catalysts based on copper species have also been developed in recent years. 

Selective oxidation of alcohols. Primary alcohols are oxidized by this RuCL complex about 50 times as rapidly as secondary alcohols. Use of benzene as solvent is critical lor this high selectivity. Little or no reaction occurs in CH3CN, THF, or DMF. Most oxidants, if they show any selectivity, oxidize secondary alcohols more rapidly than primary ones. However, ruthenium-catalyzed oxidations with N-mcthylmorpholine N-nxide and oxidations with PCC4 proceed about three times as rapidly with primary alcohols as with secondary ones. 

PDC exists in the form of stable bright-orange crystals that remain unaltered by manipulation in the open air. Its lack of hydrophylicity and almost neutral properties facilitate its handling and allows the selective oxidation of alcohols in the presence of very sensitive functional groups. 

Lactols derived from hydroxyketones cannot be oxidized to lactones. Theoretically, they could be oxidized to dicarbonyl compounds via the minor hydroxyketone equilibrating with the lactol. In practice, this reaction is usually so slow as to allow the selective oxidation of alcohols with PDC, in the presence of lactols derived from hydroxyketones. 

Although primary and secondary amines are destroyed by PDC, hindered secondary amines can resist the action of PDC long enough to allow selective oxidation of alcohols.146... 

Normally, alcohols can be selectively oxidized with PDC in the presence of tertiary amines.148 Although TV-methyl tertiary amines are transformed into formamides by PDC,149 this reaction is usually slow enough so that selective oxidation of alcohols with PDC can be possible. 

There is one report in which sulfides are oxidized by PDC in aqueous acetic acid however normally the oxidation of alcohols is quicker, so that selective oxidation of alcohols with PDC is possible in the presence of sulfur containing compounds, such as thiophenes,153 aryl sulfides,154 alkyl sulfides155 and dithioacetals.156... 

Normally, alkenes do not interfere with the oxidation of alcohols with PCC. Although alkenes do react with PCC, this normally requires quite harsh conditions, and selective oxidations of alcohols are possible. 

Ref. 268a A selective oxidation of alcohol to aldehyde is performed in the presence of an unreacting sulfide. ... 

Carboxylic acids react under Pfitzner-Moffatt conditions, resulting in the formation of methylthiomethyl esters and /V-acylureas.41 Nevertheless, although the authors are not aware of any report involving the selective oxidation of alcohols in the presence of a carboxylic acid, such outcome would be likely with carboxylic acids with little nucleophilicity, as standard Pfitzner-Moffatt oxidations are performed in the presence of trifluoroacetate that is known for not to interfere. 

Primary amides react under Swern conditions, producing the corresponding nitriles213 and minor amounts of iminosulfurans.210 Nonetheless, there is some report depicting the selective oxidation of alcohols in the presence of primary amides.214 Secondary and tertiary amides remain unaffected. 

Quite puzzlingly, other authors report the selective oxidation of alcohols in the presence of dithioacetals.40... 

Alcohols can be oxidized with TPAP in the presence of tertiary amines.88 Secondary amines are transformed into imines under the action of TPAP.89 At the time of writing, the scientific literature contains no data regarding the possibility of performing selective oxidation of alcohols in the presence of secondary or primary amines, with the exception of the following example in which a secondary amine is trapped by reaction with an aldehyde, resulting from the selective oxidation of a primary alcohol.90... 

The selective oxidation of alcohols is widely recognized as one of the most fundamental transformations in both laboratory and industrial synthetic chemistry because the resulting carbonyl compounds serve as important and versatile intermediates for the synthesis of fine chemicals [4]. Many oxidizing reagents, including permanganate and dichromate, have traditionally been employed to achieve this transformation [5]. These stoichiometric oxidants, however, have serious... 

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