Alcohols to alkanes

In general, peroxomonosulfates have fewer uses in organic chemistry than peroxodisulfates. However, the triple salt is used for oxidizing ketones (qv) to dioxiranes (7) (71,72), which in turn are useful oxidants in organic chemistry. Acetone in water is oxidized by triple salt to dimethyldioxirane, which in turn oxidizes alkenes to epoxides, polycycHc aromatic hydrocarbons to oxides and diones, amines to nitro compounds, sulfides to sulfoxides, phosphines to phosphine oxides, and alkanes to alcohols or carbonyl compounds. 

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. 

Metallic oxidants, namely, chromic acid and potassium permanganate, may be used to oxidize alkanes to alcohols or ketones, but these reagents have only limited synthetic value. Alkaline KMnC>4 is rather ineffective, mainly because of the insolubility of alkanes in the aqueous solution of the reagent. Oxidations in acidic solutions such as aqueous CF3COOH,108 or the use of special reagents such as benzyltriethylammonium permanganate109 may give better results. 

Fig. 4. Conversion after 2 hours of vigorous stirring of C5 to CIO n-alkanes to alcohols and ketones, carried out at 298 K and 0.1 MPa in a microreactor of 3 ml with 2.4 mmol t.BHP, and 6 mmol paraffin. 8.10 mmol FePc was used in 1.5 ml dichloromethane and 0.1 g FePcY in 1.5 ml acetone.

Although isobutane does not give any oxidation products in the absence of Magic Acid under the same low-temperature ozonization conditions, it was not possible for the authors to determine642 whether formation of intermediate oxidation products, such as alcohols, plays any role in the ozonization of alkanes in Magic Acid. There is no experimental evidence for reactions proceeding via the intermediacy of carbenium ions whether the initial oxidation step of alkanes to alcohols is important. This oxidation, indeed, was found to be extremely slow in the acidic media studied. 

However, attempts to develop similar selective catalysts failed in the case of reactions that require one oxygen atom, like the oxidation of methane, ethane and other alkanes to alcohols, aromatic compounds to phenols, alkenes to epoxides, and many others. These mechanistically simple reactions assume one difficult condition the presence of active sites that upon obtaining two atoms from gas-phase 02 can transfer only one of them to the molecule to be oxidized, reserving the second atom for the next catalytic cycle with another molecule. This problem remains a hard challenge for chemical catalysis. 

Oxidation of alkanes to alcohols anil or ketones.1 This dioxirane oxidizes hydrocarbons in CH2Cl2/l,l,l-trifluoro-2-propanone (TFP) at -22 to 0° to alcohols or further oxidation products in high yield. Tertiary C-H bonds are attacked more rapidly than secondary ones, and primary C-H bonds are scarcely affected. The oxidation apparently involves insertion of O-atom. Oxidations can be stereospecific, as in the case of cis- and trans- 1,2-dimethyIcyclohexane. 

Much of the work on model systems was stimulated by the observation of Udenfriend and co-workers in 19546S4a,b that a mixture of Fe(II), EDTA, ascorbic acid, and molecular oxygen could hydroxylate arenes to phenols under mild conditions. Udenfriend s reagent also hydroxylates alkanes to alcohols and epoxidizes olefins.670 6 74 The EDTA in Udenfriend s reagent probably reduces the redox potential of the Fe(II)/Fe(III) couple. The ascorbic acid functions as an electron donor, analogous to the cofactor in monooxygenases, and can be replaced by other enediols.672... 

The Udenfiiend system of 1954 was perhaps the first to be specifically presented as a model of a biological process. In this system, Fe(II) is the catalyst, EDTA the ligand, air is the primary oxidant and ascorbic acid provides the reducing equivalents called for in this monooxygenase system. Arenes can be hydroxylated to phenols, alkanes to alcohols, and alkenes to epoxides, although with modest efficiency. The NIH shift was not observed in the model, however. 

At 120°C, a mixture of PtC " and PtCl4 in the presence of oxygen can be used for the oxidation of alkanes to alcohols (70). The substrate p-toluenesulfonic acid is oxidized sequentially at the side-chain functionality, first to the alcohol and then to the aldehyde (Eq. 25). For ethylbenzene,... 

Simple alkanes can be converted to esters with dialkyloxrranes. Cyclic alkanes are oxidized to alcohols with dimethyl dioxirane. " Cyclohexane was converted to cyclohexyl trifluoroacetate with di(trifluoromethyl) dioxrrane and trifluoroacetic anhydride and also with RuCl3/MeC03H/CF3C02H. Dimethyl dioxrrane converts alkanes to alcohols in some cases. Adamantane is converted to adamantyl alcohol with DDQ (p. 1710) and triilic acid. The mechanism of oxygen insertion into alkanes has been examined. ... 

In addition to the conversion of unactivated alkanes to alcohols, cytochrome P450 hemes transform alkenes to epoxides, arenes to phenols, and sulfides to sulfoxides to sulfones. Furthermore, they are involved in the biosynthesis and biodegradation of endogenous compounds such as steroids, fatty acids, prostaglandins and leukotrienes. Under anaerobic conditions, P450 will reductively dehalogenate haloalkanes to the corresponding alkanes. 

A-hydroxy-phthalimide (NHPI) acts as a catalyst for transformation of alkanes to alcohols, ketones, carboxylic acids, and/or nitroalkanes under mild oxidation conditions [64]. Koguchi et al. [64] used NHPl-Co(OAc)j-02 system for the oxidation of alcohols in ionic liquids. They found that NHPI is separated easily from ionic liquid... 

Such transformations can also use 1-hydroxy-1/7-ben-zotriazole in place of the benzothiazoline.159 An alkane hydroxylase has been used to convert alkanes to alcohols.160 Cholesterol can be oxidized to the ketone, cholestenone, with cholesterol oxidase in reversed micelles of water in isooctane in 100% conversion.161... 

Another approach is the nucleophilic displacement of chloride from chloro-propyl-silica with a pyridine-substituted porphyrin. These materials are active in the epoxidation of alkenes, where iodosylbenzene is the preferred oxidant, and in the oxidation of alkanes to alcohols and ketones. The copolymerisation of a porphyrin containing four attached trimethoxysilane groups with tetra-ethoxysilane, leading to an active hybrid silica-porphyrin, offers another route to these important catalysts. 

The presence of a silica framework with few defects makes TS-1 a highly hydrophobic material suitable for oxidations in the liquid phase with H2O2 as oxidant. Thus, TS-1 has proven to be successful in the oxidation of alcohols, epox-idation of linear olefins, hydroxylation of aromatics, ammoximation of cyclohexanone, oxidation of alkanes to alcohols and ketones, oxidation of amines, oxidation of sulfur-containing compounds, and oxidation of ethers [66-75]. 

It is absolutely necessary to know these interconversion patterns, because they provide the framework for designing synthetic strategy. Suppose we wish to synthesize an alcohol starting with an alkane. From this chart, we see immediately that we have no direct method for converting alkanes to alcohols. We must first make a haloalkane and then use it in another reaction to make an alcohol. We set up the proposed synthesis in just that way and insert the specific reagents necessary to carry out the two synthetic steps ... 

Oxidation of alkanes to alcohols and ketones with hydrogen peroxide (52)... 

As previously mentioned, one of the earliest discoveries of homogeneous C-H activation and functionalization of alkanes was discovered by Shilov. In his initial studies, Shilov reported that solutions of K2[PtCl4] in D2O/CH3CO2D could incorporate deuterium into alkanes, even methane. Subsequent to this, he reported that addition of H2[PtCl6] to the K2[PtCl4] reaction mixture resulted in the oxidation of methane and other alkanes to alcohols and alkyl chlorides. Significantly, the observed selectivity of 1° > 2° > 3° C -H bonds reflects what is reported in other systems. 

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