Secondary alcohols oxidation to ketones

Primary alcohols oxidize to aldehydes, which, in turn, oxidize to carboxylic acids. Secondary alcohols oxidize to ketones. In each case, the reverse process is called re- duction... 

Conversely, as previously stated, the aldehydes on reduction yield the primary alcohols and in the case of benzaldehyde, which is a commonly occurring substance in oil of bitter almonds, this method is used in the preparation of the alcohol. In the case of the secondary alcohols oxidation to ketones is not easily accomplished but the reverse reaction, the reduction of the ketones to secondary alcohols does take place with ease. 

Reaction of the C-0 and O-H Bonds Primary alcohols oxidize to carboxylic acids secondary alcohols oxidize to ketones with chromium trioxide or sodium dichromate. Tertiary alcohols do not oxidize under mild conditions. With pyridinium chlorochromate (PCC) the oxidation of primary alcohols can be stopped at aldehydes. 

Oxidation of primary alcohols leads to aldehydes and oxidation of secondary alcohols leads to ketones. This oxidation also involves the loss of two hydrogen atoms. However, unlike the oxidations discussed so far in this chapter that are mediated almost exclusively by cytochromes P450, the major enzyme involved in the oxidation of ethanol is ALD (discussed earlier in this chapter) (74). Although ALD is the major enzyme involved in the oxidation of ethanol and most other low molecular-mass alcohols, cytochromes P450, especially 2E1, can also oxidize ethanol and this enzyme is induced in alcoholics. Although comprehensive studies have not been published, it appears that cytochromes P450 are often the major enzymes involved in the oxidation of higher molecular mass alcohols. 

Both primeiry and secondary alcohols can be oxidized, but tertiary alcohols won t undergo simple oxidation. Oxidation of a primary alcohol gives an aldehyde however, preventing further oxidation of the aldehyde to a carboxylic acid is difficult. Secondary alcohols oxidize to a ketone without the problem of additional oxidation occurring. 

In Chapter 15 primary alcohols, RCH2OH, were shown to be readily oxidized to aldehydes, RCHO, and secondary alcohols, R2CHOH, to ketones, R2CO, by inorganic reagents such as Cr03 and KMn04. However, it is a problem to avoid overoxidation with primary alcohols because of the ease with which aldehydes... 

The conversion of secondary alcohols (R2CHOH) to ketones can be achieved by KMn04, Na2Cr207 or Cr03 under acidic conditions. The use of Cr03 in acid is known as the Jones oxidation. 

Bis(trifluoroacetoxy)iodo]perfluoroalkanes are effective recyclable reagents for the oxidation of aliphatic and benzylic secondary alcohols 119 to ketones 120 in the presence of KBr in aqueous solution (Scheme 5.38) [103]. The reduced form of the reagent, the respective iodoperfluoroalkanes 118, can be efficiently isolated from the reaction mixture in 96-98% yield by adding three to five volumes of methanol and separating the resulting fluorous/methanolic liquid/liquid biphasic system. The recovered iodoperfluoroalkanes 118 can be reoxidized to reagents 116 and reused [103]. 

Efforts have been made since then to develop new catalytic protocols for the oxidation of alcohols with molecular oxygen as the sole oxidant in water. For instance, the water-soluble Pd(II)-biquinoUne 57 was demonstrated to be efficient for aerobic oxidation of primary and secondary alcohols in water [154]. With a catalyst loading of 1 mol%, secondary alcohols led to ketones in high yields (85-100%), while aliphatic primary alcohols were fully oxidized to the corresponding acids, and benzyl alcohols were transformed to pure benzoic acid or benzaldehydes with a relatively low amount of acids formed. 

Secondary alcohols are oxidized to ketones by the same reagents that oxidize primary alcohols... 

The S >ern oxidation is a preparatively important reaction which allows for the oxidation of primary and secondary alcohols 1 to aldehydes and ketones 2, respectively, under mild conditions, using activated dimethyl sulfoxide (DMSO) as the oxidizing agent. 

After the first hydrolytic step, secondary alcohols seem to continue biodegradation through ketone, hydroxyketone, and diketone. Diketones then produce a fatty acid and a linear aldehyde which is further oxidized to fatty acid. Finally, these two fatty acids continue biodegradation by enzymatic 3 oxidation [410],... 

Treatment of the elimination product 107 with triethylamine resulted in smooth isomerization of the olefin, to afford the a,p-unsaturated ketone 108. Ally lie oxidation of 108 then generated the secondary alcohol 109 in 72 % yield. The acetonide and silyl ether functions of 109 were cleaved in one reaction to afford a tetraol intermediate that was regioselectively acylated at the secondary alcohol functions, to provide the triacetate 110 in high yield (89 %). Hydrogenolysis of the benzyl ether... 

Another factor complicating the situation in composition of peroxyl radicals propagating chain oxidation of alcohol is the production of carbonyl compounds due to alcohol oxidation. As a result of alcohol oxidation, ketones are formed from the secondary alcohol oxidation and aldehydes from the primary alcohols [8,9], Hydroperoxide radicals are added to carbonyl compounds with the formation of alkylhydroxyperoxyl radical. This addition is reversible. 

The secondary alcohols are oxidized to ketones. In such oxidations, although air facilitates the process, but there is no oxygen uptake and since (CH3)2S has been isolated from the reaction products, it shows that DMSO is the oxidant. The mechanism in these oxidations is proabably as follows ... 

Secondary alcohols are oxidized to ketones and primary alcohols are oxidized to esters, when iodonium ion is used as a catalytic mediator as shown in Fig. 4 [35]. This method may have high potentiality in organic synthesis, since it requires only a catalytic amount of KI, whereas most of the hitherto known oxidations usually require more than one equivalent of the oxidizing agent. 

You learned earlier that primary alcohols are oxidized to aldehydes, and secondary alcohols are oxidized to ketones. You can think of the reduction of aldehydes and ketones as the reverse of these reactions. Aldehydes can be reduced to produce primary alcohols. Ketones can be reduced to produce secondary alcohols. 

New functional groups can arise as a result of oxidation of the compounds mentioned above. For example, the oxidation of a thiol yields a disulfide (R-S-S-R). Double oxidation of a primary alcohol (R-CH2-OH) gives rise initially to an aldehyde (R-C(O)-H), and then to a carboxylic acid (R-C(O)-OH). In contrast, the oxidation of a secondary alcohol yields a ketone (R-C(O)-R). The carbonyl group (C=0) is characteristic of aldehydes and ketones. 

Strong reducing agents like sodium borohydride and lithium aluminum hydride are capable of reducing aldehydes to primary alcohols and ketones to secondary alcohols. The general reaction is the reverse of the reactions used to form aldehydes and ketones by the oxidation of primary and secondary alcohols, respectively (to review, see the earlier section Oxidation reactions ). However, the mechanisms for reduction are different. 

For a synthesis of the anti-cancer drug taxol TPAP/NMO was used in three steps, two for oxidation of primary alcohols to aldehydes (by TPAP/NMO/PMS/ CHjClj) and one for a secondary alcohol to ketone (by TPAP/NMO/PMS/CHjClj-CHjCN) [66], cf. also [111] and for the SERCA inhibitor thapsigargin (two primary alcohol and one secondary alcohol oxidation steps) [112], This system was also used during synthesis of the cholesterol biosynthesis inhibitor 1233A [52], the antibiotic and anti-parasitic ionophore tetronasin [113, 114] and for the cytotoxic sponge alkaloids motopuramines A and B [115]. 

The secondary alcohol groups in PVA may be oxidized to ketones, and the primary alcohol groups in carbohydrates may be oxidized to carboxylic acids. Although these reactions do not reduce the degree of polymerization, they do increase the degree of water solubility of the polymers. 

Oxidations with chromium trioxide.6 Secondary alcohols can be oxidized to ketones in good yields by Cr03 in the presence of catalytic amounts of tetraalkyl-ammonium halides. Yields from oxidation of primary alcohols are moderate. 

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