Alcohols oxidation to ketone

TABLE 30. Comparison of the results of metal-catalyzed alcohol oxidation to ketones, carboxylic acids or aldehydes using H2O2 or TBHP... 

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... 

Supported oxo-rhenium catalysts in heterogeneous systems have also been reported, for example, the polystyrene-supported (catecholato)oxo-rhenium(VII) complexes (38), obtained from the reaction of polystyrene-supported catechol with [ReOCl3(PPh3)2], which catalyze alcohol oxidation to ketones or aldehydes with dimethylsulfoxide and epoxide... 

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. 

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

FIGURE 18.20 NAD and NADP participate exclusively iii two-electroii transfer reactions. For example, alcohols can be oxidized to ketones or aldehydes via hydride transfer to NAD(P). ... 

Since the transition state for alcohol oxidation and ketone reduction must be identical, the product distribution (under kinetic control) for reducing 2-butanone and 2-pentanone is also predictable. Thus, one would expect to isolate (R)-2-butanol if the temperature of the reaction was above 26 °C. On the contrary, if the temperature is less than 26 °C, (S)-2-butanol should result in fact, the reduction of... 

Selective oxidations are possible for certain bicyclic hydrocarbons.285 Here, the bridgehead position is the preferred site of initial attack because of the order of reactivity of C—H bonds, which is 3° > 2° > 1°. The tertiary alcohols that are the initial oxidation products are not easily further oxidized. The geometry of the bicyclic rings (Bredt s rule) prevents both dehydration of the tertiary bridgehead alcohols and further oxidation to ketones. Therefore, oxidation that begins at a bridgehead position... 

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. 

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 ... 

A very unusual Nazarov cyclization of propargyl vinyl ketones has been reported by Hashmi et al. (Eq. 13.16) [18]. Propargyl alcohol 50 was oxidized to ketone 51 with the Dess-Martin periodinane. Attempts to purify 51 by column chromatography on silica gel led to cyclopentenone 53 in 59% isolated yield. This suggests that the solid support catalyzed the isomerization of 51 to allenyl vinyl ketone 52, which was not isolated, but which underwent spontaneous cyclization to 53. This result is consistent with earlier observations of the great ease with which allenyl vinyl ketones undergo the Nazarov reaction (cf. 8, Eq. 13.2). 

Benzyl alcohols Aryl alkyl carbinols (11) can be oxidized to ketones (12) by the direct electrochemical method (Eq. 4) since they possess their oxidation potentials at around 2.0 V versus SCE (saturated calomel electrode) however, cleavage products decrease the selectivity [14]. 

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. 

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. 

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. 

Aliphatic alcohols can be oxidized to ketones, aldehydes, or carboxylic acids using oxoruthenium(IV)complexes as redox catalyst or clectrogenerated ruthenium tetroxide In the latter case, a double mediator system is used in which an electrochemically generated active chlorine species (Cl or CP ) oxidizes RuO to RUO4 (Eq. (29)). 

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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