Reductions of Carbonyl Compounds to Alcohols

Many biological processes involve oxidation of alcohols to carbonyl compounds or the reverse process reduction of carbonyl compounds to alcohols Ethanol for example is metabolized m the liver to acetaldehyde Such processes are catalyzed by enzymes the enzyme that catalyzes the oxidation of ethanol is called alcohol dehydrogenase... 

Reduction of Carbonyl Compounds to Alcohols - Sodium Borohydride-... 

It is interesting that electrocatalyzed reduction of carbonyl compounds to alcohols takes place by using trialkoxysilanes (equation 101)128. 

Addition of hydrosilane to alkenes, dienes and alkynes is called hydrosilylation, or hydrosilation, and is a commercially important process for the production of many organosilicon compounds. As related reactions, silylformylation of alkynes is treated in Section 7.1.2, and the reduction of carbonyl compounds to alcohols by hydrosilylation is treated in Section 10.2. Compared with other hydrometallations discussed so far, hydrosilylation is sluggish and proceeds satisfactorily only in the presence of catalysts [214], Chloroplatinic acid is the most active catalyst and the hydrosilylation of alkenes catalysed by E PtCU is operated commercially [215]. Colloidal Pt is said to be an active catalytic species. Even the internal alkenes 558 can be hydrosilylated in the presence of a Pt catalyst with concomitant isomerization of the double bond from an internal to a terminal position to give terminal silylalkanes 559. The oxidative addition of hydrosilane to form R Si—Pt—H 560 is the first step of the hydrosilylation, and insertion of alkenes to the Pt—H bond gives 561, and the alkylsilane 562 is obtained by reductive elimination. 

The reader is already familiar with the reductions of carbonyl compounds to alcohols, since they were described in Sections 10.2-10.4. (To complete the overall picture in a,fi-unsaturated carbonyl compounds the C=C- instead of the C=0 double bond can also be reduced according to Figure 13.20, through the Birch and L-Selectride reduction of such carbonyl compounds.)... 

The reader already is familiar with the reductions of carbonyl compounds to alcohols, since they were described in Sections 8.2-8.4. 

A variety of other electron transfer reagents have been employed in reactions which appear to be mechanistically similar to the more common metal-NH3 or metal-alcohol systems. These include K-graphite, Zn-KOH-DMSO and both Li and AP amalgams. The amalgams from Zn, Mg, Ni, Cu, Sn and Pb have been found not to be effective in the reduction of cyclohexanone in aqueous THF. Also, several low-valent metal cations have been employed in the reduction of carbonyl compounds to alcohols. Among these reagents are low-valence salts of Ti, " Ce and Sm. ... 

Reduction The stable Ni(0) complex is a useful catalyst for reduction of carbonyl compounds (to alcohols), sulfonyl azides (to sulfonamides), imines and nitro compounds (to amines) with ammonium formate. 

Colourless liq. B.p, 200°/6-8 mm., 175-80°/3 mm. Slowly solidiOes to white solid, m.p. 140°. Employed for reduction of carbonyl compounds to alcohols. Catalyst, for preparation of esters from aldehydes and alcoholysis of diketones. Adkins, J. Am. Chem. Soc., 1922,44,2178. Meerwein, Schmidt, Ann., 1925, 444, 232. Sumiya, Yamaha, Tajima, Chem. A6 stracts, 1932, 26, 3481. 

Colourless lig. B.p. 146-50°/5 mm.. Slowly solidifies to white solid, m.>. 118°. Condensing agent, also used for reduction of carbonyl compounds to alcohols. Can be employed, like aluminium tert.-botoxide, for oxidation qf alcohols., ... 

Yoneda F, Kuroda K, Kamishimoto M (1981b) Autorecycling system for reduction of carbonyl compounds to alcohols by 1,5-dihydro-5-deaza-flavins. J Chem Soc Chem Commun 1160-1162... 

FIGURE 16.65 Alcohols can be oxidized to carbonyl compounds. This reaction is the reverse of what you have just learned— the reduction of carbonyl compounds to alcohols through reactions with metal hydride reagents. 

The systems (HsC2)3SiH/H2S04 (33-50%) and (H5C2)3SiH/HCl (37-38%) have been used for the reduction of carbonyl compounds to alcohols (in acetonitrile at 25-30°C). Some of these reactions are summarised in Table 4.1. 

A simple and efficient protocol for microwave-assisted reduction of carbonyl compounds to alcohols and carboxylic acids is by Cannizzaro reaction. The reaction was achieved using a mixture of an aldehyde, sodium hydroxide, and basic alumina. Microwave irradiation of only 15 sec was reported to give almost quantitative yield of both alcohol and the carboxylic acid (Sharifi et al., 1999). 

Meerwin-Ponndorf-Verley (MPV) reduction of carbonyl compounds to alcohols is an important reaction in organic chemistry. Posner et al. (1977) carried out the efficient reduction of carbonyl compounds using isopropyl alcohol/diisopropyl carbinol and alumina under conventional heating, that has now been translated to a solvent less and expeditious reduction that uses aluminum alkoxides under micro-wave irradiation conditions and the reaction was completed in 2 min (Barbry and Torchy, 1997). 

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