Alcohols from Carbonyl Compounds Reduction

Aldehydes are easily reduced to give primary alcohols, and ketones are reduced to give secondary alcohols. 

Dozens of reagents are used in the laboratory to reduce aldehydes and ketones, depending on the circumstances, but sodium borohydride, NaBH4, is usually chosen because of its safety and ease of handling. Sodium borohydride 

Lithium aluminum hydride, LiAlH4, is another reducing agent often used for reduction of aldehydes and ketones. A grayish powder that is soluble in ether and tetrahydrofuran, LiAlH4 is much more reactive than NaBH4 but also more dangerous. It reacts violently with water and decomposes explosively when 

We ll defer a detailed discussion of the mechanisms of these reductions until Chapter 19. For the moment, we ll simply note that they involve the addition of a nucleophilic hydride ion ( H ) to the positively polarized, electrophilic carbon atom of the carbonyl group. The initial product is an alkoxide ion, which is pro-tonated by addition of H30 in a second step to yield the alcohol product. 

In living organisms, aldehyde and ketone reductions are carried out by either of the coenzymes NADH (reduced nicotinamide adenine dinucleotide) or NADPH 

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Alcohols from Carbonyl Compounds. Oxidation-Reduction and Organometallic Compounds... 

Chiral Ligand of L1A1H4 for the Enantioselective Reduction of Alkyl Phenyl Ketones. Optically active alcohols are important synthetic intermediates. There are two major chemical methods for synthesizing optically active alcohols from carbonyl compounds. One is asymmetric (enantioselective) reduction of ketones. The other is asymmetric (enantioselective) alkylation of aldehydes. Extensive attempts have been reported to modify Lithium Aluminum Hydride with chiral ligands in order to achieve enantioselective reduction of ketones. However, most of the chiral ligands used for the modification of LiAlHq are unidentate or bidentate, such as alcohol, phenol, amino alcohol, or amine derivatives. 

Reductions catalyzed by alcohol dehydrogenases formation of chiral enantio-merically pure alcohols from carbonyl compounds. 

CHAPTER 12 ALCOHOLS FROM CARBONYL COMPOUNDS Oxidation-Reduction and Organometaiiic Compounds... 

CHAPTER 12 ALCOHOLS FROM CARBONYL COMPOUNDS Oxidation-Reduction and Organometaiiic Compounds 12.20 Predict the major organic product from each of the following reactions. 

ALCOHOLS FROM CARBONYL COMPOUNDS OXIDATION-REDUCTION AND ORGANOMETALLIC COMPOUNDS... 

Alcohols can be prepared from carbonyl compounds by reduction of aide hydes and ketones See Table 15 3... 

Alcohols may be prepared (1) by hydration of alkenes (1) in presence of an acid and (11) by hydroboratlon-oxidatlon reaction (2) from carbonyl compounds by (1) catalytic reduction and (11) the action of Grignard reagents. Phenols may be prepared by (1) substitution of (1) halogen atom In haloarenes and (11) sulphonic acid group In aiyl sulphonic acids, by -OH group (2) by hydrolysis of diazonium salts and (3) industrially from cumene. 

Reduction of the carbonyl function in acetophenones using sodium in ethanol also produces an alcohol. More complex aromatic alcohols may be prepared from carbonyl compounds by reaction with Grignard reagents followed by hydrolysis (see Chapter 10). 

Let us look a little more closely at reduction by metal hydrides. Alcohols are formed from carbonyl compounds, smoothly and in high yield, by the action of such compounds as lithium aluminum hydride, LiAlH4. Here again, we see... 

The overall process, considering that the propargylic alcohols are generated from carbonyl compounds, constitutes a reductive nucleophilic substitution with additional introduction of the synthetically valuable sulfoxide functionality. 

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