Alcohols from carbonyl compounds: Reduction
المؤلف:
University of Missouri System
المصدر:
Organic Chemistry ii
الجزء والصفحة:
.................
6-10-2020
1826
Alcohols from carbonyl compounds: Reduction
Aldehydes, ketones and alcohols are very common features in biological molecules. Converting between these compounds is a frequent event in many biological pathways. However, semi-anionic compounds like sodium borohydride don’t exist in the cell. Instead, a number of biological hydride donors play a similar role.
NADH is a common biological reducing agent. NADH is an acronym for nicotinamide adenine dinucleotide hydride. Insetad of an anionic donor that provides a hydride to a carbonyl, NADH is actually a neutral donor. It supplies a hydride to the carbonyl under very specific circumstances. In doing so, it forms a cation, NAD+. However, NAD+ is stabilized by the fact that its nicotinamide ring is aromatic; it was not aromatic in NADH.
Reduction of carboxylic acids and esters
Carboxylic acids can be converted to 1o alcohols using Lithium aluminium hydride (LiAlH4). Note that NaBH4 is not strong enough to convert carboxylic acids or esters to alcohols. An aldehyde is produced as an intermediate during this reaction, but it cannot be isolated because it is more reactive than the original carboxylic acid.
Esters can be converted to 1o alcohols using LiAlH4, while sodium borohydride (NaBH4 ) is not a strong enough reducing agent to perform this reaction.
Exercises
Q1
Give the aldehyde, ketone, or carboxylic acid (there can be multiple answers) that could be reduced to form the following alcohols.
(a) 
(b) 
(c) 
(d) 
Q2
Given the following alcohol, draw the structure from which it could be derived using only NaBH4
(a) 
(b) 
(c) 
(d) 
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