Chemistry > Aldehydes and Ketones > 16.0 Reduction of Aldehyde and Ketones
Aldehydes and Ketones
1.0 Introduction
2.0 Methods of Preparation
2.1 Aldehydes by Oxidation of 1° Alcohol
2.2 Ketones by Oxidation of 2° Alcohol
2.3 Aldehydes by Reduction of Acyl Chlorides, Esters and Nitriles
2.4 Aldehydes from Acyl Halides
2.5 Aldehydes from Esters and Nitriles
2.6 By heating calcium salt of fatty acids
2.7 Hydroboration of Alkynes
2.8 Hydration of Alkynes
2.9 Gattermann-Koch Reaction
2.10 Gattermann Reaction
2.11 Freidel Crafts Acylation
2.12 By Oxidation of Alkyl Benzenes
2.13 Etard’s Reaction
3.0 Physical Properties
4.0 Relative Reactivities of Carbonyl Compounds
4.1 Relative Reactivities towards Nucleophilic addition
4.2 Rate of Nucleophilic Substitution
4.3 Reactivitiy Considerations
5.0 Addition of Carbon Nucleophiles
6.0 Haloform Reactions
7.0 Aldol Condensations
8.0 Claisen Condensation
9.0 Intramolecular Claisen Condensation
9.1 Dieckmann Condensation
9.2 Perkin Reaction
9.3 Mechanism:
9.4 Knoevenagel Reaction
9.5 Mechanism
10.0 Cannizzaro Reaction
11.0 Reformatsky Reaction
12.0 Addition of Nitrogen Nucleophiles
12.1 Mechanism and pH dependence of Rate of Reaction of Imine (>C = N-) Formation
12.2 Addition of Secondary Amines: Formation of Enamine
12.3 Mechanism for Enamine Formation
12.4 Addition of Ammonia: Reductive Amination
13.0 Addition of Oxygen Nucleophile
13.1 Addition of Water
13.2 Mechanism
13.3 Mechanism for Acid-Catalysed Hydrate Formation
13.4 Addition of Alcohols
13.5 Mechanism for the Reaction
13.6 Acid-Catalyzed Hemiacetal Formation
13.7 Base-Catalyzed Hemiacetal Formation
13.8 Acid-Catalyzed Acetal Formation
13.9 Acetals are Protecting Groups
14.0 Addition of Sulphur Nucleophile
15.0 Oxidation of Aldehydes And Ketones
15.1 Tollen’s Reagent
15.2 Fehling Solution
15.3 Benedict’s Solution
15.4 Schiff’s Reagent
15.5 Baeyer-Villiger Oxidation
15.6 Oppenauer Oxidation
15.7 Oxidation of Aldehydes And Ketones With $S{O_2}$
16.0 Reduction of Aldehyde and Ketones
16.1 Addition of Hydride Ion
16.2 Meerwein-Ponndorf-Verley Reduction
16.3 The Wolf Kishner Reduction
16.4 Mechanism for Wolff-Kishner
16.5 Clemmensen Reduction
17.0 Other Reactions Of Aldehydes And Ketones
17.1 Wittig Reaction
17.2 Pinacol-Pinacolone Rearrangement
17.3 Benzoin Condensation
17.4 Schimdt Reaction
17.5 Benzilic acid Rearrangement
17.6 The Beckmann Rearrangement
17.7 Reaction of Formaldehyde with Ammonia
16.5 Clemmensen Reduction
2.2 Ketones by Oxidation of 2° Alcohol
2.3 Aldehydes by Reduction of Acyl Chlorides, Esters and Nitriles
2.4 Aldehydes from Acyl Halides
2.5 Aldehydes from Esters and Nitriles
2.6 By heating calcium salt of fatty acids
2.7 Hydroboration of Alkynes
2.8 Hydration of Alkynes
2.9 Gattermann-Koch Reaction
2.10 Gattermann Reaction
2.11 Freidel Crafts Acylation
2.12 By Oxidation of Alkyl Benzenes
2.13 Etard’s Reaction
4.2 Rate of Nucleophilic Substitution
4.3 Reactivitiy Considerations
9.2 Perkin Reaction
9.3 Mechanism:
9.4 Knoevenagel Reaction
9.5 Mechanism
12.2 Addition of Secondary Amines: Formation of Enamine
12.3 Mechanism for Enamine Formation
12.4 Addition of Ammonia: Reductive Amination
13.2 Mechanism
13.3 Mechanism for Acid-Catalysed Hydrate Formation
13.4 Addition of Alcohols
13.5 Mechanism for the Reaction
13.6 Acid-Catalyzed Hemiacetal Formation
13.7 Base-Catalyzed Hemiacetal Formation
13.8 Acid-Catalyzed Acetal Formation
13.9 Acetals are Protecting Groups
15.2 Fehling Solution
15.3 Benedict’s Solution
15.4 Schiff’s Reagent
15.5 Baeyer-Villiger Oxidation
15.6 Oppenauer Oxidation
15.7 Oxidation of Aldehydes And Ketones With $S{O_2}$
16.2 Meerwein-Ponndorf-Verley Reduction
16.3 The Wolf Kishner Reduction
16.4 Mechanism for Wolff-Kishner
16.5 Clemmensen Reduction
17.2 Pinacol-Pinacolone Rearrangement
17.3 Benzoin Condensation
17.4 Schimdt Reaction
17.5 Benzilic acid Rearrangement
17.6 The Beckmann Rearrangement
17.7 Reaction of Formaldehyde with Ammonia
The reduction of carbonyl groups of aldehydes and ketones to methylene groups with amalgamated zinc and concentrated hydrochloric acid is known as Clemmensen reduction.
The reduction consists in refluxing the carbonyl compounds with amalgamated zinc and excess of concentrated hydrochloric acid. The reduction is useful especially for ketones containing phenolic or carboxylic groups which remain unaffected. Ketones are reducing more often than aldehydes. Such reduction is also observed in Wolff-Kishner reduction but Clemmensen reduction is easier to perform. The reduction, however, fails with acid-sensitive and high molecular weight substrates. The $\alpha ,\beta $-unsaturated ketones undergo reduction of both the olefinic and carbonyl groups.
Mechanism: Nakabayaski has suggested a mechanism on the assumption that the reducing under acid condition involves protonated carbonyl group to which electrons are transferred from the metal.
Certain types of aldehydes and ketones do not give the normal reduction products alone. Thus, $\alpha $-hydroxyl ketones give either ketones through hydrogenolysis of $OH$ group or olefins and 1,3-diketones give exclusively monoketones with rearrangement.
Certain cyclic 1,3-diketones give under Clemmensen reduction a fully reduced product along with a monoketone with ring contraction.
The latter probably is formed through a diradical with subsequent intramolecular C – C bond formation and pinacol type rearrangement.
