Chemistry > Aldehydes and Ketones > 17.0 Other Reactions Of Aldehydes 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
17.2 Pinacol-Pinacolone Rearrangement
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 acid catalysed rearrangement of vic diols (1, 2-diols) to ketones or aldehydes with elimination of water is known as pinacol or pinacol-pinacolone rearrangement. The name was given from the classical example of the conversion of pinacol to pinacolone.
Elimination of water without rearrangement – the normal reaction of alcohols – may be achieved under drastic conditions $\left( {A{l_2}{O_3},{\text{ }}450^\circ C} \right).$
The rearrangement has been successfully carried out with various polysubstituted glycols.
Mechanism:
The carbocation (I), though tertiary, prefers to form (II) for its resonance stability.
The mechanism is supported by the fact that any carbocation in which the positive charge is on the carbon adjacent to the one bearing the hydroxyl group $\left( { - \mathop {\mathop C\limits_ \oplus }\limits^| - \mathop {\mathop C\limits_| }\limits^| - OH} \right)$ also undergoes similar rearrangement. Thus,
The loss of water and migration of the alkyl group may be very rapid or simultaneous. Probably the migrating group does not become completely free before it is partially bonded (III) to the adjacent positively charged carbon, i.e., a type of intramolecular rearrangement is suggested.
Evidence in favour of this are (a) the migrating group retains its configuration, if chiral and (b) no cross-over products are obtained when a mixture of two nearly similar 1,2-diols is treated with acid.
Migratory aptitude: Migration order in general is $H > aryl > alkyl$
As the migrating group migrates with its electron pair, the more nucleophilic group might be expected to migrate. Thus, the order of migration amongst the aryl groups is $p - anisyl > p - tolyl > phenyl > p - chlorophenyl,$ etc.
Obviously, electron-withdrawing groups will retard the migration. The migratory aptitude amongst the alkyl groups is $M{e_3}C > M{e_2}CH{\text{ }} > {\text{ }}Me$ Me. However, the stability of the initially formed carbocation may offset the migratory aptitude order. The initial carbocation is formed by the loss of that hydroxyl group which results in the formation of the most stable carbocation. Thus, in the compound 1, 1-dimethyl-2, 2-phenyl glycol, the resonance-stabilized carbocation (IV) is formed instead of (V) and so it is the methyl group and not the phenyl group which migrates, contrary to the above sequence.
Steric hindrance may affect the rate of migration- p-anisyl group migrates 1000 times faster than o-anisyl group.
