Aldehydes and Ketones - Chemical Properties

Reactions

Can studied with the following grouping
A. Nucleophilic addition reactions.
B. Nucleophilic addition reactions that involve elimination of water molecule
C. Oxidation reactions
D. Reduction reactions
E. Miscellaneous reactions

A. Nucleophilic addition reactions
      1. Hydrogen cyanide: addition product is cyanohydrin

      2. Sodium bisulphite: addition proudct is bisulphite adduct.
      3. Grignard reagent: addition intermediate product, when hydrolysed gives alcohol
      4. Alcohol: product geminal dialkoxy compounds.

B. Nucleophilic addition reactions that involve elimination of water molecule
Aldehydes and ketones react with a number of ammonia derivatives in weakly acidic medium to form compound containing carbon-nitrogen double bonds with the elimination of water molecule.

1. Addition of various ammonia derivatives
i) Hydroxylamine - product oxime[The condensation of aldehydes with hydroxylamine gives aldoxime. Ketoximes are produced from ketones and hydroxylamine.Generally, oximes exist as colorless crystals and do not easily dissolve in water. Oximes can be used for the identification of ketone or aldehyde.]
ii) Hydrazine - product hydrazone
iii) Phenylhydrazine - product phenylhydrazone
iv) 2, 4 dinitrophenyl hydrazine - product 2,4 dinitrophenyl hydrazone
v) Semicarbazide - product semicarbazone

2. Addition of Ammonia
product aldehyde-ammonia ducts

3. Primary amines
product azomethines also known as Schiff bases.

C. Oxidation reactions

• Carbonyl groups in aldehydes and ketones may be oxidized to form compounds at the next “oxidation level”, that of carboxylic acids.

• Alcohols are oxidized to aldehydes and ketones (example: biological oxidation of ethanol to acetaldehyde)
• The carbonyl group may be further oxidized to carboxylic acids
• Oxidation of Aldehydes to form Carboxylic Acids: Reaction of simple aldehydes with acidic MnO4-, or CrO3/H2SO4 yields the corresponding carboxylic acid. Aldehydes oxidize very easily and it is often difficult to prevent oxidation, even by atmospheric oxygen. 
  
  Oxidation of Ketones: Ketones are more resistant to oxidation, but can be cleaved with acidic MnO4- to yield carboxylic acids.

i) Tollen's reagent - silver mirror test
[Oxidation of Aldehydes by Silver Oxide: Reaction of simple aldehydes with aqueous Ag2O in the presence of NH3 yields the corresponding carboxylic acid and metallic silver. The silver is generally deposited in a thin metallic layer which forms a reflective "mirror" on the inside surface of the reaction vessel. The formation of this mirror forms the basis of a qualitative test for aldehydes, called the Tollens Test. ]

ii) Fehling's solution - aldehydes give a red precipitate of cuprous oxide
iii) Benedict's solutin - similar to Fehling's solution
iv) Oxidation with sodium hypohalite - iodoform is the product

D. Reduction of aldehydes and ketones
1. Reduction to alcohols: aldehydes give primary alcohols. Ketones give secondary alcohols.

2. Reduction to hydrocarbons: 
i) Reduction with zinc amalgam and con HCL
ii) Reductin with basic solution of hydrazine
iii) Reductioin with HI in the presence of red phosphorus

3. Reduction to pinacols

E. Miscellaneous reactions
1. Aldol condensation
2. Cross aldol condensation
3. Cannizaro's reaction
4. Halogenation
5. Action with Schiff's reagent
6. Polymerisation
7. Sunstitution reactions of benzene nucleus in aldehydes and ketones.