Tuesday, February 5, 2008

Aldehydes and Ketones - Chemical Properties


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
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
i) Tollen's reagent - silver mirror 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.

For more detailed coverage of some reactions


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