Aldehyde and ketone

Aldehydes and ketones are the carbonyl compounds with general formula CnH2nO. Aldehydes have at least one hydrogen atom bonded to the carbonyl group and other group is either hydrogen or an alkyl or aryl group (i.e. Aldehyde has one alkyl or aryl group and one of the hydrogen bonded to the carbonyl carbon) with characteristics functional group -CHO.

1. Aldehyde and Ketone P.M. Jadhav Assistant Professor Dept. of Chemistry M.S.P. Mandals, Shri Muktanand college, Gangapur, Dist. Aurangabad.

2. Aldehydes and ketones Aldehydes and ketones are the carbonyl compounds with general formula C n H 2n O. Aldehydes have at least one hydrogen atom bonded to the carbonyl group and other group is either hydrogen or an alkyl or aryl group. Aldehyde has one alkyl or aryl group and one of the hydrogen bonded to the carbonyl carbon with characteristics functional group -CHO. In ketones , the carbonyl group is bonded to a two alkyl or aryl groups with –CO- functional group. The two groups bonded to a ketone may be similar or different resulting in a symmetrical or an unsymmetrical ketone.

3. Nomenclature of Aldehydes and Ketones Systematic names for aldehydes are obtained by replacing suffix -e of the corresponding alkane by prefix –al i.e. aldehydes are named as alkanal . The carbonyl carbon of the aldehydes is assigned 1 position. Systematic names for ketone are obtained by replacing suffix -e of the corresponding alkane by prefix –one. I.e. ketones are named as alkanone . The position of carbonyl group in the ketone is assigned by the number. Formula Compound Common name IUPAC name CH 2 O HCHO Formaldehyde Methanal C 2 H 4 O CH 3 CHO Acetaldehyde Ethanal C 3 H 6 O CH 3 CH 2 CHO Propionaldehyde Propanal C 4 H 8 O CH 3 CH 2 CH 2 CHO Butaraldehyde Butanal Formula Compound Common name IUPAC name C 3 H 6 O CH 3 -CO-CH 3 Acetone Propanone C 4 H 8 O CH 3 CH 2 -CO-CH 3 Ethyl methyl ketone Butanone C 5 H 10 O CH 3 CH 2 -CO-CH 2 CH 3 Diethyl ketone 3-pentanone C 5 H 10 O CH 3 CH 2 CH 2 -CO-CH 3 Methyl propyl ketone 2-pentanone

4. Preparation Methods 1. Rosenmunds reaction(Reduction of acid chloride ): The reduction of acid chloride in presence of palladium supported catalyst like palladium on BaSO 4 or Charcoal to give product aldehyde. 2. Gatterman Synthesis: Preparation of aromatic aldehyde by the reaction of phenol ether and HCN in presence of Lewis acid catalyst AlCl 3 or ZnCl 2 to give product substituted aromatic aldehyde .

5. 3. Gatterman - Koch Reaction: The reaction involves formation of aromatic aldehyde by the reaction of carbon monoxide and hydrochloric acid in presence of L ewis acid (AlCl 3 ) as catalyst. 4. Ketone from Nitrile or cyanide: Ketone prepared from Grignard reagent and nitrile. The Grignard reagent attack on electrophilic carbon of nitrile to give a imine salt which on hydrolysis to gives ketone. 5 . Ketone from Carboxylic acid : The calcium salt of carboxylic acid on heating to gives ketone.

6. 6. Oxidation of alcohols: Oxidation of Alcohols with oxidizing agents such as potassium permangnate (KMnO 4 ), K 2 Cr 2 O 7 /H 2 SO 4 , chromic acid or MnO 2 to give a carbonyl compounds aldehyde and ketone . 7. Ozonolysis of alkenes: Ozone reacts with alkene to form ozonide intermediate which on treatment with reducing agent to gives aldehydes this reaction is called ozonolysis .

7. Chemical Reactions 1. Formation of acetals : Aldehydes and ketones react with two molecules of alcohols to give geminal diether is known as acetal . The ketone derivatives are known as ketal . 2. Oxidation of Aldehyde and ketone: The presence of hydrogen atoms in aldehydes make easily to oxidized to carboxylic acids containing the same numbers of carbon atoms with a oxidizing agents like chromic acid, chromium trioxide. The silver oxide (Ag 2 O) in aqueous ammonia solution ( Tollen’s reagent) is mild reagent give good yield at room temperature.

8. 3. Reduction of aldehyde and ketone: The reduction of aldehydes to primary alcohol and ketones to secondary alcohol in presence of reducing agents likes LiAlH 4 , NaBH 4 etc . 4 . Knoevenagel Reaction: The condensation of aldehyde or ketone having no α-hydrogen with active methylene compound in presence of weak base to give unsaturated compound is known as Knoevenagel reaction.

9. 5. Aldol Condensation: Aldehydes having α-hydrogen atoms which undergo reaction in presence of base alkali to give codensation product β- hydroxy aldehyde is known as aldol and the reaction is called aldol condensation. The ketones also undergo condensation reaction to give product aldol of ketone . Self- aldol condensation: The aldol condensation when two same aldehydes or ketones molecule having α-hydrogen atom condensed is known as self- aldol condensation. Cross- aldol condensation: The aldol condensation when two different aldehydes or ketones molecule having α-hydrogen atom condensed is known as cross- aldol condensation.

10. 6. Perkins Reaction: The aromatic aldehyde when react with aliphatic acid anhydride in presence of sodium salt of acetic acid to give a product α,β-unsaturated acid is known as Perkins reaction . 7 . Mannich Reaction: The compound containing at least one active methylene hydrogen atom condensed with formaldehyde and ammonia, primary or secondary amine in the form of hydrochloride to give a product Mannich base (β-amino carbonyl compound) is known as Mannich reaction.

11. 8. Baeyer- Villiger oxidation : Oxidation of ketone to ester in presence of peracid or hydrogen peroxide is known as Baeyer- Villiger oxidation. The hydrogen peroxide is commonly used. Other peracids used are peracetic acid, perbenzoic acid, performic acid or m- chloroperbenzoic acid, etc . 9. Cannizzaro’s Reaction: Cannizzaro reaction is redox reaction in which two molecules of an aldehyde with no α-hydrogen when reacted with base sodium hydroxide undergo self-oxidation and reduction to produce an alcohol and the salt of corresponding carboxylic acid.

12. 10. Benzoin Condensation: The benzoin condensation is a coupling reaction of two molecules of aromatic aldehyde with no α-hydrogen in presence of potassium cyanide in ethanol as catalyst to give product Benzoin (α- hydroxy ketone) is known as benzoin condensation . 11 . Reformatsky Reaction: The reaction of carbonyl compound like aldehyde and ketone with α- haloester in presence of zinc in inert solvent ether to give β- hydroxyester this reaction is known as Reformatsky Reaction.

13. 12. Meerwin-pondorf-verly reduction (MPV ): The reduction of carbonyl compound like aldehyde or ketone in presence of aluminum alkoxide and isopropyl alcohol to give product corresponding alcohol is known as Meerwin-pondorf-verly reduction. The reduction of aldehyde gives primary alcohol whereas ketone gives secondary alcohol . 13. Clemmensen Reduction: When aldehyde or ketone heated with zinc amalgam and hydrochloric acid to gives corresponding alkane. The reaction in which the reduction of carbonyl group into a methylene groups (-CH 2 -) this reaction is known as Clemmensen reduction.

14. 14 . Wittig Reaction: The reaction of phosphorous ylides with carbonyl compound aldehyde or ketone to give alkene is known as Wittig reaction. Phosphorus ylide is from by the reaction of triphenylphosphine and alkyl halides in the presence of strong base. The phosphorous ylides react with aldehyde or ketone to give a betain as intermediate which further eliminates triphenylphosphine oxide to give alkene.

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