Preparation of Aldehydes and Ketones

Both Aldehydes and Ketones

From Alcohols

By Oxidation

Both Aldehydes and Ketones

From Alcohols

By Oxidation

• Prepared by the oxidation of alcohols with K2Cr2O7/H2SO4 or KMnO4/KOH

• Aldehydes formed oxidize to carboxylic acids on remaining in the mixture, distilled as soon as they are formed

Both Aldehydes and Ketones

From Alcohols

By Catalytic Dehydrogenation

• Suitable for volatile alcohols + industrial application

• Alcohol vapours are passed over heavy metal catalysts (Ag/Cu) at 573 K

Both Aldehydes and Ketones

From Carboxylic Acids (1)

• Passing vapours of carboxylic acids over manganous oxide (MnO) at 573 K

Both Aldehydes and Ketones

From Carboxylic Acids (2)

• By dry distillation of calcium salt of fatty acids

• Not suitable for preparation of aldehydes except HCHO, since the yields are low

Both Aldehydes and Ketones

From Hydrocarbons

By Reductive Ozonolysis of Alkenes

• Ozonolysis of alkenes followed by reaction with zinc dust and water gives aldehydes, ketones or both depending upon substitution pattern of alkene

Both Aldehydes and Ketones

From Hydrocarbons

By Hydration of Alkynes

• Addition of water to ethyne in the presence of dil. H2SO4 and HgSO4 gives acetaldehyde

• All other alkynes give ketones

Both Aldehydes and Ketones

From Hydrocarbons

From gem-dihalides

• By hydrolysis of gem-dihalides in aqueous KOH, aldehyde and ketones are obtained

Only Aldehydes

Rosenmund’s Reaction (From Acyl Chloride)

• Acyl chloride or acid chloride is hydrogenated in the presence of palladium catalyst supported over and partially poisoned by the addition of sulphur or barium sulphate (BaSO4)

• Formaldehyde cannot be prepared using this method because formyl chloride (HCOCl) is unstable at room temperature

• BaSO4 and sulphur prevent aldehyde from being further reduced to alcohol

Only Aldehydes

From Nitriles and Esters

• Nitriles are reduced to corresponding imine with stannous chloride in the presence of hydrochloric acid which on hydrolysis gives us corresponding aldehyde (Stephen’s Reaction)

• Alternatively, diisobutylaluminium hydride (DIBAL-H) is used to reduce nitriles selectively to imines which on hydrolysis give aldehydes

• Esters also reduce to aldehydes with DIBAL-H

Only Aldehydes

From Hydrocarbons

By Oxidation of Methylbenzene

• Etard Reaction : Chromyl chloride oxidizes methyl group to a chromium complex which on hydrolysis gives corresponding benzaldehyde

• Toluene or substituted toluene on treatment with chromic oxide (CrO3) in acetic anhydride gets converted to benzylidene diacetate

Only Aldehydes

From Hydrocarbons

By Side Chain Chlorination followed by Hydrolysis

• Toluene on chlorination gives benzal chloride which on hydrolysis gives benzaldehyde

• Commercial method for the manufacture of benzaldehyde

Only Aldehydes

From Hydrocarbons

Gattermann-Koch Reaction

• When benzene or its derivative is treated with carbon monoxide and hydrogen chloride in the presence of anhydrous aluminum chloride or cuprous chloride, it gives us benzaldehyde or substituted benzaldehyde

Only Ketones

From Acyl Chlorides

• Acyl chlorides on treatment with dialkylcadmium gives ketones

Only Ketones

From Benzene or Substituted Benzene (Friedel-Crafts Acylation)

• When benzene or substituted benzene is treated with acid chloride in the presence of anhydrous aluminum chloride, a corresponding ketone is obtained

Only Ketones

From Nitriles

• Nitrile is treated with Grignard reagent followed by hydrolysis, yields a ketone