Aldehydes & Ketones

Preparation Of Aldehydes


1. Oxidation of primary alcohols





2. Reduction of acid chlorides :


By heating a mixture of the calcium salts of formic acid



3. By heating a mixture of the calcium salts of formic acid and any one of its homologues.




4. Stephen's Method:




Preparation Of Ketones

1. Oxidation of secondary alcohols




2. Friedel - Crafts acylation




3. With Organometallics

a) Reaction of acid chlorides with organocadmium compounds





4. By heating the calcium salt of any monocarboxylic acid other than formic acid




Reactions of Aldehydes And Ketones

1. Oxidation










c) Strong Oxidants

Ketones resist mild oxidation, but with strong oxidants at high temperature they undergo cleavage of C - C bonds on either sides of the carbonyl group.




d) Haloform Reaction

Methyl Ketones, CH₃ CO-R, are readily oxidised by NaOI (NaOH + I₂) to iodoform, CHI₃, and RCO₂ Na



2. Reduction

a) Reduction to alcohols




b) Reduction to hydrocarbons




3. Addition Reactions of Nucleophiles to

a) The C of the carbonyl group is electrophilic



and initially forms a bond with the nucleophile.



b) Addition of cyanide

c) Addition of bisulfite





d) Addition derivatives of ammonia.








4. Addition of Alcohols ; Acetal Formation




Analysis of Aldehydes and Ketones
Aldehydes and ketones are characterized through the addition to the carbonyl group of nucleophilic reagents, especially derivatives of ammonia.

All aldehyde or ketone will, for example react with 2,4-dinitrophenylhydrazine to form an insoluble yellow or red solid.

Aldehydes are characterized, and in particular are differentiated from ketones through their ease of oxidation: aldehydes give a positive test with Tollen's reagent; ketones do not.

Aldehydes are also, of course, oxidized by many other oxidizing agents : by cold, dilute, neutral KMnO₄ and by CrO₃ in H₂SO₄.

A highly sensitive test for aldehydes the Schiff test. An aldehyde reacts with the Schiff’s reagent to form a characteristic magenta colour.

Aldehydes and ketones are generally identified through the melting points of derivatives like 2,4- dinitrophenylhydrazones, oximes, and semicarbazones.

Methyl Ketones is characterized through the iodoform test.

Aldehydes can be oxidised by Fehling's solution.
Fehling's solution, an alkaline solution of cupric ion complexed with tartarate ion (or Benedict's solution, in which complexing is with citrate ion); the deep-blue color of the solution is discharged, and red cuprous oxide precipitates.

Fehling's solution is made by mixing, Fehling A solution, which contains copper sulphate, + Fehling B solution, which contains sodium hydroxide and Rochelle salt (Sodium Potassium

Tartarate). During the oxidation of aldehydes to acids, the cupric ions are reduced to cuprous ions which are precipitated as red cuprous oxide.