XII Chemistry BIEK Topic - Aldehyde & Ketone CHO and CO

Aldehyde & Ketone CHO and CO
Definition of Aldehyde
Organic compounds that contain monovalent functional group - CHO are known as aldehydes.

General Formula of Aldehyde
They are denoted by RCHO, where R may be any alkyl group. The general formula for aldehyde is

CnH2n - CHO

Where n may be any natural number.




Structure of Aldehyde
The structural formula of aldehyde shows that it contains a carbonyl group.




Examples of Aldehyde
CH3CHO | Acetaldehyde
HCHO | Formaldehyde



Definition of Ketone
Organic compounds that contain divalent functional group - CO - are called Ketones.




General Formula of Ketone
They are denoted by R may be any alkyl group. The general formula for Ketone is

CnH2n+1 - CO - CnH2n+1

Where n may be any natural number.




Structure of Ketone
The structural formula of ketone shows that it contains a carbonyl group.




Example of Ketone
CH3COCH3 (Acetone)



Preparation of Aldehyde & Ketone
Aldehyde and Ketone can be prepared by the following methods.


1. From Dehydrogenation of Alcohol

Removal of hydrogen from a compound is called dehydrogenation. In presence of catalyst, Cu - Ni couple when alcohol is heated at 180ºC then dehydrohalogenation takes place. As a result, aldehyde and ketone are formed.

H-CH2OH ----> H-CH=O + H2

CH3-CH2OH ----> H-CH=O + H2

(CH3)2-CH-OH ----> (CH3)2-C=O + H2


2. From Oxidation of Alcohol

In presence of oxidizing agents, K2Cr2O7 or concentrated H2SO4, alcohols are oxidized to form aldehyde or ketone.

H-CH2OH + [O] ----> H-CH=O + H2O

CH3-CH2OH + [O] ----> H-CH=O + H2O

(CH3)2-CH-OH + [O] ----> (CH3)2-C=O + H2O


3. From Dry Distillation

By the dry distillation of calsium formate (Calsium salt of formic acid), form aldehyde is obtained.

Ca(COOH)2 ----> HCHO + CaCO3

By the dry distillation of calsium salt of formic acid and calsium salt of carboxylic acid, aldehydes are obtained.

Ca(CH3OOH)2 + Ca(COOH)2 ----> CH3CHO + CaCO3

By the dry distillation of calsium salt of carboxylic acid, Ketone is formed.

Ca(CH3OOH)2 ----> CH3CHO + CaCO3


4. From Ethyne

This method is used for the preparation of acetaldehyde. In presence of catalyst H2SO4 and HgSO4 when ethyne reacts with water than unstable, intermediate vinyle alcohol is formed which on rearrangement of atoms convert into acetaldehyde.

H-C≡C-H + H2O ----> H2C-HCOH ----> H3C-COH




Preparation of Acetone By Pyrolysis of Acetic Acid
In presence of catalyst MnO2, when the acetic acid is heated at about 500ºC then acetone is formed.

CH3COOH ----> CH3-CHO + CO2 + H2O




Uses of Aldehyde
1. Aldehyde is used a preservative for biological specimen, as antiseptic and as disinfectant.

2. It is used in the synthesis of resins and plastics.

3. It is used to prepare drying oils and dyes.

4. It is used in the silvering of mirror.

5. It is used in processing of anti-polio vaccine.

6. It is used to prepare highly explosive cyclonite.




Uses of Ketones
1. It is used as a solvent for organic compounds.

2. It is used for storage of acetylene in solution form.

3. It is used in the preparation of iodoform, chloroform, etc.

4. It is used in the preparation of scent.

5. It is used as nail-polish remover.

6. It is used in the preparation of smokeless gun power and synthetic rubber.