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
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.
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