2. Aldehydes & Ketones
Introduction
• Aldehydes & Ketones are organic compounds, which
contains carbonyl functional group.
• Carbonyl group is bonded to at least one hydrogen atom,
and so it occurs at the end of a chain.
• The carbon atom in this carbonyl group is bonded to
oxygen with a double bond.
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• The general formula to
represent aldehydes is given in
figure.
• Aldehydes and ketones are
present in many naturally
occurring compounds.
• Aldehyde group is present in
most sugars.
• The general formula of
homologous series of aldehydes
& Ketones is, (CnH2nO).
7. Preparation of Aldehydes
• Aldehydes are obtained by the oxidation of primary
alcohol.
• Aldehydes are prepare in industialy as well as in
laboratory.
• Formaldehyde & Acetaldehyde are common two
example of aldehyde.
8. Preparation of Formaldehyde
• Laboratory Method
• Formaldehyde is prepare in th laboratory by passing a
mixture of methyl alcohol vapours and air over platinised
asbestos or copper or silver catalyst at 300 degree C.
2 CH3OH + O2 → 2 CH2O + 2 H2O
• Air is drawn through methyl alcohol with help of section
pump.
• Methyl alcohol is oxidized to gaseous formaldehyde which
is absorbed in water.
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• The resulting mixture is
called formalin.
• Formalin is the mixture
of 40% formaldehyde,
8% methyl alcohol and
52% water.
10. Formaldehyde preparetion
• Industrial Method
• Formaldehyde manufactured by passing a mixture of
methanol vapours and air over iron oxide-molybdenum
oxide or silver catalyst at 500oC.
2 CH3OH + O2 → 2 CH2O + 2 H2O
11. Preparation of Acetaldehyde
• Laboratory Method
• Acetaldehyde prepare in laboratory by the oxidation of
ethyl alcohol with acidified sodium dichromate solution.
CH3CH2OH + 1⁄2 O2 → CH3CHO + H2O
• A mixture of ethyl alcohol and sodium dichromate
solution is run into boiling dilute sulphuric acid.
• Acetaldehyde form in liquid form and immediately
distilled off.
• This prevents the oxidation of acetaldehyde to acetic
acid.
13. Acetaldehyde preparation
. Industrial method;
• Acetaldehyde is prepared industrially by air oxidation of
ethylene using palladium chloride catalyst with a cupric
chloride promoter.
2 CH2=CH2 + O2 → 2 CH3CHO
14. Preparation of ketones
• Ketones can be prepared by the oxidation of
secondary alcohols.
1. Typically uses Jones reagent (CrO3 in H2SO4) but
many other reagents can be used
15. Preparation of ketones
2. Hydration of an alkyne to form ketones
• The addition of a hydroxyl group to an alkyne
causes tautomerization which subsequently forms
a carbonyl. Markovnikov addition of a hydroxyl
group to an alkyne forms a ketone.
17. Preparation of ketones
• Reaction of Grignard reagents with nitriles to form
ketones
• Treatment of nitriles with Grignard reagent upon
further hydrolysis yields ketones.
18. Preparation of ketones
• Alkenes can be cleaved using ozone (O3) to form aldehydes
and/or ketones
20. Preparation of ketones
• Preparation of Ketones by Dehydrogenation of
Alcohols
• Dehydrogenation of alcohol is a reaction in which
two hydrogen molecules are removed from an
alcohol molecule upon oxidation.
During oxidation of alcohol both C-O and O-H
bonds are broken for the formation of C=O bonds.
Secondary alcohols in the presence of strong
oxidizing agents undergo dehydrogenation to
produce ketones.
23. Reaction Mechanism
• The characteristic reaction of carbonyl
compounds are nucleophilic addition
reaction.
• We will discuss general mechanism of;
• (a) Base Catalyzed Addition Reaction
• (b) Acid Catalyzed Addition Reaction
24. Reaction Mechanism
1. Base Catalyzed Addition Reaction
• A base catalyzed nucleophilic addition reaction will
take place with a strong nucleophilic reagent. The
base reacts with the reagent and generates the
nucleophile. The addition is initiated by the attack of
a nucleophile on the electrophilic carbon of the
carbonyl group.
26. Reaction Mechanism
2. Acid Catalyzed addition Reaction
Acid catalyzed nucleophilic addition reaction takes
place with a weak nucleophilic reagent. The
addition is initiated by the proton (H+) liberated by
the acid. The proton combines with the carbonyl
carbon. As a result the attack of the weaker
nucleophile on the electrophilic carbon become
easier.
29. Applications Of Aldehydes
• Aldehydes have a great importance in our daily
life.
– Formaldehyde:
• Formaldehyde is used in manufacturing of resins
like Urea-formaldehyde and plastic such as
bakelite.
• It is also used in manufacturing of dyes such as
indigo,etc.
30. Applications Of Aldehydes
• Formaldehyde:
• Its aqueous solution, formalin is used in
preserving of animal specimens and sterlising
surgical instruments.
• Formaldehyde is used as a decolourising
agent in vat dyeing.
• It is also used in silvering of mirror.
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– Acetaldehyde
• It is used in production of acetic acid,acetic
anhydride,n-butanol,ethanal,vinylacetate,
ethylacetate,etc.
• Like formaldehyde, it is also used in silvering
of mirror.
• It is used as an antiseptic inhalent in nasal
infections.
32. Applications Of Aldehydes
• Acetaldehyde
• It is used to make synthetic drugs.
• It is used to make acetaldehyde
ammonia used as a rubber-
accelerator.
33. Application of ketones
• The most common ketone is acetone which is an
excellent solvent for a number of plastics and
synthetic fibers.
• In the household, acetone is used as a nail paint
remover and paint thinner.
• In medicine, it is used in chemical peeling and for
acne treatments.
34. Application of ketones
• Methyl ethyl ketone (MEK), chemically butanone,
is a common solvent. It is used in the production of
textiles, varnishes, plastics, paint remover, paraffin
wax, etc.
• MEK is also used as a welding agent for plastics
due to its dissolving properties.
• Cyclohexanone is another important ketone which
is primarily used in the production of nylon.
