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Chapter 2
Aldehydes and Ketones
Table of Contents
Introduction
1. Aldehydes
2. Nomenclature of Aldehydes
3. Physical Properties of Aldehydes
4. Chemical Properties of Aldehydes
5. Preparation of Aldehydes
6. Some Important Aldehydes
7. Ketones
Chapter 2
Aldehydes and Ketones
Table of Contents
8. Nomenclature of Ketones
9. Physical Properties of Ketones
10. Chemical Properties of Ketones
11. Preparation of Ketones
12. Acetone
Chapter 2
Aldehydes and Ketones
Warm Up
• What are the simple C-H-O compounds besides
alcohols?
• What do you think about why aldehydes and ketones are
studied together?
• Can you list down some name of solvents that you learn
so far?
Chapter 2
Introduction
• The group C=O is known as carbonyl group.
• This group is found in aldehydes, ketones, carboxylic
acids, esters and acid derivatives.
• In this group carbon atom makes sp2 hybridization.
Therefore there are one pi and three sigma bonds in
carbonyl group.
• Oxygen is more electronegative than carbon in the
carbonyl group.
Chapter 2
1. Aldehydes
• Compounds in which one hydrogen atom and one carbon
atom are bonded to the carbon atom in the carbonyl group
are called aldehydes.
• R may be alkyl or aryl group.
• CnH2nO is general formula of aliphatic aldehydes.
• The simplest member is formaldehyde, HCOH.
O
R C H or RCHO is representation of aldehydes.
Chapter 2
2. Nomenclature of Aldehydes
• Longest chain of carbon atoms containing the aldehyde
group is selected.
• Number 1 is the carbonyl carbon.
• Change –e ending in alkane names with –al.
O
O
H
C
H
Methanal
Formaldehyde
H3C
C
CH3 O
H
Ethanal
Acetaldehyde
H3C CH
CH
2-methyl propanal
Chapter 2
2. Nomenclature of Aldehydes
Example 2
Name the following compounds
CH3
A.
H3C
O
CH
C
H2
C
H
H3C
C
H2
3-hydroxyl butanal
H
CH
3-bromo-2-nitro butanal
O
D.
O
C
C
NO2
2-ethyl-3-methyl pentanal
CH
CH
H3C
C2H5
C.
O
B.
CH
OH
Br
H2
C
H
C
C
H2
3-phenyl propanal
H
Chapter 2
2. Nomenclature of Aldehydes
Example 3
Draw the structures of following aldehydes.
A. 2-chloropentanal
B. 2,3-dihydroxylpropanal
C. 2, 2-dibromohexanal
D. 3-cyclopropyl-2-methyl-pentanal
Chapter 2 3. Physical Properties of Aldehydes
• They are polar molecules.
• They do not have hydrogen bonds between their
molecules; therefore they have lower boiling points than
corresponding alcohols but higher boiling points than ethers.
• Formaldehyde is a gas at room temperature.
• The C2 to C11 are liquids. Higher than C11 are solids at
room temperature.
• Lower members are soluble in water.
• As the molar mass increases solubility decreases.
Chapter 2 4. Chemical Properties of Aldehydes
1. Oxidation Reactions
• K2Cr2O7, KMnO4 or K2CrO4 can be used in the presence of
acids.
O
R C H
aldehyde
[O]
O
H3C C H
acetaldehyde
O
R C OH
carboxylic acid
O
[O]
H3C C OH
acetic acid
Chapter 2 4. Chemical Properties of Aldehydes
Reaction with KMnO4
• Aldehydes are oxidized with KMnO4 to carboxylic acids.
O
5 R C H + 2MnO4- + 6H+
aldehyde
O
cold
5 H3C C H + 2MnO4- + 6H+ cold
Acetaldehyde
O
5R C OH + 2Mn+ + 3H2O
carboxylic acid
O
5 H3C C OH + 2Mn+ + 3H2O
Acetic Acid
Chapter 2 4. Chemical Properties of Aldehydes
2. Addition Reactions
• In the addition reactions pi bond in the carbonyl group,
C=O, is broken.
Addition of Hydrogen
• Aldehydes are reduced to alcohols in the presence of Ni and
Pt catalyst under certain conditions.
O
R C H
aldehyde
O
H3C C H
ethanal
+ H2
+ H2
Ni, Pt
Heat, Pressure
Ni, Pt
Heat, Pressure
H2
R C OH
primary alcohol
H2
H3C C
OH
ethyl alcohol
Chapter 2
5. Preparation of Aldehydes
1. Oxidation of Primary Alcohols
OH
R CH2
1o Alcohol
OH
H3C CH2
ethanol
[O]
O
R C H + H2O
aldehyde
[O]
O
H3C C H + H2O
acetaldehyde
ethanal
Chapter 2
5. Preparation of Aldehydes
2. Dehydrogenation of Primary Alcohols
OH
CuO.Cr2O3
O
R CH2
R C H + H2
o
250-300
C
o
1 Alcohol
aldehyde
OH
CuO.Cr2O3
O
H3C CH2
H3C C H + H2
o
250-300 C
ethyl alcohol
acetaldehyde
Chapter 2 6. Some Important Aldehydes
1. Formaldehyde
• Colorless gas with pungent
odor, soluble in water.
• Simplest aldehyde, discovered
by the Russian Chemist A.
Butlerov in 1859.
•Widely used in the manufacture of building materials and
household products.
• It hardens proteins and prevents them decaying.
• % 40 solution of formaldehyde is called formalin, used to
store biological products.
Chapter 2 6. Some Important Aldehydes
1. Formaldehyde
• It is produced from methanol by
dehydrogenation with a catalyst of Cu
and silver, and it is called Hoffman
Method.
O
H3C OH + 1/2O2
methanol
Cu
o
250 C
H C H + H2O
formaldehyde
Chapter 2 6. Some Important Aldehydes
2. Acetaldehyde
• Colorless, volatile and poisonous
liquid, soluble in water.
• Used to obtain many organic
compounds, such as acetic acid, ethyl
alcohol, synthetic rubber.
• It has carcinogen effect.
Chapter 2
7. Ketones
• The compounds in which the two alkyl or aryl groups
attached to the carbonyl carbon are called ketones.
O
• R C R' or RCOR' is representation of ketones.
• R may be alkyl or aryl group.
• CnH2nO is general formula of ketones.
• Ketones might be either symmetrical or unsymmetrical with
respect to alkyl groups.
Chapter 2 8. Nomenclature of Ketones
• For the simple ketones names of alkyl or aryl groups
followed by the word “ketone” are used.
O
H3C
O
C
CH3
H3C
Dimethyl ketone
acetone
O
C
H2
C
C
C
H2
H2
C
CH3
Methyl propyl ketone
CH3
CH3
Ethyl phenyl ketone
H3C CH
O
C
CH3
isopropyl methyl ketone
Chapter 2 8. Nomenclature of Ketones
• For the complex ketones IUPAC names are used.
• Longest chain of carbon atoms containing the ketone group
is selected.
• Number 1 to the carbon atom starting nearer to the carbonyl
carbon.
• Change –e ending in alkane names with –one.
CH3
H3C CH
Br O
O
C
CH3
3-methyl-2-butanone
C 2 H5
C
H
C
CH3
3-bromo-2-pentanone
Chapter 2 8. Nomenclature of Ketones
Example 7
O
Name the following aldehydes
O
A.
H3C
H
C
H2
C
C
C2H5
B.
CH3
Cl
2-ethyl cyclohexanone
4-chloro-2-pentanone
C.
O
H2
C
H2
C C
D.
H2
C
1-phenyl-3-pentanone
CH3
H2C
O
C
H
H2
C
C
4-pentene-2-one
CH3
Chapter 2 8. Nomenclature of Ketones
Example 8
Write the structural formulae of the following compounds.
A. 2-pentanone
B. 5-bromo-3-methyl-2-hexanone
C. Methyl phenyl ketone
D. Isopropyl methyl ketone
E. 3-methyl cyclopentanone
Chapter 2 9. Physical Properties of Ketones
• Lower molecular weight ketones are liquids. More than C11
atoms are solids.
• Soluble in water by forming hydrogen bonds.
• Liquid ketones are used as solvents in the preparation of
paint chemicals.
• Solubility decreases with increasing size of the molecule.
• They are polar molecules but there is no hydrogen bonding
between the molecules.
Chapter 2 10. Chemical Properties of Ketones
1. Addition Reactions
Addition of Hydrogen
O
OH
R C R' + H2
Ketone
Ni
heat, pressure
R CH R'
secondary alcohol
OH
O
H3C C C2H5 + H2
ethyl methyl ketone
Ni
heat, pressure
H3C C C2H5
H
isobuthyl alcohol
Chapter 2 11. Preparation of Ketones
1. Oxidation of Secondary Alcohols
O
OH
R CH R'
secondary alcohol
[O]
OH
CH3CHCH3 + KMnO4
Isopropyl alcohol
R C R'
Ketone
O
NaOH
CH3CCH3
Acetone
Chapter 2 11. Preparation of Ketones
2. Dehydrogenation of Secondary Alcohols
H H
R
C O
CuO.Cr2O3
250oC
R
C
R'
O + H2
R'
Secondary Alcohol
ketone
H H
H3C
C O
CH3
2-propanol
CuO.Cr2O3
250oC
H3C
C O + H2
CH3
Acetone
Chapter 2
12. Acetone
• Smallest ketone
• Colorless, volatile liquid with pleasant odor.
• It is soluble in water, alcohol and ether.
• It is a perfect organic solvent used for varnishes,
lacquers, resins, plastics, paints, oils and their derivatives.
• It burns with a blue dull flame.
• It is very difficult to oxidize.
End of the chapter 2
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