B.Sc II Sem III Chemistry College Name :- Late Ku.Durga K.Banmeru Science College Lonar University Name:- Sant Gadgebaba Amravati University Amravati

1. Late Ku. Durga K. Banmeru Science College,
LONAR DIST. BULDANA (Maharashtra), India.
“Aldehydes and Ketones”
Dr. Suryakant B. Borul
Head Of Department
Department of Chemistry
Late Ku. Durga K. Banmeru Science College, Lonar
B. Sc. IInd year Sem-IIIrd Subject:- Chemistry
Chapter- III
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2. INTRODUCTION
• Aldehydes and Ketones are the two important classes
of organic chemistry. These are the carbonyl
compounds because both the compounds contain
carbonyl group (>C=O).
• In carbonyl group carbon doubly bonded to oxygen
atom.
2

3. •Aldehydes and Ketones are the isomers of each other and
they are resemble closely on most of their properties.
•But aldehyde are quite easily oxidized and are more
reactive towards nucleophilic addition than ketones
because of the presence of free hydrogen atom.
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4. Aldehydes
Q.-What are aldehydes?
 The carbonyl compounds in which carbonyl carbon is bonded at
least one hydrogen atom such compounds are called as aldehydes.
 The first oxidation product of primary alcohol is called as
aldehyde.
They have General formula- CnH2nO,
where n= number of carbon atom
 H- or -CHO aldehydic functional group
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5.  Examples- i) HCHO formaldehyde, ii) CH3CHO Acetaldehyde,
iii) C6H5CHO Benzaldehyde
 In formaldehyde, carbonyl carbon is bonded to with two hydrogen
atoms (HCHO).
 In aldehyde carbonyl carbon is bonded to the one hydrogen atom
and one alkyl or aryl group (except formaldehyde HCHO)
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6. Ketones
Q.-What are Ketones?
 The carbonyl compounds in which carbonyl carbon is bonded with
two alkyl or aryl groups such compounds are called as Ketones.
 The first oxidation product of secondary alcohol is called as
ketones.
They have General formula- CnH2nO,
where n= number of carbon atom
 - or >CO ketonic functional group
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7.  Examples- i) CH3-CO-CH3 Dimethyl ketone (Acetone)
ii) CH3-CO-C2H5 Ethyl methyl ketone
iii) C6H5-CO-CH3 Acetophenone
 In ketone, carbonyl carbon is bonded to the two alkyl or aryl groups
or one alkyl and one aryl group
 On the basis of same or different alkyl or aryl groups attached to
carbonyl carbon ketones are classified as symmetrical and
unsymmetrical ketones
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8. Preparation of Aldehydes
Preparation of Acetaldehydes
Q. How will prepared acetaldehyde from……
1. Ethyl alcohol 2. Ethylidene chloride 3. Acetylene
1. Ethyl alcohol- When ethyl alcohol (primary alcohol) undergoes
oxidation by using acidified potassium dichromate under controlled
condition to form acetaldehyde
Here acidified potassium dichromate is used as oxidizing agent.
 Alkaline Potassium permanganate, chromium trioxide in glacial acetic
acid or MnO2 in acetone can be also used as oxidizing agent.
C
H3
OH
+ (O)
K2Cr2O7
H
+ C
H3
H
O
Ethyl alcohol nscent oxygen Acetaldehyde or Ethanal
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9. 2. Ethylidene chloride- (Geminal dihalides) When ethylidene
chloride undergoes alkaline hydrolysis it first gives unstable dihydroxy
compound, which readily loses water molecule to form acetaldehyde
C
H3
Cl
Cl
+ NaOH
2 -2NaCl C
H3
OH
OH
H
C
H3
H
O
ethylidene chloride unstable Acetaldehyde or Ethanal
3. Acetylene- When acetylene undergoes hydration by using 30%
sulphuric acid and 1% mercuric sulphate it first gives unstable vinyl
alcohol, which rearranges to form acetaldehyde
C
H CH + H OH
30% H2SO4
1%HgSO 4
C
H2
OH
H
Rearrangement
C
H3
H
O
Acetaldehyde or Ethanal
Vinyl Chloride
Acetylene
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10. Preparation of Benzaldehydes (C6H5-CHO)
1. Benzene 2. Toluene
1. From Benzene- By the formylation of benzene (Gattermann-Koch
reaction)- When the mixture of carbon monoxide & hydrochloric
acid gas passing through etheral solution of benzene containing
ACl3 & Cu2Cl2 to form Benzaldehydes. This reaction is called
Gattermann-Koch reaction.
+ CO + HCl
AlCl3 & Cu 2Cl2 H
O
+ HCl
Benzene Benzaldehyde
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11. 2. From Toluene (methyl benzene)- By Oxidation of Toluene,
toluene can oxidized by using different methods as follows-
a) By using chromium trioxide in acetic anhydride-
CH3
+ O
C
C
CH3
CH3
O
O
CrO3
O
O
C
C
O
O
CH3
CH3
C
H
O
H2O
H
+ + 2CH3COOH
Toluene Acetic anhydride Benzylidene acetate Benzaldehyde
b) Etard reaction- by using chromyl chloride in CS2 or CCl4-
CH3
2CrO2Cl2 in
CS2 or CCl 4
CH3 2CrO2Cl2
H2O
C
H
O
Toluene Benzaldehyde
Addition Complex
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12. c) by using vapour phase oxidation-
CH3
200 C O 2
V2O5
C
H
O
Benzaldehyde
Toluene
H2O
+
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13. Preparation of Ketones
Preparation of Acetone or Propanone
Q. How will prepared acetone from……
1. isopropyl alcohol 2. isopropylidene dichloride
3. Propyne
1. isopropyl alcohol-
When the isopropyl alcohol i.e. 2- propanol react with acidified
potassium dichromate under controlled condition to form acetone
CH
C
H3
C
H3
OH + (O)
K2Cr2O
H
+ C
C
H3
C
H3
O
Isopropyl alcohol
Acetone or Propanone
+ H2O
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14. 2. isopropylidene dichloride (Geminal dihalides) –
When isopropylidene dichloride undergoes alkaline hydrolysis
it first gives unstable dihydroxy compound, which readily loses water
molecule to form acetone.
C
C
H3
C
H3
Cl
Cl
+
-2NaCl
C
C
H3
C
H3
OH
OH
Isopropyl alcohol
Acetone or Propanone
+ H2O
2NaOH C
C
H3
C
H3
O
3. Propyne- When propyne undergoes hydration by using 30%
sulphuric acid and 1% mercuric sulphate it first gives unstable vinyl
alcohol, which rearranges to form acetaldehyde
C CH
C
H3 + H OH
30% H 2SO4
1%HgSO 4
C
H3 C CH2
OH Rearrangement
Propyne
Enol
C
C
H3
C
H3
O
Acetone or Propanone
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15. Preparation of Acetophenone or methyl phenyl ketone
(C6H5-CO-CH3)
1. Acetylation of Benzene 2. Oxidation of Ethyl benzene
1. Acetylation of Benzene- When benzene undergoes acetylation by
using acetyl chloride in presence of AlCl3, to form Acetophenone.
H
+ C
H3 C
O
Cl
AlCl3 CH3
O
+ Cl
H
Benzene
Acetyl Chloride
Acetophenone
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16. 2. Oxidation of Ethyl benzene-
When ethyl benzene on oxodation by using oxygen and
manganese acetate at 1260C or oxygen and vanadium pentaoxide at
500oC under pressure gives acetophenone.
CH2 CH3 +O2
Mn(CH 3COO) 2 126oC
or V2O5 500oC
C CH3
O
+ O
H2
Ethyl benzene Acetophenone
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17. Structure of Carbonyl group
 Structure of Carbonyl group can be explained on the basis of its
1. Geometry 2. Polarity
1. Geometry-
 In carbonyl group double bond in between carbon and oxygen out
of these one sigma and one pi bond.
 Both carbon and oxygen are sp2 hybridized
 Three sp2 hybrid orbital's of carbonyl carbon forms three
sigma bonds.
 One with oxygen by axial overlapping of sp2 hybrid orbital's of
carbon and oxygen.
 Another two with other groups attached to it.
 The fourth unhybridized 2p orbital of carbon laterally overlap with
unhybridized 2p orbital of oxygen to form pi bond.
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18. 18

19. 19

20. 2. Polarity
 The electrons in the pi () bond of carbonyl group are not equally
shared.
 Infact, they are pulled more toward the oxygen because of higher
electronegativity of oxygen than carbon.
 As result, the bond is polarised, with the oxygen being slightly
negative (-) and carbon being slightly positive ( +).
 Dipole moment 2.3 to 2.8 D
This is represented as below.
Resonance Structure of carbonyl compounds 20

21. Acidity of - hydrogen in Carbonyl compounds
 In carbonyl compounds, the carbon atoms adjacent to the carbonyl
carbon are called as -carbons. The hydrogen atoms attached to -
carbon are called as - hydrogen's.
 Acidity of -hydrogen in carbonyl compounds is an important
characteristic of carbonyl compounds.
 The carbonyl compounds is strongly electron withdrawing.
 This electron withdrawing effect is transmitted next to -carbon and
then -hydrogen, due to bond becomes weak between them.
 -hydrogen is willing to lose electrons to -carbon because of its
lower electronegativity as compared to both -carbon and oxygen.
 Electronegativity of H=2.1, C=2.5, O=3.5
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22. Thus in presence of strong base, - hydrogen is removed as
H+ to form carbanion.
The carbaion is stabilized by resonance to give enolate anion. The
negative charge of the anion is delocalized.
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