Chemistry – Aldehydes, Ketones & Carboxylic Acids

12
UNIT
ALDEHYDES
KETONES AND
CARBOXYLIC ACIDS
Syllabus
 Aldehydes and Ketones : Nomenclature, nature of carbonyl group, methods of preparation, physical and
chemical properties, mechanism of nucleophilic addition, reactivity of alpha hydrogen in aldehydes, uses.
 Carboxylic acids : Nomenclature, acidic nature, methods of preparation, physical and chemical properties,
uses.

Trend Analysis
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List of Concepts
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Writing the structure of product in 1Q (2 mark) 1Q (1 mark) 1Q
the reaction (3 marks) 2Q (2 marks) 2Q (2 marks)
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Chemical Tests to distinguish 1Q 1Q (1 mark)
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TOPIC-1
Aldehydes and Ketones

Revision Notes
 Carbonyl group : The functional group >C=O is called carbonyl
TOPIC - 1
group. Organic compounds containing carbonyl group are alde­
Aldehydes and Ketones .... P. 351
hydes and ketones. The general formulae of these compounds are
O O TOPIC - 2
Carboxylic Acids .... P. 373
R—C—H R — C — R’
Aldehyde Ketone
(where R=H or (where R and R'
any alkyl, aryl or may be same or
aralkyl group) different alkyl, aryl
or aralkyl group)

, Structure of Carbonyl Group :

120
+
120 C O 120 C O 120 C O
120

 Aldehydes are those compounds in which carbonyl group is attached to either two hydrogen
atoms or one hydrogen atom and one carbon containing group such as alkyl or aryl group. e.g.,
CH3CHO, C2H5CHO, C6H5CHO, etc.
 Ketones are those compounds in which carbonyl group is attached with two alkyl or two aryl
or one alkyl and one aryl group e.g., CH3COCH3, CH3COC6H5, C6H5COC6H5, etc.
 Nomenclature of Aldehydes and Ketones :
Aldehydes O

General formula : R—C—H, where R = CnH2n + 1
Structural formula Condensed formula Common name IUPAC name
O
HCHO Formaldehyde Methanal
H—C—H
O
CH3CHO Acetaldehyde Ethanal
CH3—C—H
O
CH3CH2CHO Propionaldehyde Propanal
CH3CH2—C—H
O
CH3CH2CH2CHO Butyraldehyde Butanal
CH3CH2CH2—C—H
O
CH3—CH—CHO
CH3—CH—C—H Isobutyraldehyde 2-Methylpropanal
CH3
CH3

O
CH3CH2CH2CH2CHO Valeraldehyde Pentanal
CH3CH2CH2CH2—C—H
O
CH3—CH—CH2CHO
CH3—CH—CH2—C—H Isovaleraldehyde 3-Methylbutanal
CH3
CH3
O
CH3—CH2—CH—CHO
CH3—CH2—CH—C—H a-Methylbutyraldehyde 2-Methylbutanal
CH3
CH3

O
Ketones
General formula : R—C—R' and R' = Cn'H2n'+1 (n = n', n  n')
Structural Formula Condensed formula Common name IUPAC name
O
CH3COCH3 Acetone Propanone
CH3—C—CH3
O Butan-2-one
CH3COCH2CH3 Ethyl methyl ketone or
CH3—C—CH2—CH3 Butanone

, O
Methyl n-Propyl
CH3COCH2CH2CH3 Pentan-2-one
CH3—C—CH2—CH2—CH3 ketone
O
2, 4-Dimethyl
CH3—CH—C—CH—CH3 (CH3)2CHCOCH(CH3)2 Diisopropyl ketone
pentan-3-one
CH3 CH3
O
CH3CH2COCH2CH3 Diethyl ketone Pentan-3-one
CH3—CH2—C—CH2—CH3
O
Isopropyl methyl
CH3—CH—C—CH3 (CH3)2CHCOCH3 3-Methylbutan-2-one
ketone
CH3
O
4-Methylpent-3-en-
CH3—C = CH—C—CH3 (CH3)2C= CHCOCH3 Mesityl oxide
2-one
CH3
 Methods of preparation of Aldehydes and Ketones :
(a) Preparation of Aldehydes :
(i) By oxidation of primary alcohols : Aldehydes can be prepared by the oxidation of primary alcohols.
K Cr O /H SO
RCH2OH + [O] 
2 2 7
or KMnO
2 4
→ R — CHO + H2O
4

1° Alcohol Aldehyde

R — CH2 — OH PCC
 → R — CHO
1° Alcohol Aldehyde
(ii) By dehydrogenation of alcohols :
Cu
R — CH2 — OH 573K
 → RCHO + H2

1° Alcohol Aldehyde

(iii) From hydrocarbons : From hydrocarbons aldehydes can be prepared either by ozonolysis of alkenes or
by hydration of alkynes.
(a) By ozonolysis of alkenes :
O H2O, Zn
R—CH = CH—R' + O3 R—CH CH—R' R—CHO + R'—CHO
– ZnO
Alkene O O Aldehyde

(b) By hydration of alkynes :
OH
H 2 SO4 /HgSO4 |
CH º CH+ H2O 333K ® CH3—CHOCH 2 = CH
Ethyne Ethanal
Unstable
(Acetylene) (Acetaldehyde)
(iv) From acyl chloride :
O O
Pd-BaSO4,S
R — C — Cl + H2 R — C — H + HCl
Rosenmund
Acyl chloride Reduction Aldehyde
O O
Pd-BaSO4,S
CH3—C—Cl + H2 CH3—C—H + HCl
Acetyl chloride Acetaldehyde
(v) From nitriles and esters :
SnCl2 + 2HCl ® SnCl4 + 2[H]
+H O
R — C º N + HCl + 2[H] ® R — CH = NH. HCl -
2
NH Cl
→ RCHO
4

Aldehyde

, Stephen reaction :
1. AlH (i-Bu)
R — CN 
2. H 2 O
2
→ R — CHO

Aldehyde

AIH (i-Bu)
CH3—CH = CH—CH2—CH2—CN  → CH —CH = CH—CH —CH —CHO
2
2. H 2 O 3 2 2




(b) Preparation of Benzaldehyde :
(i) By oxidation of toluene :
Etard reaction :




(ii) By side chain chlorination followed by hydrolysis :
Commercial method of preparation




(iii) By Gattermann - Koch reaction :




(c) Preparation of Ketones :

(i) By oxidation of secondary alcohols :
R K2Cr2O7/H2SO4 R
CH—OH + [O] C = O + H 2O
R' or CrO3 R'
2° Alcohol Ketone
(ii) By dehydrogenation of secondary alcohols :
R Cu R
CH—OH C = O + H2
R' 573K R'
2° Alcohol Ketone
(iii) By ozonolysis of alkenes :
R O R'
R R' C C H2O, Zn
C=C + O3 R R' RCOR + R'COR'
R R' – ZnO
O O