work-up. For example, 2-methyl-2-butene reacts with O 3 , followed by an
oxidative work-up to give acetone and acetic acid.
C
H 3
C
H 3
O
CH 3
OH
O
C
H 3
CH 3
C
H 3
H
ii. H 2 O 2 , NaOH
Acetic acid
2-Methyl-2-butene
Acetone
+
i. O 3 , CH 2 Cl 2
5.7.7 Oxidation of alkynes: preparation of diketones
and carboxylic acids
Alkynes are oxidized to diketones by cold, dilute and basic potassium
permanganate.
C C R'
R
O
O
C C R'
R
H 2 O, NaOH
Diketone
cold KMnO 4
When the reaction condition is too warm or basic, the oxidation proceeds
further to generate two carboxylate anions, which on acidification yield two
carboxylic acids.
R CO 2
O 2 C R'
R CO 2 H
R' CO 2 H
C C R'
R
KOH, heat
H 3 O +
_
+
+
_
KMnO 4
Unsubstituted carbon atoms are oxidized to CO 2 , and mono-substituted
carbon atoms to carboxylic acids. Therefore, oxidation of 1-butyne with hot
basic potassium permanganate followed by acidification produces propionic
acid and carbon dioxide.
C 2 H 5 C CH
C 2 H 5 C
O
OH
ii. H 3 O +
+ CO 2
1-Butyne
Propionic acid
i. KMnO 4 , KOH, heat
5.7.8 Ozonolysis of alkynes: preparation of carboxylic acids
Ozonolysis of alkynes followed by hydrolysis gives similar products to
those obtained from permanganate oxidation. This reaction does not require
oxidative or reductive work-up. Unsubstituted carbon atoms are oxidized to
CO 2 , and mono-substituted carbon atoms to carboxylic acids. For example,
ozonolysis of 1-butyene followed by hydrolysis gives propionic acid and
carbon dioxide.
268
CH5 ORGANIC REACTIONS