Date- 21-10-2020
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REACTION OF THE DAY
Chemistry
Wurtz Reaction
The coupling of alkyl halides by treatment with sodium to give a symmetrical product is called as the Wurtz
reaction.
Ether
2 R – X + 2Na R – R + 2NaX
Alkane
The reaction takes place in ether medium.For the same halide, the order of reactivity is pri > sec > tert and
for the same alkyl group, it is Rl > RBr > RCI.
Mechanism of Wurtz Reaction
There is strong evidence in favour of ionic mechanism. Whenever sodium reacts, it becomes Na + that too
exactly happens here.
– +
R – Cl + 2Na R Na + NaCl
Carbanion in the
form of salt
The carbanion then attacks the second molecule of alkyl halide in S N2 fashion.
R Na + R – Cl R – R + NaCl
Consider some specific examples leading to formation of symmetrical alkane.
2 Na
2CH3 – Br CH3 – CH3
Ether,
Ethane
Na
2C2H5 – Br C2H5 – C2H5
Ether,
The coupling of alkyl and aryl halide is known an Wurtz-Fittig reaction. The main product of this reaction is
always the cross product.
Na
I + CH3 – CH2 – I Ether,
CH2 – CH3
Ethylbenzene
The attempt to prepare unsymmetrical alkane by Wurtz reaction ends up with a mixture of products from
which the seperation of components is very difficult.
(1)
1 2
R – R
1 2 Na 1 1
R –X+R —X R –R Mixture of alkanes
Ether, 2 2
R –R
Wurtz reaction is also very good at synthesis of cyclopropane.
CH2 –I
Na CH2
CH2
Et2O
CH2 –I CH2 CH2
Try Yourself
1. On treating a mixture of two alkyl halides with sodium metal in dry ether, 2-methyl propane was obtained. The
alkyl halides are
(1) 2-chloropropane & chloromethane (2) 2-chloropropane & chloroethane
(3) Chloromethane & chloroethane (4) Chloromethane & 1-chloropropane
Answer of Question Based on Oxymercuration-Demercuration
1. Answer (2)
(2)
