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. Complete the following reaction
Cl Br
dry ether
+ Na
(excess)
Cl Br
Cl
(1) (2)
Br
(3) (4)
Br
(2)
2. What will be the final product of the reaction?
Br Br
Na(excess) CH 3I
x y
ether
Br Br
(1) (2)
(3) (4)
3. Complete the following reaction, final product of the reaction is
CHCl3 Ag
ether
Powder
(1) CH CH (2) Cl2CH – CHCl2
CH 2 – CH3
(3) (4)
Cl
4. Complete teh followig reaction, final product of the reaction is
Br Na
CIH2C
ether
(1) (2)
(3) (4)
(3)
5. 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 & chloroethene (4) Chloromethane & 2-chloropropene
Answer of Question Based on Stephen’s Reduction
1. Answer (1)
2. Answer (1)
3. Answer (3)
4. Answer (1)
5. Answer (3)
(4)
