Imagine you have two different Lego bricks — one is an aromatic ring with a halogen attached (aryl halide), and the other is a simple carbon chain with a halogen (alkyl halide). You want to snap them together to make a single molecule where the alkyl chain is directly attached to the benzene ring. That's exactly what the Wurtz-Fittig reaction does.
The reaction is a coupling — it takes two different organic halides and joins them at the carbon that used to hold the halogen, using metallic sodium as the "glue."
The Precise Statement
Ar−X+R−X+2NadryetherAr−R+2NaX
Here, Ar is an aryl group (like phenyl, tolyl, etc.), R is an alkyl group (methyl, ethyl, etc.), and X is a halogen (usually Br or I). The reaction is carried out in dry ether (anhydrous diethyl ether) because sodium reacts violently with water.
The product is an alkyl-substituted aromatic hydrocarbon — for example, bromobenzene and methyl bromide give toluene:
The reaction proceeds through a free radical mechanism, similar to the classic Wurtz reaction (which couples two alkyl halides).
Step 1: Sodium metal donates an electron to the halogen of the aryl halide, breaking the C–X bond and generating an aryl radical and NaX.
Ar−X+NaArX∙+NaX
Step 2: Simultaneously, the same happens with the alkyl halide, giving an alkyl radical.
R−X+NaRX∙+NaX
Step 3: The two radicals combine to form the coupled product.
ArX∙+RX∙Ar−R
Watch out
This is a free radical mechanism, not an ionic one. The solvent must be absolutely dry because water would react with sodium to produce hydrogen gas and NaOH, destroying the reagent.
Why Not Just Use Friedel-Crafts Alkylation?
You might ask: why not simply alkylate benzene using Friedel-Crafts? The Wurtz-Fittig reaction is useful when the alkyl group you want to attach is primary and you want to avoid rearrangements. Friedel-Crafts alkylation often rearranges carbocations (e.g., n-propyl chloride gives isopropylbenzene). The Wurtz-Fittig reaction gives the straight-chain product without rearrangement.
The Catch: Side Products
Because you have two different halides, the radicals can also couple with themselves:
Two aryl radicals → biaryl (e.g., biphenyl from bromobenzene)
Two alkyl radicals → alkane (e.g., ethane from methyl bromide)
So the desired Ar–R product is always mixed with Ar–Ar and R–R. This is why the reaction is most useful when the alkyl halide is cheap and the aryl halide is valuable — you can use an excess of the alkyl halide to favour the cross-coupling. …
Sodium metal can couple an aryl halide with an alkyl halide in dry ether, joining the two fragments together in a reaction closely related to, but distinct from, the ordinary Wurtz reaction. …
A mixture of an aryl halide and an alkyl halide, treated with sodium metal in dry ether, couples the aryl and alkyl groups together to form a substituted (alkylated) benzene, releasing NaX.
C6H5-X + R-X' + 2Na --dry ether--> C6H5-R + 2NaX
For example, chlorobenzene reacted with ethyl chloride and sodium in dry ether gives ethylbenzene:
Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.
CBSE 2019Set ANNUAL1 markMCQ
Q.Chlorobenzene can be converted to Toluene by
(a) reaction with CH3MgBr
(b) reaction with CH3Cl and Na in dry ether
(c) hydrolysis followed by reaction with CH3ONa
(d) reaction with CH3ONa
›Reveal solutionSolution
Coupling chlorobenzene with methyl chloride and sodium in dry ether (Wurtz–Fittig reaction) directly and cleanly installs a methyl group on the ring, giving toluene.
Chlorobenzene reacts with methyl chloride in the presence of sodium metal in dry ether (the Wurtz–Fittig reaction), coupling the aryl and alkyl groups directly: