Q.Context: A chloro compound (A) on reduction with Zn–Cu and ethanol give hydrocarbon (B) with two carbon-atoms. When compound (A) is dissolved in dry ether and sodium-metal it gives hydrocarbon with four carbon atoms. When compound (A) is treated with alcoholic KCN it gives compound (C).
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The Wurtz Reaction: Why Sodium Makes Alkanes Grow
Imagine you have two identical building blocks — say, two methyl groups (CH3−) — and you want to join them into a longer chain (CH3−CH3). That's the core idea of the Wurtz reaction. You take an alkyl halide (like bromoethane) and treat it with sodium metal in dry ether. The sodium strips away the halogen atoms, and the two alkyl fragments couple together.
The reaction was discovered by Charles-Adolphe Wurtz in 1855, and it was one of the first methods to make carbon-carbon bonds deliberately.
The precise statement
Two molecules of an alkyl halide react with two atoms of sodium metal in anhydrous (dry) ether to give a symmetrical alkane and sodium halide.
2R−X+2Nadry etherR−R+2NaX
Here R is an alkyl group (methyl, ethyl, propyl, etc.) and X is a halogen (usually chlorine, bromine, or iodine). The product R−R is always a symmetrical alkane — meaning both halves of the new molecule are identical.
How it actually works (the mechanism)
The reaction proceeds through a free-radical intermediate. Sodium metal donates one electron to the alkyl halide, breaking the C−X bond and generating an alkyl radical (R∙) and a sodium halide. Two such radicals then combine to form the R−R bond.
R−X+Na⟶R∙+NaX
2R∙⟶R−R
The solvent must be dry ether because water would react violently with sodium metal, destroying the reagent before it can couple the alkyl halides.
A concrete example
Take bromoethane (ethyl bromide) with sodium:
2CH3CH2Br+2Nadry etherCH3CH2CH2CH3+2NaBr
The product is butane — a symmetrical alkane with four carbons.
The big limitation: unsymmetrical products are a mess
If you try to couple two different alkyl halides, say CH3Br and CH3CH2Br, you get a mixture of three alkanes:
- CH3−CH3 (ethane) — from two methyl radicals
- CH3CH2−CH2CH3 (butane) — from two ethyl radicals
- CH3−CH2CH3 (propane) — from one methyl and one ethyl radical
This mixture is hard to separate, so the Wurtz reaction is practically useful only when both alkyl halides are identical.
Never use the Wurtz reaction to prepare an unsymmetrical alkane from two different alkyl halides — you'll get a hopeless mixture of three products.
Why dry ether? Why sodium? …
Working backwards from each clue's carbon count and the specific transformation described — reduction, Wurtz coupling, or reaction with KCN — pins down what compound A must be, and hence B and C. …
The clues (2-carbon reduction product, 4-carbon Wurtz product, and a nitrile from KCN) identify A as ethyl chloride; Wurtz reaction couples two alkyl halide molecules using sodium metal in dry ether to form a longer-chain alkane.
(a) Identifying A, B, C:
- A is reduced by Zn-Cu couple/ethanol to give a hydrocarbon B with 2 carbon atoms — this is a simple reduction (replacing −Cl with −H), so if B is C2H6 (ethane), A must itself have 2 carbons: A = ethyl chloride, CH3CH2Cl.
- A dissolved in dry ether + sodium metal gives a hydrocarbon with 4 carbon atoms — this is the Wurtz reaction, where two molecules of the 2-carbon alkyl halide couple to form a 4-carbon alkane: 2CH3CH2Cl+2Na→CH3CH2CH2CH3 (n-butane). This confirms A = ethyl chloride.
- A treated with alcoholic KCN gives C: alkyl halides react with KCN (via the carbon of CN−, which is a better nucleophile through carbon) to form alkyl cyanides (nitriles): CH3CH2Cl+KCN→CH3CH2CN (C)+KCl. C = propanenitrile (ethyl cyanide).
A=CH3CH2Cl,B=CH3CH3,C=CH3CH2CN
(b) Wurtz Reaction: …
Showing the 12 most recent of 14 on this concept.
- CBSE 2026Set ANNUAL1 markMCQQ.The reaction used for preparation of higher alkanes from alkyl halides is(a) Wurtz reaction(b) Kolbe's reaction(c) β-elimination(d) Friedel-Crafts acylation
›Reveal solutionSolution
The Wurtz reaction converts alkyl halides into higher (longer-chain) alkanes by coupling two alkyl groups using sodium metal in dry ether.
The Wurtz reaction: 2 R-X + 2 Na --(dry ether)--> R-R + 2 NaX
Here, two molecules of an alkyl halide (R-X) react with sodium metal in dry ether. The sodium removes the halogen atoms and couples the two alkyl (R) groups together, forming a new C-C bond and producing a symmetrical alkane with twice the number of carbons as the starting alkyl halide (plus sodium halide as a by-product).
For example: 2 CH3-Br + 2 Na --(dry ether)--> CH3-CH3 (ethane) + 2 NaBr.
…
- CBSE 2026Set ANNUAL1 markQ.Identify [A] in the reaction: CH3Br + 2Na + BrCH3 --(dry ether)--> [A] + 2NaBr
›Reveal solutionSolution
This is a Wurtz reaction; [A] = ethane (CH3-CH3).
The Wurtz reaction couples two molecules of an alkyl halide using sodium metal in dry ether, joining the two alkyl groups by a new C-C bond and eliminating two sodium halide units: 2R-X + 2Na, in dry ether, gives R-R + 2NaX.
…
- CBSE 2026Set ANNUAL1 markQ.Write chemical equation for the preparation of butane by Wurtz reaction.
›Reveal solutionSolution
Two molecules of ethyl bromide couple via sodium metal in dry ether to give butane (a symmetrical alkane) plus sodium bromide.
The Wurtz reaction couples two molecules of an alkyl halide using sodium metal in dry ether, forming a new C–C bond and a symmetrical alkane with double the carbon count of the starting halide. To get butane (C4H10, 4 carbons), the alkyl halide used must have 2 carbons, i.e. ethyl bromide (CH3CH2Br):
…
- CBSE 2025Set ANNUAL1 markMCQQ.The reaction used for obtaining of higher alkanes from alkyl halides is(a) Wurtz reaction(b) Kolbe's reaction(c) beta-elimination(d) Friedel-Crafts acylation
›Reveal solutionSolution
The Wurtz reaction couples two molecules of an alkyl halide using sodium metal in dry ether, joining their carbon chains to build a longer (higher) alkane with twice as many carbons.
The Wurtz reaction is written as:
2 R-X + 2 Na --(dry ether)--> R-R + 2 NaX
where R-X is an alkyl halide (e.g. CH3Br) and R-R is the resulting symmetrical higher alkane (e.g. 2 CH3Br + 2Na -> CH3-CH3 (ethane) + 2NaBr).
Mechanistically, sodium metal donates electrons to generate alkyl radicals (or organosodium intermediates) from two molecules of the alkyl halide, and these two alkyl fragments then couple together to form a new C-C bond, joining the two chains into one longer molecule — this is exactly how 'higher alkanes' (alkanes with more carbons than the starting alkyl halide) are synthesised in the lab from smaller alkyl halides.
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- CBSE 2025Set ANNUAL1 markQ.Write the chemical equation for Wurtz reaction.
›Reveal solutionSolution
Wurtz reaction: 2R−X + 2Na (dry ether) → R−R + 2NaX.
The Wurtz reaction couples two alkyl halide molecules using sodium metal in dry ethereal solution, forming a symmetrical higher alkane with double the number of carbons of the starting halide, along with sodium halide:
2R-X+2Nadry etherR-R+2NaX
For example, with methyl bromide:
…
- CBSE 2024Set ANNUAL1 markQ.What is Wurtz Reaction?
›Reveal solutionSolution
Sodium couples two alkyl halide molecules together (via a free-radical mechanism) to build a longer, symmetrical alkane.
In the Wurtz reaction, an alkyl halide reacts with sodium metal in dry ether solvent. Two molecules of the alkyl halide are 'coupled' together (via a free-radical mechanism, with sodium donating electrons), forming a new C-C bond between them and releasing sodium halide:
2R-X + 2Na --(dry ether)--> R-R + 2NaX
…
- CBSE 2024Set ANNUAL1 markQ.Alkyl halides react with sodium in dry ether to form symmetrical alkanes containing double the number of carbon atoms present in the halides. Name the reaction.
›Reveal solutionSolution
Sodium metal in dry ether couples two alkyl halide molecules together into one longer symmetrical alkane — this coupling reaction is named the Wurtz reaction.
When an alkyl halide is treated with sodium metal in dry ether, two molecules of the halide couple together (via a free-radical or organosodium intermediate) to form a single, symmetrical alkane containing double the number of carbon atoms of the original halide, with sodium halide as the by-product:
2R−X+2Nadry etherR−R+2NaX
For example, 2CH3Br+2Na→CH3−CH3+2NaBr (ethane from methyl bromide).
…
- CBSE 2024Set ANNUAL1 markMCQQ.The reaction used for preparation of higher alkanes from alkyl halide is(a) Wurtz reaction(b) Kolbe's reaction(c) beta-elimination(d) Friedel-Crafts acylation
›Reveal solutionSolution
The Wurtz reaction uses sodium metal in dry ether to couple two molecules of an alkyl halide, joining their carbon chains to build a higher (usually symmetrical) alkane.
Wurtz reaction: 2 R-X + 2 Na --dry ether--> R-R + 2 NaX
Two alkyl halide molecules react with sodium metal, which removes the halogen atoms and couples the two alkyl groups together, forming a new C-C bond and producing an alkane with double the carbon count of the starting alkyl halide (plus sodium halide as a by-product).
…
- CBSE 2022Set TERM21 markMCQQ.Alkyl halides react with sodium in dry either to give hydrocarbons containing double number of Carbon atoms present in the halides. The rex is known as:(a) Wurtz rex(b) Wurtz-Fittig rex(c) Swarts rex(d) None of these
›Reveal solutionSolution
Alkyl halides couple with sodium metal in dry ether to double the carbon chain — this is the Wurtz reaction.
When an alkyl halide is treated with sodium metal in dry ether, two alkyl groups couple together (Wurtz coupling), eliminating NaX and forming a higher (symmetrical) alkane with double the number of carbon atoms:
2R-X+2Nadry etherR-R+2NaX
…
- CBSE 2022Set ANNUAL1 markMCQQ.Isopropyl bromide gives on Wurtz's reaction(a) Hexane(b) Propane(c) 2,3-dimethyl butane(d) Neohexane
›Reveal solutionSolution
Wurtz reaction of isopropyl bromide gives 2,3-dimethylbutane — option (c).
From NCERT Class 11 Chemistry (Hydrocarbons): in the Wurtz reaction, 2R–X + 2Na → R–R + 2NaX.
Here R = isopropyl, (CH₃)₂CH–. Coupling two isopropyl units: …
- CBSE 2019Set ANNUAL1 markMCQQ.CH3Br + 2Na + CH3Br --Dry ether--> CH3-CH3 + 2NaBr. The reaction is(a) Friedel-Crafts reaction(b) Wurtz reaction(c) Fittig reaction(d) none of these.
›Reveal solutionSolution
Treating an alkyl halide with sodium metal in dry ether to couple two alkyl groups into a symmetrical alkane is the Wurtz reaction.
2CH3Br + 2Na --dry ether--> CH3-CH3 + 2NaBr
Sodium first forms a very reactive alkylsodium intermediate, which then displaces bromide from a second molecule of CH3Br in an SN2-like coupling, joining the two methyl groups to give ethane (CH3-CH3) and releasing NaBr. This coupling of two alkyl halide molecules using sodium in dry ether is named the Wurtz reaction (distinct from the Fittig reaction, which is t …
- CBSE 2019Set ANNUAL1 markMCQQ.Which of the following organic compounds are formed by Wurtz reaction?(a) Alcohols(b) Hydrocarbons(c) Haloalkanes(d) Haloarenes
›Reveal solutionSolution
Wurtz reaction: 2 R–X + 2Na → R–R + 2NaX (dry ether), giving a higher alkane — a hydrocarbon.
The Wurtz reaction is the treatment of an alkyl halide with sodium metal in dry ether:
2R–X+2Nadry etherR–R+2NaX
…
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