Wurtz Reaction — the NEET Chemistry reaction: mechanism, reagents, conditions, structures and exam traps.
Wurtz Reaction The Wurtz reaction is an organic coupling reaction in which two alkyl halides react with sodium metal in dry ether to form a new, longer symmetrical alkane. It involves the coupling of two alkyl groups. Sodium metal (silvery solid) is consumed. The reaction is typically exothermic. No specific color changes, precipitates, or odors are usually observed if conducted properly. If moisture is present, vigorous reaction of sodium with water may be seen. The reaction is highly exothermic due to the formation of stable C-C bonds and strong ionic Na-X bonds. 1. One electron transfer: An electron from sodium is transferred to the alkyl halide, leading to the formation of an alkyl radical and a sodium halide: R-X + Na R + NaX 2. Formation of alkylsodium (or another radical generation): The alkyl radical can either react directly with another radical or accept another electron from sodium to form an alkyl carbanion (organosodium compound): R + Na R -Na + 3. Coupling/Nucleophilic attack: Two alkyl radicals combine ( 2R R-R ) OR the alkyl carbanion acts as a nucleophile and attacks another alkyl halide molecule in an SN2-like fashion to form the alkane: R -Na + + R-X R-R + NaX Mixture of products: If two different alkyl halides (R-X and R'-X) are used, a mixture of three alkanes (R-R, R'-R', and R-R') is formed, making it unsuitable for synthesizing unsymmetrical alkanes. Elimination reactions: Tertiary alkyl halides are not suitable as they undergo elimination (E2) to form alkenes rather than coupling. Aryl halides: Aryl halides generally do not participate in the Wurtz reaction under typical conditions (requires Ullmann reaction for coupling). Presence of moisture: Sodium is highly reactive with water, leading to hydrogen gas evolution and potential fires, and undesired side reactions (hydrolysis of alkyl halides or organosodium intermediates). Methane cannot be prepared: The smallest alkane that can be prepared is ethane (by coupling two methyl groups).