A common illicit synthesis of methamphetamine involves an interesting variation of the Birch reduction. A solution of ephedrine in alcohol is added to liquid ammonia, followed by several pieces of lithium metal. The Birch reduction usually reduces the aromatic ring, but in this case, it eliminates the hydroxy group of ephedrine to give methamphetamine. Propose a mechanism, similar to that for the Birch reduction, to explain this unusual course of the reaction

Ephedrine Methamphetamine

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Mechanism for the formation of Methamphetamine

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01

Birch Reduction

Usually, the Birch reduction is used to convert arenes to cyclohexadiene but in this, in the presence of liquid ammonia and lithium metal and alcohol, it eliminates the hydroxyl group present.

02

Mechanism of the reaction

The ephedrine is treated with lithium metal and replaces hydrogen with Li which reacts with a proton to form the carbocation and then a radical. This radical on the addition of electron form a carbanion which reacts with ethyl alcohol to form the methamphetamine as the desired product.

Mechanism for the formation of Methamphetamine

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Most popular questions from this chapter

Step 2 of the iodination of benzene shows water acting as a base and removing a proton from the sigma complex. We did not consider the possibility of water acting as a nucleophile and attacking the carbocation, as in an electrophilic addition to an alkene. Draw the reaction that would occur if water reacted as a nucleophile and added to the carbocation. Explain why this type of addition is rarely observed.

Indane can undergo free-radical chlorination at any of the alkyl positions on the aliphatic ring.

indane

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