Acidic cleavage of ethers (SN2)

by James

Description: When ethers are treated with strong acid in the presence of a nucleophile, they can be cleaved to give alcohols and alkyl halides. If the ether is on a primary carbon this may occur through an SN2 pathway.

Notes: Common acids for this purpose are HI and other hydrogen halides, as well as H2SO4 in the presence of H2O.

In the case where the ether being cleaved is secondary and has a stereocenter, there will be inversion of configuration.

Examples: 

Notes: The third example could also be written “H3O+”

Mechanism: Strong acid (HI) protonates the ether oxygen, which turns it into a better leaving group (Step 1, arrows A and B). Next, the iodide ion attacks the carbon in an SN2 reaction (Step 2, arrows C and D) to give the alcohol and methyl iodide.

Notes: In cases  where the ether being cleaved is secondary and has a stereocenter, there will be inversion of configuration.

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