Q46E - Organic Chemistry (Mcmurry)

Question

What product would you expect from cleavage of tetrahydrofuran

with HI?

Step-by-Step Solution

Answer

The expected product from cleavage of tetrahydrofuran with HI is shown below:

                              Tetrahydrofuran4-iodobutan-1-ol

Step 1: Acidic Ether cleavages reaction

Acidic ether cleavages are typical nucleophilic substitution reactions and take place by either ${\mathbf{S}}_{\mathbf{N}}\mathbf{1}$ or ${\mathbf{S}}_{\mathbf{N}}\mathbf{2}$ mechanisms, depending on the structure of the substrate. Ethers with only primary and secondary alkyl groups react by an ${\text{S}}_{N}2$ mechanism, in which ${\text{I}}_2$ or ${\text{Br}}_2$ attacks the protonated ether at the less hindered site. This usually results in a selective cleavage into a single alcohol and a single alkyl halide. For example, ethyl isopropyl ether exclusively yields isopropyl alcohol and iodoethane on cleavage by HI.

Step 2: Identify the product of the given reaction

Tetrahydrofuran reacts with hydrogen iodide HI, in the aqueous medium to form 4-iodobutan-1-ol and ethyliodide. Tetrahydrofuran is cyclic ether which is sensitive towards strong acid like hydrogen iodide (HI). In the presence of aqueous solution we get the desired product as shown below:

                                     Tetrahydrofuran4-iodobutan-1-ol