Q44E - Organic Chemistry (Mcmurry)

Question

Predict the products of the following ether cleavage reactions:

Step-by-Step Solution

Answer

The products of the following ether cleavage reactions are:

(a)

(b)

Tert-butoxybenzene                    Phenol                  2 methylprop-1-ene

(c)

Ethoxyethene                          Ethyliodide                             cetaldehyde

(d)

Step 1: Acid catalyzed hydrolysis

Acidic ether cleavages are typical nucleophilic substitution reactions and take place by either ${\text{S}}_{N}1$or ${\text{S}}_{N}2$ 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 $I_2 or B{r}_2$ 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.

Ethers with a tertiary, benzylic, or allylic group cleave by either an S_N1 or E¹ mechanism because these substrates can produce stable intermediate carbocation’s. These reactions are often fast and take place at moderate temperatures. tert-Butyl ethers, for example, react by an E1 mechanism on treatment with trifluoroacetic acid at 0 °C.

Step 2: Product for reaction (a)

Cleavage of ethers by aqueous HX, (X = Cl, Br, I, F) gives an alcohol and an unhindered primary alkyl halide.

(a) Ethoxycyclohexane reacts with hydrogeniodide HI, in the aqueous medium to form phenol and ethyliodide. The reaction is shown below:

                                                Reaction (a)

Step 3: Product of reaction (b)

(b) Tert-butoxybenzene reacts with trifluroacetic acid to form phenol and 2-methylpop-1-ene. The reaction is shown below:

                                                   Reaction (b)

Step 4: Product of reaction (c)

(c) Cleavage of Ethoxyethene by aqueous HI, gives an acetaldehyde and an unhindered primary alkyl halide.The reaction is shown below:

                             Cleavage of ethoxyethene (c)

Step 5: Product of reaction (d)

(d) 1-ethoxy-2,2-dimethylpropanereacts with hydrogeniodide HI, in the aqueous medium to form 2,2-dimethylpropan-1-oland ethyliodide. The reaction is shown below: