Question

Treating 2-methylpropene with methanol in the presence of sulfuric acid gives tert-butyl methyl ether. CC(C)=CCOCC(C)(C)OO Propose a mechanism for the formation of this ether.

Short answer

Answer: The three main steps involved in the formation of tert-butyl methyl ether are: 1. Protonation of methanol by sulfuric acid, forming protonated methanol and a bisulfate ion. 2. Carbocation formation from 2-methylpropene by reacting with protonated methanol. 3. Nucleophilic attack by methanol on the tertiary carbocation, resulting in the formation of tert-butyl methyl ether and regeneration of sulfuric acid.

Step-by-step solution

Protonation of Methanol

First, the methanol molecule (CH3OH) reacts with sulfuric acid (H2SO4) to form protonated methanol (CH3OH2+) and a bisulfate ion (HSO4-). This step can be represented by the following equation: CH3OH + H2SO4 -> CH3OH2+ + HSO4-

Carbocation Formation from 2-methylpropene

The protonated methanol now acts as an acid, and the 2-methylpropene molecule acts as a nucleophile. The double bond in 2-methylpropene attacks the protonated methanol, breaking one of the O-H bonds, and forming a more stable tertiary carbocation. This step can be represented by the following equation: CH3OH2+ + CH3C(CH3)=CH2 -> CH3C(CH3)(+CH2) + H2O

Nucleophilic Attack by Methanol

In the final step, a methanol molecule acts as a nucleophile and attacks the positively charged carbon in the tertiary carbocation formed in step 2. This reaction results in the formation of the desired product, tert-butyl methyl ether, and a proton as a side product, which is then picked up by the bisulfate ion (HSO4-) to regenerate sulfuric acid. The equations for these steps are: CH3C(CH3)(+CH2) + CH3OH -> CH3C(CH3)CH2OCH3 + H+ H+ + HSO4- -> H2SO4 The overall mechanism involves a series of acid/base reactions and nucleophilic attacks, culminating in the formation of tert-butyl methyl ether from 2-methylpropene and methanol in the presence of sulfuric acid.