Question

Show how you would make 1-isopropoxyhexane starting with 1-hexene and any other reagents you need.

Short answer

Convert 1-hexene to 1-hexanol using epoxidation and hydrolysis, form isopropyl bromide from isopropanol, and finally use Williamson ether synthesis to get 1-isopropoxyhexane.

Step-by-step solution

- Epoxidation of 1-Hexene

Convert 1-hexene to 1-hexanol using an epoxidation reaction followed by hydrolysis. This can be done by treating 1-hexene with mCPBA (meta-chloroperoxybenzoic acid) to form an epoxide, followed by hydrolysis with aqueous acid to form the alcohol.

- Formation of 1-Hexanol

Perform acid-catalyzed hydrolysis of the epoxide formed in the previous step. Use dilute acid like H2SO4 or HCl to get 1-hexanol.

- Formation of Isopropyl Bromide

Convert isopropanol to isopropyl bromide. React isopropanol with phosphorus tribromide (PBr3) to obtain isopropyl bromide.

- Williamson Ether Synthesis

Carry out a Williamson ether synthesis reaction. React 1-hexanol with sodium hydride (NaH) to form the alkoxide ion, and then react this ion with isopropyl bromide to form 1-isopropoxyhexane.

Key concepts

Epoxidation of Alkenes

Epoxidation of alkenes is a reaction where an alkene reacts with an oxidizing agent to form an epoxide. An epoxide is a three-membered cyclic ether with two carbon atoms and one oxygen atom. The commonly used reagent for this purpose is meta-chloroperoxybenzoic acid (mCPBA). In our example, 1-hexene reacts with mCPBA. This reaction introduces an oxygen atom across the double bond of the alkene, forming an epoxide.
The balanced equation for this reaction is:
C_6H_{12} + mCPBA → Epoxide
The epoxidation reaction is crucial as it sets up the substrate for the next transformation.
The resulting epoxide is quite reactive, a characteristic that makes it a good starting point for further chemical reactions like hydrolysis.

Acid-Catalyzed Hydrolysis

Acid-catalyzed hydrolysis is the process of converting the epoxide to a diol or alcohol in the presence of an acid. In our exercise, the epoxide formed from 1-hexene undergoes hydrolysis in the presence of a dilute acid such as sulfuric acid (H2SO4) or hydrochloric acid (HCl). This reaction opens the epoxide ring and converts it into an alcohol, 1-hexanol.
The reaction steps are as follows:

• The protonation of the epoxide's oxygen by the acid.
• Water acts as a nucleophile attacking one of the carbon atoms in the epoxide.
• The ring opens up, and deprotonation takes place, giving us the final alcohol.

Therefore, the overall transformation can be summarized as:
Epoxide + H_2O + H^+ → 1-Hexanol

Formation of Alkyl Halides

Alkyl halides, also known as haloalkanes, are compounds containing carbon, hydrogen, and halogens. In the given exercise, we need to form an alkyl bromide from isopropanol (2-propanol). This transformation is typically done using phosphorus tribromide (PBr3). Phosphorus tribromide reacts with isopropanol to replace the hydroxyl group with a bromine atom, forming isopropyl bromide.
The balanced chemical equation for this reaction is:
(CH_3)_2CHOH + PBr_3 → (CH_3)_2CHBr + H_3PO_3
To summarize:

• Isopropanol reacts with PBr3.
• Bromine replaces the OH group.
• Isopropyl bromide is formed.

This step is essential because it produces a good leaving group required for the next step, the Williamson ether synthesis.

Williamson Ether Synthesis

Williamson ether synthesis is a popular method to form ethers, which involves the reaction of an alkoxide ion with an alkyl halide. In our exercise, 1-hexanol first reacts with sodium hydride (NaH) to form the sodium alkoxide.
The steps for forming the ether are:

• 1-Hexanol + NaH → Alkolxide ion + H_2
• Alkoxide ion + Isopropyl bromide → 1-Isopropoxyhexane + NaBr

The role of NaH is to deprotonate the alcohol to form the alkoxide ion. This strong nucleophile then attacks the alkyl halide (isopropyl bromide), leading to the formation of the desired ether.
This reaction mechanism makes Williamson ether synthesis a reliable method to synthesize complex ethers.