Question

Using your roadmap as a guide, show how to convert 1-butene into dibutyl ether. You must use 1-butene as the source of all carbon atoms in the dibutyl ether. Show all required reagents and all molecules synthesized along the way.

Short answer

Question: Outline the synthesis of dibutyl ether starting from 1-butene. Include the intermediates and reagents used in each step. Answer: The synthesis of dibutyl ether from 1-butene involves the following steps: 1. Hydration of 1-butene using H2O/H2SO4 to form 2-butanol. 2. Nucleophilic substitution of 2-butanol with HBr to form 2-bromobutane. 3. Deprotonation of 2-butanol using NaH to form sodium 2-butoxide. 4. Williamson Ether synthesis, reacting sodium 2-butoxide with 2-bromobutane to form dibutyl ether and NaBr as a byproduct.

Step-by-step solution

1. Formation of Alcohol (Hydration of 1-butene)

To start with, we first need to convert 1-butene into an alcohol. This can be done by the reaction of 1-butene with water under acidic conditions (i.e., hydration reaction). The reagent used for this step is sulfuric acid and water (H2O/H2SO4). The hydration of 1-butene will yield 2-butanol. The reaction is as follows: 1-butene + H2O/H2SO4 -> 2-butanol

2. Conversion of Alcohol to the Corresponding Halide (Nucleophilic Substitution)

Next, we need to convert the 2-butanol into a suitable halide, such as 2-bromobutane. This can be achieved by reacting 2-butanol with hydrobromic acid (HBr). This is a nucleophilic substitution (SN2) reaction where the -OH group is replaced by the -Br group. The reaction is as follows: 2-butanol + HBr -> 2-bromobutane

3. Formation of the Sodioalkoxide (Alcohol Deprotonation)

In order to form an ether from the alcohol, we must first deprotonate the alcohol to form a sodioalkoxide. We can treat 2-butanol with a strong base like sodium hydride (NaH) to form sodium 2-butoxide. The reaction is as follows: 2-butanol + NaH -> sodium 2-butoxide (NaOBu)

4. Formation of Dibutyl Ether (Williamson Ether Synthesis)

Finally, we will use the Williamson Ether synthesis to form the dibutyl ether. This involves a nucleophilic attack by the sodioalkoxide (sodium 2-butoxide) on the 2-bromobutane formed in step 2. This leads to the formation of dibutyl ether and sodium bromide (NaBr) as a byproduct. The reaction is as follows: Sodium 2-butoxide + 2-bromobutane -> dibutyl ether + NaBr By following these steps, we have demonstrated the conversion of 1-butene into dibutyl ether using 1-butene as the source of carbon atoms while showing all the required reagents and molecules synthesized along the way.

Key concepts

Hydration of alkenes

Hydration of alkenes is a crucial reaction in organic chemistry used to transform alkenes into alcohols. This is often the first step in the synthesis of more complex molecules. With alkene hydration, we can introduce a hydroxyl (-OH) group into the carbon skeleton.

The process requires the presence of water and an acid, typically sulfuric acid (H₂SO₄), to catalyze the reaction. When 1-butene undergoes hydration, water is added across the double bond. As a result, 2-butanol is formed. This is because the acid helps stabilize the carbocation intermediate that forms during the reaction.

The steps in this reaction include:

• Protonation of the double bond to form a carbocation.
• Nucleophilic attack by water leading to the addition of the -OH group.
• Deprotonation to yield the alcohol.

This mechanism exemplifies Markovnikov's rule, which states that the hydrogen atom bonds to the less substituted carbon atom. Thus, in this case, we obtain 2-butanol instead of 1-butanol from 1-butene.

Nucleophilic substitution reactions

Nucleophilic substitution reactions are vital for converting alcohols into halides. This step is necessary when transitioning from an alcohol to an ether, as it allows the introduction of a leaving group.

Specifically, converting 2-butanol into 2-bromobutane involves an SN2 mechanism. In this reaction type, a halogen like bromine replaces the hydroxyl group of an alcohol. Hydrobromic acid (HBr) provides the bromide ion which acts as a nucleophile.

Steps involved in an SN2 reaction:

• The strong nucleophile (Br⁻) simultaneously attacks the carbon linked to the -OH group.
• The -OH group is displaced as water, forming 2-bromobutane.

This one-step mechanism occurs inversely to the configuration of the chiral center (if a stereocenter is involved). SN2 reactions are bimolecular, resulting in inversion of configuration at the carbon, and work best with less hindered substrates like 2-butanol.

Ether formation reactions

Ether formation, specifically the Williamson Ether Synthesis, is a classic way to create ethers in organic synthesis. In the scenario we are considering, we aim to synthesize dibutyl ether starting from 1-butene.

The Williamson method involves the reaction between an alkoxide ion and a primary alkyl halide. First, we transform 2-butanol into its alkoxide form using a strong base like sodium hydride (NaH). This process deprotonates the alcohol, creating sodium 2-butoxide, a potent nucleophile.

Steps to form an ether:

• Reacting sodium hydride with 2-butanol yields sodium 2-butoxide.
• The resulting sodium 2-butoxide attacks 2-bromobutane in a nucleophilic substitution.

This synthesis ultimately results in dibutyl ether and sodium bromide as a byproduct.

The beauty of the Williamson Ether Synthesis lies in its ability to form symmetric or asymmetric ethers, provided we choose the appropriate alcohol and alkyl halide precursors. This method is particularly effective for forming ethers due to the efficiency of this SN2 reaction mechanism.