How is ethyl bromide prepared from :

(i) Ethyl alcohol

(ii) Ethane

(iii) Ethene

To prepare ethyl bromide, also known as bromoethane, from different starting materials, we can utilize various chemical reactions. Each method leverages the unique properties of the starting compounds to introduce the bromine atom into the ethyl group. Let’s break down the preparation from ethyl alcohol, ethane, and ethene.

Preparation from Ethyl Alcohol

Ethyl alcohol (ethanol) can be converted to ethyl bromide through a substitution reaction. The process typically involves the use of a strong acid, such as hydrobromic acid (HBr).

Steps Involved:

• Protonation of Ethanol: Ethanol is first protonated by the acid, making it a better leaving group.
• Nucleophilic Attack: The bromide ion (Br^-) from HBr then attacks the carbon atom of the protonated ethanol, leading to the substitution of the hydroxyl group (–OH) with a bromine atom.
• Formation of Ethyl Bromide: The result is ethyl bromide and water as a byproduct.

This method is efficient and straightforward, making it a common laboratory procedure for synthesizing ethyl bromide.

Synthesis from Ethane

When starting with ethane, the preparation of ethyl bromide typically involves a halogenation reaction, specifically bromination. This process requires the presence of bromine and ultraviolet light or heat to initiate the reaction.

Steps Involved:

• Initiation: The bromine molecules (Br₂) are dissociated into bromine radicals (Br·) under UV light or heat.
• Propagation: A bromine radical abstracts a hydrogen atom from ethane (C₂H₆), forming ethyl radical (C₂H₅·) and hydrogen bromide (HBr).
• Termination: The ethyl radical can then react with another bromine radical to form ethyl bromide (C₂H₅Br).

This method is less selective and can lead to a mixture of products, but it is a viable route for producing ethyl bromide from ethane.

Conversion from Ethene

Ethene (ethylene) can be converted to ethyl bromide through an electrophilic addition reaction. This method is particularly effective due to the double bond present in ethene, which is reactive towards electrophiles.

Steps Involved:

• Electrophilic Addition: When ethene is treated with bromine (Br₂) in the presence of a solvent like carbon tetrachloride (CCl₄), the bromine adds across the double bond.
• Formation of Bromohydrin: The initial product is a vicinal dibromide, which can further react with a base (like sodium bromide) to yield ethyl bromide.
• Final Product: The result is ethyl bromide, with the elimination of a bromide ion.

This method is advantageous because it allows for the direct conversion of an alkene to an alkyl halide, making it a popular choice in organic synthesis.

In summary, ethyl bromide can be synthesized from ethyl alcohol through substitution, from ethane via radical halogenation, and from ethene through electrophilic addition. Each method has its own advantages and is chosen based on the availability of starting materials and desired reaction conditions.