Question

Ethyl chloride is obtained as a product in reaction is/are : (A) \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OH} \quad \stackrel{\mathrm{SOCl}_{2}}{\longrightarrow}\) (B) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OCH}_{2} \mathrm{CH}_{3} \stackrel{\mathrm{PCl}_{\mathrm{S}}}{\longrightarrow}\) (C) \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OH} \frac{\mathrm{HCl}}{\mathrm{ZnCl}_{2} \triangle}\) (D) \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OH} \stackrel{\mathrm{PCl}_{3}}{\longrightarrow}\)

Short answer

Ethyl chloride is obtained as a product in reactions (A) and (D): - (A) \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OH} + \mathrm{SOCl}_{2} \longrightarrow \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{Cl} + \mathrm{SO}_{2} + \mathrm{HCl}\) - (D) \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OH} + \mathrm{PCl}_{3} \longrightarrow \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{Cl} + \mathrm{H}_{3}\mathrm{PO}_{3}\)

Step-by-step solution

Identifying the reactants in each reaction

Let's first identify the reactants and reagents in the given reactions. - Reaction (A): Ethanol (\(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OH}\)) with thionyl chloride (\(\mathrm{SOCl}_{2}\)) - Reaction (B): Ethyl ether (\(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OCH}_{2} \mathrm{CH}_{3}\)) with phosphorus pentachloride (\(\mathrm{PCl}_{5}\)) - Reaction (C): Ethanol (\(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OH}\)) with hydrochloric acid (\(\mathrm{HCl}\)) in the presence of zinc chloride (\(\mathrm{ZnCl}_{2}\)) and heat (\(\triangle\)) - Reaction (D): Ethanol (\(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OH}\)) with phosphorus trichloride (\(\mathrm{PCl}_{3}\)) Now, let's analyze each reaction to determine the product formed.

Reaction (A)

In reaction (A), thionyl chloride (\(\mathrm{SOCl}_{2}\)) reacts with ethanol to replace the hydroxyl group (-OH) with a chlorine atom. The product formed is ethyl chloride: \[\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OH} + \mathrm{SOCl}_{2} \longrightarrow \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{Cl} + \mathrm{SO}_{2} + \mathrm{HCl}\]

Reaction (B)

In reaction (B), phosphorus pentachloride (\(\mathrm{PCl}_{5}\)) reacts with ethyl ether, leading to cleavage of the ether bond and formation of 2 molecules of alkyl chloride. The product formed in this case is not ethyl chloride: \[\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OCH}_{2} \mathrm{CH}_{3} + 2 \mathrm{PCl}_{5} \longrightarrow 2 \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{Cl} + 2 \mathrm{POCl}_{3}\]

Reaction (C)

In reaction (C), hydrochloric acid (\(\mathrm{HCl}\)) and zinc chloride (\(\mathrm{ZnCl}_{2}\)) are used as reagents. However, this reaction does not efficiently lead to the formation of ethyl chloride. Instead, it predominantly forms ethers or no significant reaction occurs under these conditions.

Reaction (D)

In reaction (D), phosphorus trichloride (\(\mathrm{PCl}_{3}\)) reacts with ethanol to replace the hydroxyl group (-OH) with a chlorine atom. The product formed is ethyl chloride: \[\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OH} + \mathrm{PCl}_{3} \longrightarrow \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{Cl} + \mathrm{H}_{3}\mathrm{PO}_{3}\]

Conclusion

From our analysis, we can see that ethyl chloride is formed in reactions (A) and (D). Therefore, the correct answer is that ethyl chloride can be obtained as a product in reactions: - (A) \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OH} + \mathrm{SOCl}_{2} \longrightarrow \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{Cl} + \mathrm{SO}_{2} + \mathrm{HCl}\) - (D) \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OH} + \mathrm{PCl}_{3} \longrightarrow \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{Cl} + \mathrm{H}_{3}\mathrm{PO}_{3}\)

Key concepts

Alcohol to Alkyl Halide Conversion

The transformation of alcohols into alkyl halides is a key reaction in organic chemistry. When we talk about converting alcohols like ethanol (\(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OH}\)) into alkyl halides such as ethyl chloride (\(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{Cl}\)), we often involve halogenating reagents. These reagents replace the hydroxyl group (-OH) in the alcohol with a halogen atom. This conversion is significant because alkyl halides serve as important intermediates in the production of various chemicals and pharmaceuticals.
Several methods can achieve this transformation, including the use of hydrogen halides (\(\mathrm{HX}\)), thionyl chloride (\(\mathrm{SOCl}_{2}\)), and phosphorus halides. These methods allow for the synthesis of different alkyl halides depending on the reagents' nature, ensuring versatility in organic synthesis. The efficiency of these reactions can vary, with factors such as temperature and the presence of catalysts playing crucial roles in determining the products formed.

Thionyl Chloride Reaction

Thionyl chloride (\(\mathrm{SOCl}_{2}\)) is a reagent commonly used to convert alcohols into alkyl chlorides. Its reaction with alcohols such as ethanol is particularly valued because it generally proceeds with good yield and minimal side reactions. In this process, the alcohol's hydroxyl group is replaced by a chlorine atom, resulting in the formation of ethyl chloride.
One of the advantages of using thionyl chloride is the release of byproducts like sulfur dioxide (\(\mathrm{SO}_{2}\)) and hydrochloric acid (\(\mathrm{HCl}\)) as gases. This makes the separation and purification of the desired alkyl chloride product easier, as the gaseous byproducts can be readily removed from the reaction mixture. However, it's important to conduct this reaction in a controlled environment because the byproducts can be hazardous.
The mechanism involves an initial substitution where the alcohol reacts with thionyl chloride followed by the removal of the leaving group, leading to the final formation of the alkyl chloride. The reaction is typically facilitated by either pyridine or a tertiary amine to neutralize the acidic byproducts, ensuring a smoother reaction path.

Phosphorus Chloride Reactions

Reactions involving phosphorus chlorides, like phosphorus trichloride (\(\mathrm{PCl}_{3}\)) and phosphorus pentachloride (\(\mathrm{PCl}_{5}\)), are versatile methods for converting alcohols into alkyl halides. These reagents are effective in substituting hydroxyl groups with chloride ions to form alkyl chlorides, including ethyl chloride.
Phosphorus trichloride, for instance, reacts with ethanol to form ethyl chloride along with the byproduct phosphorous acid (\(\mathrm{H}_{3}\mathrm{PO}_{3}\)). This reaction is beneficial due to its relatively straightforward procedure and effective chlorine transfer.

• Phosphorus trichloride (\(\mathrm{PCl}_{3}\)) is used when milder conditions or high yield is desired.
• Phosphorus pentachloride (\(\mathrm{PCl}_{5}\)) is usually employed for more vigorous reactions or when working with complex substrates.

Understanding the nature of these chlorinating agents and their reaction conditions is essential for predicting and manipulating the outcome of the conversion process. It's also crucial for optimizing yields and minimizing unwanted reactions, especially in complex synthetic pathways.