1-Chlorobutane on reaction with alcoholic potash gives:

• (A). 1 - butene
• (B). 1 - butanol
• (C). 2 - butene
• (D). 2 - butanol

When 1-chlorobutane reacts with alcoholic potash, the primary product formed is 1-butene. This reaction is an example of an elimination reaction, specifically an E2 mechanism, where the halogen (in this case, chlorine) is removed along with a hydrogen atom from an adjacent carbon atom, resulting in the formation of a double bond.

Understanding the Reaction Mechanism

To break it down further, let's consider the structure of 1-chlorobutane. It has the following structure:

• 1-Chlorobutane: CH₃-CH₂-CH₂-CH₂-Cl

In the presence of alcoholic potash (which is a solution of potassium hydroxide in alcohol), the hydroxide ion (OH^-) acts as a base. This base abstracts a hydrogen atom from the carbon adjacent to the carbon that holds the chlorine atom. The chlorine atom is then eliminated as a chloride ion (Cl^-), leading to the formation of a double bond between the two carbon atoms.

Step-by-Step Reaction

The reaction can be summarized in the following steps:

1. The hydroxide ion attacks a hydrogen atom on the β-carbon (the carbon next to the one with the chlorine).
2. This results in the formation of a double bond between the α-carbon (the carbon with the chlorine) and the β-carbon.
3. The chlorine atom is expelled as a chloride ion, resulting in the formation of 1-butene.

Why Not Other Options?

Let’s briefly examine why the other options are not formed in this reaction:

• 1-butanol: This is an alcohol, and the reaction conditions favor elimination rather than substitution, which would be required to form an alcohol.
• 2-butene: While 2-butene could theoretically form through a different mechanism or starting material, the elimination from 1-chlorobutane specifically leads to 1-butene.
• 2-butanol: Similar to 1-butanol, this would require a substitution reaction, which is not favored under these conditions.

Conclusion

In summary, the reaction of 1-chlorobutane with alcoholic potash predominantly yields 1-butene due to the elimination mechanism that occurs. This highlights the importance of understanding the reaction conditions and the nature of the reactants involved in organic chemistry.