Preparation of alcohols from haloalkanes

Introduction:
Alcohols can be prepared from haloalkanes (alkyl halides) through a process called nucleophilic substitution. In this process, the halogen atom (e.g., Cl, Br, I) in the haloalkane is replaced by a hydroxyl group (-OH) to form an alcohol.

Explanation:
The correct option for the preparation of alcohols from haloalkanes is option B, which involves heating with aqueous NaOH (sodium hydroxide). This method is known as the alkaline hydrolysis of haloalkanes.

Alkaline hydrolysis of haloalkanes:
The alkaline hydrolysis of haloalkanes involves the reaction of a haloalkane with a strong base, such as sodium hydroxide (NaOH), in aqueous solution. The reaction proceeds through a nucleophilic substitution mechanism.

Steps involved:
1. Nucleophilic attack: The hydroxide ion (OH-) from the sodium hydroxide acts as a nucleophile and attacks the carbon atom bonded to the halogen in the haloalkane.
2. Formation of an intermediate: The nucleophilic attack displaces the halogen atom, resulting in the formation of an alkoxide ion (RO-) intermediate.
3. Proton transfer: A water molecule present in the aqueous solution donates a proton to the alkoxide ion, forming an alcohol molecule.
4. Formation of a sodium halide salt: The halogen atom reacts with sodium hydroxide to form a sodium halide salt, which remains dissolved in the aqueous solution.

Example:
Let's consider the reaction between chloromethane (CH3Cl) and sodium hydroxide (NaOH) to form methanol (CH3OH).

CH3Cl + NaOH → CH3OH + NaCl

In this reaction, the chlorine atom in chloromethane is replaced by a hydroxyl group from sodium hydroxide, resulting in the formation of methanol.

Conclusion:
Alcohols can be prepared from haloalkanes by heating them with aqueous sodium hydroxide. This method, known as alkaline hydrolysis, involves the nucleophilic substitution of the halogen atom by a hydroxyl group. It is an important process used in organic chemistry to synthesize alcohols from haloalkanes.