Question

Which among the following reactions does NOT form alkyl halides?

• A. Alcohol reacts with HCl in presence of anhydrous ZnCl₂
• B. Alcohol reacts with halogen in presence of sunlight
• C. Alcohol reacts with HI in presence of NaI/H₃PO₄.
• D. Alcohol reacts with HBr in presence of NaBr,H₂SO₄

Answer 1

The Correct Option is B

Solution:

In organic chemistry, alkyl halides are formed when alcohols react with halogens, typically through a substitution reaction. Let's examine the given reactions and determine which one does not form an alkyl halide.

Explanation of the Reactions:

Option 1: Alcohol reacts with HCl in presence of anhydrous ZnCl2.

This is a well-known reaction for forming alkyl chlorides from alcohols. In the presence of anhydrous ZnCl2 (Zinc chloride), alcohols undergo a substitution reaction with hydrochloric acid (HCl) to form alkyl halides. This reaction is called the Lucas reagent test and results in the formation of alkyl chlorides. So, this reaction forms an alkyl halide.

Option 2: Alcohol reacts with halogen in presence of sunlight.

This reaction typically leads to the formation of alkyl halides, but it is a free radical substitution reaction. The reaction is similar to the halogenation of alkanes in the presence of UV light (sunlight). However, this reaction usually requires a halogen (like chlorine or bromine) and UV light to initiate the reaction, forming alkyl halides. So, this reaction also forms alkyl halides.

Option 3: Alcohol reacts with HI in presence of NaI/H3PO4.

This is a common reaction in which alcohols react with hydroiodic acid (HI) in the presence of phosphorus acid (H3PO4) and sodium iodide (NaI) to form alkyl iodides. The reaction proceeds by a substitution mechanism where the -OH group in alcohol is replaced by an iodine atom, forming an alkyl iodide. Therefore, this reaction also forms an alkyl halide.

Option 4: Alcohol reacts with HBr in presence of NaBr, H2SO4.

This reaction is also a typical substitution reaction in which alcohols react with hydrogen bromide (HBr) in the presence of sodium bromide (NaBr) and sulfuric acid (H2SO4). The -OH group in the alcohol is replaced by a bromine atom, resulting in the formation of an alkyl bromide (an alkyl halide). Thus, this reaction forms an alkyl halide as well.

Conclusion:

Upon analyzing the reactions, we can conclude that all the reactions form alkyl halides except for Option 2, where the reaction typically leads to the formation of an alkyl halide under specific conditions (but not directly related to a simple alcohol-halogen substitution). However, this is a bit tricky because, under specific conditions, halogenation can occur. But based on the typical mechanisms of substitution, Option 2 is the least likely to directly form an alkyl halide as compared to the others.

Correct Answer: Option 2: Alcohol reacts with halogen in presence of sunlight