Question

Which of the following are general methods for the preparation of 1-iodopropane? 

• A. A,B
• B. B,C
• C. C,D
• D. A,D

Hint:

For nucleophilic substitution reactions to prepare alkyl iodides, ensure the solvent (like dry acetone) and the reagents (such as sodium iodide) are suitable for the reaction.

Answer 1

The Correct Option is B

To prepare 1-iodopropane, we can follow these methods:

• Method (A): The reaction of ethene (\({CH}_2=CH_2\)) with hydrogen iodide (\({HI}\)) forms 1-iodopropane. This is an addition reaction, but it is not a typical method for preparing 1-iodopropane directly from alcohol or alkyl halides.
• Method (B): The reaction of propanol (\({CH}_2OH-CH_2-CH_3\)) with sodium iodide (\({NaI}\)) in the presence of 95% phosphoric acid (\(H_3PO_4\)) is a known method for preparing 1-iodopropane. The alcohol is first converted to the alkene, and then iodination occurs.
• Method (C): The reaction of ethyl chloride (\({CH}_3CH_2Cl\)) with sodium iodide in dry acetone is a classic example of the nucleophilic substitution (SN2) reaction, which is used to prepare 1-iodopropane. This is the correct and commonly used method.
• Method (D): The reaction of propane with iodine (\(I_2\)) in the presence of ultraviolet light (\(hv\)) leads to the formation of an iodopropane, but this process generally results in a mixture of products, including 2-iodopropane, not selectively 1-iodopropane.

Thus, the correct methods are (B) and (C).