Question

Which of the following reagents is used to prepare alkyl isocyanides from alkyl halides $(RX)$?

• A. $KCN$ (alc.)
• B. $AgCN$ (alc.)
• C. $NaCN$ (aq.)
• D. $HCN$

Hint:

Important ambident nucleophile results:

• \(KCN/NaCN \rightarrow\) Alkyl cyanide (Nitrile, \(R-CN\))
• \(AgCN \rightarrow\) Alkyl isocyanide (\(R-NC\))
• \(KNO_2 \rightarrow\) Alkyl nitrite (\(R-ONO\))
• \(AgNO_2 \rightarrow\) Nitroalkane (\(R-NO_2\))

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The cyanide ion $(CN^-)$ is an ambident nucleophile. It can attack through Carbon or Nitrogen. The reagent determines the major product.
Step 2: Detailed Explanation:
1. $KCN$ is ionic in nature. It provides free $CN^-$ ions. Attack occurs through the more stable $C-C$ bond formation, yielding alkyl cyanides (nitriles) as major products.
2. $AgCN$ is predominantly covalent. The lone pair on Nitrogen is available for nucleophilic attack. This leads to the formation of alkyl isocyanides $(R-NC)$ as the major product.
Step 3: Final Answer:
$AgCN$ (alc.) is used to prepare alkyl isocyanides.