Question

Hydrolysis of the minor product formed from the reaction of 1-Bromo propane and ethanolic KCN given

• A. Propylamine (CH$_3$CH$_2$CH$_2$NH$_2$)
• B. Isopropylamine (CH$_3$CH(NH$_2$)CH$_3$)
• C. Propanoic acid (CH$_3$CH$_2$COOH)
• D. Isobutyric acid ((CH$_3$)$_2$CHCOOH) (Note: This is actually 2-Methylpropanoic acid. Propanoic acid family.)

Hint:

CN$^-$ is an ambident nucleophile.
With KCN (ionic), major product is nitrile (R-CN) via C-attack (S$_N$2 for primary/secondary alkyl halides).
With AgCN (covalent), major product is isonitrile (R-NC) via N-attack.
In this case (1-bromopropane + KCN), the major product is CH$_3$CH$_2$CH$_2$CN (butanenitrile). The minor product is CH$_3$CH$_2$CH$_2$NC (propyl isonitrile).
Hydrolysis of nitriles (R-CN): R-CN + 2H$_2$O $\rightarrow$ R-COOH + NH$_3$.
Hydrolysis of isonitriles (R-NC): R-NC + 2H$_2$O $\rightarrow$ R-NH$_2$ + HCOOH.
The question asks for hydrolysis of the minor product (propyl isonitrile), which yields propylamine.

Answer 1

The Correct Option is A

The reaction is between 1-bromopropane (CH$_3$CH$_2$CH$_2$Br) and ethanolic KCN. KCN provides the cyanide ion (CN$^-$), which is an ambident nucleophile. It can attack through carbon (to form nitriles R-CN) or through nitrogen (to form isonitriles R-NC). Reaction with KCN: 1-Bromopropane is a primary alkyl halide. With KCN, the primary reaction is S$_N$2 substitution. \begin{itemize} \item Major product: Attack by carbon of CN$^-$ leads to the formation of a nitrile. CH$_3$CH$_2$CH$_2$Br + KCN (ethanolic) $\rightarrow$ CH$_3$CH$_2$CH$_2$-CN (Butanenitrile) + KBr. This is the major pathway because KCN is predominantly ionic, and the C-C bond formed is stronger than the C-N bond in isonitriles. \item Minor product: Attack by nitrogen of CN$^-$ leads to the formation of an isonitrile (isocyanide). CH$_3$CH$_2$CH$_2$Br + KCN (ethanolic) $\rightarrow$ CH$_3$CH$_2$CH$_2$-NC (Propyl isonitrile or Propyl isocyanide) + KBr. This is the minor product. \end{itemize} The question asks about the hydrolysis of the *minor product*. The minor product is propyl isonitrile (CH$_3$CH$_2$CH$_2$-NC). Hydrolysis of Isonitriles (R-NC): Isonitriles are hydrolyzed to primary amines and formic acid (or formate salts depending on pH). The hydrolysis occurs in two steps typically, with the carbon of the -NC group becoming part of formic acid. R-N$\equiv$C + 2H$_2$O $\xrightarrow{\text{H}^+ \text{ or OH}^-}$ R-NH$_2$ (primary amine) + HCOOH (formic acid). In this case, R = CH$_3$CH$_2$CH$_2$- (propyl group). So, CH$_3$CH$_2$CH$_2$-NC (propyl isonitrile) on hydrolysis will give: CH$_3$CH$_2$CH$_2$-NH$_2$ (propylamine) + HCOOH (formic acid). The organic amine product is propylamine (propan-1-amine). Let's check the options: % Option (a) Propylamine (CH$_3$CH$_2$CH$_2$NH$_2$) - This matches our derived product. % Option (b) Isopropylamine (CH$_3$CH(NH$_2$)CH$_3$) - This would result if the structure was iso- or rearrangement occurred, which is not typical here. % Option (c) Propanoic acid (CH$_3$CH$_2$COOH) - This would be formed from hydrolysis of the *major* product, butanenitrile (CH$_3$CH$_2$CH$_2$CN $\xrightarrow{\text{hydrolysis}}$ CH$_3$CH$_2$CH$_2$COOH, butanoic acid, not propanoic). Complete hydrolysis of CH$_3$CH$_2$CN (propanenitrile) gives propanoic acid. % Option (d) Isobutyric acid - Not relevant. If the major product (butanenitrile, CH$_3$CH$_2$CH$_2$CN) was hydrolyzed, it would give butanoic acid (CH$_3$CH$_2$CH$_2$COOH). The question specifically asks for hydrolysis of the *minor product*. The minor product is propyl isonitrile, CH$_3$CH$_2$CH$_2$NC. Its hydrolysis gives propylamine, CH$_3$CH$_2$CH$_2$NH$_2$. So, the product is propylamine. \[ \boxed{\text{Propylamine (CH}_3\text{CH}_2\text{CH}_2\text{NH}_2\text{)}} \]