Question

Propose a synthesis of 1-hexanamine from the following. (a) A bromoalkane of six carbon atoms (b) A bromoalkane of five carbon atoms

Short answer

Question: Briefly describe the synthesis of 1-hexanamine from a six-carbon bromoalkane and a five-carbon bromoalkane. Answer: In case of a six-carbon bromoalkane, 1-bromohexane can be converted to 1-hexanamine through a nucleophilic substitution with azide ion, followed by reduction using hydrogen gas and a catalyst like palladium on carbon. For a five-carbon bromoalkane, 1-bromopentane should be reacted with potassium cyanide to elongate the carbon chain, followed by hydrolysis using a strong acid and heat to form 1-hexanamide. Finally, reduction of 1-hexanamide to 1-hexanamine can be achieved using a reducing agent like lithium aluminum hydride.

Step-by-step solution

Identify the starting material

As we need to synthesize 1-hexanamine from a six-carbon bromoalkane, the starting material will be 1-bromohexane.

Convert bromoalkane to 1-hexanamine

To convert 1-bromohexane to 1-hexanamine, we will use azide ion (N3-) in a nucleophilic substitution reaction (SN2). The azide ion will attack the 1-bromohexane, replacing the bromine atom and forming hexyl azide, as shown in the reaction: \[1-bromohexane + N_{3}^{-} \rightarrow hexyl\ azide\]

Reduce hexyl azide to 1-hexanamine

Finally, we will reduce hexyl azide to 1-hexanamine using a reducing agent like hydrogen gas (H2) and a catalyst like palladium on carbon (Pd/C). The reaction can be represented as follows: \[hexyl\ azide + H_{2} \xrightarrow{Pd/C} 1-hexanamine\] Case (b): Synthesis of 1-hexanamine from a bromoalkane of five carbon atoms

Identify the starting materials

Since we need to synthesize 1-hexanamine from a five-carbon bromoalkane, the starting materials will be 1-bromopentane and potassium cyanide (KCN).

Elongate the carbon chain of 1-bromopentane

To elongate the carbon chain by adding one carbon, perform a nucleophilic substitution (SN2) reaction between 1-bromopentane and potassium cyanide (KCN) to form pentyl cyanide. The reaction is shown below: \[1-bromopentane + KCN \rightarrow pentyl\ cyanide + KBr\]

Convert pentyl cyanide to 1-hexanamide

Perform hydrolysis on pentyl cyanide using a strong acid like hydrochloric acid (HCl) and heat, resulting in the production of 1-hexanamide: \[pentyl\ cyanide + H_{2}O + HCl \xrightarrow{heat} 1-hexanamide + KCl\]

Reduce 1-hexanamide to 1-hexanamine

Finally, we will reduce 1-hexanamide to 1-hexanamine using a reducing agent like lithium aluminum hydride (LiAlH4), as shown in the following reaction: \[1-hexanamide + LiAlH_{4} \rightarrow 1-hexanamine + LiAlO + H_{2}O\]