Question

Cadaverine \((1,5\) -diaminopentane) and putrescine (1,4-diaminobutane) are two compounds that are formed by bacterial action and are responsible for the odor of rotting flesh. Draw their structures. Suggest a series of reactions to synthesize putrescine from 1,2 -dibromoethane and any inorganic reagents.

Short answer

Draw cadaverine (NH_2-(CH_2)_5-NH_2) and putrescine (NH_2-(CH_2)_4-NH_2). Synthesize putrescine by reacting 1,2-dibromoethane with NH_3 to form ethylenediamine, then perform a Wurtz reaction with 1,2-dibromoethane, and finally displace bromines with NH_3 to get putrescine.

Step-by-step solution

Drawing the Structure of Cadaverine

Cadaverine, also known as 1,5-diaminopentane, is a molecule with a five-carbon chain and amino groups \(-NH_2\) attached to the two terminal carbon atoms. The structure can be represented as: \ NH_2-CH_2-CH_2-CH_2-CH_2-CH_2-NH_2 \.

Drawing the Structure of Putrescine

Putrescine, also known as 1,4-diaminobutane, has a four-carbon chain with amino groups \(-NH_2\) attached to the two terminal carbon atoms. The structure can be represented as: \ NH_2-CH_2-CH_2-CH_2-CH_2-NH_2 \.

First Reaction - Formation of Ethylenediamine

To synthesize putrescine, first react 1,2-dibromoethane with ammonia (NH_3) in the presence of a solvent like ethanol to form ethylenediamine (NH_2-CH_2-CH_2-NH_2). The reaction mechanism involves the substitution of bromine atoms with amino groups.

Second Reaction - Formation of 1,4-dibromobutane

Next, perform a Wurtz reaction with ethylenediamine and 1,2-dibromoethane to form 1,4-dibromobutane. This step involves coupling the two ethylene units while introducing bromine atoms at the opposite ends of the chain.

Final Reaction - Formation of Putrescine

Finally, treat 1,4-dibromobutane with excess ammonia (NH_3) to displace the bromine atoms and form putrescine (NH_2-CH_2-CH_2-CH_2-CH_2-NH_2). The bromine atoms are substituted by primary amino groups.

Key concepts

chemical structure drawing

Understanding the chemical structure of compounds is essential in organic chemistry. It helps in visualizing the spatial arrangement of atoms and predicting reactivity.

In the given exercise, we were asked to draw the structures of cadaverine and putrescine. These molecules belong to a type of organic compound known as diamines, which contain two amino groups \((−NH_2)\).

Cadaverine (1,5-diaminopentane) consists of a five-carbon chain with amino groups attached to the first and fifth carbon atoms. Its structure can be simplified as:
\[ NH_2−CH_2−CH_2−CH_2−CH_2−CH_2−NH_2 \]

On the other hand, putrescine (1,4-diaminobutane) has a four-carbon chain with amino groups at the ends. Its structure is:
\[ NH_2−CH_2−CH_2−CH_2−CH_2−NH_2 \]
Chemical structure drawing is an invaluable skill as it provides a foundation for understanding more complex concepts in organic chemistry, such as reaction mechanisms and synthesis. By mastering it, students can visualize how molecules interact with each other during chemical reactions.

reaction mechanisms

Reaction mechanisms describe the step-by-step process by which reactants convert into products. They reveal the movement of electrons, showing how bonds break and form throughout a reaction.

In this exercise, the synthesis of putrescine from 1,2-dibromoethane involves a series of reaction mechanisms. Here's a detailed look into each step:

• Step 1: Formation of Ethylenediamine
  1,2-dibromoethane reacts with ammonia (NH_3) in the presence of ethanol. Ammonia acts as a nucleophile, substituting bromine atoms with amino groups, yielding ethylenediamine (NH_2-CH_2-CH_2-NH_2).
• Step 2: Formation of 1,4-dibromobutane
  Using the Wurtz reaction, ethylenediamine reacts with another 1,2-dibromoethane molecule. This coupling involves the joining of two ethylene units (from the diamine and bromomethane) while introducing bromine atoms at the ends of a four-carbon chain, yielding 1,4-dibromobutane.
• Step 3: Formation of Putrescine
  Finally, 1,4-dibromobutane reacts with excess ammonia. This reaction substitutes the bromine atoms with primary amino groups, resulting in putrescine (NH_2-CH_2-CH_2-CH_2-CH_2-NH_2).

By understanding each mechanism, students gain insight into the stepwise transformation of reactants, crucial for mastering organic synthesis.

amino compounds synthesis

Synthesizing amino compounds is a fundamental aspect of organic chemistry. These compounds have applications in pharmaceuticals, polymers, and biochemistry. The exercise showcased the synthesis of putrescine, a simple diamine, from 1,2-dibromoethane.

Key steps in amino compound synthesis often involve nucleophilic substitution reactions and coupling reactions. Here's a recap:

• Nucleophilic Substitution: Ammonia (NH_3), a strong nucleophile, replaces bromine atoms on electrophilic carbon centres, forming new C-NH2 bonds.
  This principle was used in the transformation of 1,2-dibromoethane to ethylenediamine and in the final step where 1,4-dibromobutane was converted to putrescine.
• Coupling Reactions: The Wurtz reaction is a coupling reaction that forms longer carbon chains. In our example, it allowed the combination of two ethylene units, elongating the carbon skeleton from a two-carbon to a four-carbon chain.
  This approach is common in organic synthesis to build complex molecules from simpler precursors.

Mastering these reactions enables students to design synthetic pathways for more complex amino compounds, which are essential in several biochemical applications.