Question

What will be the major product of the reaction of 4-nitro-phthalic anhydride with n-butylamine? Explain.

Short answer

The major product of the reaction between 4-nitro-phthalic anhydride and n-butylamine is N-(n-butyl)-4-nitrophthalimide. This occurs through nucleophilic acyl substitution with n-butylamine acting as the nucleophile, attacking one of the carbonyl carbons of 4-nitro-phthalic anhydride, forming an amide bond. The presence of the nitro group reduces the nucleophilicity of the carbonyl carbon, leading to a slower reaction rate.

Step-by-step solution

Draw the structure of the reactants

First, draw the structure of 4-nitro-phthalic anhydride and n-butylamine. This will help in understanding the possible reaction pathways. 4-nitro-phthalic anhydride: \( \text{O} \\ \text{|} \\ \text{O-}\overset{ }\text{C} \overset{\text{O}}{\text{||}}\text{C}-\text{C}(=\text{O})-\text{C}-(=\text{O})-\text{C}-(=\text{O}) \\ \text{-} \\ \text{NO}_2 \) n-butylamine: \( \text{H}_2\text{N}\text{-}\text{CH}_2\text{-}\text{CH}_2\text{-}\text{CH}_2\text{-}\text{CH}_3 \)

Evaluate possible reaction pathways

Phthalic anhydride has two carbonyl groups and is known to react with nucleophiles such as amines through nucleophilic acyl substitution, where the nucleophile attacks the carbonyl carbon to form an intermediate followed by the expulsion of a leaving group. In this case, n-butylamine will act as the nucleophile, and it will attack one of the carbonyl carbons of 4-nitro-phthalic anhydride. The leaving group will be the resonance-stabilized carboxylate anion, which will promote the formation of an amide linkage.

Consider the effect of the nitro group on reactivity

The nitro group (-NO2) is a strong electron-withdrawing group, which has a significant impact on the reactivity of the molecule. The nitro group deactivates the benzene ring by pulling electron density away from the carbonyl carbon. This reduces the nucleophilicity of the carbon, making it less susceptible to nucleophilic attack. However, the reaction will still occur, albeit at a reduced rate.

Determine the major product

As the reaction involves n-butylamine attacking one of the carbonyl carbons of 4-nitro-phthalic anhydride and forming an amide bond, the major product will be N-(n-butyl)-4-nitrophthalimide. The major product has the following structure: \( \text{O} \\ \text{|} \\ \text{O-}\overset{\text{NO}_2}{\text{C}}\text{-}\text{C}(=\text{O})-\text{C}(=\\ \text{O})-\text{C}(=\text{O})-\text{NH}\text{-}\text{CH}_2\text{-}\text{CH}_2 \\ \text{-} \\ \text{CH}_2-\text{CH}_3 \) Thus, the major product of the reaction between 4-nitro-phthalic anhydride and n-butylamine is N-(n-butyl)-4-nitrophthalimide.

Key concepts

4-Nitro-phthalic Anhydride

Understanding the structure and reactivity of 4-nitro-phthalic anhydride is key to predicting its behavior in chemical reactions. This compound consists of a phthalic anhydride core, which is a cyclic dicarboxylic acid anhydride, with a nitro group (-NO₂) attached to the fourth position of the benzene ring. The presence of the nitro group, a potent electron-withdrawing substituent, plays a critical role in how this molecule interacts with other chemicals, particularly nucleophiles like amines.

The anhydride functionality in this compound is characterized by the presence of two acyl groups (carbonyl groups) connected by an oxygen atom. This structural feature makes it highly reactive towards nucleophiles that can open the anhydride ring to form new bonds. During reactions, 4-nitro-phthalic anhydride can undergo nucleophilic acyl substitution, resulting in the formation of products such as amides or esters, depending on the nucleophile.

N-Butylamine

N-butylamine is a simple linear amine, where an amino group is attached to a four-carbon (butyl) chain. Given its structure, n-butylamine is a nucleophile that has a lone pair of electrons on the nitrogen, which can be donated to electrophiles such as carbonyl carbons.

In reactions with anhydrides like 4-nitro-phthalic anhydride, n-butylamine's nucleophilic nitrogen atom can attack the electrophilic carbonyl carbon, leading to the formation of an intermediate and, ultimately, an amide bond. Due to its structure, n-butylamine can add to the steric bulk of the resulting molecule, which can influence the physical and chemical properties of the generated amide.

Amide Bond Formation

The process of amide bond formation is central to many organic synthesis reactions, especially in the formation of proteins and synthetic polymers. An amide bond, which connects a carbonyl group (C=O) with a nitrogen atom (N), is formed through a nucleophilic acyl substitution reaction.

In the context of 4-nitro-phthalic anhydride reacting with n-butylamine, the amine's nucleophilic nitrogen attacks the electrophilic carbonyl carbon of the anhydride, leading to the opening of the anhydride ring and formation of the amide bond. This reaction proceeds through a tetrahedral intermediate and ends with the expulsion of a carboxylate group. The product, N-(n-butyl)-4-nitrophthalimide, contains the newly formed amide bond, which is commonly represented as -CO-NH- in chemical structures.

Electron-Withdrawing Groups

Electron-withdrawing groups, such as the nitro group found in 4-nitro-phthalic anhydride, are substituents that pull electron density away from other parts of the molecule. These groups are highly electronegative and can affect a molecule's reactivity and stability.

The nitro group, being one of the strongest electron-withdrawing groups, makes the carbonyl carbon more positive and thus more susceptible to nucleophilic attack, albeit this can decrease the rate of the reaction due to deactivation of the aromatic ring. In the context of the reaction with n-butylamine, the electron-withdrawing effect of the nitro group not only influences the reactivity but also the orientation of the nucleophilic attack, possibly favoring the less hindered carbonyl group in the anhydride.