Question

Write the mechanistic steps to show how 1,2 -diphenyldiazene oxide and 1,2 -diphenyldiazene may be formed by base-induced condensation reactions of nitrosobenzene with N-phenylazanol and benzenamine, respectively. What product would you expect to be formed from nitrosobenzene and \(\mathrm{N}\) -(4-chlorophenyl)azanol? Give your reasoning.

Short answer

The product with N-(4-chlorophenyl)azanol is 1-(4-chlorophenyl)-2-phenyldiazene oxide.

Step-by-step solution

Understanding the Reaction Components

Before starting, identify the reactants involved. The primary reactants for the condensation reactions are nitrosobenzene and either N-phenylazanol or benzenamine. Additionally, consider N-(4-chlorophenyl)azanol for the secondary question.

Formation of 1,2-diphenyldiazene oxide

When nitrosobenzene reacts with N-phenylazanol, a condensation reaction occurs. This involves nucleophilic attack by the amine nitrogen of N-phenylazanol on the nitroso group of nitrosobenzene. Following this, a dehydration step results in the formation of the N=N double bond, producing 1,2-diphenyldiazene oxide.

Formation of 1,2-diphenyldiazene

When nitrosobenzene reacts with benzenamine under basic conditions, the lone pair of electrons on the nitrogen of benzenamine attacks the nitroso group. The reaction proceeds through dehydration (loss of water) to form the azo linkage N=N, resulting in 1,2-diphenyldiazene.

Predicting the Product with N-(4-chlorophenyl)azanol

When nitrosobenzene reacts with N-(4-chlorophenyl)azanol, similar mechanistic steps are followed as in the case with N-phenylazanol. The outcome is the expected formation of a 1,2-diphenyl-diazene oxide variant with a chloro substituent: 1-(4-chlorophenyl)-2-phenyldiazene oxide. The chlorine para to the amine group does not significantly alter the mechanism but could affect the reaction rate or yields slightly due to electronic effects.

Key concepts

Condensation Reactions

Condensation reactions are a fundamental concept in organic chemistry, where two molecules combine, often resulting in the loss of a small molecule like water. These reactions are pivotal in synthesizing organic compounds that contain complex structures. In the context of organic chemistry mechanisms, they frequently involve the formation of a new bond, typically between a carbonyl or nitroso group and another molecule.

• A condensation reaction can be facilitated under various conditions, such as the presence of a base, which often helps in moving the reaction towards completion by removing the small molecule (commonly water).
• Key types of condensation reactions include aldol condensation, Claisen condensation, and in our case, the formation of azo compounds through reactions involving nitrosobenzene.
• This mechanism is essential for forming larger, more complex molecules from simpler ones, showing their significance in both synthetic and biological chemistry.

Understanding these reactions can help in synthesizing and designing new chemicals and materials with desired properties.

Nitrosobenzene

Nitrosobenzene is a critical reactant in various organic reactions due to its unique -NO group, which is capable of engaging in both electrophilic and nucleophilic reactions.

• Structurally, it consists of a benzene ring bound to a nitroso group (-NO). This group is particularly reactive due to the electron withdrawal it imposes, making the adjacent carbon atom electrophilic.
• In many organic reactions, nitrosobenzene is utilized because it can act as a powerful electrophile, allowing nucleophiles to attack and create new bonds, a feature exploited in condensation reactions.
• The polar nature of the nitroso group makes nitrosobenzene an excellent target for nucleophilic attack, leading to subsequent chemical transformations like the formation of azo compounds, as in the exercise.

These properties make nitrosobenzene a versatile and important compound in synthetic organic chemistry.

Diphenyldiazene Oxide

Diphenyldiazene oxide is one of the compounds formed through intricate organic mechanisms like condensation reactions. The formation process involves critical steps where the nitroso group participates actively in forming the N=N double bond.

• The formation of diphenyldiazene oxide from nitrosobenzene involves a nucleophilic attack, where the nucleophile targets the electrophilic nitroso group to initiate the reaction.
• The ensuing reaction progresses through a loss of water (dehydration), facilitating the alignment of atoms to form the diazene linkage between the two phenyl groups.
• As a result of these steps, diphenyldiazene oxide emerges, notable for its distinct N=O and N=N bonds, making it unique in structure and reactivity.

This compound's creation highlights the complexity and precision of organic reactions, where specific conditions and reactants come together to form a stable, yet reactive compound.

Nucleophilic Attack

Nucleophilic attack is a core concept in understanding organic reaction mechanisms and vital in condensation reactions involving nitroso compounds.

• This process involves a nucleophile, often an atom or molecule that donates an electron pair, attacking an electrophile, which accepts electron pairs. In the described reaction, the nitrogen of N-phenylazanol or benzenamine acts as the nucleophile.
• Such attacks are pivotal for breaking and forming bonds, changing molecular structures and allowing for elaborate chemical transformations.
• The success and direction of a nucleophilic attack depend on factors such as the leaving group's nature, the stability of the transition state, and the overall reaction conditions, often influenced by temperature or solvents.

Nucleophilic attacks initiate many organic reactions, including those leading to the formation of vital compounds such as diphenyldiazene oxide, underscoring their central role in organic synthesis.