Question

Devise a synthesis of "Diamine Green B" based on nitrobenzene, aniline, phenol, and H-acid.

Short answer

To synthesize Diamine Green B from nitrobenzene, aniline, phenol, and H-acid, follow these steps: 1. Convert nitrobenzene to m-phenylenediamine through a reduction reaction followed by ammonolysis. 2. Synthesize H-acid from aniline and phenol by sulfonating aniline, oxidizing phenol, and reacting the resulting p-anilinesulfonic acid with 1,4-naphthoquinone. 3. Couple m-phenylenediamine with H-acid in a weak alkaline solution to form Diamine Green B. These three synthesis steps allow for the successful production of Diamine Green B using the given starting materials.

Step-by-step solution

Synthesize m-Phenylenediamine from Nitrobenzene and Aniline

To begin the synthesis, first convert nitrobenzene into m-phenylenediamine. This can be done through a reduction reaction followed by an ammonolysis reaction. 1. Reduction of nitrobenzene to aniline: Reduce nitrobenzene (\(C_6 H_5 NO_2\)) to aniline (\(C_6 H_5 NH_2\)) by using a reducing agent like tin (Sn) and hydrochloric acid (HCl). This process usually involves boiling the reaction mixture for several hours. The reaction is: \[ C_6 H_5 NO_2 + 3Sn/HCl ⟶ C_6 H_5 NH_2 + 3SnCl_2 + H_2 O\] 2. Ammonolysis of aniline to form m-Phenylenediamine: In a subsequent step, react the aniline with ammonia (\(NH_3\)) under pressure in the presence of a catalyst like copper chromite (CuCrO_4). Then, separate m-phenylenediamine by fractional crystallization. The overall reaction is: \[ 2 C_6 H_5 NH_2 + NH_3 ⟶ NH_2 - C_6 H_4 - NH_2 \] Now we have m-phenylenediamine as an intermediate product.

Synthesize H-acid from Aniline and Phenol

Next, we need to synthesize H-acid, which is 8-amino-1-naphthol-3,6-disulfonic acid. To do this, we'll need to convert aniline and phenol into intermediate products and then react them together. 1. Sulfonate aniline to form p-anilinesulfonic acid: React aniline (\(C_6 H_5 NH_2\)) with concentrated sulfuric acid (H2SO4) to introduce a sulfonate group (\(-SO_3 H\)) on the para-position. The reaction is: \[ C_6 H_5 NH_2 + H_2 SO_4 ⟶ C_6 H_4 (NH_2)(SO_3 H) + H_2 O\] 2. Oxidize phenol to form 1,4-naphthoquinone: React phenol (\(C_6 H_5 OH\)) with an oxidizing agent like chromium trioxide (CrO3) to transform it into 1,4-naphthoquinone. The reaction is: \[C_6 H_5 OH + 2CrO_3 ⟶ C_{10}H_6 O_2 + 2CrO_2\] 3. React p-anilinesulfonic acid with 1,4-naphthoquinone to form H-acid: In a suitable solvent like concentrated hydrochloric acid (HCl), mix p-anilinesulfonic acid and 1,4-naphthoquinone in a 1:1 stoichiometric ratio and react them over a few hours. This forms H-acid, 8-amino-1-naphthol-3,6-disulfonic acid: \[ C_6 H_4 (NH_2)(SO_3 H) + C_{10}H_6 O_2 ⟶ H-Acid\] Now we have H-acid as an intermediate product.

Couple m-Phenylenediamine with H-acid to form Diamine Green B

In this step, couple m-phenylenediamine with H-acid to form Diamine Green B. React them in a weak alkaline solution, such as sodium carbonate (Na2CO3), at room temperature under stirring: \[NH_2 - C_6 H_4 - NH_2 + H-Acid ⟶ Diamine Green B\] After this coupling reaction, a green precipitate is formed. Separate this product by filtration and dry it to obtain the Diamine Green B dye as the final product. Now we have successfully synthesized Diamine Green B using the given starting materials nitrobenzene, aniline, phenol, and H-acid in three synthesis steps.

Key concepts

Reduction Reaction

In organic synthesis, a reduction reaction is a chemical transformation where a molecule gains electrons. This often results in the decrease of oxygen content or increase of hydrogen content in the molecule. In the synthesis of organic compounds, these reactions are crucial as they can convert a functional group into a less oxidized form, making them key in transforming raw materials into more reactive intermediates.
In the provided exercise, nitrobenzene undergoes a reduction reaction to form aniline. The transformation reduces the nitro group ( NO_2) to an amino group ( NH_2). This particular reaction often uses tin (Sn) and hydrochloric acid (HCl) as reducing agents.

• Reduction of nitrobenzene: This chemical process uses Sn/HCl as the reducing system.
• Resulting compound: Aniline ( C_6H_5 NH_2).
• Typical conditions: Prolonged heating, often under reflux.

By fundamentally altering nitrobenzene's structure, reduction reactions set the stage for further transformations in the synthetic pathway.

Ammonolysis

Ammonolysis is a type of substitution reaction that involves the treatment of a compound with ammonia ( NH_3), commonly resulting in the replacement of a halogen group with an amino ( NH_2) group. In the broader context of organic synthesis, ammonolysis provides a method to introduce nitrogen into a molecular framework.
Within the context of synthesizing m-phenylenediamine, the aniline produced from reduction is further reacted with ammonia under specific conditions.

• Necessary conditions: High pressure and the presence of a catalyst like copper chromite.
• Outcome: Conversion of aniline to m-phenylenediamine ( NH_2 - C_6H_4 - NH_2).

Ammonolysis thus serves as a key intermediate step in the construction of more complex amine structures in organic compounds.

Sulfonation

Sulfonation is a chemical reaction that introduces a sulfonic acid group ( SO_3H) into a molecule. This reaction significantly alters the physical and chemical properties of the target compound. Often employed to enhance solubility or reactivity, sulfonation is a key tool in the functionalization of aromatic compounds.
In organic synthesis, particularly in the given solution, aniline is subjected to sulfonation to form p-anilinesulfonic acid.

• Reactant: Aniline ( C_6H_5 NH_2).
• Reagent: Concentrated sulfuric acid ( H_2SO_4).
• Resulting product: p-Anilinesulfonic acid ( C_6H_4 (NH_2)(SO_3H)).

This transformation introduces the necessary sulfonic acid group, paving the way for further synthesis steps such as linking or coupling with other reaction intermediates.

Oxidation Reaction

Oxidation reactions involve the increase of the oxidation state of a molecule, generally by adding oxygen or removing hydrogen. These reactions are foundational in organic chemistry for constructing complex molecular architectures.
In the synthesis process discussed, phenol undergoes an oxidation reaction to become 1,4-naphthoquinone. This conversion is facilitated by using an effective oxidizing agent, like chromium trioxide ( CrO_3).

• Starting material: Phenol ( C_6H_5 OH).
• Oxidizing agent: Chromium trioxide.
• Product: 1,4-naphthoquinone ( C_{10}H_6O_2).

Such oxidation steps are vital as they create essential intermediates with specific functional groups necessary for the subsequent synthesis stages.

Coupling Reaction

Coupling reactions are chemical processes that join two molecules to form a single, more complex one. Common in organic synthesis, they are used to create larger, multifunctional compounds, essential for producing advanced materials and dyes.
In the exercise provided, a coupling reaction is used to synthesize Diamine Green B by combining m-phenylenediamine and H-acid.

• Reagents: m-Phenylenediamine and H-acid.
• Reaction conditions: Conducted in a weakly alkaline solution.
• Final product: Diamine Green B.

This reaction underpins the synthetic strategy, enabling the construction of the desired dye from the available intermediates and raw materials.