Key Reactions and Uses of Chlorobenzene in Organic Chemistry
Chlorobenzene is a compound that has a chemical formula of C6H5Cl. This liquid is flammable and is also known as a common solvent. Chlorobenzene is commonly used to manufacture chemicals. The main use of this compound is done to produce commodities that include herbicides, rubber, and any other dyestuffs. It is also used as a solvent in various industrial applications and laboratories. It is nitrated to produce a mixture that includes 2-nitrochlorobenzene and 4-nitrochlorobenzene on a huge scale. Then, the mononitro chlorobenzenes are turned into 2-nitrophenol and other elements of chloride. Sometimes, many industries convert Aniline to chlorobenzene to use it as an agent for all the alkenes produced.
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How to Convert Aniline to Chlorobenzene?
The process to convert Aniline to chlorobenzene is quite challenging. You will have to use NaNO2/HCl to convert Aniline to benzene diazonium chloride. It then converts to chlorobenzene as the presence of CuCl affects the entire reaction. This type of reaction is called Sandmeyer Reaction.
The Formula For the Reaction is as follows:
C6H5NH2NaNO2/ HClC6H5N2ClCu2Cl2C6H5C
The entire process is completed in two steps. The temperature at which the reaction occurs stands at 0 degrees to 5 degrees centigrade.
When it comes to Sandmeyer Reaction, there are many types of reactions. You can react with benzene diazonium chloride with other solvents, including CuCI, CuCN, and many more. It forms chlorobenzene, benzonitrile, and many more.
How Can You Convert Benzene to Chlorobenzene?
The process of benzene to chlorobenzene conversion is pretty simple. You will first have to react to Benzene with Chlorine. However, you will have to ensure that a catalyst can replace the Hydrogen atoms with chlorine atoms. The room temperature is suitable for this type of reaction. You can take aluminium, chlorine, and iron in the form of catalysts.
However, it is not advised to take iron as a catalyst because, during the reaction, the particles get permanently altered. Iron has the ability to react with chlorine and form FeCl3 (Iron Chloride).
Also, you can take iron chloride in the form of a catalyst and make it behave like Aluminium Chloride (ALCL3). Then, chlorobenzene is formed when this type of reaction comes in contact with aluminium chloride.
The Process to Convert Chlorobenzene to Aniline
To convert Chlorobenzene to Aniline, you can prepare it commercially with the help of a catalyst, Nitrobenzene. You can also use ammonia on the produced chlorobenzene. All you have to do is reduce Nitrobenzene by carrying out a reaction in aqueous acid with the help of iron borings. As Aniline is considered a weak base, it tends to form salts when you dilute it in mineral acid.
How Can You Convert Chlorobenzene to Benzene?
You can convert chlorobenzene to benzene in three different steps altogether. You can start the reaction by reacting HNO3 with H2SO4 that will form Nitrobenzene. Then, you can reduce it by forming a reaction of Nitrobenzene and Sn+HCL, Fe+HCL, or H2/Pd to produce Aniline. After the reaction is completed, you can then add NaNO2+HCL to the reaction that will form benzene Diazonium Chloride. After that, you can react with Sandmeyer’s Reaction (CuCl) or Gatterman Reaction (Cu Powder). This will form Chlorobenzene.
How Can You Obtain Mono Chlorobenzene?
When you dissolve or suspend Aniline with cold aqueous mineral acid and treatment with sodium nitrite, then a diazonium salt comes into existence. This salt has to be treated with cuprous bromide to form mono chlorobenzene.
When you substitute chlorine at any given spot, then you will see that six carbons remain constant. Therefore, only one possible benzene is formed.
How Can You Prepare Chlorobenzene From Aniline?
You can prepare chlorobenzene from Aniline with the help of Sandmeyer Reaction. You can fit the reaction with diphenyl and extract it from chlorobenzene.
Here is a Step-By-Step Process to Prepare Chlorobenzene From Aniline:
Step 1: Sandmeyer Reaction: It is a chemical reaction that you can use to synthesize the aryl halides from the diazonium salts by using agents of copper salts and catalysts.
Step 2: You can follow a two-step reaction that includes converting benzene diazonium chloride by utilizing the Sodium Nitrate solutions and aqueous hydrochloric acid. Then, you can react to the benzene diazonium with cuprous chloride to form chlorobenzene.
FAQs on Chlorobenzene: Definition, Preparation, and Applications
1. What is chlorobenzene and what is its chemical formula?
Chlorobenzene is an aromatic organic compound and a type of aryl halide. It consists of a benzene ring where one hydrogen atom is substituted by a chlorine atom. It is a colourless, flammable liquid with a mild, almond-like odour. The chemical formula for chlorobenzene is C₆H₅Cl. It is also known by other names such as phenyl chloride or monochlorobenzene.
2. What are the main industrial methods for the preparation of chlorobenzene?
There are two primary industrial methods for preparing chlorobenzene:
- Direct Chlorination of Benzene: This is the most common method, involving the electrophilic substitution of benzene with chlorine gas in the presence of a Lewis acid catalyst like ferric chloride (FeCl₃) or aluminium chloride (AlCl₃). The reaction is typically carried out at moderate temperatures.
- Raschig-Hooker Process: This process involves two stages. First, benzene, hydrogen chloride (HCl), and air (oxygen) are passed over a copper-based catalyst at high temperatures to produce chlorobenzene and water. This method is less common today but was historically significant.
3. How is chlorobenzene prepared from aniline using the Sandmeyer reaction?
The preparation of chlorobenzene from aniline via the Sandmeyer reaction is a two-step process, crucial in laboratory synthesis:
- Step 1 (Diazotisation): Aniline is treated with a cold aqueous solution of sodium nitrite (NaNO₂) and hydrochloric acid (HCl) at 0-5°C. This reaction forms an unstable salt called benzene diazonium chloride (C₆H₅N₂⁺Cl⁻).
- Step 2 (Sandmeyer Reaction): The freshly prepared benzene diazonium chloride solution is then warmed with cuprous chloride (Cu₂Cl₂) dissolved in HCl. The diazonium group is replaced by a chlorine atom, releasing nitrogen gas and forming chlorobenzene.
4. Why is chlorobenzene less reactive towards nucleophilic substitution reactions than alkyl halides like chloromethane?
Chlorobenzene is significantly less reactive towards nucleophilic substitution due to several factors:
- Resonance Effect: The lone pairs on the chlorine atom are in conjugation with the benzene ring's pi-electrons. This delocalisation gives the C-Cl bond a partial double-bond character, making it stronger and harder to break compared to the pure single C-Cl bond in chloromethane.
- Hybridisation Difference: The carbon atom bonded to chlorine in chlorobenzene is sp² hybridised, which is more electronegative than the sp³ hybridised carbon in chloromethane. This holds the C-Cl bond more tightly.
- Instability of Phenyl Cation: If a substitution reaction were to occur via an Sₙ1 mechanism, it would require the formation of a highly unstable phenyl cation.
- Repulsion: The electron-rich benzene ring repels the incoming electron-rich nucleophile.
5. What are the primary industrial applications of chlorobenzene?
Chlorobenzene serves as a crucial intermediate and solvent in the chemical industry. Its major applications include:
- Synthesis of other chemicals: It is a primary raw material for manufacturing compounds like phenol (Dow's process), aniline, and the insecticide DDT (dichloro-diphenyl-trichloroethane), although the use of DDT is now heavily restricted.
- Solvent: It is used as a high-boiling point solvent in various industrial processes, including the manufacture of adhesives, paints, waxes, and as a degreasing agent.
- Manufacturing of Polymers: It is used in the production of certain polymers and rubber intermediates.
- Dyestuffs and Herbicides: It acts as a precursor in the synthesis of various dyes, pigments, and herbicides.
6. Why does the chlorine atom in chlorobenzene direct incoming electrophiles to the ortho and para positions?
The chlorine atom in chlorobenzene is an ortho, para-director due to the dominance of its +R (resonance) effect over its -I (inductive) effect in stabilising the carbocation intermediate. When an electrophile attacks:
- Ortho and Para Attack: The intermediate carbocation (arenium ion) has resonance structures where the positive charge is delocalised onto the chlorine atom. This extra stable resonance structure, involving the lone pair from chlorine, significantly stabilises the intermediate.
- Meta Attack: The carbocation formed from a meta attack does not have a resonance structure where the positive charge is delocalised onto the chlorine.
7. What are the key physical properties of chlorobenzene?
Chlorobenzene exhibits distinct physical properties based on its molecular structure. Key properties include:
- Appearance: It is a colourless liquid with a characteristic almond-like smell.
- Solubility: Due to its non-polar benzene ring, it is almost insoluble in water but is readily soluble in organic solvents like ether, ethanol, and benzene itself.
- Boiling Point: It has a relatively high boiling point of approximately 132°C because of its higher molecular mass and dipole-dipole interactions.
- Density: It is denser than water, with a density of about 1.11 g/cm³.
8. Is chlorobenzene activating or deactivating towards electrophilic aromatic substitution?
Chlorobenzene is a deactivating group towards electrophilic aromatic substitution. This might seem contradictory to it being an ortho, para-director. The reason is that chlorine has two competing effects:
- Inductive Effect (-I): Chlorine is highly electronegative, so it withdraws electron density from the benzene ring, making the ring less electron-rich and thus less reactive towards incoming electrophiles compared to benzene. This is the dominant deactivating effect.
- Resonance Effect (+R): The lone pairs on chlorine donate electron density to the ring, but this effect is weaker than the inductive withdrawal.
9. What are the environmental concerns associated with the use of chlorobenzene?
Chlorobenzene poses several environmental and health concerns. It is classified as a volatile organic compound (VOC) and is moderately toxic. Key issues include:
- Air Pollution: It can be released into the atmosphere from industrial processes. It breaks down in the air, but its presence contributes to air pollution.
- Water and Soil Contamination: Due to its low solubility in water and high density, it can sink in water bodies and persist in soil, potentially contaminating groundwater sources.
- Toxicity: Exposure to high levels of chlorobenzene can affect the nervous system, liver, and kidneys in humans and animals. It is harmful if inhaled, swallowed, or absorbed through the skin.
