What are Anilines Definition Preparation Reactions and Basicity Explained
Organic chemistry is a beautiful and magical subject if you happen to understand the core of the subject. Aniline is one such interesting organic compound with versatile materials and diverse industrial applications.
This article is complied to discuss in detail the concept of Anilines. The sole aim is to make the students fall in love with the subject to an extent that scoring high marks will no longer be an unachievable task.
In this article, we shall be discussing -
Aniline - an introduction
What is Aniline?
Anilines Structure
Anilines Physical Properties
Anilines Reactions
Anilines applications
Frequently asked questions
What is Anilines?
Aniline is a type of organic base which is used in the making of several dyes, explosives, plastics, drugs, and rubber, and photographic chemicals. Anilines are the organic compounds that lie in the class of groups coming in the organic chemistry that is referred to as aminobenzene or phenylamine. These compounds are known to be toxic and to be one of the classes of the aromatic amines. They are used in a variety of industrial applications and possess all the characteristics of that of an aromatic compound. The aniline compounds are known to have the formula C6H5NH2 in which the amino group is attached to the phenyl group.
Aniline occurs in the form of a yellowish and slightly brownish oily liquid which has a fishy and a musty odour. It smells like a rotten fish. It is a chemical substance that is a flammable liquid and has a very unpleasant odour. The compound of aniline is soluble in water which is colourless to light brown. Its chemical formula is C6H5NH2 or C6H7N. Since it consists of 6 carbon atoms, 7 hydrogen atoms, and 1 nitrogen atom in its chemical formula, it is an organic compound. Today, we will learn about what is anilines, the phenylamine structure, its physical properties and uses.
Anilines Structure C6H5NH2 Structure
Given below is the aminobenzene structure.
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The structure of benzenamine has a pyramidal shaped molecule and has a nitrogen hybridization which lies in between sp3 and sp2. Due to this, the nitrogen lone pair lies in an spx hybrid orbital and has a high p character. The amino group in aniline is much flatter than that in an aliphatic amine, which is because of the conjugation of the lone pair of electrons along with the aryl substituent.
Anilines Physical Properties
Let us discuss the physical properties of anilines which are given below.
The boiling of aniline is 184.13 °C and its melting point is −6.3 °C.
The compound of aniline is slightly soluble in water and many times freely soluble in the chemicals like alcohol and ether.
This organic compound turns darker when it is exposed to light and air.
It is known to be a weak base and when it reacts with strong acids, it tends to form an anilinium ion C6H5N3+.
It is said to be toxic when it is inhaled via the air or tends to get absorbed into the skin since it produces nitrogen oxides that are harmful to the human body as well as the environment.
Anilines Reactions
Let us now take a look at some of the reactions of anilines and the aniline compounds.
Oxidation Reaction: Oxidation reactions of the anilines compounds tend to lead to the formation of the carbon-nitrogen bonds.
Basicity: Anilines are weaker bases and on reacting with stronger acids, the compounds form anilinium ions.
Acylation: In the acylation reaction, anilines tend to react readily with the carboxylic acids and form amides.
The other reactions of anilines consist of alkylation reaction, hydrogenation, Diazotization, Wohl-Aue reaction, etc.
Anilines Uses
Anilines are used in various fields of science and everyday life. Some of the uses of anilines are given below.
Anilines have their uses in the rubber industry to process the rubber chemicals and products like car tyres, gloves, balloons, etc.
It is also used as a dyeing agent for the manufacturing of clothes like jeans, etc.
It is used for the production of drugs, for example, paracetamol, acetaminophen, and Tylenol.
It is also used in the form of pesticides and fungicides when it comes to the agricultural industry.
It is also used for the manufacturing of polyurethane which is then used for making plastics.
FAQs on Anilines Chemistry Structure Properties and Reactions
1. What is aniline in chemistry?
Aniline is an aromatic amine with the molecular formula C6H5NH2, consisting of a benzene ring attached to an amino group (–NH2).
- It is also called phenylamine.
- Structure: a benzene ring directly bonded to –NH2.
- It is a colorless to slightly yellow liquid that darkens on exposure to air due to oxidation.
- Aniline is an important starting material in dyes, pharmaceuticals, and polymers.
2. What is the functional group present in anilines?
The functional group in anilines is the amino group (–NH2) attached directly to an aromatic ring.
- This makes anilines a class of aromatic amines.
- The lone pair on nitrogen interacts with the benzene ring through resonance.
- This resonance affects basicity and reactivity compared to aliphatic amines.
3. Why is aniline less basic than aliphatic amines?
Aniline is less basic than aliphatic amines because the nitrogen lone pair is delocalized into the benzene ring by resonance, making it less available to accept a proton.
- In aliphatic amines, the lone pair is localized and readily accepts H+.
- In aniline, resonance structures show the lone pair participating in the aromatic system.
- Therefore, aniline is a weak base compared to methylamine or ethylamine.
4. How is aniline prepared from nitrobenzene?
Aniline is prepared from nitrobenzene by reduction of the nitro group (–NO2) to an amino group (–NH2).
- Common reagents: Sn/HCl, Fe/HCl, or catalytic hydrogenation.
- Balanced equation (using hydrogen):
C6H5NO2(l) + 3H2(g) → C6H5NH2(l) + 2H2O(l) - This reaction is widely used in industrial aniline production.
5. How does aniline react with hydrochloric acid?
Aniline reacts with hydrochloric acid to form anilinium chloride, a salt.
- The nitrogen atom accepts a proton (H+).
- Balanced reaction:
C6H5NH2(l) + HCl(aq) → C6H5NH3+Cl−(aq) - This demonstrates the basic nature of aniline.
6. What is diazotization of aniline?
Diazotization of aniline is the reaction in which aniline forms a benzene diazonium salt when treated with nitrous acid at 0–5°C.
- Reagents: NaNO2 + HCl (to generate HNO2 in situ).
- Balanced reaction:
C6H5NH2(aq) + HNO2(aq) + HCl(aq) → C6H5N2+Cl−(aq) + 2H2O(l) - This reaction is important in the synthesis of azo dyes.
7. What are the uses of aniline?
Aniline is mainly used as a raw material in the manufacture of dyes, drugs, and polymers.
- Production of azo dyes through diazotization and coupling reactions.
- Manufacture of polyurethane foams (via methylene diphenyl diisocyanate, MDI).
- Synthesis of pharmaceuticals such as paracetamol intermediates.
- Used in rubber processing chemicals and antioxidants.
8. What is the difference between aniline and benzylamine?
The main difference is that in aniline the –NH2 group is directly attached to the benzene ring, while in benzylamine it is attached to a –CH2 group linked to the ring.
- Aniline: C6H5NH2 (aromatic amine).
- Benzylamine: C6H5CH2NH2 (aliphatic amine).
- Aniline is less basic due to resonance delocalization.
- Benzylamine behaves like a typical aliphatic amine and is more basic.
9. How does aniline undergo electrophilic substitution reactions?
Aniline undergoes electrophilic substitution mainly at the ortho and para positions because the –NH2 group is an activating, ortho/para-directing group.
- The lone pair on nitrogen increases electron density in the ring.
- Example: bromination in aqueous solution:
C6H5NH2(aq) + 3Br2(aq) → C6H2Br3NH2(s) + 3HBr(aq) - The product is 2,4,6-tribromoaniline.
10. How can you identify aniline in the laboratory?
Aniline can be identified by the formation of a stable diazonium salt followed by an azo dye in a coupling reaction.
- Treat with NaNO2 and HCl at 0–5°C to form a diazonium salt.
- Couple with alkaline β-naphthol to produce a brightly colored azo dye.
- It also gives a white precipitate of 2,4,6-tribromoaniline with bromine water.
