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Anilines are chemical compounds that belong to the group of organic compounds known as aminobenzene or phenylamine in organic chemistry. Have you ever wondered what makes the blue pants you wear so blue? Yes, aniline, which is also utilized as a dyeing chemical in the textile industry, is most likely to be responsible for this colour. These chemicals are recognized to be hazardous and to belong to the aromatic amines class. These are recognized to possess all the features of an aromatic compound and are employed in a wide range of industrial applications.
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Key Terms: Aniline, Boiling temperature, Flammability, Amines, Amino group, Aromatic chemicals, Vapours, Water, Celsius, Air
What is Aniline?
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Aniline is a viscous yellowish to brownish liquid with a musty, fishy odour with -6 degrees Celsius melting point and 184 degrees Celsius boiling temperature; It is insoluble in water and slightly denser than water. Vapours have a higher density than air. A low aniline point indicates a low diesel index since aniline is an aromatic molecule that quickly interacts with other aromatic chemicals. High aniline point indicates that the chemical is highly paraffinic and has high flammability.
Aniline
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| Class 12 Chemistry Related Concepts | ||
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| Etard reaction | Williamson Ether Synthesis | Electrophilic Aromatic Substitution |
| Ester Hydrolysis | Reimer Tiemann Reaction | Esterification |
Structure of Aniline
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In its chemical formula of C6H7N or C6H5NH2, aniline, also known as aminobenzene or phenylamine, has 6 carbon (C) atoms, 7 hydrogen (H) atoms, and 1 nitrogen (N) atom. Because aniline contains an amino group, it is also an amine, and hence is categorized as an aromatic amine.
Structure of Aniline
The formula for these compounds is C6H5NH2, with the phenyl group (C6H5) linked to the amino group (NH2) as indicated.
It is a chemical compound that is combustible and has a foul odour. The chemical is water-soluble. It can also range in colour from white to light brown.
Physical Properties Anilines
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Let's have a look at some of the physical features of anilines, which are listed below.
- Aniline has a boiling temperature of 184.13 °C and a melting point of 6.3 °C.
- Aniline is a chemical molecule that is marginally soluble in water and often easily soluble in substances such as alcohol and ether.
- When exposed to light and air, this organic molecule darkens.
Powdered Aniline
- It's a weak base that tends to generate the anilinium ion C6H5N3+ when it combines with strong acids.
- It is poisonous when inhaled through the air or absorbed through the skin because it produces nitrogen oxides, which are damaging to both the human body and the environment.
Aniline- Reactions
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Let's look at some of the reactions that anilines and aniline compounds show.
Oxidation Reaction: Aniline compounds' oxidation reactions usually result in the creation of carbon-nitrogen bonds.
Oxidation Reaction
Basicity: Anilines are weaker bases, and when they react with stronger acids, they produce anilinium ions.
Acylation: Anilines tend to react rapidly with carboxylic acids and create Amide during the acylation reaction.
Acylation
Wohl-Aue Reaction: In the presence of an alkali base, the Wohl–Aue reaction results in the reaction of phenazine from an aromatic nitro compound and an aniline. The reaction of nitrobenzene with aniline is an example.
Wohl-Aue Reaction
Diazotisation: Diazonium salts are formed when aniline and its ring-substituted derivatives combine with nitrous acid. Sandmeyer reactions can convert the amine group to -OH, -CN, or a halide via these intermediates. In a process known as coupling, this diazonium salt can be combined with NaNO2 and phenol to form benzene azo phenol, a colour.
Diazotisation
Diazotization is the reaction of turning a primary aromatic amine into a diazonium salt. The principal aromatic amine interacts with sodium nitrile and 2 moles of HCl to generate benzene diazonium salt as the major product, as well as water and sodium chloride, in this reaction is known as Ice cold mixture because the temperature used to be 0.5 °C.
Alkylation, hydrogenation, and other aniline reactions are among them.
Uses of Aniline
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Anilines are used in a variety of scientific and common applications, as seen below:
- Anilines are used in the rubber industry to make rubber chemicals and goods including automobile tyres, balloons, and gloves, among other things.
- It is used as a colouring agent in the production of clothing such as jeans and other similar items.
- It is used to make medications like paracetamol, Tylenol, and acetaminophen.
- In the agricultural industry, it is employed as a pesticide and fungicide.
- It is used in the production of polyurethane, which is then used in the production of plastics.
Things to Remember
- Anilines are chemical compounds that belong to the group of organic compounds known as aminobenzene or phenylamine in organic chemistry.
- In its chemical formula of C6H7N or C6H5NH2, aniline, also known as aminobenzene or phenylamine, has 6 carbon (C) atoms, 7 hydrogen (H) atoms, and 1 nitrogen (N) atom.
- Because aniline contains an amino group, it is also an amine, and hence is categorized as an aromatic amine.
- Aniline is a viscous yellowish to brownish liquid with a musty, fishy odour. -6 degrees Celsius melting point; 184 degrees Celsius boiling temperature; 158 degrees Fahrenheit flashpoint Insoluble in water and slightly denser than water. Vapours have a higher density than air.
- Diazotization is the reaction of turning a primary aromatic amine into a diazonium salt. The principal aromatic amine interacts with sodium nitrite and 2 moles of HCl to generate benzene diazonium salt as the major product, as well as water and sodium chloride, in this reaction is known as Ice cold mixture because the temperature used to be 0.5 °C.
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Sample Questions
Ques. What Makes Aniline a Weak Base? (3 marks)
Ans. Because the lone pair over the nitrogen atom in the NH2 group is in conjugation with the -electrons in the benzene ring, aniline is a weaker base. It is not readily available for donation because of this. A weaker base donates its lone electron pair more frequently. It's a weaker base since the pi-electrons aren't easily available for donation from the benzene ring.
The inductive action of the electronegative sp2 carbon atom, as well as resonance effects caused by the electron lone pair of nitrogen being partially delocalized into the pi system of a benzene ring, contribute to anilines' lower basicity.
Ques. Which of the following chemicals, aniline, phthalimide, and ethanamine, will be in what order? (3 marks)
Ans. The most basic of the three is ethanamine, which is a primary aliphatic amine. Aniline is also primary, but it contains an sp2-carbon at the alpha position. This acts as an electron-withdrawing substituent, reducing the availability of the lone pair and hence lowering the basicity. Furthermore, the basicity will be reduced due to resonance effects from the benzene ring.
The weakest base is phthalimide. Next to its nitrogen, an imide has two electron-withdrawing carbonyls. One carbonyl (as in amides) is already enough to reduce basicity by a substantial proportion; adding two carbonyls will merely increase the effect. The hydrogen in phthalimide is rather acidic and can be easily deprotonated.
Ques. O-hydroxyaniline is a stronger base than aniline in what way? (2 marks)
Ans. The amount of time the lone pair of electrons spend on nitrogen determines how basic the nitrogen is. The lone pair is delocalized into the ring at least a portion of the time. A hydroxyl group, on the other hand, is an activator that drives electrons into the ring. With another activator in the proper location (ortho or para to the NH2), electrons will be sent back to the nitrogen, making the nitrogen more basic.
Ques. When brominating aniline, why is glacial acetic acid used? (3 marks)
Ans. As we know, the bromine molecule is a nonpolar molecule that will do nothing if it is treated directly with aniline, and the products will be the same as the reactants.
The purpose of acetic acid is to polarize the bromine molecule into bromine atoms with a partial negative and positive charge, followed by the production of +ve and -ve bromine atoms.
After then, electrophilic substitution occurs, meaning one electrophile displaces the other, in this case, the hydrogen ion. As a result, aniline undergoes bromination.
Ques. Is aniline more prone to meta nitration than ethyl benzoate? (3 marks)
Ans. That group in aniline is -NH2, which is o,p-directing, and activating. As a result, new aromatic electrophilic substitution groups will primarily occupy the o- and p-positions.
The ethoxycarbonyl (ester) group in ethyl benzoate is m-directing (and deactivating). As a result, introducing additional groups in aniline will be more challenging, and they will occupy m-positions relative to the ester.
Ques. When nitrobenzene is reduced by LiAlH4, do you get azobenzene or aniline? (3 marks)
Ans. When nitrobenzene is reduced by LiAlH4, azobenzene is produced.
It belongs to a well-known family of aromatic azo compounds as a parent chemical. The compounds are usually not thermally stable, but they have a bright color and are utilized as light-duty dyes (or as pH or other indicators) Some aliphatic azo compounds are chosen precisely because they are unstable and prone to fragmentation with the generation of molecular nitrogen and free radicals.
Ques. How would we get picric acid if we started with aniline? (3 marks)
Ans. By adding NaNO2 and diluted HCl to the aniline, you can convert it to phenol while keeping the temperature above 10 degrees Celsius. Because the benzene ring already has a lot of electrons and is activated by the OH group, nitration may be done by simply adding concentrated HNO3 and the NO2 groups will be substituted on ortho, para, and meta locations because phenol is an ortho para director.
Ques. Between methylamine, ethylamine, and aniline, which is the stronger base? (3 marks)
Ans. Methyl and ethyl are +I groups, meaning they give electrons, but the phenyl group of aniline is a -I group, meaning it takes electrons away.
+I group boosts the electron density on nitrogen and makes lone pair donation easier, whereas -I groups do the opposite.
As a result, the basicity order
Ethylamine > methylamine > aniline.
Ques. What is the best way to make nitrobenzene from aniline? Why can't we oxidize it directly? (3 marks)
Ans. The nitration of benzene with a mixture of concentrated sulfuric acid, water, and nitric acid produces nitrobenzene. This mixture is also known as "mixed acid." Because of the exothermicity of the reaction (ΔH = 117 kJ/mol), the manufacture of nitrobenzene is one of the riskiest operations in the chemical industry.
Ques. Why does pyridine have lower basicity than ethylamine? (3 marks)
Ans. The ability to give electrons is a basic character.
The electrons on nitrogen that are present as a lone pair are delocalized (engaged in resonance) in pyridine, making them unavailable for donation.
The lone pair of electrons on nitrogen is present in ethylamine. They're simple to donate. Furthermore, the +I-effect of the ethyl group increases electron density at nitrogen (Since the alkyl group is electron-donating, it pushes electron density towards nitrogen). As a result, the electrons on nitrogen can be easily transferred, making ethylamine more basic than pyridine.
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