Anilines

Anilines are an organic compound. It has a formula \(C_6H_5NH_2\) since it has 6 carbon atoms, 1 nitrogen atom and 7 hydrogen atoms. Anilines has a phenyl group attached to an amino group. Aniline is the simplest aromatic amine. Anilines are an industrially significant commodity chemical. Like other volatile amines, it has the odour of rotten fish. It ignites easily. It burns with a smoky flame characteristic of aromatic compounds.

Chemically, aniline is an electron-rich benzene derivative. As a consequence, aniline reacts rapidly in electrophilic aromatic substitution reactions. It is also prone to oxidation. Freshly purified aniline is a bit colourless oil, on exposure to air results in gradual darkening of the sample (to yellow or red) due to the formation of strongly coloured, oxidized impurities. Aniline is diazotized to give a diazonium salt. This salt then undergoes various nucleophilic substitution reactions.

Structure of Anilines

Aniline is a slightly pyramidalized molecule. It has hybridization of the nitrogen which is between \(sp_3\) and \(sp_2\). The nitrogen lone pair in the compound is in an \(sp^x\) hybrid orbital with a high p character. The amino group present in aniline is flatter in comparison with an aliphatic amine, owing to the conjugation of the lone pair with the aryl substituent.

The geometry shows a compromise between two competing factors that is stabilization of the N lone pair in an orbital with significant s character favours pyramidalization i.e., orbitals with s character are lower in energy. Delocalization of the N lone pair into the aryl ring favours planarity i.e., a lone pair in a pure p orbital gives the best overlap with the orbitals of the benzene ring pie system.

Basically, substituted anilines with electron-donating groups are pyramidalized. While those with electron-withdrawing groups are planar. In the parent aniline, the lone pair is approximately 12 per cent character. It corresponds to \(sp^{7.3}\) hybridization.

Physical Properties of Anilines

The physical properties of Anilines are-

• Aniline has a boiling of about \(184^o\)C and melting of about \(-6^o\).
• The compound is soluble in water. It is freely soluble in chemicals such as alcohol and ether.
• This compound tends to darken when it is exposed to air and light.
• It is said to be a weak base and on its reaction with strong acids, it forms anilinium ion \(-C_6H_5^- NH_3^+\).
• The compound is said to be toxic when it gets inhaled through the air or gets absorbed into the skin as it produces nitrogen oxides which are harmful to the environment.

FAQs on Anilines

Question 1: What are the common uses of anilines?

Answer: Anilines are in use in various fields of science and everyday life as given below-

• Anilines are in use in the rubber industry. It is for the processing of rubber chemicals and products. These are car tyres, balloons, gloves, etc.
• It is in use as a dyeing agent in the manufacture of clothes such as jeans, etc.
• It is employed in the production of drugs like paracetamol, Tylenol, acetaminophen.
• Anilines is in use as a pesticide and fungicides in the agricultural industry.
• It is in use in the manufacture of polyurethane which is, in turn, in use in the making of plastics.
• It is also in use at a smaller scale in the production of the intrinsically conducting polymer polyaniline.

Question 2: Name some common reactions of anilines.

Answer:

Oxidation Reaction- The oxidation reactions of anilines compounds lead to the formation of carbon-nitrogen bonds.

Basicity- Basicity is known that anilines are weak bases. In reaction with strong acid, it forms ions of anilinium.

Acylation- In an acylation reaction, anilines react readily with carboxylic acids forming amides.

Diazotization – Aniline and its ring-substituted derivatives react with nitrous acid give diazonium salts. Through these intermediates, aniline can be conveniently converted to -OH, -CN, or a halide through Sandmeyer reactions. This diazonium salt on reaction with \(NaNO_2\) and phenol to produce a dye benzeneazophenol, in a process coupling. The reaction of converting primary aromatic amine into diazonium salt is diazotisation. In this reaction, primary aromatic amine reacts with sodium nitrile and with 2 moles of HCl which ice-cold mixture because the temperature uses to be 0.5°C. It forms benzene diazonium salt as a major product with water and sodium chloride.

The other reactions include N-alkylation reaction, hydrogenation, Wohl-Aue reaction, etc.