Which one among the following is the primary commercial use of Amines ?

Correct — B, (b) Synthesis of medicines and fibres. Both halves of that option are genuine large-scale uses of amines, and no other option names one.

MEDICINES. Amines are derivatives of ammonia in which one, two or three hydrogens have been replaced by carbon groups, and the resulting basic nitrogen is one of the commonest features in drug molecules. Because a basic nitrogen can be turned into a salt, it also solves a practical problem — most drugs are dispensed as hydrochlorides or similar salts precisely to make them soluble and stable. Whole families of medicines are amines or are built from them: the sulpha drugs from aromatic amines, adrenaline and the other catecholamines, antihistamines, local anaesthetics, and the plant alkaloids such as morphine and quinine, which are natural amines.

FIBRES. Nylon-6,6, the classic synthetic fibre, is made by condensing HEXAMETHYLENEDIAMINE — a diamine — with adipic acid; the amide links that give the polymer its name are formed from that amine group. Aramid fibres are made from aromatic diamines. The same chemistry supports polyurethanes and a very large dyestuff industry, where aromatic amines are diazotised to make azo dyes for exactly these fibres.

So the answer follows from what an amine IS: a compound with a reactive, basic nitrogen, which makes it a building block. Amines are valuable less as end products than as intermediates from which drugs, polymers and dyes are assembled.

One link ties the two halves of the keyed option together. The reaction that joins an amine to an acid group gives an AMIDE, and that single bond is what builds both products named: the amide links of nylon are formed from a diamine and a diacid, and amide bonds are among the commonest connections in drug molecules. So 'medicines and fibres' is not a pairing of two unrelated industries but two applications of the same reaction.

Why the others are wrong

• (a)Development of explosives — There is a real connection here, which is worth stating rather than denying: RDX is a nitramine made from hexamine, and several explosives are nitrogen compounds derived from amines. But the classic explosives are NITRO compounds — trinitrotoluene, nitroglycerine, picric acid — made by nitrating hydrocarbons or alcohols, and explosives manufacture is a small trade beside pharmaceuticals, polymers and dyes. The question asks for the primary commercial use, and by any measure of tonnage or value that is not this.
• (c)Development of batteries — Battery chemistry is built on metals, metal oxides and electrolyte salts — lead and lead dioxide in the lead-acid cell, lithium compounds and graphite in lithium-ion cells. Organic amines appear at most as minor electrolyte additives. Nothing about the amine functional group suits it to storing charge, and no major battery type depends on amines.
• (d)Stem cell therapy — A biological technique rather than a use of a chemical class, and it belongs to a different subject altogether. It is included as an option that sounds current, and it can be eliminated without any knowledge of amines: stem cell therapy is defined by the cells used, not by a reagent, so no class of organic compound could be described as having it as a primary commercial use.

Amines are ammonia with its hydrogens replaced by alkyl or aryl groups — primary (one substituent), secondary (two) or tertiary (three), with quaternary ammonium salts as a fourth category carrying a permanent positive charge. The lone pair on nitrogen makes them basic and nucleophilic, so they form salts with acids and react readily to build larger molecules: with acid derivatives to give amides, with aldehydes and ketones to give imines, and, in the case of aromatic amines, with nitrous acid to give diazonium salts, which is the gateway to azo dyes. That reactivity explains their industrial role as intermediates. Aniline is the archetypal aromatic amine and the ancestor of the synthetic dye industry; the lower aliphatic amines are recognisable by their fishy smell, and the decomposition products of fish are in fact amines.

Key facts

• Amines are derivatives of ammonia; they are classified primary, secondary or tertiary by the number of carbon groups on nitrogen.
• The nitrogen lone pair makes amines basic, so they form salts with acids — the form in which many drugs are dispensed.
• A very large proportion of pharmaceuticals contain an amine group, including sulpha drugs, antihistamines and local anaesthetics.
• Alkaloids such as morphine, quinine, nicotine and caffeine are naturally occurring amines.
• Nylon-6,6 is made from hexamethylenediamine and adipic acid; aramid fibres are made from aromatic diamines.
• Aromatic amines are diazotised to make azo dyes, the largest class of synthetic dyes.
• Amines are also used in polyurethanes, rubber processing chemicals, surfactants and in scrubbing carbon dioxide from gas streams.
• Aniline is the simplest aromatic amine and the historical starting point of the synthetic dye industry.

Common traps

• Associating nitrogen compounds with explosives as a reflex; the explosives of commerce are mostly nitro compounds.
• Looking for the use of a class of compounds as an end product when its value lies in being an intermediate.
• Assuming the most modern-sounding option is the intended one.
• Forgetting that fibres such as nylon are made from amines, which is half of what makes the keyed option right.

• practice — not a real PYQ

  Nylon-6,6 is produced by the condensation of adipic acid with which one among the following ?

  • (a)Ethylene glycol
  • (b)Hexamethylenediamine
  • (c)Phenol
  • (d)Vinyl chloride

  Answer(b) Hexamethylenediamine

• practice — not a real PYQ

  Azo dyes are manufactured from aromatic amines through which one among the following reactions ?

  • (a)Saponification
  • (b)Diazotisation followed by coupling
  • (c)Hydrogenation
  • (d)Polymerisation of the amine

  Answer(b) Diazotisation followed by coupling