Aspirin is obtained by acetylation of (A) Phenol (B) Salicylaldehyde (C) 2-Hydroxybenzoic acid (D) Benzoic aci

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Q. Aspirin is obtained by acetylation of (A) Phenol (B) Salicylaldehyde (C) 2-Hydroxybenzoic acid (D) Benzoic acid

CBSECBSE Class XII Board 2026MCQ· 1mImportance★★★★★

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Concept understanding — Analgesics

What Are Analgesics?

Imagine you stub your toe. Your body sends pain signals racing from the injury site to your brain, where they register as that sharp, unpleasant sensation. An analgesic is a chemical that intercepts or dampens those signals — it relieves pain without putting you to sleep. That last part is crucial: analgesics are not general anaesthetics. You stay awake and aware; the pain just fades.

The word itself comes from Greek: an- (without) + -algesia (pain). So an analgesic is literally a "pain-remover."

The Two Families: Narcotic vs. Non-Narcotic

Pain comes in different flavours, and so do the drugs that fight it. Analgesics split into two broad classes based on how they work and how strong they are.

1. Narcotic Analgesics (Opioids)

These are the heavy hitters. They bind to specific receptors in the brain and spinal cord called opioid receptors, mimicking the body's own natural painkillers (endorphins). By locking onto these receptors, they block the transmission of pain signals and also alter the emotional response to pain — you care less about it.

The classic example is morphine, extracted from the opium poppy. It is used for severe pain: post-surgery, cancer, major injuries.

Watch out

Narcotic analgesics are addictive. They produce euphoria and tolerance, meaning you need larger doses over time for the same effect. This is why they are strictly controlled substances. Never use them without a prescription.

Other members of this family: codeine, pethidine, and the semi-synthetic heroin (which is illegal and far more dangerous).

2. Non-Narcotic Analgesics

These are the everyday painkillers. They work differently — mostly by inhibiting an enzyme called cyclooxygenase (COX) . COX is needed to produce prostaglandins, chemical messengers that cause inflammation, fever, and sensitise nerve endings to pain. By blocking COX, these drugs reduce pain at its source (the injured tissue) rather than in the brain.

The classic example is aspirin (acetylsalicylic acid). It relieves mild to moderate pain (headache, toothache, muscle ache), reduces fever, and fights inflammation.

Note

Aspirin also has a blood-thinning effect (it prevents platelet aggregation), which is why low-dose aspirin is sometimes prescribed to prevent heart attacks. But this same property can cause stomach bleeding — a major side effect.

Other members: paracetamol (acetaminophen) — which is a good painkiller and fever reducer but has almost no anti-inflammatory action — and ibuprofen, which is a stronger anti-inflammatory than aspirin.

The Key Distinction at a Glance

Feature	Narcotic (e.g., Morphine)	Non-Narcotic (e.g., Aspirin)
Site of action	Brain & spinal cord (opioid receptors)	Peripheral tissues (blocks COX enzyme)
Pain severity	Severe, deep pain	Mild to moderate pain

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Aspirin (acetylsalicylic acid) is synthesized by acetylating the phenolic –OH group of salicylic acid (2-hydroxybenzoic acid) with acetic anhydride. The answer is (C).

Aspirin is one of the most widely used drugs in the world, and understanding its synthesis reveals why the starting material must have both a carboxylic acid group and a phenolic hydroxyl group in the right positions.

The acetylation reaction replaces an active hydrogen (typically on an –OH or –NH₂ group) with an acetyl group, $\ce{-COCH3}$ . When we acetylate a phenol, we convert $\ce{Ar-OH}$ into $\ce{Ar-O-CO-CH3}$ , forming an ester. The key is identifying which compound has the structural features needed to become aspirin.

Aspirin's structure is 2-acetoxybenzoic acid: a benzene ring with a carboxylic acid group at position 1 and an acetoxy ester group (from acetylation) at position 2. Working backward, the precursor must have a carboxylic acid at position 1 and a free hydroxyl group at position 2.

Let me examine each option:

Phenol ( $\ce{C6H5OH}$ ) has only a hydroxyl group attached to benzene, with no carboxylic acid. Acetylating phenol gives phenyl acetate, not aspirin.
Salicylaldehyde has an aldehyde group ( $\ce{-CHO}$ ) at position 1 and a hydroxyl at position 2. While acetylation would modify the –OH, the aldehyde is not a carboxylic acid, so this cannot yield aspirin.
2-Hydroxybenzoic acid (salicylic acid) has a carboxylic acid ( $\ce{-COOH}$ ) at position 1 and a phenolic hydroxyl ( $\ce{-OH}$ ) at position 2. When treated with acetic anhydride or acetyl chloride, the –OH undergoes acetylation:

\ce{C6H4(OH)(COOH) + (CH3CO)2O -> C6H4(OCOCH3)(COOH) + CH3COOH}

This produces acetylsalicylic acid—aspirin. …

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Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2026Set 56/1/11 markMCQ
$Q. Aspirin is obtained by acetylation of (A) Phenol (B) Salicylaldehyde (C) 2-Hydroxybenzoic acid (D) Benzoic acid$
›Reveal solutionSolution
Aspirin (acetylsalicylic acid) is synthesized by acetylating the phenolic –OH group of salicylic acid (2-hydroxybenzoic acid) with acetic anhydride. The answer is (C).

Aspirin is one of the most widely used drugs in the world, and understanding its synthesis reveals why the starting material must have both a carboxylic acid group and a phenolic hydroxyl group in the right positions.

The acetylation reaction replaces an active hydrogen (typically on an –OH or –NH₂ group) with an acetyl group, $\ce{-COCH3}$ . When we acetylate a phenol, we convert $\ce{Ar-OH}$ into $\ce{Ar-O-CO-CH3}$ , forming an ester. The key is identifying which compound has the structural features needed to become aspirin.

Aspirin's structure is 2-acetoxybenzoic acid: a benzene ring with a carboxylic acid group at position 1 and an acetoxy ester group (from acetylation) at position 2. Working backward, the precursor must have a carboxylic acid at position 1 and a free hydroxyl group at position 2.

Let me examine each option:

Phenol ( $\ce{C6H5OH}$ ) has only a hydroxyl group attached to benzene, with no carboxylic acid. Acetylating phenol gives phenyl acetate, not aspirin.

Salicylaldehyde has an aldehyde group ( $\ce{-CHO}$ ) at position 1 and a hydroxyl at position 2. While acetylation would modify the –OH, the aldehyde is not a carboxylic acid, so this cannot yield aspirin.

2-Hydroxybenzoic acid (salicylic acid) has a carboxylic acid ( $\ce{-COOH}$ ) at position 1 and a phenolic hydroxyl ( $\ce{-OH}$ ) at position 2. When treated with acetic anhydride or acetyl chloride, the –OH undergoes acetylation:

$\ce{C6H4(OH)(COOH) + (CH3CO)2O -> C6H4(OCOCH3)(COOH) + CH3COOH}$
This produces acetylsalicylic acid—aspirin. …
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CBSE 2025Set ANNUAL1 mark
$Q. Write the name of compound obtained from the acetylation of salicylic acid.$
›Reveal solutionSolution

Acetylation (esterification) of the phenolic -OH group of salicylic acid gives aspirin, a widely used analgesic-antipyretic-anti-inflammatory drug.

Salicylic acid has both a phenolic -OH and a -COOH group. Reacting it with acetic anhydride (or acetyl chloride) acetylates the phenolic -OH specifically, converting it into an acetate ester:

Salicylic acid + (CH3CO)2O -> Acetylsalicylic acid (Aspirin) + CH3COOH

…

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CBSE 2024Set ANNUAL1 markMCQ
$Q. Aspirin is :$
(a) chlorobenzoic acid
(b) acetyl salicylic acid
(c) anthranilic acid
(d) benzoyl salicylic acid
›Reveal solutionSolution

Aspirin is the trade name for acetylsalicylic acid, made by acetylating the phenolic -OH of salicylic acid with acetic anhydride; it is used as a mild analgesic, antipyretic, and anti-inflammatory drug.

Aspirin is prepared by treating salicylic acid (2-hydroxybenzoic acid) with acetic anhydride, which acetylates the phenolic hydroxyl group (converting -OH to -OCOCH $_3$ ) while leaving the carboxylic acid group untouched: $C_6H_4(OH)(COOH) + (CH_3CO)_2O \rightarrow C_6H_4(OCOCH_3)(COOH) + CH_3COOH$ The product, 2-(acetyloxy)benzoic acid, is commonly called acetylsalicylic acid or aspirin. It is used as an analgesic (pain reliever), antipyretic (fever reducer), and anti-inflammator …

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CBSE 2017Set ANNUAL1 mark
$Q. How does aspirin act as an analgesic ?$
›Reveal solutionSolution

Aspirin blocks the enzyme that makes prostaglandins, the molecules that signal pain and inflammation.

Aspirin (acetylsalicylic acid) acts as an analgesic by inhibiting the cyclooxygenase (COX) enzyme involved in the biosynthesis of prostaglandins — hormone-like substances that mediate pain, inflammation and fever at the site of tissue injury. By blocking prostaglandin synthesis, aspirin reduces the pain and inflammatory response, in addition to …

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Q.Aspirin is obtained by acetylation of (A) Phenol (B) Salicylaldehyde (C) 2-Hydroxybenzoic acid (D) Benzoic acid

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