Drugs, Dyes, Soaps & Common Chemicals — Everyday Chemistry for UPSC

Drugs (Medicines) — Classification and Chemistry

Drugs are chemical substances that alter the body's biochemistry to produce a therapeutic effect. From a UPSC perspective, the key categories are:

Analgesics (Pain Relievers)

NSAID (Non-Steroidal Anti-Inflammatory Drugs) — aspirin and ibuprofen are NSAIDs; paracetamol is NOT an NSAID.

Antibiotics

• Penicillin — discovered by Alexander Fleming in 1928 when he noticed mould (Penicillium notatum) killing bacteria. Mass production developed by Florey and Chain during WWII (Nobel Prize 1945 to all three).
• Mechanism: inhibits bacterial cell wall synthesis (specifically transpeptidase enzymes that cross-link peptidoglycan).
• Broad spectrum antibiotics — effective against many types of bacteria (e.g., amoxicillin, tetracycline).
• Narrow spectrum — effective against specific bacteria (e.g., penicillin G against gram-positive bacteria).
• Antibiotic Resistance (AMR) — bacteria evolve resistance through mutation and horizontal gene transfer. Over-prescription and agricultural use of antibiotics accelerate AMR. The WHO Global Action Plan on AMR (2015) and India's National Action Plan on AMR (2017–21) address this. AMR is projected to cause 10 million deaths/year by 2050 if unchecked.

Antiseptics vs Disinfectants

Note: Antiseptics are safe for skin at low concentrations; disinfectants are too strong for living tissue.

Anaesthetics

• Historical: Diethyl ether and chloroform (CHCl3) were early general anaesthetics — chloroform was first used clinically in 1847.
• Modern: Halothane, isoflurane — inhalation agents; propofol — intravenous agent.
• Local anaesthetics: Lidocaine (lignocaine), novocaine — block nerve signal transmission.

Tranquillisers and Psychoactive Drugs

• Barbiturates (e.g., phenobarbital) — CNS depressants; used as sedatives and anticonvulsants; high addiction potential.
• Benzodiazepines (e.g., diazepam/Valium) — anti-anxiety; also addictive; safer than barbiturates.
• Antihistamines — block histamine receptors; used for allergies; some cause drowsiness (e.g., chlorpheniramine).

Antacids

• Neutralise excess hydrochloric acid (HCl) in the stomach.
• Sodium bicarbonate (NaHCO₃) — fast-acting but causes bloating (CO₂ released); not for chronic use.
• Magnesium hydroxide Mg(OH)₂ — "milk of magnesia"; gentle laxative effect.
• Aluminium hydroxide Al(OH)₃ — constipating; often combined with Mg(OH)₂ to balance effects.
• Reaction: Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O

Antimalarials

• Quinine — extracted from cinchona bark; used for centuries; basis of modern antimalarials.
• Chloroquine — synthetic derivative; widespread resistance has reduced its efficacy.
• Artemisinin — extracted from Artemisia annua (sweet wormwood); Tu Youyou of China won the Nobel Prize in Physiology or Medicine in 2015 for discovering artemisinin as a malaria treatment.
• Combination therapy (ACT — Artemisinin-based Combination Therapy) is now WHO's first-line treatment for Plasmodium falciparum malaria.

Dyes

Natural Dyes

Synthetic Dyes

• First synthetic dye: Mauveine (Mauve) — discovered accidentally by William Henry Perkin in 1856 while attempting to synthesise quinine. This launched the synthetic dye industry.
• Aniline dyes — derived from aniline (C₆H₅NH₂), a coal tar derivative. Perkin's mauveine was an aniline dye.
• Azo dyes — most widely used class; contain the azo group (-N=N-) linking two aromatic rings; vivid colours; used extensively in textiles and food. Some azo dyes are carcinogenic and banned (e.g., Sudan Red in food).
• Vat dyes — insoluble; must be chemically reduced to a soluble "leuco" form for application to fabric, then re-oxidised to the insoluble coloured form on the fibre. Example: indigo (hence the name — originally made in a vat with reduction). Used for denim.
• Mordant dyes — require a mordant (metal salt, typically alum — aluminium potassium sulphate) to chemically bond the dye to the fabric. Example: alizarin with alum gives red; with iron gives purple.

Food Dyes

• FSSAI regulates permitted food colours in India under the Food Safety and Standards (Food Products Standards and Food Additives) Regulations.
• Tartrazine (Yellow 5, E102) — widely used synthetic yellow dye; controversial due to alleged hyperactivity link.
• Carmine (E120) — natural red derived from cochineal insects; not vegan.
• Allura Red (E129) — synthetic red; permitted in limited quantities.

Soaps and Detergents

Saponification

Saponification is the hydrolysis of a fat or oil (triglyceride) with a strong alkali:

• Fat/Oil + NaOH → Hard soap (sodium salt of fatty acid) + Glycerol
• Fat/Oil + KOH → Soft soap (potassium salt) + Glycerol (used in shaving creams, liquid soaps)

How Soap Cleans

Soap molecules are amphiphilic — they have a hydrophobic (water-repelling) tail (long fatty acid chain) and a hydrophilic (water-attracting) head (carboxylate group –COO⁻ Na⁺).

In water, soap molecules arrange themselves into micelles — spherical structures with hydrophobic tails pointing inward (trapping grease/oil) and hydrophilic heads facing outward (interacting with water). The micelle lifts grease off surfaces and suspends it in water for rinsing.

Soap in Hard Water

Hard water contains dissolved Ca²⁺ and Mg²⁺ ions. These react with soap to form insoluble curds (scum): 2RCOONa + CaCl₂ → (RCOO)₂Ca↓ + 2NaCl

This wastes soap and leaves deposits. Synthetic detergents do not form scum in hard water — a key advantage.

Synthetic Detergents

• Sodium lauryl sulphate (SLS) — anionic detergent; most common in shampoos/toothpaste.
• Types: anionic (most common, negatively charged head), cationic (positively charged; used as fabric softeners, germicides), non-ionic (no charge; gentle; used in liquid detergents).
• Biodegradable detergents — linear chain alkyl groups are broken down by bacteria.
• Non-biodegradable detergents — branched chain structures resist bacterial breakdown; cause water body foaming and eutrophication (especially phosphate-based detergents). India and many countries now regulate or ban phosphate in detergents.

Bleaching Agents

Bleaching mechanism: Most bleaching agents work by oxidation — they break the conjugated double bond systems in chromophores (colour-producing molecules), making them colourless.

Common Lab Chemicals Reference Table

Food Preservatives

Preservatives inhibit microbial growth or chemical deterioration to extend shelf life.

FSSAI (Food Safety and Standards Authority of India) regulates permissible preservatives, additives and their maximum levels under the FSS (Food Products Standards and Food Additives) Regulations, 2011.

Additive vs Preservative: All preservatives are additives, but not all additives are preservatives. Additives include colours, flavours, emulsifiers, stabilisers etc.

Exam Strategy

• Antiseptic vs disinfectant distinction is a recurring prelims question — antiseptics on living tissue (Dettol, iodine), disinfectants on surfaces (phenol, bleach).
• Penicillin (Fleming, 1928) and Artemisinin (Tu Youyou, Nobel 2015) are frequently asked.
• Section 66A of IT Act struck down is NOT relevant here — focus on chemistry.
• Mauve/Mauveine by Perkin (1856) — first synthetic dye, from coal tar; very UPSC-relevant factoid.
• Azo dyes contain -N=N- group; know this for prelims match-the-pair questions.
• Saponification — NaOH gives hard soap, KOH gives soft soap. Soap is ineffective in hard water (scum formation) — but synthetic detergents work in hard water.
• Hydrogen peroxide as a bleaching agent is eco-friendly (decomposes to water) — useful in environment questions.
• Common chemicals table: know Plaster of Paris (CaSO₄·½H₂O), Baking Soda (NaHCO₃) vs Washing Soda (Na₂CO₃·10H₂O) — frequently confused.

Previous Year Questions (PYQs)

Prelims

• (2019) Which of the following pairs is/are correctly matched? Antiseptics used on skin / Example (tests Dettol, chloroxylenol)
• (2016) With reference to aspirin, which of the following statements is/are correct? (anti-inflammatory, antiplatelet properties tested)
• (2014) Consider the following statements about synthetic dyes... (azo dyes, first synthetic dye tested)
• (2021) Bleaching powder is a mixture of — (calcium hypochlorite and calcium chloride)
• (2020) Antibiotic resistance is a growing global concern because — (mechanism and AMR tested)

Mains

• (2018, GS3) Discuss the problem of anti-microbial resistance (AMR) in India. What steps has the government taken? (10 marks)
• (2016, GS3) Enumerate the applications of soaps and detergents and explain why synthetic detergents have replaced soaps in many applications. (10 marks)