Chemistry in the Service of Mankind

Polyethene is formed by the repeated addition of many molecules of the unsaturated monomer ethene, and nothing is lost in the process, so it is an addition polymer.

Bakelite is formed from two different monomers, phenol and formaldehyde, which join by repeated condensation between their functional groups, and small molecules like water are eliminated at every step. So it is a condensation polymer.

PVC is made of only one kind of monomer, vinyl chloride (chloroethene, \(CH_2=CHCl\)), repeated again and again, so it is a homopolymer.

Nylon-6,6 is made of two different monomers, hexane-1,6-diamine and hexanedioic acid, which alternate in the chain, so it is a copolymer.

Pests: Pests are the living organisms such as insects, weeds, herbs, fungi and rodents that are harmful to human beings, animals and crops. Examples are locusts, aphids, cockroaches, rats and weeds.

Pesticides: The chemicals used to kill, repel or control pests are called pesticides. They play an important role in agriculture and public health. Examples are DDT, BHC, malathion, parathion, zinc phosphide and ANTU.

Elastomers: Polymers that stretch easily when a force is applied and return to their original shape when the force is removed are called elastomers. Their chains are loosely coiled and flexible, with a few cross-links. Examples: natural rubber, neoprene and Buna-S.

Fibers: Polymers with strong, thread-like structure, low elasticity and great tensile strength are called fibers. Their chains are tightly packed in a crystalline arrangement, so they are stiff and long-lasting. Examples: nylon, rayon, polyester and acrylic.

Insecticides are the pesticides used to kill or control insects. They protect crops from insects and also control insect-borne diseases like malaria and dengue. Examples: DDT, BHC, malathion, parathion.

Fungicides are the pesticides used to kill or control the growth of fungi. They protect plants from diseases like mildew, rust and blight and stop spoilage of stored fruits, vegetables and grains. Examples: Bordeaux mixture (\(CuSO_4\) with lime), chloropicrin, aluminium phosphide.

Chromophore: The part of a dye molecule that is responsible for its colour is called the chromophore. It usually contains conjugated double bonds or other functional groups. Examples: the azo group \(-N=N-\), the nitro group \(-NO_2\), the carbonyl group \(-CO-\) and the p-quinoid group.

Auxochrome: A functional group that does not produce colour by itself, but when present along with a chromophore it increases the intensity of the colour or shifts it, and also helps the dye to attach to the fibre. Examples: \(-OH\), \(-NH_2\), \(-COOH\), \(-SO_3H\) and \(-NHR\).

PVC is used in plumbing pipes, cable insulation, window and door frames, flooring, raincoats, synthetic leather, IV bags and other medical equipment, packaging materials and even credit cards, because of its strength, durability and resistance to chemicals.

Mordant dyes (with a metal salt as mordant) are used for dyeing wool, cotton and nylon, and they give fast colours. The same dye gives different colours with different metal ions, so one dye can give several shades.

Herbicides kill or control unwanted plants (weeds) that harm crops. They are used in fields, gardens and lawns, to improve crop productivity and reduce the competition for nutrients, sunlight and water.

Nylon-6,6 is used to make textiles, ropes, parachutes, seat belts, carpets and mechanical parts, because of its high strength, elasticity and resistance to abrasion and heat.

Paracetamol has a hydroxyl group and an acetamido group at para positions of a benzene ring. It is an antipyretic and analgesic.

Aspirin (acetylsalicylic acid) has a carboxylic acid group and an acetoxy (ester) group at adjacent (ortho) positions. It is an analgesic, an antipyretic and an anti-inflammatory drug.

Antibiotics are chemical substances produced by microorganisms (fungi, bacteria and actinomycetes) that kill or inhibit the growth of other microorganisms in small concentrations. They treat bacterial infections. Examples: penicillin, streptomycin, chloramphenicol.

Analgesics are the drugs used to relieve pain without causing loss of consciousness. Examples: aspirin, ibuprofen, paracetamol.

Pesticides are chemicals used to kill, repel or control pests such as insects, weeds, fungi and rodents. Examples: DDT, malathion, 2,4-D, Bordeaux mixture.

Azo dyes are synthetic dyes that contain one or more azo groups, \(-N=N-\), as the chromophore, and are responsible for their bright colours. They are used in dyeing textiles, leather, food and cosmetics. Examples: p-hydroxyazobenzene, p-aminoazobenzene, methyl orange, Congo red.

Antabuse is the trade name of disulfiram, a drug used in the treatment of chronic alcoholism. It blocks the enzyme that breaks down acetaldehyde, so a person who drinks alcohol feels unpleasant effects and loses the desire to drink.

Dyes are coloured chemical substances that impart colour to materials like textiles, paper, leather and food, and stick to the material firmly. A dye has two parts, a chromophore (gives colour) and an auxochrome (deepens the colour and helps in fixing the dye). They are obtained from natural sources or made artificially.

Two natural dyes: indigo (from the plant Indigofera, blue) and turmeric (from the rhizome of the turmeric plant, yellow). Others are cochineal (from insects), henna and madder.

Narrow-spectrum antibiotics are effective against a limited range of bacteria (either gram-positive or gram-negative only). Example: penicillin (also vancomycin).

Broad-spectrum antibiotics are effective against a wide range of bacteria, both gram-positive and gram-negative. Examples: chloramphenicol and tetracycline.

Both kill or suppress the growth of microorganisms, but they differ in their application.

Sulpha drugs (sulphonamides) are synthetic drugs that contain the sulphonamide group and are used to treat bacterial infections. They were the first antibacterial drugs used before the development of penicillin. Examples: sulphanilamide, sulphadiazine and sulphaguanidine.

Drugs: A drug is a substance used for the prevention, diagnosis and treatment of disease. The World Health Organization defines a drug as any substance or product that is used or intended to be used to modify or explore physiological systems or pathological states for the benefit of the recipient. Drugs work through the chemical action of their active components on the body. Every medicine is a drug, but not every drug is a medicine.

Characteristics of an ideal drug

In short, a drug should act selectively on the target cells and should be safe.

Repeated use of drugs that cause physical or psychological dependence is called habit-forming or addictive. Such drugs include stimulants (cocaine, methamphetamine), sedatives (benzodiazepines), opioids (heroin, prescription painkillers), nicotine, alcohol and some prescription drugs. The condition is also called substance use disorder.

Signs: compulsive drug seeking, tolerance (larger doses are needed for the same effect) and withdrawal symptoms when the drug is stopped.

Causes: a complex mix of psychological, environmental and hereditary factors, like stress, peer pressure, a family history of addiction or an existing mental health condition.

Effects: chronic diseases such as liver and heart disease, brain damage, and mental health disorders like anxiety and depression. Families and communities are also affected through broken relationships, loss of money and social problems.

Education and awareness about the dangers of drugs, learning to resist peer pressure, early intervention and counselling, support from the family, school and community, support groups and medical treatment for people already addicted, and strict control on the sale of habit-forming drugs without a prescription.

Dyes are coloured substances used to colour materials like textiles, paper, leather and food. They may be natural (indigo, turmeric, cochineal, henna, madder) or synthetic (methyl orange, crystal violet, Rhodamine B). Each dye has a chromophore (the colour-giving group, e.g. \(-N=N-\), \(-NO_2\), \(-CO-\)) and an auxochrome (e.g. \(-OH\), \(-NH_2\), \(-SO_3H\)) which deepens the colour and helps in fixing it.

1. Acid dyes: Anionic dyes with azo or anthraquinone chromophores, applied in acidic medium to protein fibres such as wool, silk and nylon. Examples: Acid Orange 7, Acid Red 88, Acid Metanil Yellow.

2. Basic dyes: Cationic dyes applied in basic or neutral medium, used for acrylic fibres and also silk, wool, paper and leather. Examples: malachite green, methylene blue, crystal violet.

3. Direct dyes: Anionic dyes applied directly to cellulose fibres like cotton and rayon without a mordant, in neutral or slightly alkaline medium, with moderate fastness. Examples: Congo red, Direct Blue 1, Direct Red 28.

4. Vat dyes: Insoluble dyes that are reduced to a soluble form in an alkaline medium, applied to the fibre, and then oxidised back to the insoluble form, giving fast colours on cotton and denim. Examples: indigo, Vat Red 1, Vat Blue 1.

5. Mordant dyes: Dyes that need a mordant (a metal salt of Al, Cr, Fe, Ba) to fix onto wool, cotton and nylon. If the dye is basic an acidic mordant is used, and vice versa. Examples: alizarin, cochineal, madder.

6. Disperse dyes: Water-insoluble, non-ionic dyes applied as a fine colloidal dispersion to synthetic fibres such as polyester, nylon and acetate. Examples: Disperse Blue 1, Disperse Yellow 3, Disperse Orange 25.

Other types are reactive dyes (covalent bond with cellulose, e.g. Procion), sulphur dyes, azoic (ingrain) dyes and natural dyes.

A polymer is a large molecule (macromolecule) formed by the linking of a very large number of small repeating units called monomers. The process of linking the monomers is called polymerisation. For example, ethene (monomer) gives polyethene (polymer).

1. Homopolymers: Polymers made from only one type of monomer, \(-(A-A-A-A)_n-\). Examples: polyethene (from ethene), PVC (from vinyl chloride), Teflon (from tetrafluoroethene), polystyrene (from styrene).

2. Copolymers: Polymers made from two or more different monomers, \(-(A-B-A-B)_n-\). Examples: nylon-6,6 (hexane-1,6-diamine and adipic acid), bakelite (phenol and formaldehyde) and Buna-S (1,3-butadiene and styrene).

Apart from this, polymers are also classified by origin (natural, e.g. starch, cellulose, protein, natural rubber, and synthetic, e.g. PVC, nylon), by synthesis (addition and condensation) and by molecular force (elastomers and fibres).

A drug is any chemical substance that changes the functioning of the body or is used to modify or explore physiological systems or pathological states. Drugs include useful therapeutic substances as well as harmful ones like narcotics and poisons.

A medicine is a drug that is used in a proper (safe) dose and form for the prevention, diagnosis or treatment of a disease, and which helps the patient without serious harm.

Every medicine, like paracetamol, aspirin or penicillin, changes the body’s functioning and cures a disease, so each medicine is a drug. But substances like heroin, cocaine, nicotine and alcohol also affect the body and are drugs, but they are habit-forming and harm the body when used, so they are not medicines. Even a medicine becomes harmful in an overdose.

Hence all medicines are drugs, but all drugs are not medicines.