THE CHEMISTRY OF SOAPS AND DETERGENTS

Soaps

The sodium and potassium salts of long chain fatty acids.

Soap molecule

Consists of a long hydrocarbon chain with a carboxylic acid on one end, which is ionic bonded to a metal ion (usually sodium or potassium).

Saponification

The process of making soap by the hydrolysis of fats and oils with alkalies.

Sodium stearate

A soap example with the chemical formula C17H35COO-Na+.

Sodium oleate

A soap example with the chemical formula C17H33COO-Na+.

Salting Out

The separation of soap and glycerol by adding solid salt or brine to the mixture and allowing it to settle.

Hot Process (Boiling process)

The saponification of fat by boiling it with sodium hydroxide solution in a large cylindrical steel vessel.

Glycerol

A by-product of saponification.

Modern Continuous Process

A faster and more economical method of saponification carried out in a closed vessel at elevated temperature and pressure.

Direct Neutralization of Fatty Acids

Soap manufacture by directly neutralizing fatty acids, using continuous methods and specific catalysts.

Neat soap

The upper layer of soap obtained after the washing operation, where additional ingredients like color and scent are added.

Ittner Process

A method of hydrolyzing fat with water under pressure and elevated temperature in the presence of lime or zinc oxide as a catalyst.

Hydrolyser

A vessel where hot water and fat are fed in for the hydrolysis process.

Hydrolysis

The process of breaking down fats into fatty acids and glycerol using hot water.

Fatty acids

The products of hydrolysis that rise to the surface and are drawn out to make soap.

Glycerol

The byproduct of hydrolysis that is removed in water.

Neutralizer

Another vessel where fatty acids are pumped to be neutralized with sodium hydroxide or sodium carbonate to form soap.

Twitchell process

A method of hydrolyzing fats using a catalyst consisting of dilute sulphuric acid and aromatic sulphonic acid.

Micelles

Soap molecules that have a long hydrocarbon part (hydrophobic) and a short ionic part containing COO-Na+ (hydrophilic).

Cleaning action of soaps

When soap molecules attach to oil or grease particles on a dirty cloth, trapping them in micelles and dispersing them in water.

Advantages of soaps

They are eco-friendly and biodegradable.

Disadvantages of soaps

They are not suitable for use in hard water and have weaker cleansing properties compared to detergents.

Detergents

Sodium salts of long chain benzene sulphuric acids that are primarily surfactants and can be easily produced from petrochemicals.

Syndets

Synthetic soap-like cleansing agents that are also referred to as detergents.

Examples of detergents

Sodium Lauryl Sulphonate and Sodium n-dodecylbenzene sulphonate.

Cleansing action of detergents

Similar to soaps, detergents form micelles and emulsify oily particles, but they can lather well even in hard water.

Manufacture of detergents

Sodium Alkyl Sulphates are produced commercially from aliphatic long-chain alcohols, while ABS (Alkyl Benzene Sulphonate) type detergents are manufactured using the Fridels Craft reaction.

Advantages of detergents

They do not decompose in acidic medium, have stronger cleansing action than soaps, are more soluble in water, and save on natural vegetable oils.

Detergents

Cleaning agents that are resistant to biological agents and not biodegradable.

Biodegradable

Capable of being broken down by biological agents.

Foams

Stable bubbles produced by detergents in rivers, posing a danger to aquatic life.

Surfactants

Chemicals used in the preparation of detergents that cause the production of stable foams.

Oxidation

The process of a substance combining with oxygen.

Organic substances

Compounds derived from living organisms.

Envelope

A protective layer formed by detergents around organic substances, inhibiting their oxidation.

Constituent

Component or ingredient.

Sodium sulphate

Substance present in detergents, making up about 20% of their composition.

Inorganic phosphates

Compounds that can complex with calcium and magnesium ions in hard water, enhancing the cleaning action of detergents.

Bleaching agent

Ingredient added to detergents, such as sodium perborate, that removes stains or whitens fabrics.

Fluorescent agent

Ingredient added to detergents that makes fabrics appear brighter under UV light.

Colouring agent

Ingredient added to detergents to give them a specific color.

Odouring agents

Ingredients added to detergents to give them a specific scent.

Soaps

Metal salts of long chain higher fatty acids, prepared from vegetable oils and animal fats.

Scum

Insoluble precipitates of calcium, magnesium, iron, etc. produced by soaps in hard water.

Detergents

Sodium salts of long chain hydrocarbons, prepared from hydrocarbons of petroleum or coal, effective in soft, hard, or salt water.

Water pollution

Contamination of water bodies by detergents.

Alkyl Benzene Sulphonate (ABS)

Common synthetic detergent made from a tetramer of propylene, nonbiodegradable.

Linear Alkyl Sulphonate (LAS)

Biodegradable detergent introduced in 1966 as a remedy for water pollution caused by ABS detergents.