Preparation of Detergent

Detergents are used in every domestic household, yet have you ever pondered upon the chemistry behind it? 

Though detergents contain various chemicals for each of their specific functions, its cleansing action mainly relies on the surfactants. Surfactants are generally

made up of hydrophobic (due to an alkylate chain) and hydrophilic (due to ions/polar molecules) ends, and is used to reduce the surface tension of two liquids, In simpler words, you can imagine two immiscible liquids “mixing” by dispersion with the help of surfactants. A more specific breakdown on the cleansing action of surfactants is mentioned in the last section of this article. In this section, we will be diving into the preparation of anionic detergents.

The surfactant we will be looking at is linear alkylbenzene sulphonate (LABS), a linear hydrocarbon chain with a benzene ring and a sulfonate anion attached to it. It can be made through sulfonation of the alkylbenzene by reacting fuming sulphuric acid with alkylbenzene to form alkylbenzene sulphonic acid, followed by neutralisation of the acid with the addition of sodium hydroxide. In the process of sulfonation, sulphur trioxide is the electrophile, accepting an electron pair from the double bonds in the benzene ring hence creating a bond (diagram below). Neutralisation is important to show anionic properties of the sulfonate ion and to maintain a neutral pH for stability of the detergent. 

Last but not least, the addition of builders such as phosphates and citrates could help in water softening. Taking the case of phosphates, it helps to remove calcium ions and magnesium ions in hard water by forming stable complexes with these ions. As a result detergents do not form scum when using hard water for cleaning as opposed to regular hand soaps. Multiple additives can also be added to enhance quality and to suit specific needs. Some common examples include enzymes, fragrances, preservatives, thickeners etc. 

Preparation of Soap

• Types: Anionic, Cationic, Non-ionic

• Has hydrophilic and hydrophobic ends

Type of soap	Raw materials	Chemical reactions	Process overview
Anionic	Surfactants: Sodium salts of fatty acids  Builders: Sodium carbonate, sodium silicate Additives: Fragrance, colorants, glycerin	Fat (triglyceride) + 3 NaOH → Glycerol + 3 Soap molecules (R-COONa)	1. Saponification of oils/fats with NaOH 2. Neutralization 3. Add additives
Cationic	Surfactants: Quaternary ammonium salts Builders: Weak bases like ammonia or potassium carbonate Additives: Antimicrobial agents, fragrances, softening agents	R-NH₂ + CH₃Br → R-N(CH₃)₃Br⁻ (quaternization of fatty amines)	1. Synthesis of surfactant (quaternary ammonium salt) 2. Blending with builders 3. Add additives
Non-ionic	Surfactants: Polyethylene glycol derivatives, alcohol ethoxylates Builders: Sodium bicarbonate, sodium silicate Additives: Skin conditioners, solvents, essential oils	R-OH + n(EO) → R-O-(CH₂CH₂O)ₙH (ethoxylation of fatty alcohols)	1. Ethoxylation of fatty alcohols 2. Blending with builders 3. Add additives

Mechanism of soap cleaning action:

1. Micelle formation: Soap molecules form spherical structure called micelle in water. The hydrophobic tails are directed inwards, trapping oil and dirt, hydrophilic heads points outwards, interacting with water

2. Emulsification

   
   

   Cleansing Action of Detergent and Soap on Dirt

   • Soap and detergent have the same cleansing action. 

   • Both act as emulsifying agents that are soluble in grease, oil and water. 

   • Soap has molecules where both ends have different properties :  

   • Hydrophilic end ( Soluble in water ) 

   • Hydrophobic end ( Soluble in oil or grease )

• When soap/detergent is dissolved in water, it forms : 

• Sodium ion, Na+ or Potassium ion, K+

• Soap anion or Detergent anion 

The Process

1. Add soap / detergent into the washer. 

2. The surface tension of water will decrease, water’s ability to wet the clothes increase. 

3. Soap / Detergent will ionise in water to form ions. 

4. The hydrophilic part (anion) dissolves in water. 

5. The hydrophobic part (Na+ / K+) dissolves in water. 

6. Scrubbing and agitation cause grease to pull away from the surface of the cloth. 

7. The hydrophilic part (anion) surrounds the grease. 

8. Grease will float to the surface of the water. 

9. Grease will break into small droplets. 

10. The droplets are suspended in water. 

11. Rinse the cloth, and the droplets will remain in water.