Soaps and detergents
Fats and oils
- Fats and oils are triglycerides (triesters of glycerol)
- Fats are solid at RT, oils are liquids
- Degree of saturation, as well as cis/trans isomers, partially determines this as well
Fat and oils (esters) are reacted with sodium hydroxide (alkaline hydrolysis) to form glycerol and a sodium fatty acid/carboxylic acid.
- Usually, sodium sulphonate salts.
- Usually synthetic – reaction of sodium trioxide with a benzene etc.
A typical reaction:
Phenol alkyl ( or any alcohol) + Sulphuric acid –> sulfonic acid + water
Sulfonic acid + NaOH –> detergent + water
How soaps (and detergents i.e. surfactants) work
- The long carbon chain buries itself in the oil droplet, since dispersion forces between them are of similar strength, forming a micelle.
- The anionic part of the chain is attracted to water, which then washes away the micelle.
Problems with soap
- Precipitation in hard water (Ca2+ and Mg2+) as well as in acidic solution.
- They form insoluble calcium carboxylate.
- Detergents do not have this problem.