The first known form of soap is most likely sodium carboxylates. This can easily be prepared by boiling animal fats or vegetable oil (collectively known as fats) with an aqueous solution of sodium hydroxide. Fats are naturally occurring esters of long-chain carboxylic acids. The more exact term will be triesters of glycerol, or triglycerides.

+ 3 NaOH

The excess sodium hydroxide is then neutralized and we have a soap solution. For home preparation the products are concentrated by boiling off the water to give a cake of soap. In commercial processes it is spry-dried under reduced pressure.

Some natural occurring fatty acids (CH₃−[CH₂]_i−COOH) are

• lauric acid (i = 10),
• myristic acid (i = 12),
• palmitic acid (i = 14),
• stearic acid (i = 16), etc.

Of course we now have other soap products which are not sodium carboxylates. However all soaps will have a hydrocarbon segment (hydrophobic segment) and a hydrophilic portion. In sodium carboxylate, the carboxylate is the hydrophilic portion.

CH3CH2CH2CH2......CH2CH2CH2CH2	COO-Na+
HYDROPHOBIC SEGMENT	HYDROPHILIC UNIT

Note that hydro phobic means having a phobia towards water. To be effective the hydrophobic segment has to be sufficiently large (more than 10 carbons).

The science of washing our clothes, or ourselves, is the removal of dirt by dissolving it in water. So if our clothes are dirty we dissolve the dirt in water, rinse it and then dry the clothes.

Micelle: The pinheads are the hydrophilic unit, and the tails are the hydrophobic segments

The only problem is some dirt, like body oil or food oil, are not soluble in water. However, with the help of soap we can actually suspend the oil in the water. The oil will dissolve in the hydrophobic segment of the molecule, provided the segment is sufficiently large. Generally it is more than 10 carbon units.

So the soap molecules form a sphere with the hydrophobic segments in the core along with the oil molecules. The hydrophilic unit of the soap molecules will be on the surface of the sphere interacting with water. This is known as a micelle. So when the water is thrown out in the wash the dirt will be in it.

DETERGENT

Soap when used in "hard water" will form water insoluble deposits with the magnesium and calcium in the water. This deposit is known as "scum". This is not a serious problem when used for bathing the scum will just washed off our body. To feel good you can just soap yourself till it lathers.

However such deposits can be absorbed on your clothing, appearing as stains. So we have to come up with compounds that will not form scum in hard water. Such "soap" is known as detergent. The first detergent, formulated in 1933, were alkylbenzenesulfonates, where R is a branched alkyl chain.

It was then realised that alkylbenzenesulfonates are too stable and will not decompose easily in the environment. Being of synthetic origin they are also not metabolised by bacteria in the environment. So it stays in the rivers and lakes for a long time, and eventually ends up in fish and other marine organisms. This then led to the development of linear alkanesulfonate detergents, CH₃[CH₂]_iCH₂SO₃‾ Na⁺.

Now there are also available non-ionic detergents. The hydrophilic unit in this case are the amines.