DETERGENTS
Detergent means any substance which has the ability to clean an object .This includes soaps ,soap powders and dish Washing liquids as well as water.
Detergents fall into two main types namely:
A)soapy detergents and Soapless detergents.
SOAPY DETERGENTS
Soapy detergents or simply soaps are the sodium salts of fatty acids. They are saponification products of fats and oils.
COMMERCIAL MANUFACTURE OF SOAP
Animal fats (e.g. mutton fat) or vegetable oils(e.g.palm oil, coconut oil and olive oil) are steam_heated in large vats with sodium or potassium hydroxide until saponification is completed. A concentrated sodium chloride solution is then added to decrease the solubility of the soap (I.e.the alkaline salts), so that it separates out as a hard cake on the surface on cooling.
This is known as salting out.
The impure soap is purified with steam and water. Dyes, perfumes and disinfectants are added as required before the soap is pressed into bars or tablets .
The properties of the soap produced depend mainly on the alkali and the fat or oil used .
Hard soaps used for laundering are chiefly composed of the sodium salts of saturated acids while softer toilet soaps are composed of the potassium salts of unsaturated acids.
NATURE OF A SOAP MOLECULE
Each molecule of soap possesses a long hydrocarbon chain,R, attaches to an ionic head which is either COO-Na+ .
The hydrocarbon tail is hydrophobic, so it is insoluble in water but soluble in oil and organic solvents. The ionic head is hydrophilic , so it is soluble in water. Due to this dual nature, at the interphase of an aqueous _oil layer ,soap molecules arrange themselves.
When soap is dissolved in water ,the soap molecules form spherical clusters called MICELLES, Each Micelle may contain hundreds of molecules, which are arranged with the hydrocarbon tails pointing inwards and the ionic heads pointing outwards into the water.
Repulsion between the similarly charged ionic heads keeps the micelles apart.
ACTION OF SOAP AS AN EMULSIFYING AGENT:
IF some cooking oil is poured into a beaker of water, the oil will float on the water surface as a separate layer. if the oil_water mixture is shaken vigorously ,the oil will be suspended as tiny droplets in the aqueous layer.
This is called an oil_water emulsion.
The emulsion formed in this case is an unstable one.
However, On standing, the droplets will coalesce to form the oil layer again as well. If some soap solution is added to the oil_water emulsion, the soap molecules crowd around each oil droplet.
The hydrocarbon chains dissolve in the oil, while the ionic heads project into the surrounding water.
Electrostatic repulsion prevents the coalescing of the droplets into larger droplets, thus forming a stable emulsion of oil in water,Soap ,therefore, acts as an emulsifying agent.
CLEANSING ACTION OF SOAP:
When soap solution is applied to a grease coated piece of fabric ,the soap molecules first approach the grease spot.
At the interphase of grease and water, the hydrophobic tails of the soap particles dissolve in the grease while the hydeophilic heads dissolve in water.
The water molecules attract the polar ionic heads of the soap molecules. This action helps to lift the grease spot upwards,enabling more soap particles to dissolve in the grease. Eventually, with mechanical scrubbing, the grease patch is emulsified .On rinsing the fabric,the grease is ewmoved.
ADVANTAGES AND DISADVANTAGES OF SOAP:
Soap is a good cleansing agent in soft water. In hard water, it forms scum. In acidic water, it reacts with the excess hydrogen ions to form unionized fatty acids.
This lowers the cleansing effect of the soap, since it is the ionic polar heads of soap molecules that are chiefly responsible for its solubility in water.
Meanwhile Note that Soap is also biodegradable, I.e. and it can easily be decomposed by bacteria into simple inorganic substances. In other for it not to cause water pollution.
SOAPLESS DETERGENTS
Soapless detergents are the more favoured all purpose cleansing agents nowadays. They are available as liquids or solids.
The most widely uses Soapless detergents are the alkyl benzenesulphonates,abbreviated as ABS.like the soaps, they are adium salts of an acid (e.g. sulphonic acid in the case of ABS).
STRUCTURE
The detergent molecules has a hydrophobic tail and a hydrophilic head .The hydrophobic tail is either a long chain hydrocarbon or a benzene ring with a long alkyl group attached.
The hydrophilic head , unlike the molecules, can be positively or negatively charged, or even neutral.
The high solubility of Soapless detergents in water is due to the _SO3-Na+ group that is present in the molecules.. Soapless detergents are also known as SYNTHETIC DETERGENTS because they are made by synthetically piecing various parts of the detergent molecule together. The raw materials are petrochemicals obtained from refining crude oil.
HERE ARE THE ADVANTAGES AND DISADVANTANTAGES OF SOAPLESS DETERGENTS
First, Note that Soapless detergents do not form scum or react with hydrogen ions. They retain cleansing properties irrespective of the type of water used .In aqueous solution, detergents are neutral whereas soaps hydrolyze to give a slightly alkaline solution which may not be suitable for washing acid_sensitive fabrics.
Soapless dtergents can also be tailor _made for a specific purpose , such as breaking up oil slicks. As such ,they have a wider application than soaps.
Certain. Soapless detergents are non biodegradable and so create water pollution problems when their foams clog up waterways Nowadays, most detergents are manufactured with straight hydrocarbon chains,and so are biodegradable.
Commercial detergents (even soap) also contain substances such as perfumes, brighteners, dyes and antiseptics. The most common of these is sodium Tripoli phosphate .Since phosphates are good fertilizers ,they cause the algae in waterways to multiply beyond control. This beings about water pollution by clogging up waterways
THE CHEMISTRY OF NATURAL SOAPS :
Meanwhile, despite technical achievements and scientific developments, the classic soap is still based on the same chemistry like that of ancient soaps. However, Soap is chemically defined as the alkali salt of fatty acids. Generally , the term “soap” had taken on a more functional definition, by which any cleansing agent, regardless of its chemistry, is considered a soap.
Moreover, sometimes the misleading definition will be considered as we deal with the chemistry of the syn-thetic detergents and the soapless soap revolution.
Soap is manufactured by the saponification process, in which the triglycerides (fats and oils) or fatty acids are transformed into corresponding alkali salt mixtures of fatty acids. Nowadays we can now differentiate among three methods.
1. Direct neutral fat saponification, in which oils and fats (sometimes after purification with various agents, such as active earth) are directly~saponified with al-kali in a boiled or semi boiled kettle process.
Soap is probably the oldest skin cleanser. However, past thousands of years, this product has been obtained from the sa-ponification of oils and fats by alkali.
For most human discoveries it is true, that the first chemical saponification was found by chance. Base on Roman legend, soap was discovered accidentally close to Mount Sapo, an ancient location for animal sacrifices not far from Rome. The animal fat, mixed with wood ashes (the ancient source of alkali) and rain-water, created an extraordinary soap mixture.
However the Soapmaking became an art in the time of Phoenicians and saw significant advancement in Mediterranean countries, where olive oil of a local origin was boiled with alkali ashes. Meanwhile the famous Marseilles soap had its roots 1000 years ago in local soapmaking facilities.
The real breakthrough in industrial soap production was made by a French chemist and doctor, Nicolas Le-blanc, who invented the process of obtaining soda from common salt (L.eblanc process 1780).
Soap, which has been a luxury item affordable only to royalty and the rich only, now became the main product for everyday personal hygiene.
Nowadays, soap is still very essential base for cleansing solid bars. Even during tough economic situation of the 199Os, annual bar soap sales in the United States . The total annual toilet soap market.
