Synthetic detergents are cleansing agents which have all the properties of soaps, but which easily actually do not contain any soap. These can be used in soft as well as in hard water.
They are mainly classified into the three categories
(1) Anionic Detergents
Anionic detergens are sodium salts of sulphonated long chain alcohols or hydrocarbons. Alkyl hydrogen sulphates formed by treating long chain alcohols with conc. `H_(2)SO_(4)` are neutralised with alkali to form anionic detergents detergents. Similarly alklyl benzene sulphonates are obtained by neutralising alkayl benzene sulphoic acids with alkali.
In these detergents, the anionic part of the molecule is involved in the cleansing action.
They are mostly used for house hold work. They are also used in toothpaste.
(2) Cationic Detergents
They are quarternary ammonium salts of amines with acetates, chlorides or bromides as anionss. Cationic part posses a long hydrocarbons chain and a positive charge on nitrogen atom. Cetrimethylammonium bromide is a popular cationic detergent and is used in hair conditions.
Cationic detergents have germicidal propertis and are expensive, therefore these are of limited use.
(3) Non-ionic Detergents
Non-ionic detergents do no contain any ion in their constitution. One such detergent is formed when stearic acid reacts with polyethylene glycol.
Liquid dishwashing detergents are non-ionic type
Advantage of Synthetic Detergents over Soaps
(i) Synthetic detergents can be used in hard water without andy wastage while some of the soaps get wasted.
Synthetic detergents can be used in acidic medium while soaps get precipitated.
(iii) Synethetic detergents are more soluble in wate and hence produce lather more easily than soaps. Some synethic detergents produce lather even in ice cold water.
(iv) Synthetic detergents decrease the surface tension of water to greater extent and hence have a stronger cleansing action than soap.
Synthetic detergents have advantage love usual soaps but use of synetheti detergents over a long time creates enviorments pollution because some detergents have highly branched hydrocarbon chains.
These branches or side chains stop bacteria from attacking and breaking the chains.
This result in slow degradation of detergent molecule leading to their accumulation. Effluents containing these detergents reach the rivers, ponds etc. These persists in water even after sewage treatement and thus water gents polluted.
Since, unbranched (i.e., straight) chains are more prone to attack by bacteria. therefore, in most of the detergents used these days, the branching is kept to a minimum, so that the detergents used these branching is kept to a minimum, so that the detergents become easily biodegradable and hence pollution is prevented.
