• SYNTHETIC DETERGENTS

UNIT 5 – CHEMISTRY IN EVERGYDAY LIFE – PART 3

  1. SYNTHETIC DETERGENTS

 

 

  • SYNTHETIC DETERGENTS are cleansing agents which have all the properties of soaps, but which actually do not contain any soap. These can be used both IN SOFT AND HARD WATER as they give foam even in hard water. Some of the detergents give foam even in ice cold water.
  • Synthetic detergents are mainly classified into three categories: ANIONIC DETERGENTS, CATIONIC DETERGENTS AND NON-IONIC DETERGENTS.
  • Anionic detergents are sodium salts of sulphonated long chain alcohols or hydrocarbons. ALKYI HYDROGENSULPHATES formed by treating long chain alcohols with concentrated Sulphuric Acid are neutralised with alkali to form anionic detergents. Similarly, Alkyl Benzene Sulphonates are obtained by neutralising alkyl benzene sulphonic acids with alkali.
  • In anionic detergents, the anionic part of the molecule is involved in the cleansing action. Sodium salts of alkylbenzene sulphonates are an important class of Anionic Detergents. They are mostly used for household work. Anionic detergents are also used in
  • CATIONIC DETERGENTS ARE QUARTEMARY AMMONIUM SALTS of amines with acetates, chlorides or bromides as anions. Cationic part possesses a long hydrocarbon chain and a positive charge on nitrogen atom. Hence, these are called CATIONIC DETERGENTS. CETYLTRIMETHYL- AMMONIUM BROMIDE is a popular cationic detergent and is used in hair conditioners. Cationic detergents have germicidal properties and are expensive, therefore, these are of limited use.
  • Non-ionic detergents do not 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. Mechanism of cleansing action of this type of detergents is the same as that of soaps. These also remove grease and oil by micelle formation.
  • Main problem that appears in the use of detergents is that if their hydrocarbon chain is highly branched, then bacteria cannot degrade this easily. Slow degradation of detergents leads to their accumulation. EFFLUENTS CONTAINING SUCH DETERGENTS REACH THE RIVERS, PONDS, ETC. These persist in water even after sewage treatment and cause foaming in rivers, ponds and streams and their water gets polluted.
  • These days the branching of the hydrocarbon chain is controlled and kept to the minimum. Unbranched chains can be biodegraded more easily and hence pollution is prevented.
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