Detergents: Basic detergents are surface active compounds. The compounds which get orient at the interface (between water and air) and reduce interfacial tension/surface tension (The tendency of water of drawing the molecules from the surface towards the body is known as Surface Tension) are known as surface active compounds (surfactants) or Detergents.
Classification of detergents:
Anionic Surfactants:
When the surfactants are dissolved in water and these are ionized into anions and cations. But, if the anion becomes the dominating ion in the solution the surfactant is called an Anionic surfactant. For example, Soap is an anionic surfactant. This Sodium stearate is also known as anionic stearate.
Merits:
a) Anionic surfactants can be used as wetting agents, detergents, emulsifying agents, scouring agents, mercerizing wetting agents, levelling agents, anti-static agents etc.
b) Generally compatible with alkaline liquors.
Demerits:
a) Not compatible with cationic surfactants.
b) Not compatible with acidic solution with extreme acidity. For example, when sodium stearate (soap) solution is acidified, insoluble stearic acid is formed.
c) Ester type of anionic surfactants is not stable to highly alkaline solutions. When the ester gets hydrolysed, produces the acid and the alcohol.
Cationic Surfactants:
Ionic surface active agents which produce cation as dominating ion when dissolved in water are called as Cationic detergent. For example, Cetyl pyridinium chloride is a cationic detergent. When Cetyl pyridinium chloride is dissolved in water it is ionized Among the two ions, cation is comparatively very large than chlorine ion. So, cation acts as dominating ion here.
Merits:
a) Cationic surfactants can be used as softeners, dye-fixing agents, water repellants etc.
b) Generally compatible with acidic liquors.
Demerits:
a) Not compatible with anionic surfactants.
b) Not stable to highly alkaline liquors.
Amphoteric Surfactants:
Amphoteric surface active agents are those agents which ionize and produce large segments carrying both anionic and cationic ions (These segments are called zwitter ions), when dissolved in water. For example, amino carboxylic acids in which amino and carboxylic groups present at the molecular chain ends are dissolved in water to give the zwitter ions.
Merits:
a) The amphoteric surfactants have one outstanding feature that they can behave like cationic surfactants without the disadvantage of being incompatible with anionic surfactant.
b) They have affinity for wool and cellulosic fibres.
c) They have lubricating properties.
d) They are compatible with acids, alkali and mono valent electrolytes.
Demerits:
a) They get precipitated by calcium and magnesium salts present in hard water
Special characteristics of Amphoteric detergents:
a) In alkaline solution (pH>7) they behave like Anionic detergent.
b) In acidic solution (pH<7) they behave like Cationic detergent. c) In neutral solution (PH=7) they behave like Non-ionic detergent.><7) they behave like cationic detergent.
c) In neutral solution (pH = 7) they behave like non-ionic detergent.
Non-ionic Surfactant:
Non-ionic surfactants are those surfactants which are soluble in water and reduce the surface tension of water but, they do not generally ionise when dissolved in water. For example, a polyether ester is formed when Stearic acid is condensed with ethylene oxide.
Merits:
a) Non-ionic surfactants do not ionize into water.
b) These are compatible with either anionic or cationic surfactants.
c) These are stable over a wide range of pH (from acidic through neutral to alkaline solutions).
d) These can be used as wetting agents, detergents, emulsifying agents, levelling agents in vat dyeing, softening agents, scouring agents etc. They can also be used in polyester dyeing and printing.
Demerits:
a) Ester type of non-ionic surfactants is not stable to highly alkaline solutions. When the ester gets hydrolysed, produces the acid and the alcohol.
Difference between soap and detergents
Soap
|
Detergent
|
|
1
|
Soap is sodium or potassium salts of higher fatty acids
|
Detergent is sodium or potassium salts of long chain benzene sulphuric acids or sodium salt of long chain alkyl hydrogen sulphate
|
2
|
Soaps are made from natural oils or fats.
|
Detergents are made from hydrocarbons of petroleum
|
3
|
Soap can give effective cleaning action to only soft water.
|
Detergent can give effective cleaning action to both soft water and hard water.
|
4
|
Soaps have lower detergency power
|
Detergents have high detergency, wetting, and dispersing power
|
5
|
All soaps are detergent
|
All detergents are not soap.
|
6
|
Soap produces scum
|
Not produce
|
7
|
Biodegradable
|
Some of these are not biodegradable
|
8
|
The number of carbon atom within 9-17
|
The number of carbon within 14-36.
|
9
|
Costly
|
Cheap
|
