Industrial chemistry
Soap, Detergents and
Surfactants
Kazem.R.Abdollah
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Soap
• Soaps are cleaning agents that are usually made by
reacting alkali (e.g., sodium hydroxide) with naturally
occurring fat or fatty acids. The reaction produces
sodium salts of these fatty acids, which improve the
cleaning process by making water better able to lift
away greasy stains from skin, hair, clothes, and just
about anything else.
• Soap is produced by a saponification or basic hydrolysis
reaction of a fat or oil. Currently, sodium carbonate or
sodium hydroxide is used to neutralize the fatty acid
and convert it to the salt.
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History of Soap
• The discovery of soap predates recorded history,
going back perhaps as far as six thousand years.
Excavations of ancient Babylon uncovered
cylinders with inscriptions for making soap
around 2800 B.C.E. Later records from ancient
Egypt (c. 1500 B.C.E. ) describe how animal and
vegetable oils were combined with alkaline salts
to make soap.
• According to Roman legend, soap got its name
from Mount Sapo, where animals were sacrificed.
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General overall hydrolysis
reaction:
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• The potassium soap formed from your fat is converted to a sodium
soap by replacing the potassium ions with sodium ions. A large excess
of sodium chloride supplies the sodium ion. You may also notice that
the potassium soap is softer than the sodium soap. In addition there is
a difference in the way the sodium and potassium soaps behave in
water.
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Types of Soap:
• The type of fatty acid and length of the carbon chain
determines the unique properties of various soaps.
• Tallow or animal fats give primarily sodium stearate (18
carbons) a very hard, insoluble soap. Fatty acids with
longer chains are even more insoluble.
• Coconut oil is a source of lauric acid (12 carbons) which
can be made into sodium laurate. This soap is very
soluble and will lather easily even in sea water.
• Fatty acids with only 10 or fewer carbons are not used
in soaps because they irritate the skin and have
objectionable odors.
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Cleansing Action of Soap:
• The cleansing action of soap is determined
by its polar and non-polar structures in
conjunction with an application of solubility
principles.
• The long hydrocarbon chain is of course
non-polar and hydrophobic (repelled by
water).
• The "salt" end of the soap molecule is ionic
and hydrophilic (water soluble).
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Monolayer:
When soap is added to water, the ionicsalt end of the molecule is attracted to
water and dissolved in it. The non-polar
hydrocarbon end of the soap molecule is
repelled by water. A drop or two of soap
in water forms a monolayer on the water
surface as shown in the graphics on the
left. The soap molecules "stand up" on
the surface as the polar carboxyl salt end
is attracted to the polar water. The nonpolar hydrocarbon tails are repelled by
the water, which makes them appear to
stand up.
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Soap vs. oil vs. water:
• The oil is a pure hydrocarbon so it
is non-polar. The non-polar
hydrocarbon tail of the soap
dissolves into the oil. That leaves
the polar carboxylate ion of the
soap molecules are sticking out of
the oil droplets, the surface of
each oil droplet is negatively
charged. As a result, the oil
droplets repel each other and
remain suspended in solution
(this is called an emulsion) to be
washed away by a stream of
water. The outside of the droplet
is also coated with a layer of
water molecules.
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micelle
A micelle is an aggregate of surfactant molecules dispersed in a
liquid colloid.
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Effect of Hard Water:
• If soap is used in "hard" water, the soap will be precipitated as "bath-tub
ring" by calcium or magnesium ions present in "hard" water.
• The effects of "hard" water calcium or magnesium ions are minimized by
the addition of "builders". The most common "builder" used to be sodium
trimetaphosphate.
• The phosphates react with the calcium or magnesium ions and keeps them
in solution but away from the soap molecule. The soap molecule can then
do its job without interference from calcium or magnesium ions.
• Other "builders" include sodium carbonate, borax, and sodium silicate are
currently in detergents.
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Detergents and Surfactants
• Greasy stains do not mix with water because the main
interactions between water molecules are hydrogen
bonding and those between molecules of oils and fats
(which constitute grease) are van der Waals forces.
• To get water and grease to mix we use molecules called
surfactants or detergents.
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Chemical classification of
detergents:
• There are four main classes of detergents
1.
2.
3.
4.
Anionic detergents
Cationic detergents
Non-ionic
zwitterionic detergents (amphoteric)
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Anionic Detergents
• Anionic means a negatively
charged molecule. In the early
days always remembered this by
anionic (a negative). The
detergency of the anionic
detergent is vested in the anion.
The anion is neutralised with an
alkaline or basic material, to
produce full detergency.
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Cationic Detergents:
• Another class of detergents have a positive ionic charge
and are called "cationic" detergents. In addition to being
good cleansing agents, they also possess germicidal
properties which makes them useful in hospitals. Most of
these detergents are derivatives of ammonia.
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Neutral or non-ionic detergents:
• Nonionic detergents are
used in dish washing
liquids. Since the detergent
does not have any ionic
groups, it does not react
with hard water ions. In
addition, nonionic
detergents foam less than
ionic detergents. The
detergent molecules must
have some polar parts to
provide the necessary
water solubility.
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Amphoterics (zwitterionic
detergents )
• These have the characteristics of both anionic detergents
and cationic fabric softeners. They tend to work best at
neutral pH, and are found in shampoo’s, skin cleaners and
carpet shampoo. They are very stable in strong acidic
conditions and have found favour for use with hydrofluoric
acid.
3-[(3-Cholamidopropyl)dimethylammonio]1-propanesulfonate (CHAPS)
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Bile Salts - Intestinal Natural
Detergents:
• Bile acids are produced in the liver and
secreted in the intestine via the gall
bladder. Bile acids are oxidation
products of cholesterol. First the
cholesterol is converted to the
trihydroxy derivative containing three
alcohol groups. The end of the alkane
chain at C # 17 is converted into an
acid, and finally the amino acid, glycine
is bonded through an amide bond. The
acid group on the glycine is converted
to a salt. The bile salt is called
sodiumglycoholate. Another salt can
be made with a chemical called
taurine.
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Bleach
• Bleach refers to a number of chemicals which remove
color, whiten or disinfect, often by oxidation.
• Chlorine is the basis for the most commonly used
bleaches, for example, the solution of sodium
hypochlorite, which is so ubiquitous that most simply
call it "bleach", and calcium hypochlorite, the major
compound in "bleaching powder".
• Oxidizing bleaching agents that do not contain chlorine
most often are based on peroxides, such as hydrogen
peroxide, sodium percarbonate and sodium perborate.
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Colors in most dye and pigments are produced by
molecules which contain chromophores, such as beta
carotene. Chemical bleaches work in one of two ways:
• An oxidizing bleach works by breaking the chemical
bonds that make up the chromophore. This changes
the molecule into a different substance that either
does not contain a chromophore, or contains a
chromophore that does not absorb visible light.
• A reducing bleach works by converting double bonds
in the chromophore into single bonds. This
eliminates the ability of the chromophore to absorb
visible light.
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