ESTERS, FATS AND OILS, SOAPS - CFE HIGHER CHEMISTRY UNIT 2: NATURES CHEMISTRY - GLOW BLOGS
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CfE Higher Chemistry
Unit 2: Natures Chemistry
Esters, Fats and Oils, Soaps
27/02/2018
Lesson Starter: Name / Draw these molecules
a) b)
c) d)
e) 2-methylpentan-1-ol
f) Pentanoic acid
27/02/2018
27/02/2018 Esters Learning Outcomes : • Recognise an ester molecule and the ester link functional group • Name esters and draw the structural formulae for esters • Describe some uses of esters • Explain the formation and break down of esters by condensation and hydrolysis • Name and draw the reactants and products of a condensation or hydrolysis reaction
What are Esters?
An ester is a compound which is formed
when a carboxylic acid reacts with an
alcohol.
They contain the Ester Link functional
group (-COO- or -OCO-)
The name of the parent alcohol and
carboxylic acid give the ester it’s name.
It is easy to spot an ester from it’s name;
Ester names always finish with “oate”
Esters can be natural or synthetic and have
many uses related to their properties.
27/02/2018
Esters
Esters are formed when an alcohol reacts with a carboxylic
acid, water is also produced during this reaction.
Carboxylic acid + Alcohol → Ester + water
+
→ + H2O
Ester link
The functional group of an ester is the ester link
27/02/2018
Naming Esters
The name of the ester is made up of two parts the
alcohol (__yl) part and the carboxylic acid (___anoate)
part.
H H O H H
H C C O C C C H
H H H H
ethyl propanoate
made by reacting ethanol with propanoic acid
27/02/2018
Naming Esters
H O H O
H C OH HO C H H C O C H
H H Ester link
methanol + methanoic acid à methyl + water
methanoate
Studies have revealed that the oxygen atom in the main
chain of the ester always comes from the alcohol.
27/02/2018
Practice Question
Name the esters that the following alkanols and
alkanoic acids would produce.
1. Propanol & Ethanoic acid Propyl ethanoate
2. Butanol & Pentanioc acid Butyl pentanoate
3. Propanoic acid & Methanol Methyl propanoate
4. Methanoic acid & Pentanol Pentyl methanoate
5. Butanol & Butanoic acid Butyl butanoate
6. Octanol & Octanoic acid Octyl octanoate
7. Ethanoic acid & Heptanol Heptyl ethanoate
27/02/2018
Practice Questions
Now try the practice questions on the
worksheet.
27/02/2018
Making Esters
Esters can be prepared by reaction of an alcohol with a carboxylic
acid:
O O
C R' C R' + H2 O
R O H + H O R O
alcohol carboxylic acid ester
The reaction is slow at room temperature and the yield of ester is low.
The rate can be increased by:
1) heating the reaction mixture
2) using concentrated sulphuric acid as a catalyst.
The presence of the concentrated sulphuric acid also increases the yield
of ester.
27/02/2018Experiment: Making esters
Collect an
experiment work
card from the
front.
Acid
Alcohol
Notes:
•Copy the above diagram and explain the purpose of the
concentrated sulphuric acid; the wet paper condenser and the
water bath.
•What two pieces of evidence would indicate that an ester had
been formed?
27/02/2018Properties of Esters
Notes:
1. Esters are ______________. so we never use a naked flame
near them, we would use a heating mantle or a water bath as a
source of heat.
2. Esters have a distinctive When using them we
must ensure that we have
3. Esters are very (meaning that they turn into a
very easily)
4. Esters are in water (they form a layer with water
or other solutions).
If you learn these properties the uses are easier to recall in an
exam.
27/02/2018Uses of esters: Flavours and Scents
• Many esters are used as flavourings and in perfumes.
• Natural fruit flavours contain subtle blends of some of the esters in
the table below:
Name Shortened Structural Odour/Flavour
Formula
CH3(CH2)4CH3 Banana
Methyl Butanoate Pineapple
3-Methylbutyl Butanoate CH3(CH2)2(CH2)2CH(CH3)2 Apple
CH3COOC3H7 Pear
Methyl-1-butyl ethanoate CH3COOCH(CH3)C4H9 Banana
2-Methylpropyl Raspberry
methanoate
C3H7COOC5H11 Apricot, Strawberry
Benzyl ethanoate CH3COOCH2C6H5 Peach, flowers
Methyl 2-aminobenzoate C6H4(NH2)COOCH3 Grapes
Benzyl butanoate C3H7COOCH2C6H5 Cherry
27/02/201827/02/2018
Uses of esters: Solvents
Esters are also used as non-polar industrial solvents.
Some of the smaller esters are quite volatile and are
used as solvents in adhesives, inks and paints – pentyl
ethanoate is used in nail varnish for example.
27/02/2018Uses of esters: Decafination
Ethyl ethanoate is one of a number of solvents used to
extract caffeine from coffee and tea.
De-caffeinated products produced with ethyl ethanoate
are often described on the packaging as "naturally
decaffeinated" because ethyl ethanoate is a chemical
found naturally in many fruits.
27/02/2018Experiment: Decafination
Caffeine (C8H10N4O2) is an example of a class of compounds called
alkaloids which are produced by plants.
The name alkaloid means “alkali-like”, where alkali is a base and
hence refers to these basic properties.
Carry out the experiment to extract caffeine from tea.
27/02/2018Uses of esters
Caffeine is more soluble in the
organic solvent ethyl ethanoate
than in water, so we will extract
caffeine into the organic solvent to
separate it from glucose, tannins,
and other water soluble compounds
using a separating funnel.
.
The ethyl ethanoate portions can be
combined and the ethyl ethanoate
removed by evaporation to leave
the caffeine
27/02/2018Hydrolysis of Esters
Condensation
Alcohol + Carboxylic Acid ⇌ Ester + Water
Hydrolysis
The ester is split up by the chemical action of water, hydrolysis.
The hydrolysis and formation of an ester is a reversible reaction.
O O R
O O +
+ R C H
R C O R H H O H
Bonds broken Bonds formed
Ester + Water Carboxylic Acid + Alcohol
27/02/2018Hydrolysis of an Ester
• To reverse the formation of ester (ie hydrolyse it)
we need to react the ester with water.
• However in practice the ester is heated with either
dilute acid or dilute alkali.
• The ester is said to be heated under “reflux”.
• When sodium hydroxide solution is used the ester
is ‘split up’ into the alkanol and the sodium salt of
the acid.
• The alkanol can be removed by distillation and the
alkanoic acid can be regenerated by reacting the
sodium alkanoate with dilute hydrochloric acid.
27/02/2018Starter Questions
Name the products formed by hydrolysis of each of the
following compounds:
1) ethyl ethanoate 8) CH3CH2OOCCH2CH2CH3
2) propyl butanoate 9) CH3OOCH
3) butyl pentanoate 10)
4) methyl hexanoate
5)
6) pentyl methanoate
7) CH3CH2CH2OOCCH3Fats and Oils Learning Outcomes By the end of these lessons you will be able to: • Explain the chemistry and structure of edible fats and oils. • Explain the difference in melting points of fats and oils in terms of structural differences.
Fats in the Diet • Fats provide more energy per gram than carbohydrates. • Fat molecules are insoluble, and tend to group together and form a large droplet. This is how fat is stored in the adipose tissue. • We store our extra energy as fat. The type of fat we eat is important. Animal fats contain important fat soluble vitamins. Oils, are thought to be healthier than solid fats, as they are less likely to be deposited inside our arteries. However, there is an ongoing debate about which fats are better for us. • Polyunsaturated fats are considered to be less potentially harmful to the heart.
Fats and oils
Naturally occuring
Animal fat Vegetable oil Marine oil
lard sunflower oil cod liver oil
suet coconut oil whale oilFats and Oils 50% of your
brain is fat!
Fats and oils are a range of substances all based on glycerol,
propan-1,2,3-triol.
Natural fats and oils are a mixture of triglyceride compounds.
Each -OH group can combine chemically with one
H carboxylic acid molecule.
H C O H The resulting molecules are fats and oils. They are
H C O H
described as triglycerides.
H C O H The hydrocarbon chain in each carboxylic acid can
be from 4 to 24 C’s long.
H
The C’s can be single bonded (saturated) or double
Glycerol bonded (unsaturated).
propan-1,2,3-triolFats and oils
Both fats and oils are built from glycerol; an alcohol with
three -OH groups.
glycerol
Systematic name is propane-1,2,3-triolThe other components of fat molecules are carboxylic
acids.
Long chain carboxylic acids are known as Fatty Acids.
One such fatty acid is Stearic acid:
Stearic acid
Systematic name is octadecanoic acidExamples of Fatty Acids
C17H35COOH CH3(CH2)16COOH Stearic Acid (suet, animal fat) Saturated
H 3C CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 O
CH 2
CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 C
OH
C17H33COOH CH3(CH2)7CH=CH(CH2)7COOH Oleic Acid (olive oil) Unsaturated
H3C CH2 CH2 CH2 CH CH2 CH2 O
CH2 CH2
CH2 CH2 CH2 CH2 CH CH2 CH2 CH2 C
OHThe glycerol molecule and fatty acids form ester links.
Fats and oils are ESTERS made from
glycerol and long chain carboxylic acidsThe formation of the ester links is an example of a condensation reaction. Formation / removal of water in the condensation reaction gives - The molecular formula shown above suggests that the fat molecule is shaped like an E, but the molecule is actually shaped more like this:
Fats are mainly built from carboxylic acids with
C-C single bonds. (SATURATED)
Stearic acid in beef fat
Oils have at least one C=C bonds in the carboxylic acids
from which they are made. (UNSATURATED)
Oleic acid in olive oilOil
Double bonds in oil change the shape of
the molecules.
This makes the molecule less compact.
Less tightly packed molecules result in
weaker bonds between the molecules
this makes oils liquid.
Fat
Fat molecules pack together
more tightly, making fats solid at room
temperature.In practice both fats and oils are mixtures of esters containing both saturated and unsaturated compounds. Beef Fat Olive oil In general oils have a higher proportion of unsaturated molecules.
Notes: • How do the melting points of the fats compare with the melting points of the oils? • What is meant by saturated and unsaturated? • How does the proportion of unsaturated molecules in an oil compare with that in a fat? • Explain why fats are likely to have relatively high melting points and oils are likely to have relatively low melting points.
Unsaturation in fats and oils
1.Using a plastic pipette, add five drops of
olive oil to 5 cm3 of hexane in a conical flask.
2. Use a burette filled with a dilute solution
of bromine water (0.02 mol dm–3)
(Harmful and irritant).
3. Read the burette.Unsaturation in fats and oils
4. Run the bromine water slowly into the oil
solution. Shake vigorously after each addition.
The yellow colour of bromine disappears as
bromine reacts with the oil. Continue adding
bromine water to produce a permanent yellow
colour.
5. Read the burette. Subtract to find the volume
of bromine water needed in the titration.
6. Repeat the experiment with: five drops of
cooking oil (vegetable) and five drops of cooking
oil (animal).Fats and Oils
The degree of saturation in a fat or oil can be determined by the
Iodine Number. (bromine can also be used).
The iodine reacts with the C=C bonds, so the greater the iodine number, the greater the
number of double bonds.
Solid fats – butter, beef fat & lard have low iodine
Fat Av Iodine numbers because they are more saturated than the
No unsaturated oils.
Butter 40
Beef Fat 45 Margarine is made from vegetable oils, butter from animal
fats. One reason why margarine spreads better!
Lard 50
Olive Oil 80
Peanut Oil 100 Omega 3 fatty acids make up a large % of your
Soya Bean 180 brain’s fat.
OilHydrogenation • The addition of hydrogen to an unsaturated oil will ‘harden’ the oil. • This will Increase it’s melting point. • The hydrogen is added across the double bond. • Used with margarine, otherwise margarine would be a liquid when taken out of the fridge.
Lesson Starter: Hydrolysis of Esters
27/02/2018Soaps and Emulsions Learning Outcomes : • explain how soaps are produced • relate the cleansing action of soaps to the structure of the soap molecules.
Structures of fats and oils - Revision
• Fats and Oils are esters of glycerol and long chain fatty acids.
• Hydrolysis of a fat or oil produces glycerol (alcohol) and 3
carboxylic acids / fatty acids.
H O
H C O C R1
O
Hydrolysis
H C O C R2
O Fatty Acids + Glycerol
H C O C R3
Fatty acid part
H
Glycerol (R 1, 2, 3 are long carbon chains,
part which can be the same or different)Hydrolysis
• To hydrolyse an ester we need to react it with
water.
• However in practice the ester is heated under
“reflux” with either dilute acid or dilute alkali.
• When sodium hydroxide solution is used the
ester is ‘split up’ into the alkanol and the
sodium salt of the acid.
• The alkanol can be removed by distillation and
the alkanoic acid can be regenerated by
reacting the sodium alkanoate with dilute
hydrochloric acid.
• The equations for these reactions are:
27/02/2018Soaps
Soaps are salts of fatty acids.
Soaps are formed by the alkaline hydrolysis of fats and oils by
sodium or potassium hydroxide by boiling under reflux conditions:
H O
H
H C O C C H
17 35
O H C O H
H C O C C H + 3NaOH H C O H + 3 C17H35COO --Na+
17 35
O H C O H
H C O C C H
17 35
H
H Sodium stearate
Glycerol (soap)
Glyceryl tristearateStructure of Soaps
As most of the grime and dirt on skin, clothes and dishes tends to be trapped in
oils and greases, water alone cannot rinse away the muck.
If the oils/greases can be made to mix with water then it becomes easy to wash
off, along with the grime.
Soaps and detergents do this job in a clever way, due to the structure of the
molecules:
Sodium or potassium salts of long chain fatty acids really have two quite separate
parts in terms of their bonding types – a long hydrocarbon chain which is non
polar and an ionic ‘head’.
COO- Na +
Hydrophobic Hydrophilic
tail head
27/02/2018Structure of soap Hydrophobic
COO- Na
Hydrophilic
+
tail head
The long covalent hydrocarbon chain “tail” gives rise to the hydrophobic (water
hating) and oil-soluble (non-polar) properties of the soap molecule (represented
in yellow).
The charged carboxylate group “head” (represented in blue) is attracted to
water molecules (hydrophilic). In this way, soaps are composed of a hydrophilic
head and a hydrophobic tail:Cleansing action of soaps
The following ball and stick diagram represents the initial interaction
of soap on addition to water and material with a grease stain:
(blue for
hydrophilic head
group)
(yellow for
hydrophobic tail
group)When the solution containing soap and water is agitated (stirred vigorously) the interactions of hydrophobicity and hydrophilicity become apparent. The hydrophobic, non-polar, tails burrow into the greasy, non-polar molecule – like attracting like. In the same way the polar hydrophilic head groups are attracted to polar water molecules. The head groups all point up into the water at the top of the grease stain.
The attraction of the head group to the surrounding water, via polar-to-polar interactions, is so strong that it causes mechanical lift of the grease molecule away from the material on which it was deposited. The hydrophobic tails are anchored into the grease due to non-polar to non-polar attraction. In combination, these effects allow for the removal of the grease stain.
MICELLE
grease
O H
particle
H
O H -
Na+ OOC
H -
- O H +
COO Na O H
H O Na+ OOC H H O H
H O H
H
H
O H H O
- H
H COO Na+
-
H O Na+ OOC H O
H O H H
H -
COO Na+
- O H
H O Na+ OOC
- H
H O H O H COO Na+
H H O H
H O H
HSuccess Criteria: Soaps ü I can explain how soaps are produced by alkaline hydrolysis of fats and oils ü I can relate the cleansing action of soaps to the hydrophobic and hydrophilic nature of soap molecules. Next Lesson: Emulsions
Lesson Starter:
Emulsions Learning Outcomes : • Describe the characteristics of an emulsion, and study the chemistry of typical emulsifier molecules.
Emulsifiers • An emulsion contains small droplets of one liquid dispersed in an another liquid. • Emulsions in food are mixtures of oil and water. • To prevent oil and water components separating into layers, a soap-like molecule known as an emulsifier is added.
Experiment: Emulsifiers
Expt 2.8 (b)Emulsifier molecules Emulsifiers for use in food are commonly made by reacting edible oils with glycerol to form molecules in which either one or two fatty acid groups are linked to a glycerol backbone rather than the three normally found in edible oils. The one or two hydroxyl groups present in these molecules are hydrophilic whilst the fatty acid chains are hydrophobic. The presence of this emulsifier is shown on packaging by E-numbers, E471 and is one of the most common on food packaging.
Emulsifiers Mayonnaise contains oil and water. The emulsifier keeps these mixed and without it the oil and water separate.
Emulsifiers in food
Emulsifiers are among the most frequently used types of food
additives. They are used for many reasons:
• Emulsifiers can help to make a Foods that Commonly Contain Emulsifiers
food appealing.
• They are used to aid in the Biscuits Toffees Bread
processing of foods and also to Extruded
Margarine /
Chewing gum low fat
help maintain quality and snacks
spreads
freshness. Breakfast Frozen Coffee
• In low fat spreads, emulsifiers cereals desserts whiteners
can help to prevent the growth Topping
Cakes Ice-cream
powders
of moulds which would happen Desserts /
Dried potato Peanut butter
if the oil and fat separated. mousses
Chocolate
Soft drinks Caramels
coatingsEmulsifiers in food Foods that Commonly Contain Emulsifiers Biscuits Toffees Bread Extruded snacks Chewing gum Margarine / low fat spreads Breakfast cereals Frozen desserts Coffee whiteners Cakes Ice-cream Topping powders Desserts / mousses Dried potato Peanut butter Soft drinks Chocolate coatings Caramels
Success Criteria: Soaps and Emulsions • I can explain how soaps are produced by alkaline hydrolysis of fats and oils • I can relate the cleansing action of soaps to the hydrophobic and hydrophilic nature of soap molecules. • I can define an emulsion. • I can explain why emulsifiers are added to food. • I can describe how emulsifiers are made and how they work Next Lesson: Proteins
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