Download Essential oils - Uddingston Grammar School

Uddingston Grammar
Higher Chemistry Fragrances and Skin Care
Uddingston Grammar
CfE Higher Chemistry
Sub Topic F & G
Nature’s Chemistry
Fragrances and Skin Care
Pupil Notes
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Uddingston Grammar
No.
Higher Chemistry Fragrances and Skin Care
Learning Outcome
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Essential oils are concentrated extracts of the
volatile, non-water soluble aroma compounds from
plants.
Essential oils are widely used in perfumes,
cosmetic products, cleaning products and as
flavourings in food.
Essential oils are mixtures of organic compounds.
Terpenes are key components in most essential
oils.
Terpenes are unsaturated compounds formed by
joining together isoprene (2-methybuta-1, 3-diene)
units.
Terpenes are components in a wide variety of fruit
and floral flavours and aromas.
Terpenes can be oxidised within plants to produce
some of the compounds responsible for the
distinctive aroma of spices.
Ultraviolet radiation (UV) is a high-energy form of
light present in sunlight.
Exposure to UV light can result in molecules
gaining sufficient energy for bonds to be broken.
This process is responsible for sunburn and
contributes to aging of the skin.
Sun-block products prevent UV light reaching the
skin.
When UV light breaks bonds, free radicals are
formed.
Free radicals have unpaired electrons and, as a
result, are highly reactive.
Free radical chain reactions include the following
steps:
 Initiation
 Propagation
 Termination
Many cosmetic products contain free radical
scavengers; molecules which can react with free
radicals to form stable molecules and prevent
chain reactions.
Free radical scavengers are also added to food
products and to plastics.
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Uddingston Grammar
Higher Chemistry Fragrances and Skin Care
SubTopic 2F – Fragrances
Essential Oils
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Essential oils are concentrated extracts of the volatile, nonwater soluble (hydrophobic) aroma compounds from plants.
The oils have the aroma of the plant from which they are
extracted e.g. lavender, peppermint, orange, lemon, and eucalyptus.
Unlike essential amino acids (which are essential as some living
things cannot make them) essential oils simply mean oils related to
the essence of the plant (so are described as essential).
They are extracted from plant sources by a process called steam
distillation.
In this process the
volatility of the oil is
important so that it is
carried by the steam.
More water can be added
from the funnel.
The essential oil collects
as a mixture of oil and
water, but as the two do
not mix, they are easily
separated.
A simpler laboratory
extraction can be
achieved with the
apparatus shown.
This simple steam
distillation process will
produce a scented
product in the beaker
within about 5 minutes.
Various plant materials
can be tried.
Page 3 of 10
Uddingston Grammar
Higher Chemistry Fragrances and Skin Care
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Essential oils are widely used. They are mixtures of organic
compounds rather than just one pure compound.
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An important component in essential oils is known as a terpene.
Terpenes
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Terpenes are key components in most essential oils.
They are components in a wide variety of fruit and floral flavours
and aromas.
Terpenes may be unsaturated hydrocarbons, or they may contain
oxygen and be alcohols, ketones or aldehydes.
Oxygen containing terpenes are called terpenoids. E.g. alcohols,
ketones or aldehydes
Terpenes can be oxidised within plants to produce some of the
compounds responsible for the distinctive aroma of spices.
Structures of Terpenes
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Terpenes contain carbons in multiples of five.
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The building block is called isoprene , C5H8
Therefore, the building block for all terpenes contains five
carbons.
The systematic name for isoprene is 2-methylbuta-1,3-diene.
Page 4 of 10
Uddingston Grammar
Higher Chemistry Fragrances and Skin Care
You will need to
be able to draw
and recognise
isoprene molecules
within structures.
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Terpenes are unsaturated compounds formed by joining together
isoprene units.
Isoprene units can be linked head to tail to form linear terpenes or
in rings to form cyclic terpenes.
Limonene is a cyclic terpene found in citrus fruits. It is made of
two isoprene units linked in a ring.
Limonene has 10 carbons in total, meaning that it is made up of 2
isoprene units.
Β-carotene is a linear terpene found in carrots. It is made from 8
isoprene units linked head to tail. (40 carbons in total).
Menthol is a cyclic terpenoid – a terpene which has been oxidised.
It is found in peppermint and has a distinctive aroma.
Page 5 of 10
Uddingston Grammar
Higher Chemistry Fragrances and Skin Care
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You may be asked to circle an isoprene unit in a terpene.
It would be a section with 5 carbons, a methyl branch and one
double bond. e.g.
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You could circle either of the parts above to identify an isoprene
unit.
Essential Oils, Edible Oils and Mineral Oils
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You need to know the difference between essential oils, edible oils
and mineral oils.
Essential oils are the concentrated extracts of the volatile aroma
compounds from plants. Their key components are terpenes and
terpenoids.
Edible oils are also found in plants, but these are made up of
triglycerides i.e. the esters of the alcohol glycerol and the
carboxylic acids known as fatty acids.
Mineral oils are derived from crude oil and contain a variety of
long chain alkanes in the range C15 to C40.
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Uddingston Grammar
Higher Chemistry Fragrances and Skin Care
Skin Care Products
Effect of Ultraviolet Light
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Ultraviolet radiation (UV) is a high-energy form of light, present
in sunlight.
Exposure to UV light can result in molecules gaining sufficient
energy for bonds to be broken.
This leads to reactions which destroy skin tissue.
This is the process responsible for sunburn and also contributes to
aging of the skin.
Repeated exposure to UV radiation over a longer period may
produce skin cancers, especially among fair-haired, light-skinned
people.
Here, the UV radiation breaks bonds in the DNA molecules,
causing damage to genes.
Aging of the skin gives it a wrinkly and leathery appearance. This is
caused by the UV radiation destroying collagen, one of the
proteins responsible for the firmness of skin.
Sun-block products prevent UV light reaching the skin.
Sun-block contains zinc oxide and titanium dioxide which reflect
UV radiation.
Sun-screen products can also be used, but are less effective.
Sun-screen contains products which absorb some of the UV
radiation so less reaches the skin.
Free Radical Reactions
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When UV light breaks bonds free radicals are formed.
Free radicals are atoms or groups of atoms with an unpaired
electron and, as a result, are not stable they are highly reactive.
Free radical chain reactions include the following steps:
Initiation,
Propagation
Termination
An example of a free radical chain reaction is as follows:Hydrogen reacts explosively with chlorine in the presence of U.V.
light.
The overall reaction can be shown as follows:
H2(g) + Cl2(g)
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2HCl(g)
Uddingston Grammar
Higher Chemistry Fragrances and Skin Care
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The reaction follows a free radical chain reaction, initiated by U.V.
light. For convenience, the reaction can be split into three stages.
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Initiation
U.V. light provides the energy for the required to break the
chlorine-chlorine bond and to split some of the chlorine molecules
into free radicals.
Cl2(g)
Cl• (g)
Chlorine molecules
+
Cl• (g)
Chlorine free radicals
(the dot represents an unpaired
electron)
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These chlorine free radicals are extremely unstable and highly
reactive.
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Propagation
In this stage, free radicals collide with other species but the
number of free radicals is maintained (hence the term
propagation).
H2(g) + Cl•
H• (g) + HCl(g)
The product of this reaction is known as a hydrogen radical.
H• (g) + Cl2(g)
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HCl(g) + Cl• (g)
Termination
In this stage, free radicals are used up by collision with each other.
H• (g) + Cl• (g)
H• (g) + H• (g)
Cl• (g) + Cl• (g)
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HCl(g)
H2(g)
Cl2(g)
Uddingston Grammar
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Higher Chemistry Fragrances and Skin Care
Another free radical reaction takes place when halogen is
substituted into an alkane in the presence of UV light. This
reaction is not explosive and results in the decolourisation of
bromine.
Free radical substitution of halogen into alkanes
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Alkanes react with chlorine and bromine in the presence of U.V.
light, though the reaction with bromine is slow.
The reaction can be shown as follows:
CH4(g) + Cl2(g) 
CH4(g) + Br2(g) 
CH3Cl(g) + HCl(g)
CH3Br(g) + HBr(g)
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The slow substitution reaction follows a free radical chain reaction,
initiated by U.V. light
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Initiation
Propagation
Br2(g)
Br.(g) + .Br(g)
CH3-H(g) + .Br
CH3.(g) + HBr(g)
The organic product of this reaction is known as a methyl radical.
CH3.(g) + Br2(g)
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CH3 - Br(g) + Br. (g)
Termination
Br.(g) + .Br(g)
CH3.(g) + .Br(g)
CH3.(g) + .CH3(g)
Br2(g)
CH3 - Br(g)
CH3 - CH3(g)
Free-radical Scavengers
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When UV radiation interacts with compounds in the skin, free
radicals are produced.
In turn, these free radicals can initiate chain reactions which can
cause severe damage to the cells.
Free radicals remove electrons from skin cells and damage them
and wrinkles start to develop.
To counteract this, compounds known as free radical scavengers
are used.
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Uddingston Grammar
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Higher Chemistry Fragrances and Skin Care
They react with free radicals to form stable molecules,
therefore stopping the chain reactions from taking place.
Vitamin C and E are common free radical scavengers added to
skin creams and cosmetics to reduce the damaging effects
caused by exposure to UV radiation.
Link to Oxidation of Foods
The oxidation reactions that happen when food “spoils”, also
involve the production of free radicals and this explains why free
radical scavengers such as Vitamin C and E are added to food
products.
 Therefore, antioxidants are free radical scavengers.
 Free radical scavengers are also added to plastics to prevent
their disintegration on prolonged exposure to UV light from the
sun.
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Fragrances and Skincare - Glossary
Word
Meaning
Unsaturated
Compounds which have double (or triple) covalent bonds
between carbon atoms e.g. alkenes such as ethane.
Solvent Extraction
A method to separate compounds based on their relative
solubilities in two different immiscible liquids.
Free Radical
A reactive unit made when a covalent bond is broken and each
fragment has an unpaired electron. Radicals can be atoms e.g.
H. or fragments of molecules such as a methyl radical, CH3.
Initiation
Propagation
The starting reaction of a chain reaction
A stage in a chain reaction where the numbers of radicals is
maintained.
Termination
The last stage in a chain reaction, where all of the remaining
radicals are used up.
Substitution
A reaction where one atom is replaced by another atom.
Free Radical
Scavenger
A molecule that can react with and remove free radicals.
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