Essential oils

1. Starter

3. Fragrances
Overview
In this section, learn about the
chemistry of terpenes and
essential oils, key components of
fragrances.

4. a) Essential oils
Learning intention
Learn about the constitution,
properties and uses of essential
oils.

5. Essential oils
• Essential oils are the concentrated
extracts of volatile, non-water-soluble
aroma compounds from plants.
• Essential oils are widely used in perfumes,
cosmetic products, cleaning products and
as flavourings in foods.

6. Essential oils
• Essential oils are mixtures of organic
compounds.
• Terpenes are the key components in
most essential oils.

7. Modern uses
Essential oils
Cosmetics Flavours
Perfumes Medical
Cleaning
Insect
repellents
Dentistry Adhesives

8. What are essential oils?
• ‘Essential’ refers to the fact that the oil
carries the distinctive essence (scent) of the
plant.
• Concentrated, volatile, non-water soluble
aroma compounds extracted from plants.
• Contain no artificial substances, unlike
perfumes and fragrance oils.

9. Essential oils – chemistry
• The distinctive character of an essential oil
can be attributed to the functional group
present in its key molecule.
• Esters, aldehydes, ketones and alcohols are
all found in essential oils.

10. Essential oils – perfume
• The ester linalyl acetate is found in the
essential oil lavender.
• This ester is often added to perfumes.
C
H3
C
CH
CH2
CH2
C
CH
CH2
O
C
C
H3
O
CH3
CH3
Linalyl acetate

11. Essential oils – cleaning
• The essential oil known as lemon oil contains the
terpene d-limonene.
• It is known for its ability to act as a natural
solvent and a cleanser.
C
H2
C
H2
C
CH
CH2
CH
C
CH2
C
H3
CH3
Limonene
(skin of citrus fruits)

12. Essential oils – cosmetics
• The essential oil geraniol is added to some
cosmetics to balance and revitalise the skin.
C
H3
C
CH
CH2
CH2
C
CH
CH2
OH
CH3
CH3
Geraniol

13. Steam distillation
• Steam distillation is one of the methods used
to extract essential oils from plants.
• Steam passes over the plant and extracts
the essential oil.
• The mixture evaporates and passes into the
condenser.
• The essential oil vapour is chilled and
collected.

14. Steam distillation

15. Essential oils – summary
• Concentrated extracts of volatile, non-water-
soluble aroma compounds from plants.
• Widely used in perfumes, cosmetics, cleaning
products and flavourings.
• Mixtures of organic compounds.
• Terpenes are the key components of most
essential oils.

16. b) Terpenes
Learning intention
Learn about the chemistry and
uses of terpenes, a key group of
unsaturated molecules based
upon isoprene.

17. Terpenes
• The name ‘terpene’ is derived
from the Greek word ‘terebinth’.
• Terebinth is a type of pine tree
from which terpene-containing
resins are obtained.

18. What are terpenes?
• Natural organic compounds.
• Components of a variety of fruit and
floral flavours and aromas.
• Used in perfumes, essential oils and
medicines.

19. Spices contain terpenes
• Terpenes in plants can be oxidised to
produce the compounds responsible for
the distinctive aroma of spices.
• Terpenes containing oxygen or other
functional groups are known as
‘terpenoids’.
• Common spices containing terpenes
include cloves, cinnamon and ginger.

20. Terpenes are unsaturated
• Terpenes are unsaturated compounds.
• All terpenes are built up from units of
isoprene.

21. Isoprene
• Isoprene is the common name for
2-methylbuta-1,3-diene
C
H2
C CH
CH2
C
H3
C
H2 C CH CH2
CH3

22. Isoprene
C
CH3
CH2
CH
CH2
Head Tail
Isoprene
(2-methylbuta-1,3-diene)
=
One isoprene unit contains five carbon
atoms

23. Building terpenes from isoprene
Isoprene units can be linked:
• head to tail to form linear terpenes
• in rings to form cyclic terpenes.

24. Myrcene – a linear terpene
• Myrcene is a component of plants, including
bay, ylang-ylang and thyme.
Head Tail
C
C
H3
C
H2
CH
CH2
Head Tail
C
C
H3
C
H3
CH
CH2
C
CH2
C
H2
CH
CH2
C
C
H3
C
H2
CH
CH2

25. Limonene – a cyclic terpene
C
H2
C
H2
C
CH
CH2
CH
C
CH2
C
H3
CH3
Limonene
(skin of citrus fruits)

26. Menthol – a cyclic terpenoid
C
H2
CH
CH
CH2
CH
C
H2
CH3
OH
CH
CH3
C
H3
Menthol
(peppermint)
This terpene has been
oxidised to a terpenoid

27. Absinthe – a cyclic terpenoid
C
H2
C
C
H
CH
C
CH2
O
CH3
CH
CH3
C
H3
Thujone
(Absinthe)
This terpene has been
oxidised to a terpenoid

28. Camphor – a cyclic terpenoid
C
H2
CH2
CH
C
C
C
CH2
O
C
H3
C
H3
CH3
Camphor
(Camphor tree)

29. a-Selinene – a cyclic terpene
3 isoprene units
15 carbon atoms
CH2
CH2
C
H2
CH
C
C
H2
CH3
C
C
C
CH2
CH2
CH2
CH2
CH3
H
a-Selinene

30. Starter

33. β-carotene – a linear terpene
8 isoprene units
40 carbon atoms
CH2
CH2
CH2
C
C
C
CH3
C
H3
CH
CH
C
CH
CH
CH
C
CH
CH
CH
CH
C
CH
CH
CH
C
CH
CH
C
C
C
H2
C
H2
CH2
C
CH3
C
H3 CH3
CH3 CH3
CH3
CH3
C
H3
-carotene

34. Questions
• Which unit makes up every terpene?
• How many carbons are there in an isoprene
unit?
• What is the systematic name for isoprene?
• What is an oxidised terpene known as?

35. Answers
• Which unit makes up every terpene?
Isoprene unit
• How many carbons there are in an isoprene unit?
Five
• What is the systematic name for isoprene?
2-methylbuta-1,3-diene
• What is an oxidised terpene known as?
Terpenoid

36. Summary
• Terpenes are unsaturated compounds formed by
joining together isoprene units.
• Terpenes are components in a wide variety of fruit and
floral flavours and aromas.
• Terpenes can be oxidised within plants to produce the
compounds responsible for the distinctive aroma of
spices.