2. Terpene Hydrocarbons
I- Acyclic (Aliphatic)
II-Alicyclic
III- Aromatic
e.g. Styrene,
Cymene
I.1.Unsaturated Monoterpene
e.g. Myrcene, Ocimene
I.2. sesquiterpenes
e.g. sesquicitronellene
and farnesene
II-1. Monoterpene
II.2.Sesquiterpene.
Bicyclic
e.g. a-Pinene
Monocyclic
e.g. Limonene,
Sylvestrene
Monocyclic
(e.g. zingiberene).
Bicyclic
(e.g. derivatives
of azulenes).
Tricyclic
(e.g. santalene).
3. General Methods for Isolation of Terpene Hydrocarbons
1. Fractional Distillation:
• This usually takes place under vacuum or in an atmosphere of inert gas, as many hydrocarbons
are sensitive to heat in atmospheric oxygen.
• This can carried out by gradual increase of the distillation temperature by (1-5o
C) or (5-10 o
C)
according to the boiling point of components.
2. Preparation of the Corresponding Crystalline Additive Products “Adducts”:
Characteristic addition products are formed by N2O3, N2O4, NOCl and NOBr to yield nitrosites,
nitrosates, nitrosochlorides, and nitrosobromides, respectively.
3. Counter-current Extraction Method:
By using two solvents forced against each other, usually one solvent dissolves the terpene more
than the other.
4. Chromatographic Techniques:
One or more of the following methods can be used:
• Column chromatography (CC).
• Gel filtration
• Gas liquid chromatography (GLC).
• Gas liquid chromatography coupled with mass spectroscopy (GLC-MS).
• Thin layer chromatography (TLC).
4. I- Acyclic….. Unsaturated Monoterpene Hydrocarbons
Name
Structure
(2methyl, 6 methylene ∆ 2:7
octadiene)
(2,6-dimethyl ∆ 1:5:7
octatriene)
Occurrence oil of hops (Humulus lupulus family
Cannabinaceae)
oil of Basil (Ocimum basilicum family
Labiatae)
Isolation The distilled oil is treated with NaOH to give soluble part, which contains the
phenolic compounds, while the insoluble part is subjected to fractional
distillation under vacuum
Identification of myrecene in presence of ocimene
Myrecene
2
3
4
5
6 7
Ocimene
2
1
3
4
5 7
6
oxidation
KmnO4
(Rhombic form crystals)
Myrecene
+
Ocimene
Mixture of acids
Needle-shaped crystals
(Complete degradation)
pb++COOH
HOOC
Succinic acid
Myrecene
Ocimene
Lead salts
pb++
5. SourceSource
Farnesene: oil of hops.
the sesquiterpenoid analogue of myrcene
(both give succinic acid on oxidation).
Sesquicitronellene is obtained oil of
citronella
SesquicitronelleneFarnesene
preparation of Sesquicitronellenepreparation of Sesquicitronellene
1- Fractional distillation for oil….. fraction distills at 268-270º C
2- Remove of Isoeugenol and traces of other oxygenated constituents by
extraction with alcohol 60-70 %.
3- remove remaining traces of alcohol by Repeated fractional distillation over Na
metal
Acyclic….sesquiterpenes
6. III- Aromatic Hydrocarbone…Para-cymene
p-Cymene
Source:Source: widely spread in essential oils e.g. lemon, sage, thyme, origanum,
lavender, nutmeg, cinnamon et… It is probably an artefact formed during hydrodistillation
of monoterpenoids.
preparationpreparation
I-I- IsolationIsolation
1- Fractional distillation of oil. The fraction containing p-cymene contains cineole and terpenoid
hydrocarbons.
2- The terpenoid hydrocarbons are removed by oxidation with cold dilute KMnO4.
3- Cineole is removed by formation of its crystalline hydrobromide.
II-II- Semi-synthesis from monoterpenoidsSemi-synthesis from monoterpenoids
Properties:Properties: p-Cymene is a stable, colorless optically inactive liquid
Identification:Identification: solid p-hydroxy-isopropyl benzoic acid
which is identified by its melting point.
Uses:Uses: perfuming soaps and all kinds of technical preparations and
is an important constituent in imitation essential oils
Thymol
OH
Reduction
p-Cymene
COOH
H3C CH2OH
p-Cymene
Oxidation
Hot KMnO4
p- Hydroxy isopropyl
benzoic acid
7. II. Alicyclic 1. Monoterpene
Monocyclic
• Monocyclic (1 ring, 2 double bonds).
• These are derived from one of the three isomeric Menthanes
(ortho, meta and para)
p-menthane p-menthene p-menthadiene m-menthadiene
Limonene Sylvestrene a, b
8. (+)-Limonene
∆1:8(9)
p-menthadiene, 1-methyl,4-isopropenyl-1-cyclohexene
OccurrenceOccurrence
• The d-form present in orange oil “80%”,
grape fruit, Dill, and Fennel “60%”.
• The l-form is present in oil of Star Anise,
peppermint, and Pinus.
• The racemic (dl) form is known as dipentene
and occurs in the oil of Lemon grass, and Nutmeg.
Isolation:Isolation:
By careful fractional distillation, or by preparation of certain derivatives
as tetrabromide, and regeneration by zinc and acetic acid.
(+)-Limonene
9. Properties:
• Colorless oil, with orange like odor.
• On exposure of the oil to the moisture or to high temperature,
autoxidation takes place and carvone and carveol are produced
giving the oil caraway-like odor.
.
Uses:
It is widely used for flavoring of pharmaceuticals, Soaps
and in cosmetic preparations.
(+)-Limonene
air/moisture
autoxiadtion
Carvone
O
Carveol
OH
(caraway-like odor)
10. OH
OH OH
O OH
Limonene
& Dipentene
+
++
p-Cymene
p-Cymeneα-Terpinene
Carvone Carveol
Terpin hydrate Terpineol
cold mineral acids
hot mineral acids
air &
moisture
heat with S or Se
Degradation of limonene
11. 1
8
3
4
2
7
Union of C2 & C4
Thujane skelton
Pinane skeleton
Carane skeleton
Camphane
skeleton
p-Menthane
Fenchane
skeleton
(Has CH2
bridge)
Union of C2 & C8
Union of C3 & C8
Union of C1 & C8
Different Groups of
Bicyclic Monoterpenoids
Bicyclic Monoterpene Hydrocarbons: They usually composed of two condensed rings… 1st
ring 3-, 4-, 5-membered and 2nd
ring 6-membered … fusion with one double bond.
They may be regarded as derived from: 1) p-Menthane by direct union of two carbons
(thujane, pinane, carane, and camphene). 2) Methylated cyclohexanes (fenchane).
12. α-Pinene
6
4
1
2
35
8
9
10
(+)-α-Pinene (−)-α-Pinene
1
2
3
4
5
6
8
9
10
Occurrence: widely distributed in many oils
as in oil of turpentine, lemon, Coriander and
American Peppermint.
Isolation
1- By fractional distillation: at 155-165 o
C
2- As nitrosochlorides derivative (ppt) (with Tilden‘s reagent) and α-pinene is
regenerated by treatment with aniline.
Properties: Colorless oil with boiling point 156 o
C, optically active.
• The l-form presents in French turpentine, while the d-form present in
the American one.
Uses:
1- Raw material for manufacture of borneol, camphor,
terpineol, insecticides and plasticisers.
2- Sobrerol or pinol hydrate, used as mucolytic in cough mixtures
is formed by auto-oxidation of α-pinene in the presence of water and especially
in sunlight.
3- It is an important ingredient in many imitation essential oils.
OH
OH
Pinol hydrate
13. HO
Cl
Cl
HCl gas
- 10 o
C
isomerization KOH
(+)-α-Pinene Pinene HCl Bornyl chloride
(white ppt.)
Borneol
(pinnane to camphane)
O
Camphor
HNO3
Oxid.
α-pinene therefore used for preparation of synthetic Camphor
molecular
rearrangment
Semi-synthesis of borneol and camphor form α-pinene
15. II. Alicyclic 2. Sesquiterpene Hydrocarbons
• Many volatile oils contain in the fraction boiling between
250-280 o
C hydrocarbons of formula “C15H24” which have
been named sesquiterpenes.
• They are usually more viscous with faint odors, and sparingly soluble
in alcohol.
• Sesquiterpenes are classifiedclassified into four groups including:
1) Monocyclic sesquiterpenes (e.g. zingiberene).
2) Bicyclic sesquiterpenes (e.g. derivatives of azulenes).
3) Tricyclic sesquiterpenes (e.g. santalene).
16. Monocyclic sesquiterpenes
Zingiberene
Occurrence: the main constituent of oil of Ginger.
Isolation: by fractional distillation under vacuum (due to its high boiling point).
Properties
•It is a colorless oily liquid.
•easily resinifies on storage.
Zingeberene
S / Heat
Cadalene
naphthalene derivative
dehydrogenation
cyclization
17. Bicyclic sesquiterpenes
Naphthalene derivatives Cadinenes
H
H
β− Cadinene
Source: oils of cade, savin, cubebs, lemon grass etc…
IsolationIsolation
1- fractional distillation under reduced pressure.
2- The fraction containing cadinene (125 – 140º C) is diluted with 1/3 its volume of
glacial acetic acid and treated with a current of HCl gas (chloroderivative).
3- The crystalline cadinene hydrochloride derivative is then decomposed by
treatment with aniline to regenerate cadinene.
PropertiesProperties
It occurs as a viscid, colorless, very stable liquid.
On heating with S or Se, it is dehydrogenated and yields the naphthalene hydrocarbon
cadalene (similar to zingeberene).
UsesUses
1- It is occasionally used in perfuming soaps.
2- Oil of cade itself has been used as anti-eczematic.
18. Derivatives of Azulene
• Azulene are colored hydrocarbons, which vary in color from blue to violet or
even green.
• They occur in several essential oils and usually named after the names of the
plants in which they present e.g. chamazulene (Blue color) from oil of chamomile
and Guaiazulene in Guaiacum wood
• They are formed of bicyclic hydrocarbons with the formula “C15H18”commonly
called “azulenes” in which five- and seven-membered rings are fused together.
Azulene Chamazulene Guaiazulene
1
4
7
2
3 5
89
10
6
19. Isolation/Identification of azulenes:
• By preparation of derivatives or adducts which are used also for their
identifications:
1- They form addition compounds with strong mineral acids as phosphoric and
sulfuric acids, which decomposed in water to give the free azulenes.
2- With aq. ferrocyanic acid, they form azulene ferrocyanate that decompose in
water giving the azulene.
3- Nitrocompounds derivatives have sharp melting points used for their
identifications and azulene can be regenerated with alkali as NaOH.
OH
NO2
NO2O2N
OH
NO2
NO2O2N
CH3
NO2
NO2O2N
OH
Picric acid Styphnic acid Tortylic acid