2. Serial no Topics Slide no
1 Definition of citral 3,4
2 Physical properties of citral 5
3 Isoprene units of citral 6
4 Occurrence of citral 7,8,9,10
5 Isolation of citral 11,12
6 Industrial synthesis of citral 13,14
7 Reactions of citral 15,16,17,18,19
8 Structure elucidation of citral 20,21,22,23,24,25,26
9 Uses of citral 27
3. Definition
Citral, or 3,7-dimethyl-2,6 octadienal or lemonal, is
either a pair, or a mixture of terpenoids with the
molecular formula C10H16O.
The two compounds are double bond isomers.
The E-isomer is known as geranial or citral A.
The Z-isomer is known as neral or citral B.
Due to cis–trans isomerism at the C=C bond nearly the
aldehyde group obtained from essentials oils of plant
sources.
4. Definition
The isomer geranal has strong lemon odour.
The isomer neral has lemon odour is less strong and
sweeter.
Geranal Neral
5. Physical properties of citral
Citral is a clear yellow colored liquid with a lemon-like
odor. Less dense than water and insoluble in water
Melting point of citral is <-10°C
Density of citral is 0.9 g/cm³
Citral is not stable to alkanes and strong acid
When heated to decomposition it emits acrid smoke and
irritating fumes
6. Isoprene units of citral
C
H
O
Citral is an α,β-unsaturated aldehyde classified as
a monoterpenoid compound from the 3,6-dimethyloctane
series, characterized by a head-to-tail linkage of two
isoprenoid subunits
C
H
O
7. Occurance
Citral is present in the oils of several plants including
lemon myrtle
cultivated in Australia for flavouring and essential oil.
It is the highest natural source of citral.
Citral as an isolate in steam distilled lemon myrtle oil is
typically 90–98%,
8. Occurrance
Lemon grass
It is cultivated in India, south east Asia and Africa
Lemon grass is a good source of lemon grass oil which is a
good source of natural citral
Lemon grass oil contain 85-65%
9. Occurrence
lemon tea-tree
It is grown in plantations in Kenya, South Africa, and
Australia.
The essential oil of tea tree contain 70-80% citral.
10. Occurrence
Lemon balm
The lemon balm contain 11% citral
It is cultivated in to south-central Europe, North Africa,
the Mediterranean region, and Central Asia
11. Isolation of citral
Citral is isolated from lemon grass oil which is obtained from lemon grass by
steam distillation.
Method:
Lemon grass (chopped or un chopped) is filled in the distillation flask and
fitted tightly so that the vapours and oils was not leaked out now the steam is
injected in to it so that the upcoming steam carries away the essential oil from
the plant material then the lemon grass oil as well as the vapours are passed
through the condenser where they condensed as the oil is lighter then water so
it will float through the surface of water and it is then easily seprated now the
thus obtained is the lemon grass oil which contain 85%
12.
13. Industrial synthesis of citral
First part clasien rearrangement
Involves and oxygen in a chair like transition state
Second part cope rearrangement
Only carbon is involved in a chair like transition state
These two reactions happen in succession when the two
starting materials are heated together, and the reaction is
driven by formation of conjugated carbonyl group in the
product
14.
15. Reactions of citral
Reduction of citral
Citral is reduced to either citranellal or nerol/geraniol
The H2 catalyst either reduce the double bond or it will
reduce the aldehyde to alcohol
CHO
H2
catalyst
CHO CH2OH
Citral citronellal nerol or geraniol
16. Reactions of citral
Synthesis of ionone from citral in which an aldol
condensation reaction followed by the rearrangement
reaction
First step is the nucleophillic addition of carbanion of
acetone on carbonyl carbon of citral is the base catalyzed
reaction
The aldol condensation product eliminate water through
enolate ion
18. Reaction of citral
Step 2 the reaction is proceed by acid catalysis where a
double bond opens to from the carbocation
A rearrangement reaction followed by ring closure then
the proton is abstracted from the molecule by proton
acceptor Y to form ionone
20. Structure elucidation of cital
Citral form both mono and di bisulfite by the addition of
sodium bisulfite to reveal the presence of conjugated
aldehyde group its UV spectrum displayed a band at 238
nm to confirm this.
CHO
OH
SO-3
Na
+ NaHSO3
21. Structure elucidation of citral
Mass spectrum
Molecular mass of citral is 152
Citral show a peak at m/z 29 due to hemolytic alpha
cleavage
It shows a peak at m/z 69 due to beta cleavage
It shows a peak at m/z 124 due heterolytic alpha cleavage
25. Structure elucidation of citral
C-13 NMR
The chemical shift of C1 185 to 220 ppm
The chemical shift of C2 and C3, C7
and C8 100 to 150 ppm
The chemical shift of C4, C9, C10 8-30 ppm
The chemical shift of C5 and C6 15 to 55 ppm
CHO
1
2
3
4
5
6
10
7
9
8
26. Structure elucidation of citral
Proton NMR
Proton at C1 has chemical shift value 9.4-9.8 ppm
No of protons at C2 and C3 has chemical shift value 5.0-
6.0 ppm
No of protons at C5 and C4 has chemical shift value 1.9
ppm
No of protons at C6, C7 and C8 has chemical shift value
1.7ppm
CHO
1
2
3
4
5
67
8
27. Uses of citral
Citral is an aroma compound used in perfumery for its
citrus effect
Citral is used as a flavor and for fortifying lemon oil
Citral has strong antimicrobial qualities
Citral is used in the synthesis of Vitamin A. ionone and
methylionone,
Mask the smell of smoke
