chemistry of citral

1. Citral
Prepared by
Dr. N.GOPINATHAN
ASSISTANT PROFESSOR
DEPARTMENT OF PHARMACEUTICAL CHEMISTRY
FACULTY OF PHARMACY
SRI RAMACHANDRA UNIVERSITY
CHENNAI-116
TAMILNADU
INDIA

2. Structure

3. Presence of two double bond
• It takes up two molecule of bromine
that shows presence of two double
bond.

4. On ozonolysis yield acetone laevulaldehyde and
glycol

5. Presence of aldehyde group
• Presence of CO group with
hydroxylamine yield oxime

6. With phenyl hydrazine

7. Nature of CO group

8. • On reduction with Na/Hg yields
alcohol geraniol .
• On oxidation with silver oxide yield
geranic acid contains same number
of carbon atom therefore the CO
carbon is aldehyde.
• It reduces fehling solution further
confirms the presence of aldehyde
group [ aliphatic ]

9. Citral as an acyclic group
• Presence of two double bond and an
aldehyde group in citral

10. • The saturated hydrocarbon
C10H22 which corresponds to
general formulae CnH2n+2 for
Acyclic compounds.
• It indicates that the citral
must be a Acyclic compound

11. Carbon skeleton
• When heated with potassium hydrogen
sulphate [ dehydration ] .
• It cyclised to p-cymene, a cyclic
compound of known structure

12. Formation of p-cymene and products of
ozonolysis reveals the carbon skeleton.[ It
contains two isoprene unit which are joined by
head to tail arrangement.
Formation of P-Cymene reveals the position of
methyl isopropyl group

13. On oxidation with alkaline KMNO4 followed by
chromic acid reveals the product acetone, oxalic
acid and laevulic acid. It is possible only if citral
has this structure

14. Evidence for structure
• On treatment with sodium bi sulphite
forms mono and di sulphite which
indicates the double bond is conjugated
with carbonyl group.

15. • α - β unsaturated
carbonyl group is
confirmed by UV
spectrum.
• λ max – 238 nm

16. Evidence for structure
• Citral with potassium carbonate is
coverted into acetaldehyde and an
unsaturated ketone where it is identified
as 6 methyl hept-5ene-2 one by its
ozonolysis to actone and laevulinic acid

18. Cis trans isomerism

19. Isomerism of citral Cis Trans isomerism
• Citral exist in two forms differ in
arrangement aldehydic group about the
double bond in the 2,3 position in one
aldehyde group is cis with respect to the
methylene group of main chain wherein
the other it is transwo chiral two
• Both forms in natural so it is actually a
mixture of these two

20. Existence of two forms proved chemically
• It forms two different semicarbazone.
• On reduction trans citral gives geraniol
hence it is known as geranial or citral a
while cis gives nerol hence it is neral or
citral b.
• Citral that cyclise easily to alpha terpineol is
cis isomer while the other is trans.
• Neral is found to be cis which cyclise 9
times as rapid as geranial

21. In nerol the alcoholic group is more close to the
carbon involved in the ring formation than in
geraniol

22. Evident by NMR
• Value of CH2 [a] and CH3 [b] are
different due to different magnetic
shielding effect of the carbonyl double
bond in CHO.

23. THANK YOU