1. Answer all parts.
a) Piperine, one of the main constituents in black pepper can be extracted from solvent
extraction methods.
(i) Briefly explain one such extraction method with reasons for the selection.
Soxhlet extraction
A hot continuous method
Can extract heat-labile products
Use a minimum amount of solvents and run multiple times with the same
solvent content.
Efficient extraction
(12 marks)
(ii) Discuss one purification method of piperine from the crude extract obtained
from the above-mentioned extraction technique.
Purification of piperine
Base (potassium hydroxide) solution is added to the filtrate to precipitate
insoluble materials from the free alkaloids.
Alcoholic supernatant was separated, and was kept overnight, to facilitate the
crystal formation.
Filter off crude crystals and recrystallized using suitable solvent
(12 marks)
(iii)Name three different analytical methods used to determine the purity of the
extracted piperine.
Melting point analysis
Spectral analysis
TLC analysis with the standards
(06 marks)
(30 marks)
b) Piperine (C17H19NO3) and chavicine are geometrical isomers. The structure
determination of piperine was carried out using the chemical tests and other analyses
given below.
(i) Based on the results of the analyses deduce possible structures of piperic
acid.
Piperine structure:
(12 marks)
Catalytic hydrogenation and bromination
Presence of two double bonds
• The presence of carboxylic group was confirmed by the reaction with NaHCO3
• When piperic acid is oxidized with KMnO4, piperonal (aldehyde)
and the piperonylic acid yields by further oxidation
When piperonylic acid is heated with HCl at 200 0C under pressure, Formaldehyde
and protocatechuric acid formed
(12 makrs)
(ii) If piperic acid is known to possess trans-trans arrangement which is the correct
structure for piperic acid?
A structure
(06 marks)
(iii) Propose structures for piperine and chavicine based on the results you
obtained for part (i) and (ii)
By coupling with piperidine (C5H9)
(10 marks)
(40 marks)
c) Morphine, an Opium alkaloid has been used since ancient times to create analgesic
and narcotic effects.
(i) What is the class of alkaloids that morphine belongs to?
Isoquinoline alkaloids
(06 marks)
(ii) Discuss the significance of the two -OH groups to the reactivity of the
molecule.
OH group on the 3rd C is essential for activity and OH on the 6th is not
necessary for the activity
(06 marks)
(iii) Propose a plausible laboratory synthetic method for the synthesis of heroin
from morphine.
(08 marks)
(iv) Discuss why heroin is showing a more potent narcotic effect than morphine.
Conversion of two OH groups to OAc groups makes the molecule very
nonpolar
Facilitates the BBB crossing
Potent CNS stimulant and act as a strong narcotic
(10 marks)
(30 marks)
2. Answer all parts.
a) Geranyl PP (GPP) can act as a precursor for the synthesis of acyclic monoterpenoids
(myrcene) and monocyclic monoterpenoids (alpha-terpineol). Using a suitable
diagram explain this statement.
(25 marks)
b) Myrcene, is an acyclic Monoterpenoid with the molecular formula of C10H16. The
structure of myrcene could be either A of B given below.
(i) The following data was observed for a structure elucidation of myrcene. Using
the below given data deduce the correct structure of myrcene from A and B.
I.
II. Myrcene can form an adduct with Maleic anhydride.
III. Ozonolysis of Myrcene gives Acetone + Formaldehyde and keto
aldehyde [C5H6O3]
IV. Ketoaldehyde [C5H6O3] oxidizes to Succinic acid [(CH2)2(COOH)2]
• Molecular formula: C10H16
Test for unsaturation
It contains three double bonds
Presence of conjugated double bonds
• Myrcene is able to form adduct with Maleic anhydride.
• Therefore one conjugation
Ozonolysis
Possible structure of myrcene is B
(30 marks)
c) Based on the reaction scheme given below for the synthesis of alpha terpineol
answer the following questions.
I. Write down the missing intermediates of A, B,C, D, and E and
Reaction conditions of F and G.
S O 3H OH
F u m in g H 2 S O 4 KOH
COOH COOH COOH
N a /E tO H
p -to lu ic a c id
Br OH
P y rid ie n HBr
heat
COOH COOH
COOH
( )
i. R e s o lu tio n
ii. C 2 H 5 O H /H C l
i. C H 3 M g I
ii. H 3 O + i.M e M g B r
ii. H y d r o ly s is OH
C O 2E t O
a lp h a -te rp in e o l
II. Show a plausible mechanism for the conversion of D to E.
CH3MgBr addition to the carbonyl carbon followed by hydrolysis
mechanism
III. Write down the products you will obtain from the reaction of alpha-
terpineol .
I. With Dilute H2SO4
II. With Conc. H2SO4 and heating
OH
H 2O / H +
OH OH
a lp h a -te rp in e o l H e a t w ith A c id
(45 marks)
