1. Chemistry project
ORGANIC SYNTHESIS
- V.SUCHARITA (class 12)
S.B.O.A.SCHOOL AND JUNIOR
COLLEGE
ACKNOWLEDGEMENT:
I would first of all like to thank my project mentor, Prof.S.Sankararaman from the
department of chemistry, IIT-Madras for giving such an exciting project to work on and for
helping and guiding me throughout the course of the project. I would also like to extend my
thanks to the 2 PhD students working under Prof., namely Mr.Jeelani Basha Shaik and
Mr.Sureshbabu who taught me everything and helped me completely with the lab work and
theory in spite of their researches. I would also like to express my thanks to Mohan sir
from the Chemistry department, IIT-Madras for teaching us about the various instruments
used in the department (e.g. Mass spectrometer, Raman spectrometer, NMR, etc.) and for
letting me use the NMR for the project. Our sincere thanks to RSI-C 2013 and the PSBB
group of schools and all the other institutions for this wonderful opportunity. Last but not
the least I extend my heartfelt gratitude to my school, S.B.O.A School and Junior College and
our Principal, Mrs.P.C.Selvarani because of whom I got the chance to experience this
wonderful program.
1. PREPARATION OF PURE 1,4-DIOXAN
O
O
1.1. Cutting sodium metal :
Sodium metal which is an alkali metal as we all know reacts easily and vigorously with air
as well as when exposed to moisture. So care should be taken in storing and using sodium
metal as it can explode on contact with air or moisture!
2. The sodium metal chunk is stored in hexane (C6H14) to prevent it from reacting violently
with air or moisture. Take it out and since it is a soft metal, it is cut into small pieces using a
knife. Then it is rolled into a thin sheet. Many such required amounts of sheets are
prepared.
Take a round bottom flask and pour in sufficient amount of impure 1,4-dioxan. Put
adequate amount of the previously made sodium metal pieces into the round bottom flask.
Then add benzophenone (C6H5COC6H5) to it. benzophenone acts as an indicator. As soon as
it is added, the colour of the solution changes to dark blue colour. It indicates that the Na
gets oxidized and benzophenone gets reduced (ie) the reaction is in progress. This round
bottom flask is attached to a condenser. The round bottom flask is placed on the heater
which consists of a heating mantle with a wire mesh made of Tungsten.
CONDENSER – SETUP: A condenser is a device used for reducing a gas or vapor to a liquid.
Condensers operate by removing heat from the gas or vapor. Once sufficient heat is
eliminated, liquefaction occurs. A heat conductive metal, such as copper, is commonly used to
transport the vapor.
In the condenser column there are 2 slots for connecting the inlet and the outlet tubes from
the turbine. The lower slot should always be connected to the inlet pipe because only then it
maintains the regular/uniform flow of water through the condenser pipe and the top slot is
for the outlet. A constant supply of water is provided to the set up through a turbine.
The reaction should be carried out in an oxygen free
atmosphere since there is Sodium metal and it reacts
3. vigorously with oxygen and gets oxidized and may turn violent.
Therefore this reaction has to be done under Nitrogen
atmosphere and hence a balloon filled with nitrogen has to be
connected to the top valve and the tube should be free of
oxygen. Teflon is wrapped around the attached tube and valves
to keep it air tight.
NOTE : After adding benzophenone, if the colour of the solution has not become dark blue; it
means that there is not adequate amount of sodium or 1, 4-dioxan and hence the reaction will
not take place as expected and therefore more amount of either one has to be added. This is
not advised as disturbing the setup again and again will lead to failure in the preparation of
the required compound.
The temperature of the heating coil is set to about 120˚C and it takes about 20-30 minutes
for the reaction to complete. The aim of this reaction is to prepare pure sample of 1, 4-
dioxan (i.e.) the sample of 1, 4-dioxan should be free from water.
The pure sample of 1, 3-dioxan gets separated in the condenser and we arrive at the
desired product which is 1,4-dioxan without and water.
PYRENE
MOLECULAR FORMULA – C16H10
MOLECULAR MASS – 202
MOLAR MASS - 202.25 g/mol
APPEARANCE – COLOURLESS SOLID (sometimes yellow due to
impurities)
DENSITY – 1.271 g/ml
MELTING POINT - 145-148 °C (418-421 K)
BOILING POINT - 404 °C (677 K)
SOLUBILITY IN WATER - 0.135 mg/l
4. PYRENE is a polycyclic aromatic hydrocarbon (PAH) consisting of four fused benzene rings,
resulting in a flat aromatic system. This colorless solid is the smallest peri-fused PAH (one
where the rings are fused through more than one face). Pyrene forms during incomplete
combustion of organic compounds.
Pyrene was first isolated from coal tar, where it occurs up to 2% by weight. As a peri-fused
PAH, Pyrene is much more resonance-stabilized than its five-member-ring containing
isomer fluoranthene.
It undergoes a series of hydrogenation reactions, and it is susceptible to
halogenation, Diels-Alder additions, and nitration, all with varying degrees of selectivity.
Pyrene and its derivatives are used commercially to make dyes and dye precursors, for
example pyranine and naphthalene-1, 4, 5, 8-tetracarboxylic acid.
Suzuki coupling reaction
PALLADIUM-CATALYZED CARBON-CARBON BOND FORMATION VIA CROSS
COUPLING:
In coupling reactions, the most commonly used catalyst is palladium. The principle
of a palladium-catalyzed cross coupling reaction is that 2 metals are gathered on the metal
through the formation of bonds. Due to this the carbon atoms bound to palladium are
brought close to each other. They later couple with one another and this leads to the
formation of a new carbon-carbon single bond.
In 1979, Akira Suzuki and his co-workers found out that organoboron compounds in the
presence of a base can be used coupling partners in palladium-catalyzed cross coupling
with vinyl and aryl halides. This reaction has later on been extended to also include
couplings with alkyl groups. We have copied the Suzuki coupling reaction and extended it
to the formation of 1,3,6,8-tetraphenylpyrene and 1,3,6,8, tetrakis(4-ethoxyphenyl)pyrene.
5. CATALYST USED:
Trans-bis(1,4-dimesityl-3-methyl-1,2,3-triazol-5ylidene)
palladium(ll)dichloride :
trans-Bis(1,4-dimesityl-3-methyl-1,2,3-triazol-5-ylidene) palladium(II) dichloride has been
shown to be an excellent catalyst for the multiple Suzuki-Miyaura coupling reactions of
polybromoarenes to the corresponding fully substituted polyarylarenes.
PREPARATION OF PALLADIUM(O) CATALYST :
Palladium(0) catalyst is as such not available. Hence we take palladium(II)
catalyst and add it to the reaction mixture and in the course of the reaction
palladium(0) catalyst is prepared in situ.
REACTION MECHANISM :
Ar : Aryl group L : Ligand
NaOH
+
+ B OH
OH
OH
Ar Ar+L2Pd(0)
+ Na Br
L2Pd(II)Cl 2 L2Pd(0)
Active catalyst
7. METHODOF PREPARATION OF1,3,6,8 – TETRAPHENYLPYRENE :
200mg (0.386 mmole) of 1,3,6,8 – tetrabromopyrene, 282.6mg (2.3166 mmole) of
phenylboronic acid were weighed separately using a weight balance and were taken in a
reaction tube containing a magnetic pellet. Palladium catalyst (2 mole%) ,
triphenylphosphene (4 mole%) were weighed separately and were added to the reaction
tube. 6ml of 1,4- dioxan was added to the reaction tube. 123.5mg (3.088 mmole) of sodium
hydroxide (crushed pellets) was added to the reaction tube under Nitrogen atmosphere. It
is done under Nitrogen atmosphere as NaOH is present and as we all know Sodium is very
reactive with air and water and may causes explosion. Hence we use a balloon filled with
nitrogen to keep the reaction atmosphere oxygen and moisture free.
The reaction tube was placed in an oil bath which had a heating plate and was heated to
about 105 O C. The reaction took roughly about 8-10 hours to complete.
1,3,6,8-tetrabromOpyrene phenylboronicacid 1,3,6,8-
tetraphenylpyrene
8. THIN LAYER CHROMATOGRAPHY:
Chromatography is used to separate mixtures of substances into their components. All
forms of chromatography work on the same principle.
They all have a stationary phase (a solid, or a liquid supported on a solid) and a mobile
phase (a liquid or a gas). The mobile phase flows through the stationary phase and
carries the components of the mixture with it. Different components travel at different
rates. TLC can be used to monitor and observe the progress of a reaction, determine the
purity of the product and identify the various compounds present.
Thin layer chromatography is done exactly as it says - using a thin, uniform layer of silica
gel or alumina coated onto a piece of glass, metal or rigid plastic.
9. The silica gel (or the alumina) is the stationary phase. The stationary phase for thin layer
chromatography also often contains a substance which fluoresces in UV light. The mobile
phase is a suitable liquid solvent or mixture of solvents.
METHODOF PREPARATION OFTLC :
A pencil line is drawn near the bottom of the plate and a small drop of a solution of
the dye mixture is placed on it.
Any labeling on the plate to show the original position of the drop must also be in
pencil. If any of this was done in ink, dyes from the ink would also move as the
chromatogram developed.
When the spot of mixture is dry, the plate is stood in a shallow layer of solvent in a
covered beaker. It is important that the solvent level is below the line with the spot
on it.
The reason for covering the beaker is to make sure that the atmosphere in the
beaker is saturated with solvent vapour. To help this, the beaker is often lined with
some filter paper soaked in solvent. Saturating the atmosphere in the beaker with
vapour stops the solvent from evaporating as it rises up the plate.
As the solvent slowly travels up the plate, the different components of the dye
mixture travel at different rates and the mixture is separated into different coloured
spots.
10. PREPARATION OF1,3,6,8-TETRAKIS (4-ETHOXYPHENYL) PYRENE :
CHEMICALS USED :
1. 1,3,6,8 – tetrabromopyrene (C16H6Br4 )
2. Para ethoxyphenylboronic acid (C8H11BO3 )
3. Palladium (ll) catalyst (PdCl2MTz )
4. Triphenylphosphene (PPh3 )
5. Sodium hydroxide (NaOH)
6. 1,4 – dioxan (
O
O )
COMPOUND /
REAGENT
MOLECULAR
WEIGHT (g)
WEIGHT (OR)
VOLUME (mg/ml)
NUMBER OF
MMOLES
NUMBER OF
EQ. UNITS
C16H6Br4 518 200 0.386 1
C8H11BO3 165 382.24 2.3166 6
PdCl2MTz 814 6.28 0.0077 0.02
PPh3 262 4.046 0.015 0.04
NaOH 40 123.5 3.088 8
1,4-dioxan 6ml
11. METHODOF PREPARATION OF1,3,6,8 – TETRAKIS (4-
ETHOXYPHENYL) PYRENE:
200mg (0.386 mmole) of 1,3,6,8 – tetrabromopyrene, 382.4mg (2.3166 mmole) of para
ethocyphenylboronic acid were weighed separately using a weight balance and were taken
in a reaction tube containing a magnetic pellet. Palladium catalyst (2 mole%) ,
triphenylphosphene (4 mole%) were weighed separately and were added to the reaction
tube. 6ml of 1,4- dioxan was added to the reaction tube. 123.5mg (3.088 mmole) of sodium
hydroxide (crushed pellets) was added to the reaction tube under Nitrogen atmosphere. It
is done under Nitrogen atmosphere as NaOH is present and as we all know Sodium is very
reactive with air and water and may causes explosion. Hence we use a balloon filled with
nitrogen to keep the reaction atmosphere oxygen and moisture free.
The reaction tube was placed in an oil bath which had a heating plate and was heated to
about 105 O C. The reaction took roughly about 8-10 hours to complete.
REACTION :
1,3,6,8-tetrabromopyrene phenylboronicacid 1,3,6,8-tetrakis(4-
ethoxyphenyl)pyrene
13. METHOD OF ISOLATION OF PRODUCTS:
1. USING A ROTAVAPOUR :
(http://www.thefreedictionary.com/Rotavapor )
What is a rotavapour?
Rotary evaporator or rotavapouris a device used in chemistry laboratories in which a
liquid is evaporated by reducing the pressure through a vaccum pump thereby reducing the
boiling point of the solvents and applying heat, while rotating the round bottom flask (in
which the solvent along with the compound is put). The reduced pressure speeds the
evaporation process and allows the evaporation to be conducted at temperatures lower
than would otherwise be possible, thus reducing decomposition of unstable substances.
The rotation also serves to increase the surface area from which evaporation takes place
and to reduce the effect of "bumping", the sudden burst of vaporization that can scatter
liquid exposed to reduced pressure.
Design:
Main components of a rotavapour –
1. A motor unit that rotates the
Evaporation flask or vial containing the
Sample.
2. A vapour duct that is the axis for sample
rotation, and is a vacuum-tight conduit for
the vapor being drawn off of the sample.
3. A vacuum system, to substantially reduce
the pressure within the evaporator system.
4. A heated fluid bath (in our case water) to heat the
sample.
5. A condenser with either a coil passing coolant, or
a "cold finger" into which coolant mixtures such
as dry ice and acetone are placed.
14. 6. A condensate-collecting flask at the bottom of the condenser, to catch the distilling solvent
after it re-condenses.
7. A mechanical or motorized mechanism to quickly lift the evaporation flask from the heating
bath.
( From Wikipedia, the free encyclopedia )
Howto separate solvent and product using the rotavapour:
i. The tube in which the reaction is carried is called the reaction
tube. Take the reaction tube containing 1,3,6,8-
tetraphenylpyrene along with the solvent and other
unreacted compounds.
ii. Since the reaction tube is kept in the oil bath in the heating
plate, which contains oil, the oil has to be washed away. For
this purpose we use n-hexane to remove all the excess oil
sticking to the reaction tube.
The colour of the product, which has settled, was
in ash-green colour.
iii. To the reaction tube, add little amount of water.
The product (i.e. 1,3,6,8-tetraphenylpyrene) is insoluble in
water and is seen suspended. When viewed under Ultra
Violet and fluorescence it showed both UV and
Fluorescence characters.
iv. Pour the mixture in a separating funnel. Once again add H2O
to it.
v. Add dichloromethane (DCM) to the separating funnel. The
funnel has to be shaken in a particular manner; else the funnel may burst due to DCM
vapours accumulation. The funnel is shaken so that the product (soluble in DCM) dissolves
in it and we get 2 different layers.
15. Method for shaking the separating funnel after adding DCM:
After adding DCM to the separating funnel containing the product and water, the funnel has
to be shaken so that the product dissolves in DCM. The separating funnel should be closed
with a stopper on top and the bottom should be closed using the turning switch. Then the
funnel is to be held horizontal and shaken 4 to 5 times. Then it should be help upside down
and the turning switch is opened to let the DCM vapours escape. If we don’t let the DCM
vapours escape, then they will accumulate inside the separating funnel and after a point it
may burst out. This is carried on for 6-7 times until all the vapours are released.
DCM being heavier and denser than water settles down and water floats on the top.
The funnel contains the product (i.e. 1,3,6,8-tetraphenylpyrene) and a little bit of 1,4-
dioxan dissolved in DCM and impurities and unreacted products dissolved in water.
The stopper of the funnel is opened and the bottom layer (the DCM layer) is collected in a
round bottom flask.
The round bottom flask is then placed in the Rotavapour machine.
The rotavapour rotates the RBF in water and heats it, The DCM in the RBF evaporates, goes
into the chamber, condenses and is collected in another rather bigger RBF.
The reaction mixture was left with 1,4-dioxan and we evaporated the 1,4-dioxan using the
same technique in the rotavapour and got our product.
The product was obtained in a powdered form which was in yellow colour.
2. FILTRATION :
Filtration was used to separate the 2nd product 1,3,6,8 – TETRAKIS (4-
ETHOXYPHENYL)PYRENE.
The product along with the unreacted reactants and impurities was taken. A big conical
flask was taken and a funnel along with a filter paper was taken and placed on the conical
flask. Anhydrous Sodium sulphate was taken and placed on the conical flask. Sodium
sulphate is taken because it absorbs the water present in our product.
The reaction mixture was taken and the whole thing was poured into the filtration setup.
Once all the solvent passes through the filter paper, our product was obtained on the paper.
It was then dried and was scraped out of the filter paper carefully making sure that no
paper also got mixed with our product.
The product obtained was in the form of green coloured powder.
16. 1,3,6,8-tetraphenylpyrene 1,3,6,8-tetrakis(4-
ethoxyphenyl)pyrene
After getting the products dried, they were weighed to calculate the
weight and the percentage yield.
1. 1,3,6,8 – TETRAPHENYLPYRENE:
Weight of the product obtained – 248 mg
%yield = (Moles of product/Moles of the starting mixture) *100
= [(Weight/molecular weight)P/( Weight/molecular weight)SM ]*100
= [(248/506)/0.386]*100
= 1.269*100
= 126.9 %
2. 1,3,6,8 – TETRAKIS (4-ETHOXYPHENYL) PYRENE :
Weight of the product obtained – 289 mg
%yield = (Moles of product/Moles of the starting mixture) *100
= [(Weight/molecular weight)P/( Weight/molecular weight)SM ]*100
= [(289/683)/0.386]*100
= 1.096*100
= 109.6%
17. NUCLEAR MAGNETIC RESONANCE [NMR]:
From Wikipedia, the free encyclopedia
Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in
a magnetic field absorb and re-emit electromagnetic radiation. This energy is at a
specific resonance frequency which depends on the strength of the magnetic field and the
magnetic properties of the isotope of the atoms. The most commonly studied nuclei
are 1H and 13C. A key feature of NMR is that the resonance frequency of a particular
substance is directly proportional to the strength of the applied magnetic field.
The principle of NMR usually involves two sequential steps:
The alignment (polarization) of the magnetic nuclear spins in an applied,
constant magnetic field H0.
The perturbation of this alignment of the nuclear spins by employing an electro-magnetic,
usually radio frequency (RF) pulse. The required perturbing frequency is dependent upon
the static magnetic field (H0) and the nuclei of observation.
The angular momentum associated with nuclear spin is quantized. This means both that the
magnitude of angular momentum is quantized (i.e. S can only take on a restricted range of
values), and also that the orientation of the associated angular momentum is quantized.
The associated quantum number is known as the magnetic quantum number, m, and can
take values from +S to −S, in integer steps. Hence for any given nucleus, there is a total
of 2S + 1 angular momentum states.
18. NMR spectroscopy is one of the principal techniques used to obtain physical, chemical,
electronic and structural information about molecules due to either the chemical
shift, Zeeman effect, or the Knight shift effect, or a combination of both, on the resonant
frequencies of the nuclei present in the sample. It is a powerful technique that can provide
detailed information on the topology, dynamics and three-dimensional structure of
molecules in solution and the solid state.
Here in the lab, to characterize the products, which we synthesized, we used the 4000 and
500 MHz NMR.
Inside the NMR machine there are basically 2 huge tubes.
The outer tube contains liquid Nitrogen. The inner
Tube/container consists of liquid Helium and super conductor.
SUPER CONDUCTIVITY – Super conductivity basically
means that the resistance will become zero. What this does is
that it liquifies and cools the material inside it to below liquid
helium temperature. This is done because it allows free flow
of electrons. This is used for magnetic field production in NMR.
When current is passed to the NMR machine, magnetic field
is produced. The nucleus inside the magnetic field (I.e. the
proton and the electron) will align themselves and rotate.
This phenomenon is known as precision.
Using the NMR we measure the absorbed energy. Depending
on the surrounding conditions, it absorbs a certain amount of
E. The 2 variables involved are :
1. Magnetic Field
2. Radio frequency.
Tetramethylsilane (TMS) is used as a reference for NMR. The NMR must have a uniform
scale and it is in PPM (Parts per Million).
Why do we use TMS?
TMS is inert.
It is highly volatile.
It absorbs very high magnetic field than organic compounds.
While giving a compound for NMR, we used a Deuterium substituted solvent, mostly CDCl3.
Why deuterium is is used in NMR?
Generally deuterium substituted solvents are used for NMR. This is for obtaining a uniform
magnetic field. It will adjust the magnetic field to get uniform magnetic field. This is called
locking the magnetic field.
19. PURIFICATION OF COMPOUNDS:
1. CRYSTALLIZATION –
Crystallization is a natural/artificial process of
formation of solid crystals precipitating from a solution. Crystallization is also a
chemical solid–liquid separation technique, in which mass transfer of a solute
from the liquid solution to a pure solid crystalline phase occurs. For
crystallization, we should select solvents carefully in such a way that the
compound to be purified is sparringly soluble in it. If it is completely soluble,
then the whole thing will evaporate (i.e. the final product along with the
impurities) and finally we will have nothing left.
For our 1st product, 1,3,6,8-tetraphenylpyrene we selected a mixture of 1,2-
dichloroethane, dichloromethane and cyclohexane as solvents. The compound
was dissolved in these solvents and placed in a crystallization container and was
closed with cotton to let the solvents evaporate. Care should be taken that we
should not crystallize it to dryness. If this happens, then it will be a waste. There
should be small amounts of the solvent left which is called as mother liquor.
Once this stage is reached what we did was to decant the mother liquor and
scrape out the crystals from the crystallization container and dry it using a
vaccum tube.
20. As seen from the pictures above, the crystals of the first compound was found to be
greenish in colour. Due to little bit of impurities some blue colouration is also seen. But
after recrystallization, we finally arrived at pure crystals.
For our second product (i.e.) 1,3,6,8-tetrakis(4-ethoxyphenyl)pyrene, the same method was
followed but the only difference was that the solvent mixture contained only 1,2-
dichloroethane and cyclohexane.
21. The crystals of our second product was also found to be green in colour but the shape of it
resembled that of small, sharp needles.
22. FLUROSCENCE AND UV ACTIVITY :
The starting material pyrene itself is very UV and fluorescence active. Therefore it is only
obvious that our 2 products should also be UV and fluorescence active as they are all
pyrene derivatives.
1,3,6,8-tetraphenylpyrene under UV light and fluorescence
1,3,6,8-tetrakis(4-ethoxyphenyl)pyrene :
23. APPLICATIONS / USES :
These compounds are used in the production of Organic Light Emitting Diodes.
OLED : An OLED (organic light-emitting diode) is a light-emitting diode (LED) in which the
emissive electroluminescent layer is a film of organic compound which emits light in
response to an electric current. This layer of organic semiconductor is situated between
two electrodes. Generally, at least one of these electrodes is transparent. OLEDs are used to
create digital displays in devices such as television screens, computer monitors, portable
systems such as mobile phones, handheld games consoles and PDAs.
Due to their wonderful fluorescence activity, they have significant potential for
luminescence applications.
In general, The compounds produced by using Suzuki coupling have enormous application
in the medical field, for example : in anti-inflammatory drugs, etc..
The 2nd compound prepared by us 1,3,6,8-tetrakis(4-ethoxyphenyl)pyrene we are proud
to say that this is the 1st time in chemistry literature that this compound in prepared. That
is, the synthesis of this compound has so far not been recorded in literature so far. Due to
this, its applications are yet to be found!
