Cindy Lee
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Synthesis of Azulene
March 9, 2006-April 6, 2006
Introduction & Background
Azulene is a simple, beautiful, blue compound with many unusual properties (Lemal et.
al.,1999). It is also quite expensive (Alrich 2006: $194 /g, 99% pure). This aromatic
hydrocarbon is an isomer of naphthalene. However, it is less stable than naphthalene
because it has less resonance structures.
The fundamental difference between the two is that naphthalene is an alternant
hydrocarbon, while azulene is a non-alternant. This results in azulene not having “mirror
related” molecular orbitals and a dipole moment, from non-uniform charge distribution.
The reason azulene is blue, is also due to the fact it is non-alternant. Though azulene’s
HOMO and LUMO gap are close to that of anthracene, which is colourless, it isn’t
colourless. Since azulene is non-alternant, the HOMO and LUMO are not mirror-related
so the atomic orbital coefficients in these two orbitals differ greatly at many of the
skeletal atoms. The gap between the HOMO and LUMO is smaller than anticipated
because promotion of one of the pairs of electrons from the HOMO to the LUMO
increases the average distance between the members of the pair, which reduces the
mutual repulsion of that pair considerably and a lower transition energy results. This
lower transition energy correlates to blue light.
In this experiment, we plan to synthesize azulene by an adapted synthesis of Copland,
Leaver, and Menzies. This involves preparation of the intermediates 3,4dibromotetrahydrothiophene and 6-dimethylaminofulvene. 3,4dibromotetrahydrothiophene is then reacted with strong base to form thiophene-1,1dioxide. This thiophene and the 6-dimethylaminofulvene are reacted together to form
azulene. Each intermediate and the product were analyzed by physical properties,
infrared, and 1H NMR spectroscopy. We were successful in synthesizing azulene, with
an overall yield of 114% (end product contained some impurities).
References
Synethesis of Azulene, a Blue Hydrocarbon. David M. Lemal and Glenn D. Goldman,
Journal of Chemical Education (1999) 65: 923
Chemistry 361/363 Laboratory Manual 2005-2006 Edition L.M. Browne pp 187-198
Organic Chemistry Experiments Chemistry 161/163 2002-2003 Edition L.M. Browne pp
317-322
Chemfinder www.chemfinder.com
SDBS http://www.aist.go.jp/RIODB/SDBS/cgi-bin/cre_index.cgi
NIST Chem Webbook http://webbook.nist.gov/chemistry/
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Balanced Equations
(1)
(2)
(3)
(4)
(5)
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Overall Mechanism Scheme
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Table 1. Table of Reagents
Compound
MW
(g/mol)
2,5118.1502
dihydrothiophene
dioxide
alumina
101.96128
bromine
159.82
wt/vol
used
5.0g
column
6.8g
moles density mp/bp
mmol g/mL
oC
42
mp=64.65
43
3.97
3.102
mp=2030
bp=59.5
1.500
bp=61-62
0.859
bp=130-133
0.89
bp=104
chloroform
cyclopentadiene
dimethylformamide
diethyl acetal
dimethylformamide
dimethyl acetal
ethanol (95%)
ethyl acetate
119.38
66.1024
147.2168
46.07
88.11
0.816
0.9
bp=78
bp=76-77
hexane
86.18
0.659
bp=69
iodine
253.81
mp=133
nitrogen
28.0134
pentane
72.1498
0.640
mp=-209.95
bp=-195.86
mp=-129.7
bp=36.1
bp =35-60
0.868
bp=67
119.164
2.7g
41
4.88g,
41
5.45mL
5.45mL 41
0.626
petroleum ether
potassium
hydroxide
anhydrous
tetrahydrofuran
56.11
72.11
80mL
Hazardous
Properties
highly toxic,
oxidizer
highly toxic
moisture
sensitive
flammable
flammable
flammable,
irritant
flammable,
irritant
corrosive,
highly toxic
flammable
flammable,
toxic
corrosive,
toxic
flammable,
irritant
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Part 1: Preparation of 3,4-Dibromotetrahydrothiophene
Objective:
1. React bromine and 2,5-dihydrothiophone dioxide to produce 3,4dibromotetrahydrothiophene
2. Recover the product and wash with chloroform.
Mechanism:
Procedure and Observations
Procedure
-Fill balloon with N2 to ~20cm in diameter,
store on top of a small flask
-Dry a 50 mL 3-neck flask, stir bar,
dropping funnel, condenser
-Take apparatus to fumehood where the
reaction will be carried out
-Charge an addition funnel with 6mL
CHCl3 and 6.8g Br2 (0.043mol)
-Introduce 8mL CHCl3 into the 3-neck
flask and 5.0g (0.042mol) 2,5dihydrothiophene dioxide
heat and stir
add Br2 over 30-45 minutes
reflux for 2 hours
cool to room temperature then on ice
-Filter bright red mixture with sintered
glass funnel
wash with chloroform until crystals are
colourless
(if necessary, concentrate on rotovap and
recrystallize the product from CHCl3)
Observations
March 9, 2006
-filled balloon with a line in the fumehood
-flame-dried glassware
-greased joints
-added 8mL of CHCl3 in 3-neck flask
-added 4.952g of butadiene sulphone to
flask
-stirred to dissolve (heated with rheostat at
20)
-added 6mL of CHCl3 to addition funnel
added 2.2mL of Br2 (solution was an
orange colour)
-slowly added ~1 drop/second over 40
minutes
-(red) crystal crashed out after addition was
completed
-crystals were transferred to a sintered glass
funnel (added 1mL of CHCl3 to dissolve)
 mixed to a suspension
 turned on vacuum
washed with CHCl3 until crystals were
white (small yellow crystals in the white
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-combine crystals and dry with suction in
the Buchner funnel
(more dibromide can be recovered from
mother liquor if desired)
Characterization
-physical properties
crystals were washed but didn’t turn white)
-white solid cystals
- yield: 29.192g- 21.931g=7.261g
-dissolved in CHCl3 and did a film cast
-IR
-1H NMR
-dissolved end of scoopula amount in
~0.5mL CDCl3
-Store product in foil-wrapped labeled vial
in the fridge in W1-03
Product – Properties And Yield
Balanced Equations and Theoretical Yield Calculations

+
n = 42 mmol*
m = 5.0 g
M = 118.1502 g/mol
n = 43 mmol
m = 6.8 g
M = 159.82 g/mol
n = 42 mmol
m (theoretical) = 11.67g
M = 277.958 g/mol
* 2,5-dihydrothiophene-1,1-dioxide is the limiting reagent
Table 2. Table of Products
Product
3,4dibromotetrahydrothiophene


MW
(g/mol)
277.958
Properties
Found
white
crystals
Theoretical
11.67g
(42 mmol)
Yield
Actual
7.261g
(26.12mmol)
%
62.2
Theoretical  moles2,5dihydrothiphene1,1dioxide * MW 3,4dibromotetrahydrothiophene 42mmol* 277.959g /mol  11.67g
actual
7.261g
%yield 
*100% 
*100%  62.2%
theoretical
11.67g
The product 3,4-dibromotetrahydrothiophene was obtained as white crystals after
washing with chloroform. The 1H NMR showed that the product was fairly pure with a
couple small solvent peaks. The % yield for this reaction was 62.2%.
Characterization
The infrared spectrum of the compound indicates a C-H stretch at about 3015.9
cm-1. There is a peak at 1313.7 cm-1, which is part of the sulfone group, (S=O stretch).
There are also peaks at 905.4 and 836 cm-1which could be the C-S and C-Br stretches.
Table 3 lists and explained the characteristic peaks.
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Table 3. IR Data for 3,4-dibromotetrahydrothiophene
Frequency (cm-1) Intensity Shape Assignment
3015.9
weak
sharp
C-H (sp3)
1313.7
medium
sharp
S=O
905.4/836.1
medium
sharp
C-Br or C-SO2-R
Structure
The 1H NMR spectrum is fairly clean, with a couple of small solvent peaks, and
shows the 3 different hydrogen peaks. The products that are formed are enantiomers,
complicating the spectrum. There are each pairs of hydrogen (A, B, and C) are
chemically equivalent but not magnetically equivalent. This creates second order
coupling, and the multiplicity is too complicated to determined for peak A. Peaks B and
C are doublets of doublets. Both have one J value that is large (~14Hz) which correlates
to geminal coupling (to proton B or C) and one J value that is smaller (~5Hz) that
correlates to vicinal coupling to proton A. The three peaks are shifted downfield (35ppm) indicating they are connected to carbons attached to electron withdrawing groups
(bromine and sulfone). Table 4 lists the 1H NMR data.
Table 4. 1H NMR Data for 3,4-dibromotetrahydrothiophene
Label (ppm) Area Splitting
J (Hz)
Structure and Signal
Assignment
A
4.79
2
multiplet
B
4.026
2
C
3.548
2
doublet of
doublets
doublet of
doublets
JB,A=5.56 (vicinal)
JB,C=14.52 (geminal)
JC,A=5.46 (vicinal)
JC,B=13.84 (geminal)
The 13C NMR only contains two peaks, which shows that the molecule is
symmetrical. The two peaks are in the 40-60ppm region indicating the carbons are next
to electron withdrawing groups. The sulfone group is more electron withdrawing than
the bromine so the more downfield peak would be the C-S carbon. Table 5 lists the 13C
NMR data.
Table 5. 13C NMR Data for 3,4-dibromotetrahydrothiophene
Label
Structure and Signal Assignment
(ppm) Type of Carbon
1
60
C-S (sulfone)
2
46
C-Br
Discussion and Conclusion
The 1H NMR and infrared spectra showed that 3,4-dibromotetrahydrothiophene was
successfully produced. The hydrogens in the 1H NMR spectrum were shifted downfield
indicating they were attached to electron withdrawing groups, the bromine and sulfone.
The spectrum was not simple to analyze because enantiomer products were formed and
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there was second order splitting. 1H NMR spectrum was very clean indicating the
product was fairly pure. The reaction ran very smoothly and we did not have to reflux
the reaction for very long before crystals crashed out. The % yield was 62.2%.
Part 2: Preparation of 6-dimethylaminofulvene
Objective:
1. Prepare cyclopentadiene for the reaction. (Carried out by TA)
2. React cyclopentadiene with dimethylformamide diethyl acetal to produce 6dimethylaminofulvene
3. Purify 6-dimethylaminofulvene by recrystallization from petroleum ether.
Mechanism:
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Procedure and Observations
Procedure
Carried out by TA: Preparation of
cyclopentadiene
-50mL round-bottom flask, place
10mL dicyclopentadiene and boiling
chips
-fit flask with Vigreux column with
distillation adapter and
thermometer, attach to condenser
with vacuum adapter
-cool receiver in ice-salt bath
-protect from atmospheric moisture
with drying tube connected to
vacuum outlet
-distill very slowly
-store in tightly stoppered flask in
freezer
Preparation of 6dimethylaminofulvene
-dry 25mL round bottom flask,
water-cooled condensor
-use nitrogen balloon to flush
system with nitrogen
-add 41 mmol of
dimethylformamide diethyl acetal
(4.88g, 5.45mL)
-quickly add cyclopentadiene
(41mmol, 2.7g)
-flush with N2

-heat at a moderate reflux for 3
hours (should turn orange-red)

-TA will put stuff away and store in
fridge
Purification
-Rotavap to remove volatiles
Observations
March 16, 2006
-assembled 25mL round bottom flask and Vigreux
column in the fumehood
-dried with a heat gun
-used nitrogen line in fumehood to flush system
-added 5.45mL of dimethylformamide dimethyl
acetal (instead of diethyl acetal)
nM
0.041mol *119.164g /mol
V

 5.49mL
density
0.89g /mL
-added (cold) 3.4mL cyclopentadiene
nM
0.041mol * 66.1024g /mol
V

 3.4mL
density
0.8g /mL
-heat at ~35 on Variac
-when reluxing, switched from nitrogen line to
CaCl2 drying tube
-the reaction was supervised by Leah and
everything was taken down by her after ~3 hours
and stored in the fridge (in foil)
March 23, 2006
-combined Jason and my reacted solutions
(brown-yellow colour)
-rotovap to remove volatiles
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-recrystallize from petroleum ether
using a steam bath (large volume of
petroleum ether may be required)
-yield of yellow crystals is ~1.5g
(30%)
Characterization
-physical properties
-transferred to Erylenmeyer flask (crystals crashed
out)
-heated ~300mL of petroleum ether and added to
crystals to dissolve (with crushing to break up the
crystals)
-black particles didn’t dissolve
-hot gravity filter to remove black particles
-yellow solution as filtrate
-heated on steam bath to reduce volume to
~100mL
cooled to room temp and then ice to induce
crystallization (yellow flaky crystals formed)
filtered with a Buchner funnel
-took the filtrate and reduced the volume further
(repeated above steps twice)
-yellow flaky crystals
-yield= 10.980g - 9.782g=1.198g
-dissolved in CDCl3 and did a film cast
-IR
-1H NMR
-store in the fridge, in the dark (light
sensitive)
-dissolved crystals in ~1mL CDCl3 (0.5mL for
Jason, 0.5mL for myself)
-wrapped in foil before next step
Product – Properties And Yield
Balanced Equations and Theoretical Yield Calculations

+
n = 41 mmol
m = 2.7 g
M = 66.1024 g/mol
n = 41 mmol
m = 6.8 g
M = 147.2168 g/mol
n = 41 mmol
m (theoretical) = 4.97 g
M = 121.2 g/mol
(with partner
4.97 g * 2 = 9.9 g)
*both reactants were the same moles, so they were both limiting.
. Theoretical  moleslimiting * MW 6dimethylaminofulvene 41mmol*121.2g /mol  4.97g

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Table 6. Table of Products
Product
MW
(g/mol)
6-dimethylaminofulvene 121.2
%yield 

Properties
Found
Theoretical
gold flaky
9.9g
crystals
(41 mmol)
Yield
Actual
1.198g
(9.884 mmol)
%
12.1
actual
1.198g
*100% 
*100%  12.1%
theoretical
9.9g
The product 6-dimethylaminofulvene was obtained as gold flaky crystals. The crude
product was combine with Jason’s and recrystallized together because the yield for this
reaction is normally low, ~30%. Our yield was very low, 12.1%. Unfortunately, as
shown by the 1H NMR, the sample was not free of the petroleum ether that was used for
recrystallization. (This may have been due to the weak vacuum during recovery of the
crystals.)
Characterization
The infrared spectrum showed two characteristic stretches of alkenes, the peak at
3068.1cm-1 is the C-H (sp2) stretch and the peak at 1619.0 cm-1 (and possibly those at
1300 cm-1)is the C=C stretch. There are also unlabeled peaks at about 2900cm-1. 1170
cm-1 is a typical frequency for a C-N stretch of a tertiary amine. Table 7 lists and
explains the characteristic peaks.
Table 7. IR Data for 3,4-dimethylaminofulvene
Frequency (cm-1) Intensity Shape Assignment
Structure
3068.1
weak
sharp
C-H (sp2)
~2900
1619.0
(1373.3 / 1353.6)
1170
weak
strong
sharp
sharp
C-H (sp3)
C=C
medium
sharp
C-N
Unfortunately, there was no enough sample in the NMR tube so the signal to
noise ratio of the 1H NMR spectrum is not very good. There is also some petroleum ether
is clearly present. The signal peaks are still visible, but I used Natalie’s spectrum for ease
of analysis.
The protons in the 5 membered ring are not chemically equivalent due to the double bond
being asymmetrical, so each proton has their own distinct chemical shifts. There are 5
peaks from 6.3-7.2ppm that are a little higher than characteristic chemical shifts of
vinylic protons. The compound is not aromatic but the electrons are delocalized around
the ring, which may the reason for the higher shift. The farthest downfield peak is a
singlet, which is the vinylic proton of the alkene with the amine group attached (only
vinylic proton with no neighbours). The other 4 peaks are doublets of doublets of
doublets. They couple to their neighbouring protons (ortho J~4Hz, meta J~2Hz). The
most upfield peak is a singlet with an integration of 6, which are the protons on the
methyl groups of the amine. The chemical shift of this peak is shift downfield slightly,
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indicating it is close to an electron-withdrawing group (nitrogen). Table 8 lists the 1H
NMR peaks.
Table 8. 1H NMR Data for 3,4-dimethylaminofulvene
Label
Area
Splitting
J (Hz)
Structure and Signal
(ppm)
Assignment
A
7.2
1
s
B
6.624
1
ddd
1.65
2.01
4.76
C
6.591
1
ddd
1.83
1.83
4.39
D
6.448
1
ddd
2.15
2.15
4.3
E
6.37
1
ddd
1.60
2.61
4.21
F
3.3
6
s
The 13C NMR has 8 peaks indicating the molecule is asymmetrical (there are 8 carbons in
the compound). The 6 most downfield peaks are those of the alkenes. The 2 most
upfield peaks belong to the methyl groups of the amine; because the molecule is
asymmetric, the methyl groups are not chemically equivalent. Table 9 lists the 13C NMR
peaks.
Table 9. 13C NMR Data for 3,4-dimethylaminofulvene
Label
Structure and Signal Assignment
(ppm) Type of Carbon
1
149
C=C
2
126
C=C
3
125
C=C
4
120
C=C
5
117
C=C
6
114
C=C
7
23
-CH3
8
15
-CH3
Discussion and Conclusion
Though the 1H NMR looked messy due to the signal to noise ratio, the peaks
characteristic of 6-dimethylaminofulvene are still present. The spectrum had a lot of
other peaks, indicating impurities. These impurities are likely solvents (petroleum ether)
and because the compound is light sensitive, there may also be some decomposed product
because the sample was exposed to light during the preparation of the NMR sample. The
infrared spectrum confirmed the presence of alkene groups and the methyl groups of the
tertiary amine.
Hence, we were successful in producing 6-dimethylaminofulvene, which was in
the form of gold flaky crystals. My crude product was combined with Jason and purified
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together by recrystallization to obtain a % yield of 12.1%. This is a low yield, but is
typical of the reaction.
Part 3: Preparation of Azulene
Objective:
1. Prepare thiophene-1,1-dioxide by reacting 3,4-dibromotetrahydrothiophene (from
Part 1) with powdered potassium hydroxide
2. React thiophene-1,1-dioxide with 6-dimethylaminofulvene (from Part 2) to
produce azulene
3. Purify azulene with an alumina column
4. Recrystallize azulene.
Mechanism:
Procedure and Observations
Procedure
Preparation of Thiophene-1,1-dioxide
-place 2.22g (8.00 mmol) 3,4dibromotetrahydrothiophene in 3 neck,
100mL round-bottom flask, with stir bar,
condenser, drying tube, nitrogen balloon
with 3-way adaptor, and glass stopper
-flush system with nitrogen
-add 80mL anhydrous THF
-cool mixture in ice-bath, with stirring
-quickly add 4g (0.1mol) of finely
powdered potassium hydroxide
stir vigorously under nitrogen
Observations
March 30 , 2006
-filled nitrogen balloon
-added 2.22g of 3,4dibromotetrahydrothiophene
-added ~4g KOH
-added 80mL THF
-solution turned purple almost immediately
after addition of THF
-flush with nitrogen
-stirred vigorously
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-monitor reaction by TLC (1:1 hexane:
ethyl acetate eluent) visualize with UV
lamp and iodine
-monitor reaction by TLC (1:1 hexane:
ethyl acetate)
-visualized with UV light
-when reaction is complete, filter the cold
mixture through a filter-aid pad
-use clear, colorless filtrate right away
-filtered with Celite-pad, used vacuum to
full filtrate through
-the residue was black, the filtrate was a
clear yellow solution
-kept cold
-250mL round-bottom flask with condenser -setup flask, stir bar, and condenser with
with nitrogen inlet
N2 inlet in fumehood
-add stir bar and 6-dimethylaminofulvene
-added the 6-dimethylaminofulvene
-flush system with nitrogen
-add cold thiophene-1,1-dioxide
-added cold thiophene-1,1-dioxide
-stir to dissolve the fulvene, producing a
-upon addition the solution became redred solution
orange
-note colour change
-after 10 minutes, it was yellow-orange
-reflux for 4 hours
-TA will take down and put away flasks.
-Leah supervised the reaction and took
everything down and stoppered and placed
in the fridge.
Purification
-remove tetrahydrofuran at room
-removed THF by rotavap
temperature with rotavap
-dry packing for alumina column:
1)cotton plug
2)alumina
3)pack with pentane
4)sand
-triturate residue with 2mL pentane and
-added 2 pipettes of pentane to residue
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place the blue soluntion on top of column
-allow sample to be adsorbed and repeat
the procedure with additional very small
portions of pentane until solvent is no
longer strongly coloured
-elute with pentane, collect only the blue
band
from rotavap: 1 to Jason, 1 to me
-added 4 pipettes of pentane, 2 to Jason, the
rest to me, but not all was used for the
column
-collected 5 flasks (pentane as eluent):
1)before the blue band (clear)
2)beginning of blue band (light blue)
3)majority of blue band (dark blue)
4)end of blue band (light blue)
5)after blue band (clear)
-checked purity with TLC (pentane as
eluent); visualized with UV light
-evaporate solvent, weigh the blue
crystalline
-recrystallize with very small amount of
95% ethanol
-after cooling on ice, remove mother liquor
with pipet, quickly wash crystals with
small amount of ice-cold ethanol
-suction to dry
Characterization
-physical properties
-IR
-1H NMR
-pooled fractions 2, 3, and 4
-evaporated on rotavap
-blue crystals remained
-did not do recrystallization
-dark blue crystals
-yield = 87.766g – 87.353g = 0.413g
(Jason obtained 0.757g)
-dissolved in CDCl3 and did a film cast for
IR
-dissolved in CDCl3 for 1H NMR
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Product – Properties And Yield
Balanced Equations and Theoretical Yield Calculations

+
n = 9.884 mmol
n = 7.987 mmol*
n = 7.987 mmol
m = 1.198 g
m = 2.22 g
m (theoretical) = 1.024 g
M = 121.2 g/mol
M3,4-dibromo = 277.958 g/mol
M = 128.17 g/mol
*thiophene-1,1-dioxide (assuming reaction from 3,4-dibromotetrahydrothiophene was
100% complete) is the limiting reagent.
Theoretical  moles3,4dibromotetrahydrothiophene* MW azulene  7.987mmol*128.17g /mol  1.024g

Table 10. Table of Products
Product
MW
Properties
(g/mol) Found
Azulene
128.17
vibrant
blue
crystals
%yield 

Theoretical
1.024g
(7.987
mmol)
Yield
Actual
0.413g
(3.222 mmol)
combined with Jason:
0.413g + 0.757g = 1.170g
(9.129 mmol)
%
114
actual
1.170g
*100% 
*100%  114%
theoretical
1.024g
The product azulene was obtained as vibrant blue crystals after rotavaping off the pentane
solvent. We did not recrystallize the crystal, so the final product was impure, which also
showed in the 1H NMR that had large pentane peaks. The % yield of this reaction was
114%. It’s very likely that we had impurities (mainly pentane) in our product because the
yield was over 100%.
Characterization
The infrared spectrum of azulene showed the characteristic peaks of aromatic
compounds. The C-H (sp2) stretch is present at 3078.0cm-1 and the C=C stretches are
present at 1578.1 and 1392.1cm-1. (There is also another peak at 1476.4cm-1, but after
comparing the spectrum to that on NIST Chem Webbook, it is likely from CDCl3 that
was used to dissolve the azulene to prepare the thin film.)
Table 11 lists and explains the characteristic peaks.
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Table 11. IR Data for Azulene
Frequency (cm-1) Intensity Shape
3078.0
weak
sharp
Assignment
C-H (sp2) stretch
1578.1 / 1392.1
C=C stretch
medium
sharp
Structure
There are only 5 peaks present in the 1H NMR indicating an axis of symmetry in
the compound. The peaks have the characteristic chemical shift of aromatic hydrogens
(7-8.4ppm). The peaks all showed ortho coupling, but some had very small meta
coupling constants. The assignment was done by using the integration and coupling
constants. (C is ortho coupled to E and meta coupled to A, A and E are ortho coupled to
each other, B and D are ortho coupled to each other. Thus, B and D must be hydrogens
on the 5 membered ring and A, C, and E are hydrogens on the 7 membered ring.) There
are pentane peaks presents indicating that not all pentane solvent was removed with the
rotavap. There are also other compounds present, such as dichloromethane, so the
product was not pure. Table 12 list the 1H NMR peaks.
Table 12. 1H NMR Data for Azulene
Label (ppm)
Area Splitting J (Hz)
Structure and Signal
Assignment
A
8.38
2
d(d)
JA,E=9.705
(J=0.675)*
B
7.95
1
t(d)
JB,D=3.77
(J=0.407)
C
7.616
1
t(dd)
JC,E=9.925
(J=0.917 and
1.47)
D
7.438
2
d
JD,B=3.78
E
7.197
2
t
JE,AC=9.865
*J=(Hz) means I am not certain which protons are being coupled
The 13C NMR only showed 6 peaks, which indicates symmetry within the
molecule (there are 10 carbons). The chemical shifts are typical of sp2 carbons. The 13C
NMR peaks are listed in Table 13.
Table 13. 13C NMR Data for Azulene
Label
Structure and Signal Assignment
(ppm) Type of Carbon
1
140
2
137
3
136
C=C
4
136
5
123
6
118
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Cindy Lee
1041791
Discussion and Conclusion
The 1H NMR and infrared spectrum confirmed that we were successful in preparing
azulene, which were brilliant blue coloured crystals. The 1H NMR spectrum showed
pentane peaks, indicating that not all the pentane solvent was evaporated off and our
sample is impure. The infrared spectrum was compared to that in the SDBS and NIST
Chem Webbook (online resources) and it was very similar, with the addition of a couple
CDCl3 peaks.
This reaction ran smoothly and the purification was very simple due to the colour of our
product. The % yield of this reaction after purification on the alumina column was
114%. Since this is over 100%, which is not theoretically possible, there must be some
impurities in the final product, likely the pentane that was observed in the 1H NMR.
CONCLUSION
This experiment was successful in synthesizing azulene. The final yield was 114%, so
the final product contained some impurities, namely pentane that was used as a solvent in
purification. To generate this final product, we first synthesized and isolated two
intermediates: 3,4-dibromotetrahydrothiophene and 6-dimethylaminofulvene. The %
yield for 3,4-dibromotetrahydrothiophene, a white solid crystal compound, was 62.2%
and for 6-dimethylaminofulvene, a gold flaky crystal compound, it was 12.1%.
The experiments ran very smoothly. There was a problem with the 1H NMR of 6dimethylaminofulvene because there was not enough compound in the sample creating a
bad signal-to-noise ratio. However, the peaks from our product could still be seen.
The final product was characterized by physical properties, blue coloured crystals,
infrared, and 1H NMR and was confirmed to be azulene, with some impurities. Overall,
this experiment was successful.
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