NITRATION OF BROMOBENZENE
NOTE
WEAR GLOVES DURING THE ENTIRE PROCEDURE
Bromobenzene and the two nitrobromobenzenes are irritating to sensitive skin areas. If you should have these materials on
your hands and then accidentally touch your face, this can cause a severe burning sensation in the affected area. If this
should happen, IMMEDIATELY:
1. Go to the restroom and wash the affected area with lots of soap and water.
THE SOAP IN THE LAB IS NOT SUITABLE FOR THIS PURPOSE.
2. Return to the lab and apply mineral oil to the affected area.
3. The summary to this warning is NOT TO TOUCH ANY PART OF YOUR BODY
WHILE PERFORMING THIS EXPERIMENT.
If you must leave the lab for any reason:
1. First dispose of your gloves in the waste container
2. Immediately go to the restroom and wash your hands
thoroughly with soap and water.
AGAIN, LAB SOAP WILL NOT DO A SUFFICIENT CLEANING
JOB
3. Upon returning to the lab, obtain another pair of
gloves from the front of the room, and proceed with
the experiment.
NITRATION OF BROMOBENZENE
Equation:
H2SO4
C6H5Br + HNO3 --------------> C6H4BrNO2 + H2O
Table of Physical Constants
Compound
C6H5Br
o-NO2C6H4Br
p-NO2C6H4Br
HNO3
H2SO4
M.W.
157.0
202.0
202.0
---------
density
1.522
-----------------
mp
-31
43
127
-----
bp
156
258
254
-----
Table of Amounts of Reactants and of amounts of Products Theoretically Possible
M.W.
C6H5Br
HNO3
H2SO4
C6H4BrNO2
H2O
157
63
98
202
18
10ml
10ml
15.6
18.0
-
-
Moles
Grams
mL
M
1.
2.
3.
5.3
-
------------------------- FOR SAFETY REASONS -------------------------Add 700mL of tap water to your 1 L Beaker.
Discard any acid washings, plus the contents of the filter flask (from step 9 below) into your 1 L Beaker, WITH
STIRRING.
Wash the contents of your 1 L Beaker down the sink.
PROCEDURE
1.
Prepare a mixture of 10 mL conc HNO3 and 10 mL conc H2SO4 in a 125 mL Erlenmeyer flask, and cool it to room
temperature by means of a water bath.
2.
To the flask, add 5.3 mL bromobenzene IN 2 - 3 mL INCREMENTS over a period of about 5-10 min; gently
swirlling the flask to mix the reaction vessel contents after each addition. Keep the reaction mixture between 50 - 55
o
C. DO NOT ALLOW THE REACTION MIXTURE TO EXCEED 60 oC. The temperature may be controlled
by allowing more time between the addition of successive portions of bromobenzene and by cooling the reaction
flask as necessary with an ice water bath.
3.
After the addition is completed and the exothermic reaction has subsided, heat the flask for 30 min., using your hot
plate to maintain the temperature in the reaction vessel below 60 oC during this period. The settings on your hot
plate should be between dial markings 2 & 3 (approximately 2.6 & 2.8).
4.
Cool the flask in an ice bath to room temperature.
5.
Pour the reaction mixture into 100 mL of distilled water which is in a 250 mL beaker. The water should be less than
25oC.
6.
Isolate the crude product by vacuum filtration.
7.
Wash the filter cake thoroughly with cold (0-10oC) distilled water and dry the filter cake by allowing the vacuum
apparatus to draw air through it after you have finished washing.
8.
Transfer the crystals to a TARED 125 mL Erlenmeyer flask and obtain the weight of your wet product. Place the
washings into the 1L beaker. Put your filter paper into the plastic jar at the front of the lab.
9.
Calculate the volume of 95%(v/v) ethanol needed to just dissolve the nitrobromobenzenes at 78.2 oC (the boiling
point of 95%(v/v) ethanol). You will need approx. 5 mL 95% ethanol per gram of crude product. Now, add 1 mL
more of solvent. SHOW THIS CALCULATION IN THE PROCEDURE PORTION OF YOUR REPORT.
10.
Bring this mixture to boiling to dissolve the crude product. If the product does not completely dissolve after 2
minutes of boiling, add 5 mL of 95%(v/v) ethanol. If solid still remains you will have to do a hot filtration. Once
your crude product has dissolved, set the flask onto your lab bench and allow the contents to cool slowly to room
temperature.
11.
Isolate the nearly pure crystals of 4-nitrobromobenzene by vacuum filtration. If there is solid material in the filter
flask at this point, pour it into a beaker and vacuum filter this solution again through the funnel containing the first
crop of nitrobromobenzene. Save the filtrate.
12.
Wash the crystals with a little ICE COLD ethanol, allowing the washes to drain into the filter flask containing the
filtrate.
13.
Allow air to be drawn through the Buchner funnel for 5 min. then detach the vacuum hose from the filter flask, turn
off the water and transfer the solid from the Buchner funnel onto a large (18.5 cm diameter) filter paper which is on
a large watch glass. Spread the solid over most of the filter paper, breaking large clumps into small particles and put
it in your drawer to dry overnight. Place another piece of 18.5 cm filter paper lightly over the crystals to keep the
dust out.
14.
Pour the filtrate from step 12 into a beaker, either 125 ml or 250 ml. The volume of your filtrate should be no more
than 2/3 the volume of the beaker. If the class period is about over, place a watch glass over the beaker and place
the combination into a hood.
15.
Place the beaker containing the filtrate on a hot plate, adjust the dial to "6", place a small stirring rod in the solution
and place the combination in a hood. If the boiling is too vigorous, change the setting to "4".
16.
Reduce the volume to 50 ml by boiling the solution then remove the beaker from the hot plate onto the bench and let
it cool to room temperature. Keep the beaker in your hood.
17.
If crystals are present, remove them by vacuum filtration using a 125 ml filter flask and wash the crystals with 5 ml
of ice cold ethanol.
18.
Now transfer the contents from the filter flask to a beaker (choose the correct size) and evaporate the volume to 10
ml under a hood using a hot plate.
19.
Remove the beaker and cool to room temperature. You might have a mess in the beaker (I did). Some 4nitrobromobenzene crystals (white) may be present. Some yellow crystals (2-nitrobromobenzene) crystals might be
present & a yellow oil might be present. A yellow solution will be present. It is composed of 2-nitrobromebenzene
in ethanol. Take another beaker. Remove the oil, which is probably sitting at the bottom of the beaker, with either a
plastic 1 ml disposable pipette or a glass Pasteur disposable pipette to which you have attached a medicine dropper
top, and put it into the tared beaker. If you find any YELLOW crystals, add them also. Keep this for T.L.C.
20.
Your crystals of 4-nitrobromobenzene should be dry now so weigh them and determine the melting point of the
compound. Record both in the Results section of your lab notebook & in your lab report. After
running the TLC on your 2 and 4-nitrobromobenzene, put the remainders into the appropriate recovery
bottles at the front of the lab.
Thin-Layer Chromatography
1.
Take a few crystals of the 4-nitrobromobenzene isomer, place in a 5 ml beaker, and add 10 drops of chloroform to
the beaker to dissolve the crystals.
2.
Take a 2.5 x 7.5 cm strip of silica gel, mark the origin 1 cm from bottom and make 2 pencil marks lightly on the
origin.
3.
Apply one drop of the solution containing the 4-nitro isomer on one spot & one drop of oil containing the 2-nitro
isomer on the other spot. Be sure that neither application results in a spot more than 2 mm in diameter. Allow the
strip to dry at your hood workstation .
4.
Place dried strip in jar containing the solvent solution Hexane: Chloroform 9:1.
5.
When the solvent system reaches within 1 cm of the top of the strip, remove the strip, allow to dry at your hood
workstation & view under ultraviolet light in the U.V. box. Outline the spots with a pencil by stippling around each
spot while the chromatogram is still in the U.V. box.
6.
Put the rest of the oil, in the beaker, into the jar provided in the hood & place your 4-nitro solid jar on the tray
provided.
Again, before you leave, wash down your benchtop with 95% ethanol in the same fashion as yesterday.
TLC Lab Report
Follow the outline given under Laboratory Reports on pg. 5 of the Laboratory Manual. In addition, record the distance that
each compound traveled and the distance the solvent traveled. Calculate the P f for each compound and place the distances
and Rf's in a table. Example:
Solution
Oil
Solvent
Distance
Rf
1.00