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 :
H
2
SO
4
C
6
H
5
Br + HNO
3
--------------> C
6
H
4
BrNO
2
+ H
2
O
Table of Physical Constants
Compound M.W.
C
6
H
5
Br 157.0
o-NO
2
C
6
H
4
Br 202.0
p-NO
2
C
6
H
4
Br 202.0
HNO
3
H
2
SO
4
-----
----- density mp
1.522 -31
----- 43
----- 127
----- ---
----- --- bp
156
258
254
---
---
Table of Amounts of Reactants and of amounts of Products Theoretically Possible
C
6
H
5
Br HNO
3
H
2
SO
4
C
6
H
4
BrNO
2
H
2
O
63 98 202 18 M.W.
Moles
Grams
mL
157
2.6 5ml 5ml
M - 15.6 18.0 - -

1.
2.
3.
1.
3.
4.
5.
6.
7.
8.
9.
14.
15.
16.
2.
10.
11.
12.
13.
------------------------- 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 8 below into your 1 L Beaker, WITH
STIRRING .
Wash the contents of your 1 L Beaker down the sink.
PROCEDURE
Prepare a mixture of 5 mL conc HNO
3
and 5 mL conc H
2
SO
4
in a 50 mL beaker, take it back to your hood workstation and clamp it to your hotplate/stirrer, immersing the beaker in a 150 mL beaker containing 100 mL tap water. Allow the beaker contents to cool to 30 deg. C, measured using your glass thermometer.
To the beaker, add 2.6 mL bromobenzene, gently stirring to mix the contents. Continue to stir/agitate the beaker contents until the oily top layer of bromobenzene begins to transform into solid 2&4-bromonitrobenzene immersed in the acid mixture. Keep the reaction mixture between 50 - 55 o C. DO NOT ALLOW THE REACTION
MIXTURE TO EXCEED 60 o C.
After the exothermic reaction has subsided, heat the beaker for 10 min. on your hot plate set at ~ 2.5 to maintain the temperature below 60 o C during this period.
Cool the beaker in an ice bath to room temperature.
Pour the reaction mixture into a 250 mL beaker containing 100 mL of distilled water.
Isolate the crude product by vacuum filtration.
Wash the filter cake thoroughly with cold (0-10 o C) distilled water and dry the filter cake by allowing the vacuum apparatus to draw air through it after you have finished washing.
Place the washings into the 1L beaker and transfer the crystals to a TARED 50 mL beaker and obtain the weight of your wet product. Put your filter paper into the plastic jar at the front of the lab.
Calculate the volume of 95%(v/v) ethanol needed to just dissolve the nitrobromobenzenes. You will need approx. 5 mL 95% ethanol per gram of crude product. Round the amount of ethanol needed to the next 5 mL increment.
(e.g.: 5.6 g. x 5 mL/g = 28 mL => use 30 mL). SHOW THIS CALCULATION IN THE PROCEDURE
PORTION OF YOUR REPORT .
Bring this mixture to boiling to dissolve the crude product. If the product does not completely dissolve after 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 beaker onto your lab bench and allow the contents to cool slowly to room temperature.
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.
Wash the crystals with a little ICE COLD ethanol, allowing the washes to drain into the filter flask containing the filtrate.
Allow air to be drawn through the Buchner funnel until no more liquid drips from the funnel - then detach the vacuum hose from the filter flask, turn off the vacuum and transfer the solid from the Buchner funnel onto a large filter paper. 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 large filter paper lightly over the crystals to keep the dust out.
Pour the filtrate from step 12 into a 50 mL beaker. The volume of your filtrate should be no more than 2/3 the volume of the beaker.
Place the beaker containing the filtrate along with a boiling stick on a hot plate, adjust the dial to "4. If the boiling is too vigorous, change the setting to "3".
Reduce the volume to half 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.
19.
Now transfer the contents from the filter flask to a 20 mL beaker and evaporate the volume to 10 ml .
Remove the beaker and cool to room temperature. Some 4-nitrobromobenzene crystals (white) may be present.
Some yellow crystals (2-nitrobromobenzene) might be present & a yellow/orange oil might be present. Take another beaker. Remove the oil, which is probably sitting at the bottom of the beaker, with a plastic disposable pipette, and put it into a tared beaker. If you find any YELLOW crystals, add them also. Keep this for T.L.C.
20. During the Arene reflux period in the next lab period, weigh your crystals and determine the melting point(s).
Record 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.
5.
Place dried strip in jar containing the solvent solution Hexane: Chloroform 9:1.
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 R f
's in a table. Example:
Solution Oil Solvent
Distance
R f
1.00