Bromination of Pringles
When crushed "Pringles" potato chips are added to an Erlenmeyer flask containing bromine vapor, the unsaturated fats in the chips are brominated. The vapor in the flask changes from the characteristic orange color associated with bromine to colorless.
This demo is appropriate for an organic chemistry class when electrophilic addition to a double bond is being discussed. This demo takes about three minutes to perform.
Elemental halogens add to carbon-carbon double bonds through the process of electrophilic addition. In this case, one of the electronegative bromine atoms in the Br2 molecule is attracted to the electron rich pi bond of the carbon-carbon double bond. The Br2 bond cleaves heterolytically to form a cyclic bromonium ion and a bromide ion. A bromide ion thus formed can then add to one of the electron-poor carbons of the bromonium ion. The net effect is thus antiaddition to form a vicinal dibromide.
- Can of Pringles
- Zip-loc Baggie
- 500 mL Erlenmeyer flask w/stopper containing bromine vapor
- large powder funnel (big enough that the crushed chips don't clog the neck)
- White background box.
- Place 5 potato chips in the baggie and crush them.
- Remove the stopper from the flask. Using the funnel, quickly add the crushed chips and replace the stopper. (It's OK if you spill a few crushed chips; the main thing is to get the stopper back on quickly so you don't get a big whiff of bromine vapor.)
- Shake the flask while holding it in front of the white background. The orange color should disappear within a minute
Bromine vapor is corrosive and toxic; avoid breathing it. Add the chips quickly and restopper the flask immediately to avoid releasing a lot of bromine vapor. This demo should be performed in a room with adequate ventilation. If the flask breaks, evacuate the room.
The flask is filled with bromine vapor by simply adding five drops of liquid bromine to an empty 500 mL Erlenmeyer flask under the vent hood and stoppering it. Be sure to wear gloves and goggles when handling bromine.