1. Organic Chemistry Lab II, Spring 2010
Reactions of Alkenes 1: Miniscale Synthesis Bromination of Fumaric Acid
Organic Chemistry Lab II, Spring 2010
Dr. Milkevitch
March 8 & 10, 2010

2. Addition Reactions Today: Conduct an addition reaction
One of the fundamental reactions of alkenes
What you will learn/observe:
Review/introduce the bromination of alkenes
Bromination fumaric acid
Fumaric acid is alkenyl dicarboxylic acid
Look at the products formed
stereoisomers possible
See which product will predominate
racemic and meso forms possible
MP determination may differentiate

3. Addition Reactions Let’s Look at: Bromination of alkenes
Addition reaction: a fundamental organic reaction
Two species are added to a substrate
Variety of organic families have this reaction
Alkenes have many addition reactions
Result is an entirely new compound
Bromination of alkenes
Addition of Br2 to an alkene
multiple step process
Proceeds through a bromonium ion intermediate
Both carbons of the original C=C end up with a Br

4. General Mechanism

5. Some Notes on this Reaction
Halogen atoms are electrophilic
and nucleophiles can attack them
Examples:

6. More Notes An alkene can also be viewed as a nucleophile
can attack a halogen atom
Intermediate is called a bromonium ion
note the 3-membered ring
positive charge on the bromine
3-membered ring has considerable ring strain
combined with positive charge on bromine
Ring opening reaction likely
form a stable product

7. Stereochem of this Reaction
Called anti addition
Because the 2 bromines “end up” in an anti configuration
Why? because of the mechanism
must be a back-side attack of the nuclophile (Br -)

8. Mechanism: Bromination of Fumaric acid

9. Why Meso Product
Bromide can attack either carbon of the bromonium ion

10. Procedure Use a 10 ml RB flask
Add 200 mg of fumaric acid to this flask
Now, add 2.5 ml of bromine stock solution
swirl to mix, add magnetic stirrer
Attach a condenser
No need to hook up water lines
Start stirring and heating (low setting…5)
should turn orange (~15 min)
then a precipitate should form, solution turns yellow
If it turns clear, add a few more drops (2-3) of bromine solution
Continue heating for 15 more minutes
Remove solution, put in ice bath

11. Procedure II Collect product by vacuum filtration use a Hirsh funnel
Wash crystals with ice-cold water
Recrystallize from water
Air-dry until next week
Next week:
weigh crystals
check MP of crystals
MP should be 255°-256° C
but a racemic compound could form!!!
has a MP of 166°-167° C
If it doesn’t melt by 175°C, assume you have the meso compound

12. For Your Report Formal lab report required. Conclusion:
State amount of crystals produced
State % yield
Report MP
Analyze: did you get the racemic mixture or the meso compound?

13. Additional Question to Answer
It appears that the racemic compound could be formed in this reaction. Could you come up with a mechanism by which this could happen? (HINT: it’s a similar mechanism but something else is different)

14. Your Report Formal Report Required
Make sure to include the mechanism of the reaction in your report (separate section)
Results Section:
Make sure to state all results
Prove that you made the alkenes
Include GC chromatogram (annotated)
Determine % of your alkenes
IR spectrum, annotated (if completed)
Conclusions section:
Was the experiment successful?
How much of the alkenes are produced?
Any leftover 3,3-dimethyl-2-butanol?
If unsuccessful, any ideas why?

15. Miniscale Apparatus for Distillation