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Reactions of Alkenes 1: Miniscale Synthesis Bromination of Fumaric Acid. Organic Chemistry Lab II, Spring 2010 Dr. Milkevitch March 8 & 10, 2010. Addition Reactions. Today : Conduct an addition reaction One of the fundamental reactions of alkenes What you will learn/observe:
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Reactions of Alkenes 1: Miniscale Synthesis Bromination of Fumaric Acid Organic Chemistry Lab II, Spring 2010 Dr. Milkevitch March 8 & 10, 2010
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
Addition Reactions • Let’s Look at: • 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
Some Notes on this Reaction • Halogen atoms are electrophilic • and nucleophiles can attack them • Examples:
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
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 -)
Why Meso Product • Bromide can attack either carbon of the bromonium ion
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
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
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?
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)
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?
