Presentation on theme: "Organic Chemistry Lab II, Spring 2010"— Presentation transcript:
1 Organic Chemistry Lab II, Spring 2010 Reactions of Alkenes 1: Miniscale Synthesis Bromination of Fumaric AcidOrganic Chemistry Lab II, Spring 2010Dr. MilkevitchMarch 8 & 10, 2010
2 Addition Reactions Today: Conduct an addition reaction One of the fundamental reactions of alkenesWhat you will learn/observe:Review/introduce the bromination of alkenesBromination fumaric acidFumaric acid is alkenyl dicarboxylic acidLook at the products formedstereoisomers possibleSee which product will predominateracemic and meso forms possibleMP determination may differentiate
3 Addition Reactions Let’s Look at: Bromination of alkenes Addition reaction: a fundamental organic reactionTwo species are added to a substrateVariety of organic families have this reactionAlkenes have many addition reactionsResult is an entirely new compoundBromination of alkenesAddition of Br2 to an alkenemultiple step processProceeds through a bromonium ion intermediateBoth carbons of the original C=C end up with a Br
5 Some Notes on this Reaction Halogen atoms are electrophilicand nucleophiles can attack themExamples:
6 More Notes An alkene can also be viewed as a nucleophile can attack a halogen atomIntermediate is called a bromonium ionnote the 3-membered ringpositive charge on the bromine3-membered ring has considerable ring straincombined with positive charge on bromineRing opening reaction likelyform a stable product
7 Stereochem of this Reaction Called anti additionBecause the 2 bromines “end up” in an anti configurationWhy? because of the mechanismmust be a back-side attack of the nuclophile (Br -)
9 Why Meso ProductBromide can attack either carbon of the bromonium ion
10 Procedure Use a 10 ml RB flask Add 200 mg of fumaric acid to this flaskNow, add 2.5 ml of bromine stock solutionswirl to mix, add magnetic stirrerAttach a condenserNo need to hook up water linesStart stirring and heating (low setting…5)should turn orange (~15 min)then a precipitate should form, solution turns yellowIf it turns clear, add a few more drops (2-3) of bromine solutionContinue heating for 15 more minutesRemove solution, put in ice bath
11 Procedure II Collect product by vacuum filtration use a Hirsh funnel Wash crystals with ice-cold waterRecrystallize from waterAir-dry until next weekNext week:weigh crystalscheck MP of crystalsMP should be 255°-256° Cbut a racemic compound could form!!!has a MP of 166°-167° CIf 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 producedState % yieldReport MPAnalyze: 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 resultsProve that you made the alkenesInclude GC chromatogram (annotated)Determine % of your alkenesIR 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?