Lab E: Diels Alder Reaction Flashcards
Draw out the reaction schematic for the Diels Alder reaction scheme. Label all products and reagents.
Refer to notes
Why does the product(4-cyclohexene-cis-1,2-dicarboxylic anhydride) need to be soluble in the initial solvent(i.e. xylenes)?
You need product to be soluble in solvent because otherwise it will crash out before you isolate.
Diel-Alder is a __________(1) reaction in which two ____________(2) molecules react to form a ring.
(1) cycloaddition
(2) unsaturated
Why are Diels-Alder reaction among the most useful reactions available?
It produces functionalized six-membered rings, which are ubiquitous in important organic molecules including a wide range of pharmaceuticals.
The Diels-Alder reaction works for an enormous variety of dienes and dienophiles. however, it works best if the dienophile contains
an electron withdrawing group directly attached to the alkene. This is because the dienophile is the electrophile of this reaction, and so the more electron-deifinicent the alkene is, the more reactive it is.
What is the electrophile of this reaction?
the dienophile which is malice anhydride
What is the diene? What is the dienophile?
Refer to notes
What is the dienophile in this experiment?
maleic anhydride
Why is malice anhydride extremely reactive?
It has two electron withdrawing substituents making it an extremely reactive dienophile
The Diels-Alder reaction is a ____________(1) reaction; bond breaking and bond forming occur simultaneously.
concerted
What is a direct benefit of the concerted nature of the Diels-Alder reaction? Apply this to our specific experiment.
It is stereospecific; one can reliably predict the stereochemistry of the product based on the stereochemistry of the starting materials. For example, if the substituents on the dienophile are cis, they will be cis in the product, and likewise for a trans-dienophile. In our case, Maleic anhydride is a cis-alkene(it is cis because it is cyclic) and so the fused bicyclic ring system in our Diels-Alder product is cis.
Make a drawing to demonstrate the stereospecificity of the Diels-Alder reaction.
Refer to notes
Why is 1,3-Butadiene not used directly in this experiment?
1,3-butadiene is a gas at room temperature. The use of gases as reagents is common in synthetic organic chemistry, however, it requires the use of special equipment that is not amenable to this lab course. We will instead use Butadiene sulfone, which is an easily manipulated solid, to generate 1,3-butadiene within the reaction flask or in-situ.
Who discovered the diets-alder reaction?
Otto Fiels and Kurt Alder
What are the hazards associated with Maleic anhydride adn Butadiene sulfone?
Both are corrosive solids that can cause burns to the skin and eyes. If inhaled, malice anhydride can cause an allergic reaction or irritation. Butadiene sulfone is also a respiratory irritant and has a foul smell.
What are the hazards associated with petroleum ether and xylenes?
both are toxic and flammable organic solvent. You should avoid inhalation adn skin contact with both solvents.
What are the hazards associated with sulphur dioxide?
Sulfur dioxide is a toxic foul-smelling gs that will be evolved during the course o this reaction.
How can you avoid all of the hazards associated with the chemicals in this lab?
Keep you hood down to prevent the gas from escaping from the hood
What is the waste disposal procedure for xylenes, petroleum ether, pipettes, and waste acetone?
The filtrate, which contains xylenes and petroleum ehter should be disposed of in the specially labelled “diels-alder waste container”
All pipettes should go into the sharps contianer
waste acetone should go into the
“diels-alder waste container”
There are some important safety considerations in this lab. Firstly, the RBF should NOT be set directly on the _____(1), without the heating mantle. If you do this, ________(2). Secondly, the heating mantle is made up of _________(3) that supports the base of the RBF. If this is cracked or in very brittle condition, _____________(4). The heating mantle should be secured firmly by _______(5) and plugged into the ________(6). The heating mantle should never be plugged into _____(7). This is because ___(8)
(1) surface of the hotplate
(2) you will end up boiling away all of the organic solvent in the flask and it would not classify as a reflux reaction. Moreover, the organic solve is flammable.
(3) insulate fiberglass
(4) do not use the heating mantle
(5) looping the cord around the cylindrical bar in front of your fume hood
(6) Variac
(7) wall outlet
(8)The heating mantle is capable of producing enough heat to completely evaporate any or all of the organic material if used on full power, which is why it is plugged into a varian.
Draw a reflux schematic
refer to notes(print out) and the back of the DA checklist sheet
Summarize this reaction
- In a RBF, obtain maleic anhydride, butadiene sulfone, xylenes, and stir bar
- Reflux set-up: place heating mantle on hot-plate/stirrer. Rest the clamped RBF flush inside the heating mantle. Attach a water-cooled reflux condenser to the top of the RBF. Ask TA to plug the heating mantle into the variac below the fume hood. Only turn on stirring on the hot-plate/stirrer and NO HEAT.
- Use a piece of foil to insulate the RBF until it comes to a boil. This is the start of the reflux time period. Reflux for 30 mins with gentle stirring.
- At the end of the reflux, allow the reaction to cool for 3 minutes
- Add xylenes to the RBF
- Place clamped RBF inside a warm water bath. Then decant the supernatant solution into a beaker(leaving behind any brown sludge that may have formed)
- add 10 mL of petroleum ether to the beaker and you should observe the dials-alder product precipitate out.
- Cool the beaker in an ice-water bath
- Do a vacuum filration for 5 minutes. record wet mass
transfer a small amount of the ample into a vial for IR analysis.
What is the solvent in this reaction?
xylenes
Why is it important that the RBF sits flush inside the heating mantle?
Ensures efficient heat transfer from heating mantle to RBF
