Organic Chemistry II  | Lecture | Laboratory 

Organic Chemistry Laboratory II
The Diels Alder Reaction:  Reaction of 2,4-Hexadien-1-ol with Maleic Anhydride

Experimental Procedure

In the hood, fill a crystallization dish about 1/2 to 3/4 with water and set it on a stirrer/hot plate.  Tare a 50 ml Erlenmyer flask and weigh out 2,4-hexadien-1-ol (0.40g) into the flask.  (Note:  This may be challenging as the compound is low melting, meaning is may start out as a liquid but solidify as you work with it.).  Add toluene (5ml) to the flask using a glass pipet, rinsing down any of the compounds that may have adhered to the side of the flask.  Use a piece of weigh paper to weigh out maleic anhydride (0.40g) and transfer to the flask.  Clamp the flask so that it is emersed in the water bath..

Insert a stir bar and begin heating the water bath to boil and monitor the reaction mixture.  (The diene and maleic anhydride should completely dissolve once the reaction is heated.) Heat for ~5 minutes, being careful not to overheat.  After 5 minutes, turn off the heat and check the reaction progress by thin layer chromatography (TLC) while continuing to heat the reaction mixture.

Set up a second beaker (~150ml) and watchglass for TLC analysis.  Set up a TLC plate (silica gel) to simultaneously analyze the two starting materials and the product (Figure 2).  Spot the plate with a solution of 2,4-hexandien-1-ol, a solution of maleic anhydride and the crude reaction mixture.  Develop the plate in 30:70 ethyl acetate:hexane.  View the plate under UV light and circle any spots that appear.  Place the plate in an iodine chamber and allow it to stain.  If the plate indicates that product has formed ("new spot") and no starting materials remain, allow the reaction to cool completely.  (If no product has formed, heat the reaction for an additional 5 minutes and repeat the TLC analysis).Calculate the Rf values for each spot.

Figure 1: Reaction Set up

 



Figure 2: TLC Analysis

                          

Once cooled, empty the hot water from the crystallization dish and replace it with ice.  Emerse the clamped flask containing the reaction mixture into the ice bath and allow it to sit for ~10 minutes to ensure complete crystallization of the product occurs.  While the reaction is cooling, set up an apparatus for vacuum filtration.

Clamp a 250 ml side-arm vacuum flask to a ring stand and fit the flask with an adapter and Buchner funnel (Figure 3).  Place a piece of filter paper into the funnel and attach a vacuum hose to the flask.  Connect the hose to the vacuum. Check the reaction mixture for formation of crystals.  If crystals have formed, filter the reaction mixture.  Turn on the vacuum. Wet the filter paper with ~2-5ml of toluene.  While the filter paper is wet, unclamp the cooled test tube containing the reaction mixture and gentyl swirl it and pour it into the Buchner funnel to filter the crystals formed.  Rinse the flask with 2-3 ml of cooled toluene and filter to collect any residual product.  Collect the product from the filter paper and transfer to a clean watchglass.  Allow the product to dry in the hood.

    

Figure 3: Vacuum filtration


While the product is drying in the hood, run an IR spectrum of the two starting materials.  Students may work in groups of four to run these spectra.  Each bench should run one spectrum of the 2,4-hexadien-1-ol and one spectrum of maleic anhydride. For infromation regarding IR spectroscopy click here.

Label a small vial with your name, date, lab section, and Diels-Alder product. Transfer the product from the watchglass to the vial.  Hand in your product to the lab instructors for storage until week 2.

Waste Disposal (Waste containers located in the back hood.)
Dispose of all non-halogenated organic compounds/solvents  in “non-halogentaed organic waste”. Glass microcapillary pipets and pipets should be disposed of in designated containers.  Filter paper is disposed of in the solid waste

End of Week 1

Collect your product vial from the previous week  from your lab instructor.  Weigh the dried product, record the mass and calculate the percent yield.  Determine the melting point of your reaction product and record this value along with the literature melting point value of the product in your notebook.  Run an IR spectrum of your product. (Each individual student must run their own spectrum). Compare the IR spectrum of your product with the spectra of the starting materials.  Tabulate the major peaks in each spectrum and the corresponding bond/functional groups in the structures that give rise to these peaks.  Print a copy of the proton NMR spectrum of the product.

End of Week 2