Diels-Alder Reaction in Organic Laboratory l - Lab 5 | CHEM 2130, Lab Reports of Organic Chemistry

Download Diels-Alder Reaction in Organic Laboratory l - Lab 5 | CHEM 2130 and more Lab Reports Organic Chemistry in PDF only on Docsity! Lab 5: Diels-Alder Reaction The laboratory procedure used was written by Dr. John Barbaro of Rocky Mountain College. The Diels-Alder reaction is a well known example of cycloaddition chemistry. It is commonly known as [4+2] Cycloaddition. The reactants in the Diels-Alder reaction are a 1,3-diene and an alkene called the dienophile. The dienophile usually contains an electron-withdrawing group that is in conjugation to the double bond, making the double bond “electron poor”, thus initiating the addition reaction. The double bond of the dienophile adds to the diene to give a product that has a six-membered ring. EWG + Solvent Heat EWG The Diels-Alder reaction occurs through a concerted step (in a single step). Two chemists, Otto Diels and Kurt Alder, were awarded the Nobel Prize in Chemistry in 1950 for this reaction. Diels-Alder Reaction (Diene Synthesis). FIRST CITATION: O. Diels and K. Alder, Ann. 460, 98 (1928); 470, 62 (1929) Ber. 62, 2081, 2087 (1929) Stereoselectivity: The Diels-Alder reaction is stereospecific. The configuration of reactants are maintained during the Diels-Alder reaction. In the case of cyclic dienes, these give stereoisomeric products as well. In order to see what the products of these reactions look like, please click here! VERY COOL LINK! If the link above does not work on your PC, you might need to download the program, Jmol. Click here to go to the download page. Also, since this is a synthesis, two ADDITIONAL steps are ALWAYS performed: draw a correct mechanism for the production of the product from the starting materials and PROPERLY calculate a percent yield. The mechanism is part of the prelab; the percent yield is part of the post lab Properly assembled, your reflux apparatus will look like this: PLEASE NOTE two clamps, not clips! Gray Heating Mantle with sand Transformer Round bottom flask with boiling chips Condenser Water in Water Out Clamp Experiment: Reaction of Anthracene with Maleic Anhydride O OO O O O Solvent Heat + Anthracene Maleic Anhydride 9,10-Dihydro-9,10- ethanoanthracene-11,12- Dicarboxylic Anhydride In this lab, the 4 electrons of the diene (anthracene) will react with the 2electrons of the dienophile (maleic anhydride) to give the polycyclic Diels-Alder product. The reaction will be conducted under reflux conditions. Safety and Waste Disposal: Xylene is flammable, so keep it away from flames and hot plates. Experimental Procedure: Place 1.0 g of anthracene and 0.5 g of maleic anhydride in a 100-mL round-bottom flask. Add 15 mL of xylene and a boiling chip. Attach a reflux condenser to the flask (Remember to grease the joints so that the glass will not stick at the end of the experiment). Run cool water through the condenser to prevent any escaping vapors. Heat the mixture under reflux for 30 minutes. At the end of the reflux, cool the flask to room temperature and then you will need to keep the flask in an ice bath for about ten minutes to completely crystallize the product. Collect the crystals by vacuum filtration using a Büchner funnel and wash the solid with 15-20 mL of ice-cold xylene and keep the vacuum filtration on for 8-10 minutes. Allow product to dry on the piece of filter paper for a further 10 minutes. Record the weight of the product and calculate the percent yield for the reaction. Don’t worry about getting a melting point (lit. mp 261-262 oC) for your product, since the melting point is too high. POSTLAB QUESTIONS: Explain why a 4M solution of maleic anhydride is made in CH2Cl2 and not in water. Show the reaction between maleic anhydride and water. Give structures for the major Diels-Alder product of the following reactions: 1,3-cyclohexadiene and tetrachloroethene 1,3-cylcohexadiene and fumaric acid, the trans isomer of maleic acid