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Standard Synthesis Lab Report Format
Typology: Lab Reports
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General Diels-Alder Reaction : A conjugated “diene” reacts with a “dienophile” to produce a cyclohexene ring. The “dienophile” is activated by electron-withdrawing substituents (carbonyls). The diene must be in a “cisoid” conformation in order to react. Attachments to the reactants remain attached as spectator atoms. Overview of Actual Reaction : Anthracene (1) will serve as a student-friendly low-smell Diels-Alder diene, with the labeled carbons functioning as the reactive diene. Maleic anhydride (2) will function as the dienophile. Xylene (dimethylbenzene) is used as a high-boiling solvent so that the reaction will work fast enough to complete conveniently. In terms of activation, notice that maleic anhydride is a highly reactive dienophile, due to the presence of two electron-withdrawing carbonyl substituents. Anthracene, however, is an unusually unreactive diene. This is due to both steric effects, but more importantly because the “diene” is really part of an aromatic ring system and is thus stabilized. This stabilization in the reactant reduces the reactivity (stability/reactivity principle). The “cyclohexene” ring produced in every Diels-Alder reaction is hard to visualize, but consists of the six labeled atoms in the product. Reaction Setup: Flame dry a 25-mL round-bottomed flask with a small stir bar. (The maleic anhydride is slightly water sensitive). Weigh out 0.80g of anthracene and 0.40g of maleic anhydride (both are solids). Add the two solids into the flask. (Be sure the flask has cooled for at least two minutes before adding the solids, or they will melt.) Carry the round-bottomed flask to the hood (carefully), and add 10mL of xylene via syringe. Carry the mixture back to your hood, and clamp the flask very securely above a hot-plate/stir-plate near a sink. Attach a reflux condenser, and tubing so that water can flow through the condenser. (The array needs to be set up near a sink so that the tubes will reach.) Reaction Conditions: Turn the magnetic stirrer on, then warm the solution to “reflux” (until it boils steadily) by setting your hot plate to setting 8 (for the heater). Note: the boiling point for the xylene solvent is 138º; the actual temperature is actually somewhat hotter than that, because the dissolved solutes elevate the boiling point to some degree. Once the solution has begun to reflux, reduce the heat 1 2 3 4 5 6 1 2 3 4 5 6
O O O
xylene solvent ( 3 ) heat O O O 1 5 5 6 6 anthracene- 1 mw = 178 mp = 216 maleic anhydride - 2 mw = 98 mp = 60 Diels-Alder Product ( 4 ) mw = 276 mp = 2 21 (^3 ) 4 4 230 - 300 range
setting to 5, or whatever it takes to maintain a gentle boil. Reflux the solution for 30 minutes. (Write up your report while you wait! Be sure to include observational details, including colors and color changes and solubilities and solubility changes.) Allow the solution to cool to room temperature, then place it in an ice bath for 10 minutes to complete the crystallization of the product. Isolation of the Product: Collect the crystals by vacuum filtration using a Buchner funnel. Make up a mixture of 4 mL ethyl acetate and 4 mL of hexane in a grad cylinder. Disconnect the aspirator, add half of the ethyl acetate/hexane mixture, and reconnect the aspirator. Repeat this sequence again with the other half. Vacuum dry for at least 8-10 minutes before weighing the product for a yield calculation and taking the melting point. Caution: Xylene and ethyl acetate are both strong smelling chemicals. Be very careful to rinse them out only in the hood. And be very careful to keep them covered to reduce fumes. Lab Report: Should follow the standard synthesis layout. (See website and/or handout)
Standard Synthesis Laboratory Report Format : The following layout is standard for a “synthesis reaction” report. Provide the parts and information in the sequence specified.