Electrophilic aromatic substitution (EAS) is one of the primary methods for functionalizing aromatic rings. A wide variety of EAS reactions exist and the one you will be studying in this lab is nitration (see pp 576-7 in your text, there is a cool animation of this reaction at: www.cm.utexas.edu/groups/iverson/eashm2.htm). Two substituted aromatic rings will be nitrated: veratrole and methyl benzoate. You and your partner will nitrate both compounds and analyze and identify the products by thin-layer chromatography, melting point, IR, and NMR.

Make a solution of 1.2 mL of glacial acetic acid (concentrated sulfuric acid) and 0.60 g veratrole (methylbenzoate) in a 5 mL conical vial. Cool this solution to 0°C in an ice bath. Add dropwise a mixture of 0.4 mL glacial acetic acid (concentrated sulfuric acid) and 0.4 mL concentrated nitric acid, keeping the mixture in the ice bath. Using a stirring rod, keep the reaction well mixed during the addition and keep the addition slow enough that the vial does not become warm to the touch. After the addition of nitric acid, remove the mixture from the ice and, after 15 min, pour the mixture into ~5 g of ice in a small beaker. Isolate the product by vacuum filtration. Wash the product with cold water and ice cold methanol. Weigh the crude product and save a small amount of it for TLC analysis. Recrystallize the remainder from methanol (you may need to do a water/methanol mixed solvent recrystallization). Vacuum filter the recrystallized product and allow it to dry before running the IR and NMR.

TLC: Dissolve some of your crude solid in dichloromethane in a small test tube. In another test tube dissolve some of your purified solid. There will be a TLC standard of both veratrole and methyl benzoate starting material. Spot a TLC plate with crude produce, purified product, and starting material. Develop it with dichloromethane. You will need UV light to visualize the spots. Make a sketch of your TLC plate in your notebook.

IR: The easiest way to run an IR of your solid is to make a concentrated solution of it in dichloromethane (don’t use this for the TLC) and then carefully put a few drops of it on a NaCl plate (you don’t need the other plate). When the dichloromethane evaporates, a thin film of your solid will remain. Obtain the IR normally at that point and then wash off the plate with acetone. It might help you to overlay your spectrum on the starting material spectrum to see the differences.

NMR: Put a few crystals of your solid in a test tube, add CDCl₃ and transfer the solution to an NMR tube. Run the NMR as usual. Don’t use the solid that has been dissolved in dichloromethane, or you will get a big peak from CH₂Cl₂ in the NMR.

There are a number of products that could result from each reaction, especially when you consider that dinitrations and trinitrations are possible. You need to propose a product for both reactions (use your partner’s data) and then prove that it is the correct one using all the evidence possible. Compare your melting point to the appropriate literature value (look it up)? Is the IR and NMR evidence consistent with your proposed product? What does the TLC evidence indicate? In addition to determining the structure of the two products, comment on the purity and percent yield of your product. How can you improve the purity and percent yield? Discuss which products should be formed based on your understanding of the mechanism. Include any pertinent intermediates.