In a 5-mL round bottom flask, add 120 mg of 4-aminobenzoic acid (often called PABA for p- aminobenzoic acid), 1.5 mL of absolute ethanol (absolute ethanol is completely free of water and can be found on the hooded shevles), and 3 boiling chips. Heat this mixture on a sand bath until all the solid dissolves. Cool in ice and then add 0.25 mL of concentrated sulfuric acid dropwise. (One drop at a time.) A large amount of precipitate will form when the sulfuric acid is added, but this will dissolve during the reflux that follows. Attach an air condenser from the microscale kit, and reflux gently for 60- 75 min. Check periodically to be sure that the mixture is refluxing gently, and that the ring of condensation of solvent lies somewhere along the inner surface of the air condenser; loss of solvent will cause overheating and a significant decrease in yield. Detach the air condenser from the reaction tube and allow the reaction mixture to cool to room temperature. Using a Pasteur pipet, transfer the reaction solution to a 10-mL Erlenmeyer flask and add 3 mL of distilled water. Dropwise, add saturated sodium bicarbonate (about 3 mL, approximately 10% or 1 M) to neutralize the excess sulfuric acid and the ammonium sulfate salt form of the amino ester (making it neutral and insoluble in water). After each addition of the sodium bicarbonate, agitate the solution to mix thoroughly. Extensive CO2 evolution (gas) and frothing will be observed until the mixture is nearly neutralized. As the pH increases, a white precipitate of benzocaine is produced. When gas no longer evolves as you add a drop of sodium bicarbonate, check the pH of the solution with "Alkacid" pH paper and, if it is less than 8, add further portions of saturated sodium bicarbonate solution. Collect the benzocaine by vacuum filtration using a Hirsch funnel. Use three 1-mL portions of cold water to wash the product crystals from the flask onto the funnel. Make sure the product is rinsed thoroughly with cold water water. After the product has dried thoroughly by leaving it in an open container until the next lab period, weigh it, calculate the % yield, and determine its melting point. The m.p. of pure benzocaine is 92°C.
Benzocaine Data Sheet
1) Draw the reaction scheme
2) Find the limiting reactant, and calculate the theoretical yield: 2.41g
3) Provide the mass of recovered product, and calculate the percent yield: 200 F
4) Provide the melting point and melting point range of your product. Compare it to the literature value
5) Below is the structure of benzocaine. Correlate each proton to the corresponding peak in the 1H NMR spectrum
H2N 5) Below is the structure of benzocaine. Correlate each proton to the corresponding peak in the iH NMR spectrum H H CH
