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I've made an effort throughout this book to make things out of chemicals that are commonly available, but for this project we'll need aniline and acetic anhydride, neither of which are available "over-the-counter," as it were. Aniline, first encountered in Chapter 22, is a brown oily liquid prepared from coal tar or, more recently, from petroleum. Acetic anhydride is a colorless liquid that smells like vinegar on steroids. Both of these chemicals must be obtained from chemical suppliers as they have no household uses.
In order to make acetanilide, you'll need to answer the usual stoichiometric questions:
Q: Given Equation 26-1, how many grams of acetic anhydride are needed to react with 1 gram of aniline? We'll need to use excess acetic anhydride because some of it will be hydrolyzed by the water used as a solvent for the reaction. So multiply your calculated weight of acetic anhydride by 1.1 to provide a 10% excess.
Weigh out 1.0 gram of aniline and add it to 10 mL of water in a 100-250 mL beaker. The aniline will sink to the bottom of the beaker, since it's not very soluble in water. Now weigh out your acetic anhydride and add it to the beaker a few drops at a time, stirring the contents of the beaker between drops. In just a few minutes the acetanilide product will crystallize. This crude acetanilide is contaminated with acetic acid and aniline acetate. Such contamination cannot be tolerated in a pharmaceutical and it must be removed. Fortunately for us, the solubility of acetanilide differs substantially from that of acetic acid and aniline acetate.
Acetanilide is quite soluble in boiling water, but not in cold water. By contrast, acetic acid and aniline acetate are just as soluble in cold water as in hot water. If you have paid any attention to the previous chapters, it ought to be obvious to you that we need to do some recrystallization. Add another 25 mL of water to the crude acetanilide in your beaker and heat it on a hot plate or over a spirit lamp until the water comes to a boil. All of the solids should dissolve in the boiling water; if they don't, add a little bit more water until they do. Remove the beaker from the heat and set on the counter top to cool.
If you've been earthified to any extent, you'll remember that the slower the recrystallization goes, the purer the crystals will be. So I'm going to suggest that you not rush it; let the hot solution cool slowly and your crystals will be large and pure. The acetic acid and aniline acetate will remain in solution. When the solution reaches room temperature, fold a piece of filter paper, place it into a funnel, and filter your purified acetanilide product. Rinse your crystals with a few mL of cold water, return them to the beaker, and allow them to dry overnight. The spent solution can be poured down the drain. Weigh your dried crystals and express the actual yield as a percentage of the theoretical yield.
Your acetanilide should take the form of flat, virtually odorless crystals. Record the amounts of materials used and your percent yield in your notebook. Tape a photograph of your crystals into your notebook as a record of your achievement.