Synthesis of Aspirin and Oil of Wintergreen Lab, Lab Reports of Chemistry

Download Synthesis of Aspirin and Oil of Wintergreen Lab and more Lab Reports Chemistry in PDF only on Docsity! 1 Experiment 22 Synthesis of Aspirin and Oil of Wintergreen GOALS: In this two-week experiment the important area of organic chemistry will be illustrated by the preparation and characterization of two compounds. The usefulness of functional groups will be illustrated as well as the use of NMR, IR, and melting point in characterizing a product. The analysis will be done next week in Experiment 23. INTRODUCTION: Synthesis and use of organic compounds is an extremely important area of modern chemistry. Approximately half of all chemists work with organic chemicals. In everyday life, many if not most of the chemicals you come in contact with are organic chemicals. Examples include drugs, synthetic fabrics, paints, plastics, etc. Synthesis of Aspirin and Methyl Salicylate. The two compounds we will be preparing, aspirin (acetylsalicylic acid) and oil of wintergreen (methyl salicylate), are both organic esters. An ester is a compound that is formed when an acid (containing the –COOH group) reacts with an alcohol (a compound containing an –OH group). Eqn 1 Here R1 and R2 represent groups such as CH3– or CH3CH2–. The reaction type shown above may be called a condensation reaction because the small molecule H2O is eliminated from the reactants while the remaining bits of the reactants condense together to give the main product. This reaction may also be called an esterification, since the product of the reaction is an ester, a compound containing the CO2R group (see chapter 20 for definitions of acids, esters, and alcohols). Esters usually have pleasant, fruit-like odors and are the chemicals responsible for the odors and flavors of many fruits (oranges, bananas, pineapples) and flowers. In most cases, such natural products get their properties from a mixture of organic compounds. In this experiment you will prepare two esters of o-hydroxybenzoic acid, more commonly known as salicylic acid. One of the esters, acetylsalicylic acid, is aspirin, the common analgesic. We will synthesize aspirin by mixing salicylic acid with acetic anhydride. The second ester product is oil of wintergreen, or methyl salicylate, which we prepare by allowing salicylic acid to react with methanol. This compound, which has a familiar odor is used as a flavoring agent and in rubbing ointments. Both of these reactions are shown below. This experiment illustrates several properties of organic synthesis. While both product compounds in the experiment are esters of the same compound (salicylic acid), they are quite different in structure. Aspirin involves a reaction of the –OH group of salicylic acid, while methyl salicylate involves a reaction of the –COOH group of salicylic acid. Organic chemistry is the broad field of studying the tremendous variety of such reactions of organic functional groups. C O R1 O H + O H R2 C O R1 O R2 + H O H acid alcohol ester water 2 C C C C C C O H C O O H H H H H + salicylic acid CH3O H H+ methanol C C C C C C O H C O O CH3 H H H H + methyl salicylate (oil of wintergreen) H O H water Preparation of methyl salicylate Purification by Recrystallization. After preparing the aspirin, we will purify it. Most solids can be purified by recrystallization, at a cost of lower percent yield. Recrystallization is usually done by dissolving the substance in a suitable solvent, which is hot. If insoluble particles are present, the hot solution is filtered to remove them (we will skip this hot filtration step). The solution is allowed to cool slowly, and is eventually cooled in ice. The crystals that form slowly are more pure than the original solid. We can also get a solute to re-precipitate by adding a second solvent in which it is less soluble. HAZARDS: Acetic anhydride is caustic and has a very strong odor. It must be dispensed in a hood. Keep your reaction in the hood as well. Both ethanol and methanol are flammable. No open flames are allowed in lab this week. LABORATORY OBSERVATIONS AND DATA: Be sure that you record what you do and make good qualitative observations, noting initial colors, odors, etc. in each step of the procedure. Clearly label all numerical data. C C C C C C O H C O O H H H H H H3C C O CH3C O O C C C C C C O C C O O H H H H H O CH3 H3C C O O H + H+ + salicylic acid acetic anhydride acetylsalicylic acid (aspirin) acetic acid Preparat ion of acetylsalicylic acid