Chemistry 238 Name:

Sample Lab Test #2 Forty-five minutes; closed book, notes, handouts; open lab notebook 1. a. An experiment is performed to determine the distribution coefficient for an

unknown organic compound. A 0.055 g sample of the compound is added to a conical vial. Two mL of water and 2.0 mL of methylene chloride is added to the vial. After shaking, the organic layer is transferred to another container and the water is removed by a drying step. The dried layer is transferred to a tared test tube and the solvent is evaporated. After weighing the test tube, the weight of solid in the tube is determined to be 0.032 g. Calculate the distribution coefficient for this compound between methylene chloride and water. (Show your work.) (4 points)

b. The following table is taken from the International Critical Tables, 33rd edition, and

lists the solubility of succinic acid in a binary solvent mixture with water as one of the components. If you are going to isolate succinic acid in an easily evaporatable (volatile) solvent, which solvent from the table below would you use, and why? Hint: must you do an extraction only once? (3 points)

Equilibrium concentration, succinic acid, wt %

Solvent name Formula

Water layer Organic layer 4-methyl-2-pentanone C6H12O 0.16 0.030 2-pentanone C5H10O 0.16 0.070 2-butanone C4H8O 0.16 0.160 cyclohexanone C6H10O 0.16 0.176

2. In an extraction procedure, a student extracts 1 mL of an aqueous solution that

contains an organic product with 2 mL of methylene chloride. After shaking the mixture and letting the layers separate, the student transfers the organic layer to a test tube. The student observes that there are a few drops of water adhering to the inside surface of the test tube below the surface of the organic layer. Describe what procedure you would follow to remove all of the water from this organic layer. At the end of your procedure the dried organic layer should be in test tube with nothing else present. Give enough detail so that another student could follow your procedure, even if he or she had never done this procedure. Assume that only one extraction is required in this experiment. (6 points)

3. A C=O bond absorbs light at 5.2 mm. What is this value in wavenumbers

(

†

n )? Show your work. (3 points)

4. Interpret the following IR spectrum for acetophenone. That is, identify the significant peaks by labeling the peak or peaks with the group of atoms that are associated with that peak. Label the peaks directly on the spectrum. [Note: The carbonyl (C=O) peak is shifted slightly from its normal position because of conjugation with the benzene ring.] (10 points)

Peaks corresponding to the following groups (if found in the compound)

should be identified on the spectrum: CH (sp3) CH (sp2) CH (aldehyde) OH C=O C=C (aromatic) aromatic substitution pattern CO CX NH NO2

5. Each of the following 3 spectra corresponds to one of the following compounds: hexane, 1-hexene and 1-hexanol. Write the name of the compound in the lower right corner box of the appropriate spectrum. You do not need to justify your answer. [Note: all of these spectra on this exam came from http://www.aist.go.jp/RIODB/SDBS/menu-e.html, the Integrated Spectral Data Base System for Organic Compounds maintained by the National Institute of Advanced Industrial Science and Technology in Tsukuba, Japan.] (4 points)

6. A chemistry student follows a procedure for synthesizing acetaminophen. In this procedure the student reacts 0.149 g of p-aminophenol (MW = 109.1) with 0.160 mL of acetic anhydride (MW = 102.1, d = 1.08 g/mL), with 0.45 mL of water as the solvent. The reaction is stirred for 30 minutes at 115 °C in a 5-mL conical vial with a water-jacketed condenser attached. At the beginning of the reaction period, everything is in solution. As the reaction proceeds, solid acetaminophen precipitates from the reaction mixture. The crude product is isolated by vacuum filtration on a Hirsch funnel. The crude product is contaminated with p-aminophenol and water after this filtration step. The crude acetaminophen is then purified by crystallization using water as the solvent.

+ Æ

+ CH3COOH a. Explain why a condenser is used in this experiment. (2 points) b. Outline a separation scheme for isolating pure acetaminophen from the reaction

mixture. Start by listing all the components present at the end of the reaction period Use a flow chart to show all the steps used to isolate the final product. (4 points)