Experiment A. Introduction to the Organic Laboratory and Characterization Techniques

Transcription

1 Experiment A. Introduction to the Organic Laboratory and Characterization Techniques 1. EXPERIMENTAL OBJECTIVES: a. To identify the safety features and physical layout of the organic laboratory. b. To locate and operate instruments and equipment in the laboratory. c. To recrystallize a pure sample of either benzoic acid (compound 1) or naphthalene (compound 2). O OH 1 2 d. Characterize benzoic acid (1), naphthalene (2), and a mixture of these two by melting point analysis. e. To conduct thin layer chromatography and analysis of common household products (Anacin, Excedrin, Tylenol, aspirin, caffeine). 2. SPECIAL INSTRUCTIONS: a. You will not turn in your lab notebook pages for grade. You will only turn in the fill in the blank style report for grade at the end of the second three-hour period. You should, however, complete your lab notebook according to procedures as described in your SICOC to familiarize yourself with laboratory notebook requirements. For notebook purposes, this is your practice lab. b. Efficiently inventory your bench drawers throughout the lab period. Do not spend an inordinate amount of time on the inventory. Become familiar with the equipment, note discrepancies and replenish as appropriate. c. Calibrate the sand-bath hotplate at your bench position throughout lab period. d. Choke point for lab is melting point determination. e. Chemicals and solvents Chemical Abstract Service [CAS]: (1) Benzoic Acid, [ ] (2) naphthalene, [ ] (3) hexane, [ ] Page 1 of 12 1/7/08

2 3. PROCEDURES: (4) methanol, [ ] (5) acetone, [ ] Perform the following tasks. Remember, you must multitask to be successful. 1. Sandbath Calibration. Immediately begin the sandbath-hotplate calibration (G&M, Fig 2.28, p. 48) by setting up the equipment as shown. Do not allow the thermometer to come in contact with the bottom of the sandbath. Record temperature (ºC) vs. control setting at each control setting number. Allow the sandbath to equilibrate at each setting (about 10 minutes) before recording the temperature. Do not exceed the temperature range of the thermometer. Draw a graph of hotplate setting vs. temperature, and record the serial number of your hotplate, in your laboratory notebook. You will refer to your calibration chart throughout the two semesters of organic chemistry laboratory. 2. Inventory and Orientation. Inventory the contents of your lab bench drawers. If you are missing anything, attempt to re-stock your drawers from the various equipment supply points. If an item is unavailable, bring it to the attention of your instructor. Inventory sheet is attached. Conduct an inspection of the laboratory facilities to identify the safety items, equipment, function, and apparatus locations, and waste disposal receptacles. Record on the attached page and laboratory map; attach the map permanently into your laboratory notebook and identify its location in the Table of Contents. 3. Thin-Layer Chromatography. Using the five compounds, prepare each sample in a 3-mL disposable test tubes using about 1 ml of the prepared solvent mixture (1:1 hexane: acetone) as the dissolving solvent and a smallest quantity of solid on your spatula tip. a. Prepare a TLC developing chamber (G&M, Fig 6.3, p. 177), using the prepared solvent mixture (1:1 hexane:acetone) as the developing solvent. b. Prepare two TLC plates (G&M, Fig 6.2, p. 177): (1) Prepare a plate with caffeine, aspirin, and acetaminophen; prepare a second plate with Unknowns A and B. (2) Label your TLC plates per G&M. Use only pencil. Draw a sketch of your plates in your lab notebook. (3) Spot each of the samples on the TLC plate, ensuring that the spot is above the solvent level in the developing chamber. c. Elute the plate in the developing chamber. Stop the process before the solvent front reaches the top of the TLC plate. Remove the plate and immediately mark the solvent front with pencil. d. Observe the elution by visualizing the TLC spots under UV light, tracing around the spots observed and marking the center mass of each spot. e. Calculate the R f values (G&M, p. 179) of each compound in the samples by determining the ratio of distance of sample travel/distance of solvent travel in the space provided on your lab report. f. Include the fully labeled and analyzed TLC plates with your lab report. Page 2 of 12 1/7/08

3 4. Capillary Melting Point Analysis. Prepare three capillary tubes (G&M, Fig 2.16, p. 39 and Fig 2.19, p. 40) for melting point analysis of pure benzoic acid, pure naphthalene, and a 80%- 20% benzoic acid/naphthalene mixture of the two (already prepared for you). Determine the melting point range for each sample, record the data in your notebook, and enter it in your lab report. 5. Craig Tube Recrystallization; Centrifuge Operation. Ensure the hotplate sandbath is heated to at least 80 C for this procedure. a. Record the exact mass of either approximately g of either pure benzoic acid or g of naphthalene and place it into a Craig tube (G&M, Fig 2.47, p. 66). For benzoic acid, add add about 1 ml water to the solid; for naphthalene, add about 1 ml methanol. b. Heat "gently" on the sandbath until the solid dissolves. It is best to tap the Craig tube to aid dissolution rather than stirring, as stirring with the spatula results in transfer losses. If you must stir, use the microspatua. (Note: heating "gently" is an art form that means use your calibrated senses to heat the tube enough to get the contents just warm enough to aid solvation but not too hot to cause boiling. Too much solvent inhibits recrystallization, so selecting the solvent and its volume is also an art form.) c. Upon dissolution, remove the Craig tube from the sandbath and set it in a small beaker to keep it upright while cooling in air. d. After the reaching room temperature, cool the tube in an ice bath for a few minutes to enable crystal growth. e. After crystals have formed, insert the glass plunger with wire into the Craig tube to form the "Craig tube assembly," (G&M, Fig 2.47, p. 66). Now remove the solvent by inverting the Craig tube assembly into a centrifuge tube (G&M, Fig 2.55, p. 71). Place the inverted Craig tube assembly into the centrifuge, balance the centrifuge, and then spin the mother liquors from the crystals to the bottom of the centrifuge tube. f. After spinning, carefully remove the centrifuge tube with the Craig tube assembly, pull the wire to remove the Craig tube from the centrifuge tube, then disassemble the Craig tube assembly and carefully collect the crystals from the plunger and the Craig tube. Determine the mass of the recovered product and record it on the lab report. 6. Disposal of Chemical and Solid Waste. Discard pipets and weighing boats in trash receptacles; discard any glass in the glass waste box. Solvents go in the solvent bottles in the hood. Page 3 of 12 1/7/08

4 Inventory Sheet Top Drawer: 1 sand bath (crystallizing dish containing sand) 1 aluminum heating block 4 round bottom flasks (1 with threaded compression cap, septum, and o-ring) 4 conical vials (2x3 ml and 2x5 ml, all with threaded compression caps, septa, and o-rings) 1 conical vial cap 1 centrifuge tube cap 3 types of stir bars (1 spin-vane and 2 bars) 1 Hirsch funnel with neoprene adapter 1 filter flask 4 beakers (2x10 ml and 2x30 ml) 3 Erlenmeyer flasks (2x5 ml and 1x 25 ml) 1 permanent marker 2 spatula 1 glass rod with rubber policeman 1 pair of tweezers 1 rubber adapter 1 long thermometer 1 microscale lab kit (blue box), containing: 4 conical vials (2x1 ml, 1x3 ml and 1x5 ml, all with threaded compression caps, septa, and o-rings) 2 V bottom vials (both with threaded compression caps, septa, and o-rings) 1 Hickman-Hinkel still head 1 condenser 1 syringe 1 air condenser 1 Craig tube for recrystallization 1 plunger for Craig tube 1 drying tube 1 Claisen head 1 round bottom flask (with threaded compression cap, septum, and o-ring) 1 thermometer adapter 2 collection tubes 1 collection tube adapter (metallic) 2 nd Drawer: 2 beakers (1x250 ml, 1x100 ml) 1 separatory funnel 3 funnels (2 glass, 1 plastic) 1 wide-mouth jar for TLC development 1 graduated cylinder 1 ruler 1 brush 1 evaporating dish 1 watch glass Page 4 of 12 1/7/08

5 Supplies of: red litmus paper blue litmus paper micropipettes boiling stones filter paper (5.5 cm and 1 cm) melting point tubes matches phydrion paper TLC plates Third drawer: 1 test tube clamp 1 pair forceps 1 towel 1 test tube rack 1 hose clamp 1 wire gauze 1 fiberglass hot mat 1 hose clamp Bottom drawer: Assortment of hoses 5 clamps (all different types) 1 ring 1 cork ring 1 microburner Page 5 of 12 1/7/08

6 Orientation to the Organic Laboratory Identify and record the location of the items listed in the laboratory. Keep this page for successive lab periods. Nearest fire extinguisher/spill Control Center Nearest eyewash station/shower Instructor s bench Ms. Wade s office Nearest telephone; phone number Material Safety Data Sheet (MSDS) folder CRC, spectra, and reference books Solid, liquid organic waste disposal bottles Broken glass/glass disposal box Chemical dispensing hoods Sandbath equipped drying hood Icemaker Drying oven UV lamps for visualization Centrifuges Melting temperature apparatus Heating lamps Balances Gas Chromatography (GC) instruments Infrared (IR) Spectroscopy instruments Student sample temporary storage cabinet Page 6 of 12 1/7/08

7 A Building, Room 1290 Schematic: Organic Chemistry Laboratory Layout Door Prep Room Door Page 7 of 12 1/7/08

8 Experiment A Report Name: Date: (12) 1. Thin Layer Chromatography a. (True/False) For a given sample, a single TLC spot is an absolute indication of sample purity. Explain. b. If a solvent such as ethanol (instead of a solvent mixture such as acetone/hexane) were used to elute the samples on the TLC plate, would you expect the R f values to be greater or less than those you recorded? Explain your answer. c. Show your calculations for the R f values of each of the 5 compounds below. Page 8 of 12 1/7/08

9 d. Unknown A and Unknown B are common over the counter (OTC) analgesics Anacin and Excedrin. Which unknown is Anacin and which is Excedrin? How do you know? (15) 2. Capillary Melting Point Analysis a. Complete the table below. Compound Lit m.p. ( o C) Heating rate (deg/min) Starts Melting Stops Melting ΔT (T stop -T start ) ΔT 2 o C? benzoic acid naphthalene 80%-20% mixture Page 9 of 12 1/7/08

10 b. How close was the range to the expected melting point values for the compounds? c. Were these compounds pure? Explain. d. What impact did the presence of the other compound have on the melting point range of the mixture? Page 10 of 12 1/7/08

11 e. Is the melting point of the mixture exactly between the melting point temperatures of the pure samples? Consider the breadth of range and relation to literature m.p. Why or why not? Discuss your melting point analysis in the framework of colligative properties you learned in general chemistry. In addition, you may discuss instrument calibration in your explanation. (12) 3. Craig Tube Recrystallization a. Set up and calculate % recovery for your recrystallized product. b. Discuss your percent recovery in the framework of less than, greater than, or equal to 100% recovery. Page 11 of 12 1/7/08

12 c. Would a solvent such as hexane dissolve benzoic acid as effectively as water? Why or why not? d. Compare color of the solvent before adding the solid with color of solvent after centrifuging. Explain. e. What differences, if any, did you observe in the physical appearance of your recrystallized compound and the initial starting material? Explain. (1) 4. Sand Bath Calibration. What do you conclude about your sand bath as a heating source? Page 12 of 12 1/7/08