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Chemistry 301L Organic Laboratory Professor Kelli Khuong |
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| SCHEDULE and WEEKLY NOTES |
WEEKLY NOTES WEDNESDAY LAB
Week 1: Spartan Exercise
Due at the end of lab: Spartan '04 Data Sheet and an electronic copy of the word document with the ESP maps
For Week 2: § Read Ch 9 pp 123-127 § Prepare your notebook (title, purpose, table, procedure; there are no balanced reactions for this lab) to perform experiment 1. § In a separate experiment (leave several blank pages after experiment 1), prepare your notebook (title, purpose, table, procedure) to perform a modified exp 4. The two colored solids you’ll be using are ferrocene and acetylferrocene. The solvents you’ll have at your availability are dichloromethane, ethyl acetate, acetic acid, ethanol, hexane, cyclohexane, and toluene. § Your specific goals for exp 4 will be to determine the following: (1) what solvent or solvent mixture will give an Rf value of ~0.5 for ferrocene; (2) what solvent system will give an Rf values of ~0.5 for acetylferrocene; (3) what solvent system will give a difference in Rf values of at least 0.2 for ferrocene and acetylferrocene. § bring a pencil for Week 2 lab
Week 2: TLC
Due at the end of lab: Procedure and observations
Due by Monday 2/12 at 11:15 am: Results, exp 1 § any calculations; summary of Rf values for pure analgesics and for all spots in the OTC tablets (1-3)
Discussion, exp 1 § Did you accomplish the purpose of the experiment? Briefly explain. § Do your Rf values support the predictions based on our in class analysis of which analgesics were polar and which were nonpolar? § One unknown contains three analgesic compounds. Use the relative size of the three TLC spots to estimate whether there are equal amounts of the three analgesics or whether one of the analgesics is present in greater or lower concentration than the other two.
Results, exp 4 § any calculations; summary of all your findings for various solvents and the resulting Rf values for ferrocene and acetylferrocene
Discussion exp 4 § Did you accomplish the purpose of the experiment? Briefly explain. § Which solvent system gave the best separation of the two compounds? § What is the appearance of a TLC plate if a solvent of too low polarity is used for development? Too high polarity?
For Week 3: § Read Ch 8 pp 103-114 § Prepare your notebook (title, purpose, table, procedure) to perform experiment 1. You do not need to prepare a flow sheet (we will do this together in lab). § Note that you will carry out the procedure up to the point of isolating the crude p-dimethoxybenzene, crude t-butylphenol, and crude benzoic acid. You do not need to include instructions for recrystallization of each of the three compounds. You will save the three crude products until the next week.
Week 3: Extraction
Due at the end of lab: Procedure and Observations
Due by Monday 2/19 at 11:15 am: Results § Calculation of % recovery for each of the three crude products based on the assumption that the original mixture was equal proportions of benzoic acid, 4-t-butylphenol, and dimethoxybenzene § Tabular summary of results
Discussion § Did you accomplish the purpose of the experiment? Briefly support your answer. § Answer question 1 from text (p. 121). § What is the approximate density of 1.5 M aqueous NaOH? Briefly explain. § How many moles of benzoic acid are in the mixture to be separated in this experiment? Show all work. § What volume of a 3M aq NaHCO3 is needed to convert all the benzoic acid (from the previous question) to its conjugate base? Show all work. § Draw a flowchart that illustrates the procedure for how a mixture of naphthalene (a neutral substance) and 4-chloroaniline (a basic substance) can be separated by extraction. Use what you learned today in lab. Use the flowchart we did together in lab as an example.
For next week: § Read Ch 3 pp 32-43, 47-48 § Prepare your notebook (title, purpose, table, procedure; no reactions) to perform a recrystallization of naphthalene, benzoic acid, and dimethoxybenzene. Use the procedure listed below. § After completing the recrystallization of naphthalene, you will use the same general procedure for the recrystallization of crude products from week 3. You do not need to recopy the recrystallization procedure a second and third time into your notebook. Simply add a final step or two that tells you to carry out the additional recrystallizations.
WEEK 4 Procedure. The steps for a general recrystallization are discussed in Williamson, pp. 32-43. The first goal is to do a recrystallization of a 1 g sample of commercial naphthalene to determine the efficiency of the recrystallization technique. Methanol is to be used as the solvent for recrystallization. Add 1 g of commercial naphthalene to a 25 mL Erlenmeyer flask. Add methanol and a boiling stone to a second Erlenmeyer flask. The exact volume of methanol that will be needed for the recrystallization is an unknown quantity. It is best not to boil too much methanol (it takes a long time for it to boil) and not to boil too little methanol (running out of solvent during the recrystallization also costs time). Place the Erlenmeyer flask with the methanol on the hot plate and heat it to boiling. Once the solvent is boiling, use a pipet to transfer small portions to the Erlenmeyer flask containing the naphthalene. At this point, both Erlenmeyer flasks should be placed on the hot plate. Continue adding hot methanol to the naphthalene sample until all of the naphthalene has dissolved. To encourage dissolution of the naphthalene, swirl the Erlenmeyer flask periodically. Because commercial naphthalene is being used, steps do not need to be taken to decolorize the solute or to filter suspended solids. Remove the saturated solution of naphthalene in methanol and place on an insulated surface, like a cork ring. Allow the solution to cool to room temperature. Further cool the solution using an ice bath. During the cooling process, ensure that the remaining solvent (aka mother liquor) does not evaporate as the crystals of naphthalene form. If crystallization has not started, several strategies can be used: (1) scratch the inside of the Erlenmeyer flask with a glass rod or (2) add a seed crystal. After crystallization is complete, vacuum filter the mixture using a Buchner funnel to separate the naphthalene crystals from the mother liquor. The crystals may be washed with cold methanol. Solids may form in the mother liquor in the filter flask; record this observation, but do not attempt to isolate these crystals. Allow the collected naphthalene crystals to dry. Record a final mass of the recrystallized naphthalene. After completing the naphthalene recrystallization, use the same basic procedure to recrystallize the crude products obtained in the Week 3 lab. Before carrying out each recrystallization, set aside a small amount of each crude product to be saved for next week. Benzoic acid is recrystallized from water, dimethoxybenzene is recrystallized from methanol. In these cases, if you do notice the formation of crystals in the filtrate in the filter flask, you will want to refilter and collect these crystals, allowing you to maximize percent recovery.
Week 4: Recrystallization
Due by Monday at 11:15 am: Results § masses of crude and recrystallized products § % recovery of crude products (this is a repeat of the calculations you did last week) § % recovery of recrystallized products (use the crude product mass as the theoretical/expected mass)
Discussion § What conclusions can you draw from the naphthalene portion of the experiment? § Did you successfully purify benzoic acid and dimethoxybenzene? Briefly explain whether or not you have conclusive evidence. § What are the two main requirements for a recrystallization solvent? § Why is it important to have some solvent remaining at the end of the recrystallization, to be filtered off from the purified crystals? § Listed below are solubility vs temperature data for an organic substance A dissolved in water.
a. Graph the solubility of A vs temperature. Connect the data points with a smooth curve. (This can be done by hand or using excel. If done on the computer, tape a copy in your notebook and on the carbons.) b. Suppose 0.5 g of A and 5 mL of water were mixed and heated to 80 oC. Would all of A dissolve? c. The solution prepared above is cooled. At what approximate temperature will crystals of A appear? d. Suppose the cooling described above were continued to 0 oC. How many grams of A would come out of solution? How many grams of A would remain dissolved in solution. Explain how you obtained your answer.
For next week: § Read Ch 4 pp 50-57 § Prepare your notebook (title, purpose, table, procedure) to perform Ch 4, exp 2 and exp 4. You may group these two procedures into a single experiment in your notebook. Make sure your purpose statement encompasses both exp 2 and 4. You should include the unknowns in table 4.2 in your table of reagents – the key property to record is mp. Note: you will be using a mel-temp apparatus like the one shown in Figure 4.3. Melting point capillaries will be provided for you. § Leave several blank pages, and in a separate experiment prepare your notebook to perform melting points of crude and recrystallized samples from the week 4 lab: benzoic acid, 1,4-dimethoxybenzene, 4-t-butylphenol (only crude). The procedure here does not need to be extensive. You can refer the reader (either you or me) to the basic procedure that you write for Ch 4, exp 2.
Week 5: Melting Points
Due by Monday 3/5 at 11:15 am: Results Ch 4 Exp 2, 4 § report mp data
Discussion § Did you accomplish the goal(s)? Comment on your results. § Your thermometer is broken. What is the best method for determining if two compounds are the same?
Results (mp of crude and recrystallized compounds from Week 3-4) § report mp data
Discussion § Did you accomplish the goal(s)? Comment on your results. § One of the most common causes of inaccurate melting points is too rapid heating of the capillary tube. Under the circumstances, how will the observed melting compare to the true melting point. § You have an unknown with an observed melting point of 90-94oC. Is your unknown compound A with a reported melting point of 95.5-96oC or compound B with a reported melting point of 89.5-90oC. Explain.
For next week: § Read Ch 44 pp 439-440 § Prepare your notebook (title, purpose, reaction, table, procedure) to perform Ch 44. The book procedure is to be modified as detailed below. There is one acid-base reaction to include in the reaction section.
Modified procedure:
1. Rather than starting with two tablets of Excedrin, you will be starting with a mixture of pure acetaminophen, aspirin, and caffeine (so no binder is present). The ratio is still 250:250:65. You will be starting with the amount of analgesic that would normally be in 4 tablets of Excedrin, so please double all of the amounts in the book procedure.
2. Place the solid mixture in an Erlenmeyer flask. Add 20 mL CH2Cl2 to the mixture and a boiling stone and warm the solution to boiling on a hot plate. Next you will do a gravity filtration (with the wide-stemmed funnel) with fluted filter paper, and collect the solid acetaminophen that did not dissolve in the CH2Cl2 (remember there is no binder). Pour the warm solution through the filter paper in three portions, keeping the Erlenmeyer flask warm between portions. This is your crude acetaminophen on the filter paper. Save a small amount of the crude acetaminophen.
3. The filtered dichloromethane contains the dissolved aspirin and caffeine. If there is solid material in the CH2Cl2, reheat the filtrate to redissolve the solids. Allow the CH2Cl2 to evaporate until the volume of the solution to decreases to 15 mL or less. You will separate the aspirin and caffeine using a base extraction. Add the dichloromethane filtrate to the separatory funnel. Then add 8 mL of 3 M NaOH (remember the volumes are doubled). Remove the aqueous layer and save it. Add 4 mL of water to the separatory funnel. Remove the aqueous layer, combining it with the first aqueous layer. The conjugate base of the aspirin is in the basic aqueous layer. The caffeine remains in the organic CH2Cl2 layer.
4. Dry the organic layer with CaCl2 as specified in the book. Decant solution, and discard the CaCl2. Isolate your crude caffeine by evaporating the CH2Cl2 using the rotavap. Save a small amount of the crude caffeine.
5. Follow the book directions for how to isolate the aspirin from the aqueous layer (acidify the aqueous layer with 3 M HCl). Try to collect and save a small amount of this crude aspirin. The aspirin is then recrystallized from the water already present in the flask with the aspirin. Collect the recrystallized aspirin by vacuum filtration. Save the recrystallized aspirin.
6. Purify the crude caffeine by recrystallization (see book for solvents) not sublimation. Collect crystals by vacuum filtration, and save the sample.
7. Purify the crude acetaminophen by recrystallization from boiling water. None of the steps with ethanol will be done. After recrystallizing, collect crystals by vacuum filtration and save the sample.
8. Once you have all crude and recrystallized samples in hand, you will test their purities using both mp and TLC. You can use the same TLC conditions as in Week 2 (2:1 ethyl acetate to hexanes).
9. Turn in all recrystallized products.
10. Calculate the % recovery for the three analgesics. The theoretical yield is based on the amount of the mixture you start with at the beginning of the experiment. The actual yield is based on the masses of the three recrystallized (and hopefully dried) products.
Week 6-7: Separation and Purification of Excedrin
Due Monday 3/19 by 11:15a: Results § starting mass of mixture § theoretical amount of each of the 3 compounds in starting mixture § final masses of each of the 3 compounds § % recovery of each of the 3 compounds § mp data for crude and recrystallized samples § Tape your TLC plates into your results section on the carbons that you turn in. The TLC should confirm the identity of the three compounds and should give an indication of the purity of the crude and recrystallized samples. Calculate Rf values. § Do your best to make the summary data table(s) as organized and clear as possible. Think about what info you can include in the summary table(s) to make your data easy for a reader to interpret.
Discussion § Did the separation work? Briefly explain, citing evidence. § Did the purification work? Briefly explain, citing evidence. § You are a contestant on a reality TV game show. The bottle of Excedrin you brought has been ground up and poisoned with 1,4-dimethoxybenzene. This is a problem because you have developed a significant headache (your fellow contestants are driving you crazy!!!), so you must figure out a way to remove the poison in order to cure your headache. Develop an appropriate separation protocol assuming the starting mixture contains aspirin, acetaminophen, caffeine, and dimethoxybenzene. Present your answer as a flow chart that shows the structures of the compounds at each stage of the separation. At the end of the flow chart, you should have isolated each of the 4 components as crude solids. Use what you have learned in the week 6-7 labs to guide your separation.
For next week: § Complete the ChemDraw assignment (due at the beginning of week 8 lab). This assignment constitutes your prelab preparation for the week 8 lab. § Quiz next week. § Bring model kits and notebooks to lab next week.
Week 8: Stereochemistry
For next week:
Week 9:
Column Chromatography Due by Tuesday 4/10 at 10:00a: Results § starting mass of mixture § final masses of each of the 2 compounds § % recovery of each of the 2 compounds § TLC data, including Rf values
Discussion § Did you accomplish the goal of the reaction? Briefly explain, citing evidence. § The column in this experiment was run by adding hexanes first and then 50:50 hexanes:ether. Describe what would happen if the order were reversed. Be specific. § When applying a sample to the top of a column, it is desirable to use the minimum amount of solvent necessary to place the sample on the column, and only add more solvent above the column after all of the sample has been absorbed into the column material. Why? § In general, a better separation can be obtained if more fractions of smaller volume are collected than if fewer fractions of greater volume are collected. Why is this true? § If a mixture could be equally well separated by chromatography using toluene as by using methylene chloride, which solvent would you choose to use, and why? (Hint: How do you recover a solid compound after it has been eluted from the column?)
For next week:
Week 11: Distillation
Due Monday 04/16 by 11:15a: Results § plot of boiling point (y-axis) versus volume of distillate (x-axis) for the simple distillation and both fractional distillations; include titles for the plots and labels for the axes; annotate the key features of the plots (for example, a line indicating bp of cyclohexane and bp of toluene on the simple distillation), these labels can be done by hand; a summary table is not necessary
Discussion § Briefly comment on the results of the simple distillation. Based on your plot, would it have been possible to collect any fractions of pure cyclohexane or pure toluene? If no, justify your choice. If yes, explain which portion(s) of the distillate you would have collected as pure fractions. § Repeat the above series of questions for the fractional distillation of cyclohexane and toluene. § What effect does the reduction of atmospheric pressure have on the boiling point? Can cyclohexane and toluene be separated if the external pressure is 350 mm Hg instead of 760 mm Hg? Explain. § Identify the 2 liquids in your unknown sample and estimate the ratio of the liquids in the unknown. Briefly explain how you arrived at your answers.
For Week 12: § read Ch 17, pp 226-231
§ You will need to include the section “Balanced Reactions” in your lab notebook. It is not necessary to write out 20 equations. You can represent all the alkyl halides by R-X. § You will be working with 8 alkyl halides: 1-chloro-2-methylpropane, 1-chlorobutane, 1-bromobutane, 2-chlorobutane, 2-chloro-2-methylpropane, 1-chloro-2-butene (cis/trans), 2-bromobutane, bromobenzene § In your “other properties” section of your table, please include whether a given alkyl halide is 1º, 2º, 3º, or aromatic. Also, predict whether the alkyl halide will react by SN1, SN2, both, or neither. This should be listed in addition to other relevant properties. § Quiz week 12
Week 12: Substitution Reactions
Due Monday 4/23 by 11:15am: Results: Include two summary tables: one that organizes the SN2 rate data and a separate one that organizes the SN1 rate data. It is NOT necessary to rewrite all of your observations again in the results, but do include enough information so that the trends in rates are obvious
Discussion: be sure to compare “apples to apples” and be concise 1. Present evidence that indicates that leaving group ability influences the rate of SN2 reactions. Present evidence that indicates that leaving group ability influences the rate of SN1 reactions. Briefly explain the origin of the observed trends. (What makes a leaving group “good”?) 2. Present evidence that indicates that the structure of the alkyl halide (simple 1º, 2º, 3º) influences the rate of SN2 and the rate of SN1 reactions. Briefly explain the origin of the observed trends. 3. Present evidence that indicates that the structure of the 1º alkyl halide (straight-chain versus branched) influences the rate of SN2. Briefly explain the origin of the observed trend. 4. How does the allylic halide behave under SN2 and SN1 conditions? Briefly explain why the allylic halide should be able to undergo both SN2 and SN1 mechanisms. 5. Present evidence that indicates the effect of solvent polarity on the SN1 reaction. Briefly explain the chemical origin of the observed trend. 6. How did temperature affect the reaction rate? Choose an example and briefly discuss why/how temperature influences rate. 7. Did you observe any results that didn’t match your initial predictions? Point these out, either by highlighting them in the results table or listing them in the results section. No explanation necessary since your above answers should indicate the expected trends.
For Week 13 lab:
Week 13: Alkene hydration
Due Monday 04/30 by 11:15 am: Results: Make a table that includes the following information for all three alkenes: (1) structure of starting alkene; (2) structure of three possible product alcohols; (3) label each product alcohol as Markovnikov, anti-Markovnikov, or rearranged; (4) GC percentages; (5) structure of the corresponding carbocation; and (6) the calculated energies for the carbocation intermediates. Some of this information you will obtain from the class data set.
Discussion: § For each of the three alkenes, do the following: (a) Draw a mechanism that shows formation of the major product. Is the major product formed via the most stable carbocation intermediate? Are there any surprising results? § Propose an explanation for why it is so important to stir the reaction mixture as vigorously as possible. (Hint: Are aqueous sulfuric acid and the alkene miscible?) § The source of this experiment provided us with a list of which alcohols are possible products and therefore should be used as standards for the GC. One of these alcohols is 3-methyl-1-pentanol, presumably formed by hydration of 2-ethyl-1-butene. Draw a complete mechanism for the formation of 3-methyl-1-pentanol by hydration of 2-ethyl-1-butene. Explain why this mechanism is unlikely to occur.
For Week 15 lab: § 30 point final quiz; emphasis will be on the last couple of labs, but big picture ideas from the semester as a whole are also important; review your quizzes and graded reports § check out will follow the quiz; if you believe that you may owe more than $10 in breakage fees, you may want to bring cash or check
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