Homework answers / question archive / Experiment 41: Isomerization of a Cyclic Ketone (from Lehman text, 2nd edition) Goal: To determine the identity of the product formed from the acid-catalyzed isomerization of carvone by analyzing the product’s NMR and IR spectra

Experiment 41: Isomerization of a Cyclic Ketone (from Lehman text, 2nd edition) Goal: To determine the identity of the product formed from the acid-catalyzed isomerization of carvone by analyzing the product’s NMR and IR spectra

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Experiment 41: Isomerization of a Cyclic Ketone (from Lehman text, 2nd edition) Goal: To determine the identity of the product formed from the acid-catalyzed isomerization of carvone by analyzing the product’s NMR and IR spectra. The Reaction: O H2SO4 C10H14O carvone * Read the entire lab experiment in the Lehman text (pages 354 – 360) to obtain a more complete understanding of Experiment 41 (Note: The full experiment is provided on Canvas). Procedure Notes: *Note: We will using the Standard Scale procedure (You can ignore the microscale procedure). Reaction: • • • • Combine carvone, H2SO4 and magnetic stir bar in a 50 mL round-bottom flask and set up apparatus for heating under reflux. Use a H2O bath (with boiling chips) to heat your reaction mixture. Make sure to maintain vigorous stirring throughout the reaction period. Start timing your reaction once the mixture begins to boil/reflux. After the reaction period is over, cool the reaction mixture in an ice/water bath and clean condenser with acetone right away (the product is corrosive). Separation: • • • • • Prepare labeled beakers for “Aqueous” and “Organic” Layers Extract product with two separate 10-mL portions of petroleum ether (Note: the organic (petroleum ether) layer is the top layer). Wash the combined petroleum ether extracts with a 15-mL portion of aqueous sodium bicarbonate (shake gently and vent often at first!). Dry organic layer with MgSO4, then gravity filter it into a clean, dry beaker that has been pre-weighed. Evaporate the solvent over low heat on a hot plate until you obtain a constant mass (Record the final mass of the beaker + product). Analysis: • IR and NMR spectra of the product are provided on Canvas. Lab Report Instructions: 1. Title Page 2. Analysis: • Draw the structure of the product • Calculate your theoretical yield and % yield of the product (Show calcs). • Provide a table with important IR peaks for your product. The table should have two columns labeled bond type and wavenumber (cm-1). • Draw a structure of the product in which all of the hydrogens are labeled as either Ha, Hb, Hc, etc, corresponding to the labeled peaks on the given NMR spectrum (More info about the NMR spectrum is provided below after the lab report instructions). • Provide answers to Exercises 1, 2 and 3 from Experiment 41 in the Lehman text. Additional NMR info: The following information corresponds to the peaks on the product’s NMR spectrum provided on Canvas. Peak Ha: doublet (6 hydrogens) Peak Hb: singlet (3 hydrogens) Peak Hc: multiplet (1 hydrogen) Peak Hd: singlet (1 hydrogen) Peak He: singlet (1 hydrogen) Peak Hf: doublet (1 hydrogen) Peak Hg: doublet (1 hydrogen) 354 Part II EXPERIMENT Isomerization of a Cyclic Ketone 41 Correlated Laboratory Experiments Isomerization. Reactions of Alkenes. Reactions of Carbonyl Compounds. Infrared Spectrometry. Operations OP-7 OP-8 OP-10 OP-18 OP-19 OP-24 OP-25 OP-39 OP-40 Heating Cooling Mixing Extraction Evaporation Washing Liquids Drying Liquids Infrared Spectrometry Nuclear Magnetic Resonance Spectrometry (optional) Before You Begin 1. Read the experiment, read or review the operations as necessary, and write an experimental plan. 2. Calculate the mass of 10.0 mmol (SS) or 2.00 mmol (µS) of carvone, and the theoretical yield of the product. Scenario In chemistry, to digest something is to soften or disintegrate it by means of moisture, heat, or a chemical reaction. Thymol is an isomer of carvone and the main component of thyme’s essential oil. New-age herbalist Basil Wormwood (see Experiment 18) often steam distills chopped-up spearmint leaves to isolate their essential oil, whose main component is (R)-carvone. This time he decided to digest the leaves in aqueous sulfuric acid before distillation to reduce their volume and make it possible to process a larger batch each time. He was surprised to find that the resulting oil smelled more like thyme than spearmint. Curious about this outcome, he carried out the same procedure with ground caraway seeds, which he knew to contain (S)-carvone (the enantiomer of spearmint’s carvone), and obtained the same thyme-scented product. Despite its odor, the unexpected product isn’t thymol—but, like thymol, it is mildly acidic. CH3 O CH2 C H CH3 (R)-carvone CH3 CH3 O H C CH2 CH3 (S)-carvone OH CH CH3 CH3 thymol Experiment 41 355 Isomerization of a Cyclic Ketone Your assignment is to carry out the reaction of either (R)- or (S)carvone with sulfuric acid and identify the product. Your supervisor has already had the product analyzed and found its molecular formula to be C10H14O, the same as that of carvone, so Basil must have carried out an acid catalyzed isomerization reaction—one in which a compound is converted to one of its possible isomers. Applying Scientific Methodology There should be enough clues in the Scenario and elsewhere to help you formulate a reasonable working hypothesis about the structure of the product, based on the structure of the reactant and your knowledge of the chemistry of C “ C and C “ O double bonds. You will test your hypothesis using spectral analysis. Chemicals from Herbs and Spices The carvones that are found in spearmint leaves and caraway seeds also occur in other herbs and spices, such as dill seed, which contains (S)-carvone. An herb is a flowering plant that has a non-woody stem, or parts of such a plant, such as thyme leaves. A spice is a pungent or aromatic plant product used as a seasoning, often a dried fruit or seed or even the bark of a tree, such as cloves and cinnamon. Spices are at their best when bought whole and ground just before use because powdered spices lose their volatile flavor components rapidly. A good cook will have dozens of herbs and spices in the cupboard to add flavor to foods and to make teas and other beverages. Many of the flavorful chemicals found in herbs and spices, including carvone, are terpenes. For example, coriander seeds contain linalool, camphor, a-pinene, and a host of other terpenes. CH3 OH CH3C CHCH2CH2CCH CH3 CH3 See Experiment 33 for a discussion of terpenes. O CH2 CH3 CH3 CH3 CH3 linalool CH3 camphor a-pinene Aromatic compounds—some of which are also terpenes—are major flavor constituents of many herbs and spices. These include aromatic aldehydes, ketones, and ethers, such as cuminaldehyde from cumin seed, cinnamaldehyde from cinnamon, zingerone from ginger, eugenol from cloves, and anethole from fennel seeds. O CHO CH CHCHO CH 2CH2CCH3 CH2CH OCH3 OH CH CH3 CH2 CH OCH3 OH OCH3 CH3 cuminaldehyde cinnamaldehyde zingerone eugenol anethole CHCH 3 356 Experiment 29 describes some other vanilloids. Part II Correlated Laboratory Experiments Turmeric, a major ingredient of curry powder, is used widely in East Indian and other Asian cooking, and has also been used as a food coloring for mustard and other food products. Its main constituent is a yellow pigment, curcumin, which appears to be effective for treating digestive disorders, osteoarthritis, and cancer; and for preventing the buildup of plaque in arteries. Curcumin is easily oxidized to vanillin, the main flavor ingredient of vanilla. In fact, curcumin—along with zingerone and eugenol—contains the same 4-hydroxy-3-methoxy combination found in vanillin. These substances are therefore classified as vanilloids. CH3O O HO CH OCH3 O CHCCH2CCH CH OH curcumin CH3O O HO CH vanillin Several of the previous compounds are phenols—compounds having one or more OH groups on an aromatic ring. Phenols are abundant in the plant kingdom. They include simple phenols such as thymol, the main flavor ingredient of thyme, and carvacrol, which occurs in both winter savory and summer savory. Apigenin, which occurs in parsley, is one member of a chemical family called the flavones. Flavones and similar multi-ring phenolics, which are lumped under the term flavonoids, are widely distributed in the plant world. Flavonoids are potent antioxidants that contribute to the health benefits of plant-based foods. The Mediterranean diet is particularly high in flavonoids. For example, Greeks consume unusually large quantities of apigenin from parsley, which is an essential ingredient of the grain salad tabouli. CH3 CH3 OH OH O HO OH CH CH3 CH3 thymol CH CH3 CH3 carvacrol OH O apigenin Pungent herbs and spices such as garlic, horseradish, and mustard usually contain sulfur compounds. A sulfoxide called alliin is an important constituent of garlic. When garlic cloves are crushed or otherwise damaged, the cell membranes are ruptured so that alliin comes into contact with an enzyme, alliinase, which catalyzes a reaction that forms allicin. Allicin is actually a chemical defense agent for the garlic plant, protecting it from insects and fungi. It is also partly responsible for the characteristic “garlicky” odor that many people enjoy but others find offensive. Allicin is quite unstable and rapidly decomposes into other Experiment 41 357 Isomerization of a Cyclic Ketone substances such as diallyl disulfide, so the flavor of garlic changes with cooking or standing. O O CH2 O alliinase CHCH2SCH2CHCOH CH2 CHCH2S NH2 alliin CH2 SCH2CH CH2 allicin CHCH2S SCH2CH CH2 diallyl disulfide Horseradish roots contain sinigrin and the enzyme myrosinase, which combine when the root is grated, forming some very pungent sulfur compounds that include allyl isothiocyanate. Most store-bought horseradish is not very potent, but when the root is fresh it generates enough of this volatile substance to cause a nose-clearing burst of stinging vapors that can bring tears to your eyes. S CH2 CHCH2C sinigrin C6H11O5 NOSO3K myrosinase CH2 CHCH2N C S etc. allyl isothiocyanate Sinigrin is also a constituent of the black mustard plant; white mustard contains a related compound, sinalbin, which yields a different isothiocyanate after an enzyme-catalyzed reaction analogous to that of sinigrin. Such isothiocyanates produce the “heat” of prepared mustards, which usually contain both black and white mustard seeds. The Japanese use a relative of horseradish called wasabi to flavor sashimi (raw fish), sushi, and noodles. Like horseradish and mustard, wasabi produces pungent isothiocyanates by an enzyme-catalyzed reaction. True wasabi is very expensive and, when fresh, loses its flavor within 15 minutes, so most of the “wasabi” that makes its way to North America is a paste or dry powder that consists mainly of artificially colored European horseradish and may contain less than 0.1% real wasabi. Understanding the Experiment The isomerization of carvone is catalyzed by aqueous mineral acids, so you will heat your carvone under reflux with 6 M sulfuric acid. The reaction mixture has a tendency to boil up rather violently; therefore, it is important to use vigorous magnetic stirring or a sufficient number of boiling chips to prevent bumping. You will separate the unknown product from the reaction mixture by extraction with low-boiling petroleum ether, which is not a true ether but a mixture of low-boiling hydrocarbons. Because of its low boiling range (usually '35–60°C), this solvent can be removed easily by evaporation. The product is somewhat corrosive, so you should clean your glassware thoroughly after use. It also darkens over Key Concept: The first step in an acidcatalyzed reaction of an unsaturated compound is usually addition of a proton to one or more double bonds. A Greener Way: You can recover the petroleum ether by evaporating it under vacuum using a cold trap. 358 Part II Correlated Laboratory Experiments time, so it is best to record its infrared (IR) spectrum on the same day that you prepare it. From the IR spectrum of your product, you should be able to identify its functional group(s) and determine what family or families of organic compounds it belongs to. That will help you check (and perhaps modify) your working hypothesis and come up with a reasonable structure for the product, which you may be able to verify by comparing your IR spectrum to standard spectra in The Aldrich Library of FT-IR Spectra or some other collection of IR spectra listed in the Bibliography. At your instructor’s discretion, you can also obtain the 1H NMR spectrum of the product and use it to confirm your structure or figure out a better one. This is a relatively green experiment; it has a high atom economy, and the organic solvent used for extraction can be recovered and recycled. Sulfuric acid is harmful to aquatic organisms, so it should not be released into the environment. Reactions and Properties Table 41.1 Physical properties CH3 O H2SO4 C10H14O C carvone sulfuric acid mol wt bp d 150.2 98.1 230 290 0.965 1.84 Note: bp is in °C; density is in g/mL. CH3 CH3 carvone CH3 O (R)-carvone CH2 C CH3 Figure 41.1 IR spectrum of (R)-carvone H 2922.7 1674.9 1434.3 1367.0 1246.8 1110.7 1057.8 899.0 802.2 Experiment 41 359 Isomerization of a Cyclic Ketone DIRECTIONS At the instructor’s discretion, students can use different enantiomers of carvone and compare their results. Sulfuric acid causes chemical burns that can seriously damage skin and eyes. Wear gloves and avoid contact. The product can cause chemical burns to skin and eyes. Wear gloves and avoid contact. Standard Scale Reaction. Combine 10.0 mmol of (R)- or (S)-carvone with 15 mL of 6.0 M sulfuric acid in a 50-mL round-bottom flask. Add several small boiling chips (preferably microporous chips) or a stir bar, and attach a condenser. Start the stirrer [OP-10] (if you are using one), and heat the reaction mixture under gentle reflux [OP-7] for 35 minutes. Cool [OP-8] the reaction mixture in an ice/water bath, and then disassemble the apparatus. Use acetone to rinse (into a waste container) any glassware that comes in contact with the product. Separation. Under a fume hood, transfer the reaction mixture to a separatory funnel, and use two 8-mL portions of low-boiling petroleum ether to extract [OP-18] the product from the reaction mixture (wear gloves during the extraction). Wash [OP-24] the combined petroleum ether layers with 5% aqueous sodium bicarbonate; this process releases CO2 gas, so stir and shake gently at first. Dry [OP-25] the organic layer over anhydrous sodium sulfate or magnesium sulfate, and then evaporate [OP-19] the solvent. Analysis. Weigh the product and record its infrared spectrum [OP-39]. If requested, record its 1H NMR spectrum [OP-40] or obtain one from your instructor. Safety Notes 3 0 W 1 sulfuric acid Take Care! Wear gloves, and avoid contact with sulfuric acid. If severe bumping occurs, cool the reaction mixture and add more boiling chips (if you are using them). Raise the flask just enough so that it doesn’t contact the heating manual, and resume heating. Waste Disposal: Put the aqueous layers and any recovered solvent in appropriate waste containers. Microscale Reaction. Combine 2.00 mmol of (R)- or (S)-carvone with 3.0 mL of 6.0 M sulfuric acid in a 10-mL round-bottom flask. Equip the flask with a watercooled condenser and a stir bar. Heat the reaction mixture gently under reflux [OP-7], with vigorous stirring [OP-10], for 35 minutes. Cool [OP-8] the reaction mixture in an ice/water bath, and then disassemble the apparatus. Use acetone to rinse—into a waste container—any glassware that comes in contact with the product. Separation. Under a fume hood, transfer the reaction mixture to a conical centrifuge tube, and use two 2-mL portions of low-boiling petroleum ether to extract [OP-18] the product from the reaction mixture (wear gloves during the extraction). Wash [OP-24] the combined petroleum ether layers with 5% aqueous sodium bicarbonate; this process releases CO2 gas, so stir and shake gently at first. Dry [OP-25] the organic layer over anhydrous sodium sulfate, and then evaporate [OP-19] the solvent. Analysis. Weigh the product and record its infrared spectrum [OP-39]. If requested, record its 1H NMR spectrum [OP-40] or obtain one from your instructor. Take Care! Wear gloves, and avoid contact with sulfuric acid. Waste Disposal: Put the aqueous layers and any recovered solvent in appropriate waste containers. 360 Part II Correlated Laboratory Experiments Exercises 1. Write a reasonable mechanism for the isomerization of carvone in the presence of sulfuric acid. 2. (a) Derive the IUPAC name of your product, and give its common name. (b) List several herbs that contain the product as a major component. 3. Describe and explain the possible effect on your results of the following experimental errors or variations. (a) You used high-boiling petroleum ether for the extraction. (b) You used 5% sodium bisulfate rather than 5% sodium bicarbonate to wash the petroleum ether solution. (c) After adding 5% sodium bicarbonate to the petroleum ether solution, you immediately capped the separatory funnel (or centrifuge tube, for microscale work) and shook the mixture vigorously. 4. (a) Calculate the atom economy and reaction efficiency of your synthesis. (b) Describe some green features of your synthesis, and any that aren’t so green. 5. Following the directions in Appendix V, construct a flow diagram for the synthesis of your product. 6. Identify the terpenes (see Experiment 33), excluding the compounds identified as such, whose structures are shown in “Chemicals from Herbs and Spices.” 7. Outline a synthesis of vanillin from curcumin. Other Things You Can Do (Starred items require your instructor’s permission.) *1. Following the procedure for solubility tests in Part IV, test your product for solubility in 5% NaOH and 5% NaHCO3, and explain your results. *2. Carry out the isomerization reaction of dimethyl maleate described in Experiment 17, and use a spectrometric method to show that the expected isomerization has taken place. 3. Starting with sources listed in the Bibliography, write a research paper about the components and therapeutic applications of some culinary herbs.