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CHEMISTRY 122 Virtual Laboratory Manual Spring 2021 0 Table of Contents Exp

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CHEMISTRY 122 Virtual Laboratory Manual Spring 2021 0 Table of Contents Exp. # Title of Experiment Page How to Succeed in Chemistry Lab 2 Intro to BeyondLabz and Installation Guide 3 Lab #1: Lab Techniques: Synthesis of an Ester 4 Lab #2: Organic Structure, Isomers, and Geometrical Shape 8 Lab #3: Reactions of Hydrocarbons 10 Lab #4: Reactions of Alcohols 15 Lab #5: Organic Acid-Base Reactions 22 Lab #6: Lab Techniques: Grignard Reactions 29 Lab #7: Oxidation and Reduction 33 Lab #8: Synthesis of Aspirin 36 1 How to succeed in Chemistry lab 1. Prepare. Read the experiment thoroughly before your lab period, so you are prepared to ask questions and understand the procedure. The more prepared you are each week, the less time you will probably need to finish the lab, and the better your data. Students who do not read the experiment before lab and are not prepared may not able to finish the entire experiment during the assigned lab period. Some students find it helpful to visualize each step of the procedure. While reading, consider sketching the equipment and preparing a flow chart of the process in your lab notebook. Highlight any new vocabulary words, and learn the definitions. These words may come up repeatedly in the experiments, as well as in the lecture material. Read all the way through the “Post Lab” questions at the end of the experiment. Often, the post-lab analysis will ask you about events that occurred during the experiment. You should reflect on these things while you are doing the lab. 2. Read. Read the instructions carefully. The procedure is prepared stepwise, so students can successfully complete each experiment. If any step in the procedure is unclear, ask your instructor or other students for assistance. Be especially careful regarding safety hazards associated with the use of toxic and corrosive chemicals or the use of a Bunsen burner. More importantly, if you fail to read instructions, you pose a safety hazard to yourself and to everyone else in the laboratory. If your instructor feels that you may endanger yourself or other students, you will be asked to leave the lab, and you will be given a zero for the experiment. 3. Think. The importance of common sense cannot be overemphasized. Last year, one student worked for hours to synthesize a sample of acetylsalicylic acid, dried his product for a week in a locker, and then lost it all as he carelessly walked across the lab with the loose powder balanced on top of a piece of paper. The more you think about what is done in each step, and why, the easier the lab will be, and the more you will learn. All the experiments are chosen and written to reinforce lecture material. Take advantage of the opportunity to experience hands-on chemistry! 4. Reflect. Treat the “Post Lab Analysis” seriously. The questions are worth a lot of points, and they’re related to concepts in the homework assignments, exams, and quizzes. Do not allow the concepts learned in lab to become stale in your mind by procrastinating. Lab will be most helpful if you answer the questions and do calculations as soon as possible after completing each experiment. Often, you’ll be asked to think about possible sources of error in your lab work. The following are not acceptable responses: “There could have been errors in some of the measurements…” or “I may have made calculation errors.” 2 Introduction to BeyondLabz Welcome to Chem122 Lab. The labs for this course will primarily utilize the BeyondLabz platform, which you will need to install on your computer, mac, windows pc, or chromebook. If you can’t run Beyond Labz on a device you have access to, you will be utilizing a program called “Labstats” to remotely access one of several copies we’ve installed on school computers. Directions for doing this are available on Canvas. Contact me if this is you; I will make sure you connect with a workable set-up. Some of the labs will use other online simulators; instructions for these simulators will be given in the individual experiments. Install the Client If you have a previously installed version of Beyond Labz 1.7 from an earlier quarter that is functioning smoothly, keep using that. If not, or if you’ve been having issues running the program, follow the directions given in the Installation Guide for Beyond Labz v2.0 available on Canvas just below the Lab Manual. Activation After installation the labs will work for 2-days for free, but after 2 days an Activation code is required. If you have an activated license from a previous quarter, copy that here. Otherwise, click on “License” and enter the code for Spring: SEATTLE-COLLEGE-Student_User-Spring2021. Let me know if you have any issues getting the software up and running! The Landing Page 1. To launch a lab, go to the Labs tab and click Open next to the lab you need to use – the experiments specified in this lab manual will tell you which of these labs you need to select. Most of the time, it will be the Organic Chemistry lab, although we may also do an experiment from one of the other labs. A separate Landing Page will open for the chosen subject, from which you will then select one of the lab setups. Again, the experiments in this lab manual will tell you which of these to select. The Landing Page for Virtual ChemLab 2. The Help menu on the Landing Page can be used to access extensive descriptions of each lab bench. 3. Once you are in the “lab”, you will carry out the experiments/worksheets specified in this lab manual. You will want to keep a copy of this lab manual open (either on screen or printed out) so you can follow the instructions and record your data. You will then submit your lab via Canvas. 3 Experiment 1 Lab Techniques: Synthesis of an Ester Purpose: Explore the virtual lab environment and gain familiarity with the technique of using thin layer chromatography (TLC) to follow the course of a reaction. Successfully synthesis the specified ester and apply what you learn from this reaction to the synthesis of different esters. Background: Thin layer chromatography (TLC) is a simple and relatively fast analytical tool that is used to measure the extent of a reaction or measure the relative polarity of a molecule. A TLC plate is a sheet of glass that is coated with a thin layer of adsorbent such as silica (or occasionally alumina). A small amount of the mixture to be analyzed is placed or spotted near the bottom of this plate. When monitoring reactions, it is common to place the starting materials on one side of the plate (or in the left lane) and the reaction mixture in the right lane. The TLC plate is then placed in a shallow pool of a solvent (20% ethyl acetate/hexanes) so that only the very bottom of the plate is in the liquid. This solvent, or the eluent, is the mobile phase, and it slowly rises up the TLC plate by capillary action. As the solvent moves past the spot that was applied, it carries the spotted mixture up the plate where a competition occurs between the solvent carrying the mixture and the silica on the plate. Since the silica adsorbent is polar, polar molecules in the mixture will rise very little up the plate, but nonpolar molecules will have little attraction to the silica and will consequently rise to the top. Molecules of intermediate polarity will stop somewhere in between these two extremes. When the solvent has reached the top of the plate, the plate is removed from the solvent, dried, and then the separated components of the mixture are visualized by exposure to a UV lamp. The positions of each spot on the TLC plate are identified and recorded by assigning Rf values from 0.0 to 1.0, where a 0.0 indicates the spot is at the bottom of the plate and a 1.0 indicates the spot is at the top: Rf = Distance traveled by the compound/Distance traveled by the solvent. In this assignment, you will be guided through the steps of a simple esterification reaction as a demonstration of how to use thin layer chromatography as a tool to monitor a reaction until it reaches completion. This assignment will also serve as a tutorial to teach you how to utilize the various parts of the organic simulation that will be used in later assignments. 4 O R O OH + HOR' H2SO4 R' R O + H2O Procedure: 1. Launch the BeyondLabz program. When the client opens, select “Organic Chemistry”. Ensure that it is configured to higher ed. Select the Synthesis laboratory. You should see a lab bench containing reagents on the back of the bench, aqueous reagents on the right, a lab rack containing necessary laboratory equipment, a red disposal bucket for cleaning up the lab, and the organic stockroom in the back. Other pieces of laboratory equipment will be used in other assignments. The blackboard lists specific experimental set-ups; click on the top choice “Esterification.” Mousing over the word reveals the structures of the starting materials available in this set-up, these materials are available in the stockroom (top shelf) along with water and two solvent choices: ethanol and diethyl ether (bottom shelf). The red book in front is your virtual lab notebook, use it to keep track of data in this and future experiments. 2. You will find a round bottom flask located on the stockroom counter. Select the starting materials for the reaction by first clicking on the bottle containing 2-phenylacetic acid (PhAcOH) and dragging and dropping the scoop on the mouth of the flask. Now do the same for 3-methyl-1-butanol (PentOH) except this time a syringe will be used since this starting material is a liquid. Note the bottle labels are small, but you can see the full name and structure of each starting material by mousing over the bottle. Now click on the flask and drag it to the stir plate on the lab bench. It should snap into place when you are at the right location. 3. The round bottom flask containing the two starting materials should now be on the stir plate. The two starting materials should be listed on the chalkboard, and mousing over the listed starting materials will display their structures on the chalkboard. Help on using Virtual ChemLab can be found by clicking on the bell on the stockroom counter. 4. In order to perform an esterification reaction, sulfuric acid (H2SO4) must be added to the starting materials. This is done by clicking on the H2SO4 bottle on the reagent shelf on the back of the lab bench and dragging the syringe to the round bottom flask. The acid can also be added by doubleclicking on the H2SO4 bottle. The chalkboard should now show that the acid has been added to the reaction mixture. 5. Before the reaction can be started, we must be able to heat the reaction mixture so the reaction can proceed at a suitable rate. This is done by adding a heating mantle to heat the reaction mixture, adding a condenser so the mixture can be refluxed, and then adding nitrogen gas to maintain an inert atmosphere and to prevent pressure buildup. Click on the Heating Mantle and drag it to the round bottom flask to place it on the stir plate. Now click on the Condenser from the lab rack and drag it on top of the round bottom flask. Finally, click on the nitrogen gas hose to the right of the stir plate and drag and drop it on top of the condenser. Now click on the Stir Plate button to start the reaction. You should see the reaction mixture stirring in the round bottom flask. 6. Before waiting too long, perform a TLC measurement by clicking on the TLC jar located in front of the analytical equipment and drag the TLC plate and drop it on the round bottom flask. A window should now open showing the TLC results. In the starting material lane (the left lane) you should see 5 two large spots near the bottom representing the two starting materials in this reaction and in the reaction lane (the right lane) you should see the same two spots. Click “save” to sketch the TLC plate in your lab notebook for later reference. Not everything shows up on the TLC! A missing spot likely means the material has too low a boiling point, it evaporates off the TLC plate rather than move up the plate. 7. Close the TLC window and now advance the reaction forward 15 minutes (or you can just wait 15 minutes) by advancing the time on the laboratory clock. This is done by clicking on the appropriate button under the minutes, tens of minutes, or hours digits on the clock. Now perform a new TLC measurement on the reaction mixture. 8. Close the TLC window again and now advance the laboratory time forward until all of the starting materials have been consumed. You will need to monitor the reaction with TLC measurements until you observe that the starting materials have been consumed. You will notice that some time passes each time you perform the TLC. 9. When a reaction is complete, the reaction mixture is rinsed or “worked up” by adding an aqueous reagent of an appropriate pH to the reaction mixture in a separatory funnel. After you shake the funnel to thoroughly rinse the reaction mixture, the water-soluble products will be in the aqueous phase and all others will be in the organic phase. Click on the separatory funnel on the lab rack and drag it to the round bottom flask. The reaction mixture should now be in the funnel. Now select the NaOH aqueous reagent and drag it to the top of the funnel to add it. There will now be two layers, the top being the organic phase and the bottom the aqueous phase. Click on the organic phase to extract the product and drag it to the cork ring on the lab bench. Perform a TLC measurement on the solution in the flask to confirm that it is the same product produced in the reaction. Calculate Rf values for each spot noted over the course of the reaction. Rf values are proportions; the size of your computer screen won’t make a difference to the value so long as you can measure accurately. Measure the distance the solvent travelled (start line to finish) and the distance each spot travelled (starting line to center of spot) Rf = distance traveled by the compound/distance traveled by the solvent; a unitless number between 0 (little movement) and 1 (movement with the solvent). The lab rack also contains a distillation set-up; a crystallization dish is located in front of the lab rack to the right of the aqueous reagents. These will be used in later labs. To the right of this are located all the spectroscopy instruments for analysis of organic materials; feel free to ignore these as we’re not covering spectroscopy in CHEM 122. Next to the TLC jar is a melting point apparatus; we will be using this later. Ice is available from the stockroom as needed. In front of the instruments is the disposal bucket—useful if you need to start over. If something happens you don’t expect, take notes! You may have missed some small detail in the procedure—or you may have discovered something new. 6 Lab Report Answer all questions on separate notebook paper or a different computer file and upload to Canvas by next Monday evening. 1) In the initial TLC plate, why are the spots the same for both the right and left lanes? 2) What is the new spot which shows up partway through the reaction? What has happened to the size of the original spots? Provide a brief explanation for the change. 3) Approximately how much in lab time did it take to perform each TLC? Why is using a TLC plate not instantaneous? 4) How much in lab time did it take to complete the reaction? What are the R f values for both starting materials and the product? 5) What can you say about the relative polarities of the 3 compounds on your TLC plate? 6) What is the name of the ester you synthesized? What other esters could you synthesize with the materials available in this lab? Keep in mind the ester synthesis requires one carboxylic acid and one alcohol. Some combinations work better than others—but the basic procedure is the same. The goal here is not to demonstrate perfect insight into organic synthesis or lab technique—there is much here we haven’t covered yet! The goal here is to get used to the virtual lab setting. Organize the data for at least two additional esters you successfully synthesized in something like the following data table: Carboxylic acid (Rf value) Alcohol (Rf value) Ester Product (Rf value) 7 Time of Reaction Experiment 2 Organic Structures, Isomers, and Geometrical Shape No Pre-Lab or formal Lab Report is required for this first experiment; just answer all questions on separate notebook paper or a different computer file and upload to Canvas by next Monday evening. Purpose: Using a model kit construct models of different organic compounds, using these to determine geometrical shape, bond angles, polarity, and to investigate structural or geometric isomers. Procedure: 1. Construct a molecule of methane (CH4). Use a black ball for the carbon atom and white balls for the hydrogen atoms. a. Sketch a picture of your model of methane. b. What geometrical shape is methane? c. What are the bond angles? d. Does methane display any carbon-carbon single bond rotation? e. Is methane a polar molecule? f. Remove one of the hydrogen atoms. The remaining group of atoms is a methyl group CH3—; sketch its picture. g. What are the bond angles within a methyl group? 2. Replace one of the hydrogen atoms with a chlorine atom (green ball). This is a model of chloromethane. a. Sketch a picture of your model of chloromethane. b. What geometrical shape is chloromethane? c. Are the bond angles the same as for methane? d. Is chloromethane a polar molecule? 3. Replace a second hydrogen atom with another chlorine atom. This molecule is dichloromethane. a. Sketch a picture of your model of dichloromethane. b. What geometrical shape is dichloromethane? c. What are the bond angles? d. Is dichloromethane a polar molecule? 4. Assemble a model of pentane (C5H12, linear). a. Sketch a picture of your model of pentane. b. What geometrical shape is pentane about each carbon atom? c. What are the bond angles? d. Does pentane display any carbon-carbon single bond rotation? e. Is pentane a polar molecule? 8 5. Using five carbon atoms and twelve hydrogen atoms construct as many different molecules as you can. a. Sketch a picture of each different model of C5H12. b. Describe the geometrical shape of each of your different structures. c. In each case give the bond angles. d. Describe the polarity of each molecule. e. Give each of your models an IUPAC name. 6. Construct a model of ethene (C2H4, with a double bond between the two carbon atoms). a. Sketch a picture of your model of ethene. b. What geometrical shape is ethene? c. What are the bond angles? d. Is ethene a polar molecule? e. Does ethene display any carbon-carbon rotation about the double bond between the two carbon atoms? 7. Construct a model of ethyne (C2H2, with a triple bond between the two carbon atoms). a. Sketch a picture of your model of ethyne. b. What geometrical shape is ethyne? c. What are the bond angles? d. Is ethyne a polar molecule? e. Does ethyne display any carbon-carbon rotation about the bond between the two carbon atoms? 8. Create as many molecules as you can with the formula C2H2Cl2. a. Sketch pictures of each different molecule (remembering geometric isomers). b. Give each molecule an IUPAC name. c. Describe the geometry of each molecule. d. Determine the bond angles. e. Describe the polarity of each molecule. f. Do any of these molecules display carbon-carbon bond rotation about the double bond between the two carbon atoms? 9. Construct a model of both cis and trans 1,2-dichlorocyclobutane. a. Sketch pictures of both molecules. b. Describe the geometry of each molecule. c. Determine the bond angles. d. Describe the polarity of each molecule. e. Is there any bond rotation about any of the bonds between two carbon atoms? 10. Construct mirror images of the two molecules from question 9. A mirror image is how the molecule would look if held up to a mirror. Assume the space between the two models is a mirror and the second molecule is its reflection. a. Sketch pictures of each of the pairs of molecules. b. Give an IUPAC name for each molecule. c. Which of the molecules are identical and which are different? Try stacking one on top of another (called superimposing) to see if they are identical. 9 Experiment 3 Reactions of Hydrocarbons Purpose: This experiment explores a variety of electrophilic alkene addition reactions by targeting a specific series of compounds, observing the differences in how the syntheses proceed. Background Information: Reaction with Water. Alkenes will not react with water alone, the presence of an acid catalyst (H 2SO4) is required. The reaction is the addition of a hydrogen to one side of the double bond, hydroxide to the other: H2O OH H2SO4 Heat may or may not be required, depending on the strength of the carbocation intermediate. Where different products are possible, the product that results from the most stable carbocation intermediate is favored. TLC is necessary to follow the course of the reaction. Reaction with Hydrochloric acid. This reaction is the addition of the elements of hydrochloric acid to the carbons of the multiple bonds: Cl HCl diethyl ether Where different products are possible, the product that results from the most stable carbocation intermediate is favored. The reaction may proceed at room temperature but will take place more efficiently with heat. TLC is necessary to follow the course of the reaction. 10 Reaction with Bromine. Alkenes react rapidly with bromine, often at room temperature. The reaction is the addition of the elements of bromine to the carbons of the multiple bonds: Br2 diethyl ether Br Br The bromine solution is orange; the product that has the bromine atoms attached to carbon is colorless. Thus, a reaction has taken place when there is a loss of color from the bromine solution and a colorless solution remains. This may be confirmed by observing a different spot on the TLC. The size of the bromine may impact the specific product seen. Procedure: Launch the BeyondLabz program. When the client opens, select “Organic Chemistry”. Select the Synthesis laboratory. Select “Alkene Hydration” from the options on the blackboard. Part A: Hydration The target compounds that you should synthesize for part A are 1-methyl-cyclohexanol and 1-phenyl ethanol. 1. Identify the appropriate starting materials required to synthesize 1-methyl-cyclohexanol from the available reagents on the stockroom shelf and add them to the round bottom flask. Now add water (H2O) as a solvent and drag the flask to the stir plate on the lab bench. 2. The round bottom flask containing the starting materials should now be on the stir plate, and the contents of the flask should be visible on the chalkboard. From the group of reagents found on the lab bench, select the correct reagent to synthesize the target compound and add it to the flask on the stir plate. Now attach the heater, condenser, and N 2 gas to the round bottom flask so the reaction mixture can be heated. 3. Start the reaction by clicking on the Stir button on the front of the stir plate. You should be able to observe the reaction mixture stirring in the flask. Monitor the progress of the reaction using TLC measurements as necessary until the product has formed and the starting materials have been consumed. You can advance the laboratory time using the clock on the wall. Keep track of your data in the electronic lab book on the stockroom counter. 4. When the reaction is complete (record time of reaction), “work up” your reaction by first dragging and dropping the separatory funnel on the flask and then adding H2O to the funnel. Extract the organic layer in the funnel by clicking on the top layer and dragging it to the cork ring on the lab bench. Your target compound should now be in this flask. Examine the product to determine the location of the new functionality. If something happens you don’t expect, take notes! You may have missed some small detail in the procedure (eg failure to add H2SO4 often results in formation of “black tar” after one day)—or you may have discovered something new. Repeat steps 1-4 targeting 1-phenyl ethanol. 11 Part B: Hydrochlorination The target compounds that you should synthesize for part B are 2-chlorohexane and 2-chloro-3,3dimethylbutane. 1. Identify the appropriate starting materials required to synthesize 2-chlorohexane from the available reagents on the stockroom shelf and add them to the round bottom flask. Now add diethyl ether as a solvent and drag the flask to the stir plate on the lab bench. Steps 2-4 proceed as in Part A. Repeat steps 1-4 targeting 2-chloro-3,3-dimethylbutane. Pay close attention to the final product. Any surprises? Part C: Bromination The target compounds that you should synthesize for part C are 1,2-dibromo-1-methylcyclohexane and 1,2dibromo-3,3-dimethylbutane. 1. Identify the appropriate starting materials required to synthesize 1,2-dibromo-1-methylcyclohexane from the available reagents on the stockroom shelf and add them to the round bottom flask. Now add diethyl ether as a solvent and drag the flask to the stir plate on the lab bench. Steps 2-4 proceed as in Part A, except bromination usually takes place just fine at room temperature. The expected color change provides a visual clue as to when the reaction is done; back this up with TLC data. Pay close attention to the structure of the final product. Repeat steps 1-4 targeting 1,2-dibromo-3,3-dimethylbutane. 12 Lab Report Answer all questions on separate notebook paper or a different computer file and upload to Canvas by next Monday evening. Part A: Hydration Organize the data for your reactions in a data table like the following: Starting material(s) (Name or structure, Rf value) Solvent, reagent Product(s) (Name or structure, Rf value) Time of Reaction (minutes) 1. Write a 3-step arrow pushing mechanism for the formation of 1-methyl-cyclohexanol: 2. Which reaction proceeds through the more stable carbocation? Briefly explain. Part B: Hydrochlorination Organize the data for your reactions in a data table like the following: Starting material(s) (Name or structure, Rf value) Solvent, reagent Product(s) (Name or structure, Rf value) 13 Time of Reaction (minutes) 1. Write a 2-step arrow pushing mechanism for the formation of 2-chlorohexane: 2. Provide a brief explanation for the unexpected product noted in your second reaction, targeting 2-chloro-3,3dimethylbutane. Use your observations as evidence. Part C: Bromination Organize the data for your reactions in a data table like the following: Starting material(s) (Name or structure, Rf value) Solvent, reagent Product(s) (Name or structure, Rf value) Time of Reaction (minutes) 1. Provide a brief explanation for the regioselectivity of the product noted in your first reaction, targeting 1,2dibromo-1-methylcyclohexane. 2. Provide a brief explanation for the differences noted between the bromination of 3,3-dimethyl-1-butene and the hydrochlorination of 3,3-dimethyl-1-butene. 14 Experiment 4 Reactions of Alcohols Purpose: In this assignment you will be given an unknown alcohol for which you will need to determine the general classification. Possibilities include six types: 1o alcohol, 2o alcohol, 3o alcohol, benzylic alcohol, 1,2-glycol, or phenol. The tools we will be using to perform this analysis include 3 of the functional group tests available: Chromic acid test (Jones oxidation), Lucas test and Periodic Acid test You will test the following known alcohols as references for comparison: benzyl alcohol (1o benzylic alcohol); 3-methyl-1-butanol (1o alcohol), tert-butanol (3o alcohol) and 2-methyl-1,2-butanediol (1,2glycol). Background: Specific groups of atoms in an organic molecule can determine its physical and chemical properties. These groups are referred to as functional groups. Those hydrocarbons that contain the functional group –OH, the hydroxyl group, are called alcohols. Alcohols are important commercially and are used as solvents, drugs and disinfectants. The most widely used alcohols are methanol or methyl alcohol, CH3OH; ethanol or ethyl alcohol, CH3CH2OH; and 2-propanol or isopropyl alcohol, (CH3)2CH2OH. Methyl alcohol is found in automotive products such as antifreeze and “dry gas”. Ethyl alcohol is used as a solvent for drugs and chemicals but is more popularly known for its effects in alcoholic beverages. Isopropyl alcohol, also known as “rubbing alcohol” is an antiseptic. Alcohols may be classified as primary, secondary or tertiary, depending on what kind of carbon the –OH group is attached to. If the hydroxyl group is attached to a primary carbon, then it is considered to be a primary alcohol. If the hydroxyl group is attached to a secondary carbon, then it is considered to be a secondary alcohol, and so forth. Classification of carbons depends on how many other carbon atoms it is attached to. If a carbon is not attached to another carbon, it is referred to as methyl. If it is attached to one other carbon then it is a primary carbon. If a carbon is attached to two other carbons then it is called 15 a secondary carbon. If a carbon is attached to three other carbons then it is a tertiary carbon. Attachment to four carbons affords a quaternary carbon. For example, consider the following alcohols: CH3 CH3CCH3 CH3CHCH3 CH3CH2OH OH OH Ethanol Primary alcohol 2-Propanol Secondary alcohol tert-butyl alcohol Tertiary alcohol Two special types of alcohols will also be considered in this lab. The benzylic alcohol has the hydroxy group attached to a carbon which is also attached to a benzene ring, and the 1,2-glycol has two hydroxy groups on adjacent carbon atoms: OH OH HO Benzyl alcohol Benzylic alcohol ethylene glycol 1,2-glycol Phenols bear a close resemblance to alcohols structurally since the hydroxyl group is present. However, since the –OH group is bonded directly to a carbon that is part of an aromatic ring, the chemistry is quite different from that of alcohols. Phenols tend to be more acidic than alcohols. They do not give the characteristic reactions with chromic acid or Lucas reagents. Concentrated solutions of the compound phenol are quite toxic and can cause severe burns. Phenol derivatives are found in medicine: for example, thymol is used to kill fungi and hookworms. CH3 OH OH Phenol Thymol (2-isopropyl-5-methylphenol) 16 Chemical Properties: The chemical behavior of the different classes of alcohols can be used as a means of identification. Quick, simple tests that can be carried out in test tubes will be performed. Please note that although the mechanisms of these reactions may be unknown to you, each of them is accompanied by definite visual changes (cloudiness, color change, etc.) which can be used in the “Real World” as well to identify substances. E.g.: The common “breathalyzer” used in determining whether a person is driving after ingesting too much alcohol contains an oxidizing agent which will change colors after oxidizing the ethanol to acetaldehyde and then to acetic acid exactly like the Chromic acid test explored in this lab. 1. Chromic acid test. This test (also described as Jones oxidation) is used to distinguish primary and secondary alcohols from tertiary alcohols. Using acidified dichromate solution, primary alcohols are first oxidized to aldehydes, and then further oxidized to carboxylic acids. Secondary alcohols are oxidized to ketones, which are resistant to further oxidation. Tertiary alcohols are not oxidized. In the oxidation, the orange-red of the chromic acid changes to a blue-green solution. Phenols are slowly (too slowly to notice much) oxidized to nondescript brown masses. O || RCH2OH + H2CrO4 + H2SO4 → RCOH + Cr2(SO4)3 green O || R2CHOH + H2CrO4 + H2SO4 → RCR + Cr2(SO4)3 green R3COH + H2CrO4 → + H2SO4 no reaction 2. Lucas Test. This test is used to distinguish between primary, secondary and tertiary alcohols. The reaction proceeds through a carbocation intermediate. The reagent is a solution of zinc chloride in concentrated hydrochloric acid, HCl. Tertiary alcohols react rapidly and give an insoluble white layer containing the corresponding alkyl chloride. A secondary alcohol reacts more slowly (within 15 minutes; slight heating may be required); and a primary alcohol does not react appreciably under these conditions. Benzylic alcohols, whether 1o, 2o, or 3o, will also react rapidly as they can form a carbocation comparable to a 3o alcohol. The formation of an emulsion, cloudiness or milky solution is a positive test. Phenols will not react at all with the Lucas reagent. RCH2OH R2CHOH R3COH + + + HCl HCl HCl ZnCl2 → no reaction ZnCl2 → R2CHCl + H2O (insoluble) ZnCl2 → 17 R3CCl + H2O (insoluble) 3. Periodic Test. This test is positive only for 1,2 glycols—two hydroxy groups on adjacent carbon atoms. Periodic acid, HIO4, oxidizes the glycol to a pair of aldehydes, breaking the C—C bond between them and forming a cloudy white precipitate: R OH R HIO4 HO H O R' O H R' The most common application is the Periodic Acid Schiff reaction, which looks for evidence of carbohydrates. After oxidation with periodic acid, the aldehydes so formed are visualized with Schiff’s reagent (not used in this lab) which turns bright red in the presence of aldehydes: + HIO4 = 1-2-glycol Aldehyde Summary of expected test results: Classification of alcohol Primary (1o) o Secondary (2 )* Tertiary (3o) Benzylic (PhCH2OH)* 1,2-glycol (-CH[OH]CH[OH]-) Phenol (PhOH) Chromic acid Lucas Test Periodic Acid + + + + + + + + + - - - * Secondary and Benzylic alcohols need additional tests to distinguish 18 PROCEDURE: Launch the BeyondLabz program. When the client opens, select “Organic Chemistry”. Select the Qualitative Analysis laboratory. Select “Alcohols” from the options on the blackboard. 1. On the reagent shelf you will find the four practice unknowns and another bottle that is your assigned unknown. Click on the bottle labeled “Benzyl alcohol” and use the syringe to add this alcohol to the round bottom flask. Now drag the flask from the stockroom counter to the cork ring on the lab bench. 2. The round bottom flask containing benzyl alcohol should now be on the cork ring on the lab bench. The boiling point is listed on the chalkboard. Check the polarity by performing a TLC measurement. Record this information in your lab notebook. 3. To perform the functional group tests, click on benzyl alcohol and drag a test tube containing the unknown to the clamp over the stir plate. You should see a picture of your unknown on the chalkboard. Now perform the chromic acid (Jones oxidation) test by clicking on the reagent bottle labeled H2Cr2O7 and dragging the pipet to the test tube. The results of the test are shown on the chalkboard with either a picture or a short video clip. Record the results of the test as positive or negative (also include a description) in your lab notebook. Discard the test tube by dragging it to the red disposal bucket. Repeat this procedure for the Lucas test (labeled ZnCl2) and the Periodic Acid test (labeled HIO4). 4. Repeat steps 1-3 for the other 3 known compounds (3-methyl-1-butanol, tert-butanol, and 2-methyl1,2-butanediol) and for your unknown compound. 5. Using the data you have now collected, determine the general classification of your unknown alcohol: primary (1o), secondary (2o) or benzylic, tertiary (3o), 1,2-glycol, or phenol. Be sure to include your unknown number, shown on the chalkboard. 19 Lab Report Answer all questions on separate notebook paper or a different computer file and upload to Canvas by next Monday evening. Data Submit a copy of your lab notebook pages or format your data into a table like the following: TEST benzyl alcohol 3-methyl-1butanol tert-butanol 2-methyl-1,2butanediol Unknown Boiling point (oC) TLC (Rf value) Chromic Acid Test Lucas Test Periodic Acid Include descriptions (e.g. color changes, formation of a precipitate) as well as classification of each test result as positive (+) or negative (-). Unknown # ________ General classification: ______________________________________________ Justify your classification by citing the results obtained which led to your conclusion. 20 1. Write unbalanced generalized chemical reactions for the three tests you performed on your unknown: Chromic acid test (unknown) Lucas test (unknown) Periodic acid test (unknown) You discover a set of three additional unknown compounds containing hydroxyl groups—Unknown Lily, Unknown Rose, and Unknown Poinsettia. 2. Unknown Lily is fast—quickly changing the orange-red of the chromic acid solution to a lovely turquoise, and turning Lucas reagent to milk in the blink of an eye without resorting to heat. Lily is, however, stumped by the Periodic test; no reaction here. What could the general classification of Unknown Lily be? Justify your choice briefly. 3. Unknown Rose is stubborn—chromic acid remains orange-red, and both Lucas and Periodic tests remain colorless, even given the gentle application of heat. What could the general classification of Unknown Rose be? Justify your choice briefly. 4. Unknown Poinsettia is an enigma—no change to the orange-red of the chromic acid solution, but producing modestly cloudy solutions with both the Lucas reagent (no heat) and the Periodic test. Not one of the six possibilities outlined in this experiment fits! Unless Poinsettia is a really strange compound, the most likely explanation is one of these three tests has generated bad data and should be repeated. Which test could this be? Assuming you’ve correctly identified the bad test result, what could the general classification of Unknown Poinsettia be? Justify your choice briefly. 21 Experiment 5 Organic Acid-Base Reactions Purpose My 2nd favorite in-person lab experiment: Analysis of Aspirin and Vitamin C Tablets (Titration). I did find a virtual version, British A-level Chemistry, the “Titration Screen Experiment”: https://virtual.edu.rsc.org/titration/experiment/2 Procedure Visit the “Titration Screen Experiment” site and begin. Register formally (use your name as it shows up on my class roster) so you can save your place and your data. Levels 1-3 are required; you will be turning in two separate lab reports for this lab. The first lab report will be your collected data from the Titration Screen Experiment exercise—the downloaded .pdf files of your lab notebook for each of the first 3 parts. The second part is a formal lab report write-up. Don’t be afraid to test things out—I learned a lot more going through this intentionally making errors! You are encouraged to repeat any level you like, to improve your score (which does affect your grade); please do, and please upload only one version of your lab notebook for each level to Canvas when you are done. I got partway through level 1 in Firefox, then something failed to load; switching browsers (I used Microsoft’s Edge) allowed me to finish. 22 Lab Report Download your lab notebook (pdf) after you finish each level. Upload your final version of Levels 1, 2 and 3 to Canvas by next Monday evening. That’s it! Formal Lab Report About two pages typed; upload this to Canvas as a separate document by Monday May 24. • • • • • • Title of the Experiment Brief purpose/goals statement—2-3 sentences, summarizing the overall point of the experiment. Chemical reactions—three balanced chemical equations, one representing the chemistry going on in each titration. Summary of Procedure—2-3 sentences, laying out where your data came from. Keep this short, not much explanation is required here. Results—a summary; don’t repeat your calculations here, give final results only with minimal description. Part 1: I’m looking for the experimentally determined concentration of hydrochloric acid and pH of the river at sites B and C, compared to the normal pH of the river. Part 2: I’m looking for the experimentally determined mass of aspirin per tablet, compared to the manufacturer’s claim. Part 3: I’m looking for the experimentally determined mass of ammonia per bottle of hair product, compared to the manufacturer’s claim. Discussion—end your report with a page of discussion. What did you learn from this virtual series of titrations? Part 1: Is the concentration of acid in the river at a safe level? What advice do you have for the nearby population? Part 2: Were all aspirin titration runs in agreement, or did one need to be discarded? Why? Is the manufacturer playing fair and following recommended guidelines? How important is this, considering the tablet contains aspirin? Part 3: Were all hair care titration runs in agreement, or did one need to be discarded? Why? Is the manufacturer playing fair and following recommended guidelines? How important is this, considering the toxicity of ammonia? 23 (Background only!) I have included the complete on-campus/live version of the CHEM 122 Analysis of Aspirin and Vitamin C Tablets for a different perspective; this may be useful in writing your Formal Lab report. We are doing the virtual version, **not** this one! Analysis of Aspirin and Vitamin C Tablets Purpose: Measured amounts of aspirin and vitamin C will be titrated with sodium hydroxide to determine the amount of organic acid present. The mass of acid in each sample will be compared to the original weight of the tablet to find what percent of each sample is acid. Background: Titrimetric analysis of consumer products is routinely carried out by the FDA to safeguard that consumers get “what they paid for”. Although it may appear trivial, the labels are trusted by millions of us every day and in some cases, overdoses or not enough of the active ingredient can cause very harmful side effects. The analytical technique to be investigated here is simple and very accurate. Aspirin is one of the most amazing medicines known to man. It is an effective pain reliever and antipyretic (reduces fever), and is employed for a variety of ailments including the aches, pains, and fever due to colds, flu, tension, rheumatism and arthritis. Inexpensive, easily produced, and non habitforming, it is the most common of all over-the-counter medications. Pain relievers containing aspirin are widely available, but ignoring the fancy additives, the active ingredient is still the same, acetylsalicylic acid (ASA). As the name indicates, the chemical is a carboxylic acid and that is why it causes severe irritation to the lining of the stomach and should be taken with lots of water. Commercial aspirin contains 5 grains of ASA per tablet. One gram is equal to 15.432 grains, or 1.00 gram = 15.432 grains. This is only an approximate guide to the weight of a tablet, due to binders such as starch which are added to hold it together. Since many steps are employed in the manufacture of the millions of tablets of aspirin containing products, the final tablets may vary in their ASA content. Quality control necessitates that samples be analyzed to insure that the variation in the amount of active ingredient is not larger than about 5 %. In your experiment you will analyze at least three tablets from the same bottle of aspirin, comparing your results to each other and to the label on the bottle. Ascorbic acid (Vitamin C) is present in a variety of foods. Citrus fruits contain 50 to 75 mg per 100 g of juice. Scurvy, a disease associated with long sea voyages and abnormal living conditions, is characterized by a marked tendency to hemorrhage and by structural changes in cartilage, bone and teeth. It was recognized in the mid 1700’s that a diet including fresh fruit decreased the appearance of the disease, but it wasn’t until 1917 that vitamin C deficiency was found to be the cause of scurvy. Although the FDA recommends a daily intake of 60 mg/day, the actual amount that we need is still a mystery. Linus Pauling was fond of saying that he took up to 17 grams/day to ward off colds and other diseases. Ascorbic acid is also used as an antioxidant to preserve the flavor and color of foods and beverages. It is added to orange juice, tomato juice, cereals, cosmetics, hair dyes, and plastics. The 24 (Background only!) ascorbic acid content of tablets can be determined easily by titration with a base, such as NaOH. Although a quick inspection of the structure of ascorbic acid does not clearly reveal the acid group, it will be recognized that it is a cyclic ester (lactone) and as such will react with the NaOH by undergoing saponification. O COOH O OH HO OCOCH3 Acetyl Salicylic Acid (Aspirin) OH OH Ascorbic Acid Titration is the name given to the process used to determine the volume of a solution needed to react with a given mass (or volume) of an unknown sample. We will use this process to quantitatively study the reaction between an acid (ASA and ascorbic acid) and a base (NaOH). The hydrogen ion from the R-COOH reacts with the hydroxide ion from the NaOH to produce water and a salt. Phenolphthalein will be used as an indicator since it gives a vivid color change (colorless to pale pink) at the endpoint of the titration. The endpoint signals that the acid is all gone, leaving just salt and water. The volume of the base is recorded after the end point is achieved. The data recorded in a titration experiment, namely the volumes of the acid and base required, along with the concentration of the base, can easily be converted into the concentration of the acid, using the molar ratios contained within the balanced equation. PROCEDURE: I. Analysis of ASA found in an aspirin tablet. a. Weigh three aspirin tablets (from the same bottle) on a balance separately and record their masses to three decimal places. Place each tablet in a separate Erlenmeyer flask (125 or 250 mL). b. Add about 25 mL of 95% ethanol/water solution into each flask. The ASA is more soluble in ethanol and this will make the titration proceed faster. Swirl the flasks to dissolve the ASA. You may use your stirring rod to gently crush the tablet. If you are using a coated tablet, the crushing may be harder. Be aware that binders and coated buffers may not dissolve, thus the solution may be cloudy or slightly colored. Add 25 mL of distilled water to each of the flasks. c. Obtain a stirrer, stir bar, buret, buret clamp, ring stand, and some standard NaOH solution. Be sure to record the exact molarity on the stock bottle in your laboratory notebook. Take about 75 mL of sodium hydroxide in a small beaker or flask back to your work area. d. Rinse the buret with a small amount of sodium hydroxide, by placing about 5 mL in the buret and swishing the solution about the buret by holding it horizontally. Allow the rinse to coat all parts of the buret, then drain the NaOH into the sink via the stopcock. This avoids any dilution of the base by water that might have remained in the buret. Fill the buret with NaOH and allow some to drain through the tip to get rid of all bubbles. 25 (Background only!) e. Place the stir bar carefully into one of the flasks with the dissolved ASA, add a few drops of phenolphthalein, then position the flask on the stirrer, with the tip of the buret over the mouth of the flask. Start the stirrer motor slowly and adjust for a smooth stirring action. Avoid splashing. f. Record the initial volume reading of the buret to the nearest 0.01 mL. Note that the volume markings on the buret likely read from the top down, not from the bottom up. Start dispensing the base into the flask slowly until you reach the endpoint, marked by a faint pink color persisting for at least 30 seconds. When nearing the endpoint, slow the addition of base to a drop at a time. A good endpoint is reached when one drop of base causes the solution to go from colorless to a very pale pink. If you miss the endpoint by adding too much base, you will have to start all over again. Record the final volume reading of the buret at the end of the titration. Now you are ready for the second tablet—which should go much faster, as you have an approximate idea how much base you will need to add. g. You may pour the neutralized solutions down the drain, but do not allow the stir bar to go down the drain!! Rinse the bar, place it in the second flask and perform the remainder of the titrations as before. Be sure to record all volume readings before and after titration to two decimal places (0.01 mL). Add more base to your buret as needed, making sure to record the volumes. When done with the experiment, make sure no one else needs your sodium hydroxide solution, then it pour it into the sink. Sodium hydroxide = Draino—today is “clean out the lab sinks” day! II. Analysis of Vitamin C Tablets. Perform the titrations as described above, with the following modifications: a. Use three commercial Vitamin C tablets (from the same bottle), each having approximately 500 mg of ascorbic acid. Weigh each tablet and record the masses to three decimal places. b. Place the tablets in flasks as before, but add 50 mL of water. Crush the tablets with your stirring rod and heat gently on a hot plate to dissolve. The binder may not dissolve. When most of the tablet has dissolved, cool the solution and add a few drops of phenolphthalein. Titrate as above. 26 (Background only!) Pre-Lab To be completed in your lab notebook before the start of the lab period: • Title of the experiment • A short purpose. • A brief summary of the procedure you will use; about one page will suffice. Do not copy the procedure verbatim from the packet! • Using the hints from previous labs, prepare two Data Tables for this lab (one for aspirin, one for ascorbic acid). Each table should be neat and clear, with enough room allowed for the following: Brand of Tablet used Weights of all three tablets (include balance name and #) Molarity of the NaOH used Amount of phenolphtalein added Buret readings before and after each titration run • Do the following exercise in your lab notebook: a. Using your text, lecture notes or other sources, write complete structures for the reaction of acetylsalicylic acid (ASA) with sodium hydroxide. Refer to the structures given here. (Hint: this is an acid-base reaction.) b. Using the data given in this lab, calculate how many mg of ASA may be found in a 5 grain tablet. c. Calculate the molar mass of ASA. d. Assuming that a particular ASA-containing tablet weighed 0.380 g and that it required 17.00 mL of 0.1051 M NaOH to titrate to a phenolphthalein endpoint, calculate the mg of ASA in the tablet and the % of the tablet which is ASA. Show all calculations clearly!! 27 (Background only!) Lab Report To be completed outside your lab notebook by the beginning of the next lab period: • Title of the Experiment • Brief purpose/goals statement • Observations and data—what happened in lab, all measurements and results. Should include a copy (typed/written anew, or photocopied, your choice) of the data tables from your lab notebook. • Calculations—do a separate calculation for each of the six titrations, tabulating the following pertinent information: Weight of tablet Volume of NaOH used Moles of NaOH used Moles acid present Grams of acid in sample % of acid in tablet Weight of acid claimed on label % Error* *% • Error = (|g acid obtained – g acid claimed|/g acid claimed) x 100% Discussion—end your report with a paragraph of discussion of your results as usual. Compare the tablet contents to each other and to the manufacturer’s claim. Are you getting your money’s worth? Any comments on the procedure, unusual happenings and results can be included; what went wrong, how the lab could be improved on. 28 Experiment 6 Lab Techniques: Grignard Reactions Purpose: Successfully create three target larger organic compounds by picking the correct pairing of smaller organic compounds and putting them together by way of a Grignard Reaction. Background Information: Consider the formation of a new C--C bond; one of the most critical pieces of organic synthesis, yet difficult to accomplish. One carbon must be the electrophile—think any carbon with a decent ?+ on it; any carbon attached to an oxygen or halogen meets this requirement. The second carbon must be the nucleophile—a carbon with a measurable ?- on it. Not on the usual list of organic molecules—but if we had one, these two pieces would come together making a new covalent bond between carbons, making a larger organic molecule from two smaller pieces. O :CWhen you add Mg to an alkyl halide, usually an alkyl bromide, the Mg *inserts* itself into the C-Br bond—forming a Grignard reagent. This works with any alkyl halide, even a bromobenzene: Br Mg 29 MgBr Phenylmagnesium bromide—a very unusual compound, but it works. When "bound" to a metal, more electronegative carbon effectively becomes a carbanion, a carbon with a distinct ?-. Grignard reagents are so reactive they will make a bond with the next ?+ thing they meet. The trick is to make the Grignard reagent in the presence of an aldehyde, ketone, even CO2--ensure that "the next ?+ thing" makes a very predictable and useful C—C covalent bond. To complete the reaction, add a source of acid to obtain an alcohol or carboxylic acid. O OH OHCl BrMg It is important to keep water out of the reaction until this last step—otherwise the Grignard reagent will react with water forming an alkane. Glassware must be washed and dried in the oven ahead of time, assembled with drying tubes containing CaCl2, and flame-dried to get the last traces of atmospheric water out of the set-up. Anhydrous ether is the solvent of choice for a Grignard reaction; almost anything else will react with the Grignard reagent. Something to keep in mind, though the virtual lab does not require quite this attention to detail. BrMg H2O + 30 BrMgOH Procedure: Launch the BeyondLabz program. When the client opens, select “Organic Chemistry”. Select the Synthesis laboratory. Select “Grignard Addition” from the options on the blackboard. The target compounds that you want to synthesize are 2-phenyl-2-propanol, 1-phenyl-1-propanol, and cyclohexane carboxylic acid. 1. Identify the appropriate starting materials required to synthesize 2-phenyl-2-propanol from the available reagents on the stockroom shelf and add them to the round bottom flask. Add diethyl ether as a solvent and drag the flask to the stir plate on the lab bench. 2. The round bottom flask containing the starting materials should now be on the stir plate, and the contents of the flask should be visible on the chalkboard. Attach the heater, condenser, and N 2 gas to the round bottom flask so the reaction mixture can be heated. 3. Start the reaction by clicking on the Stir button on the front of the stir plate. You should be able to observe the reaction mixture stirring in the flask. Monitor the progress of the reaction using TLC measurements as necessary until the product has formed and the starting materials have been consumed. You can advance the laboratory time using the clock on the wall. Keep track of your data in your notebook. 4. When the reaction is complete (record time of reaction), “work up” your reaction by first dragging and dropping the separatory funnel on the flask and then adding HCl(aq) to the funnel. Extract the organic layer in the funnel by clicking on the top layer and dragging it to the cork ring on the lab bench. Your target compound should now be in this flask. Repeat steps 1-4 targeting 1-phenyl-1-propanol, and again targeting cyclohexane carboxylic acid. 31 Lab Report Answer all questions on separate notebook paper or a different computer file and upload to Canvas by Wednesday June 2. Organize the data for your reactions in a data table like the following: Starting materials (Name or structure, Rf value) Solvent, reagent Product (Name or structure, Rf value) Time of Reaction (minutes) 1. Outline each of the three Grignard reactions you conducted in lab today with a pair of balanced chemical equations. 2. What happens if you grab the wrong bottle and use water or ethanol as the solvent instead of diethyl ether? Go ahead and try this! What product is formed? Write a balanced chemical equation explaining the formation of this product. 3. Did you synthesize anything unexpected? If yes, what compound and what do you think led to this compound? If not, discuss what preparation you did before attempting the lab to successfully thwart the unexpected! 4. What is a different alcohol you could put together from the reagents available to you? Write one more pair of balanced chemical equations outlining how you might make your new Grignard target. 32 Experiment 7 Oxidation and Reduction Purpose: Oxidation and reduction reactions, when applied correctly, allow for simple interchange of functional groups. Your challenge: design an effective synthesis using available reagents to interconvert benzyl alcohol, benzaldehyde, and benzoic acid. Background: Primary (1o) alcohols oxidize to aldehydes and carboxylic acids. Aldehydes oxidize to carboxylic acids and reduce to 1o alcohols. Carboxylic acids reduce through the aldehyde to a 1 o alcohol. Benzaldehyde O H O OH OH Benzyl alcohol Benzoic acid Oxidizing agents you should consider: H2Cr2O7/H2SO4 and PCC. Chromic acid is the standard; PCC is more selective but leaves pyridine as a basic side product which must be dealt with in the work-up. Reducing agents you should consider: NaBH4 and BH3. BH3 (Borane-THF) is similar to LiAlH4 in reactivity—stronger and will reduce more functional groups but is somewhat prone to explosions and not always available. Both require a source of hydrogen added as a second step to complete the reaction. 33 In principle you should be able to start with any one of these three compounds—benzyl alcohol, benzaldehyde, or benzoic acid—and proceed around the triangle clockwise or counterclockwise moving to each of the other two compounds in turn. Six possible reactions! In practice only five of these reactions work. Deduce how to set up these 5 working reactions and test them in the lab, reporting back with your observations as to reagents required, products formed, times of reactions and TLC data. Similarly, secondary (2o) alcohols oxidize to ketones and ketones reduce to 2o alcohols: OH O 1-phenylethanol methyl phenyl ketone Avoiding redundancy, we will not be exploring this cycle. Procedure: Launch the BeyondLabz program. When the client opens, select “Organic Chemistry”. Select the Synthesis laboratory. 1. Benzyl alcohol may be found in the “Alcohol Oxidation” option on the blackboard, benzaldehyde under “Carbonyl Reduction” and benzoic acid is in the “Acid Chloride” section. Pick the option appropriate to your targeted reaction and begin. 2. Identify the appropriate starting materials required from the available reagents on the stockroom shelf and add them to the round bottom flask. Add diethyl ether as a solvent and drag the flask to the stir plate on the lab bench. 3. The round bottom flask containing the starting materials should now be on the stir plate, and the contents of the flask should be visible on the chalkboard. From the group of reagents found on the lab bench, select the correct reagent to synthesize the target compound and add it to the flask on the stir plate. Now attach the heater, condenser, and N2 gas to the round bottom flask so the reaction mixture can be heated. 4. Start the reaction by clicking on the Stir button on the front of the stir plate. You should be able to observe the reaction mixture stirring in the flask. Monitor the progress of the reaction using TLC measurements as necessary until the product has formed and the starting materials have been consumed. You can advance the laboratory time using the clock on the wall. Keep track of your data in your notebook. 5. When the reaction is complete (record time of reaction), “work up” your reaction by first dragging and dropping the separatory funnel on the flask and then adding the appropriate aqueous solution (H2O, HCl or NaOH) to the funnel. Extract the organic layer in the funnel by clicking on the top layer and dragging it to the cork ring on the lab bench. Your target compound should now be in this flask. Clear the lab and repeat steps 1-5 for your remaining targeted reactions. Modify goals as necessary! 34 Lab Report Answer all questions on separate notebook paper or a different computer file and upload to Canvas by next Monday evening. Organize the data for your reactions in a data table like the following: Starting material (Name or structure, Rf value) Solvent, reagent Product (Name or structure, Rf value) Time of Reaction (minutes) 1. Outline each of the five reactions you successfully conducted in lab today with balanced chemical equations. 2. What reaction is not possible? Write a balanced chemical equation outlining this hypothetical reaction, briefly explaining why it won’t work. 3. Propose the best way to make each of the three target compounds, starting from one of the others. Ie, is it better to make benzoic acid from benzyl alcohol or benzaldehyde? Do you make benzaldehyde from benzyl alcohol, or from benzoic acid? Benzyl alcohol from benzoic acid, or from benzaldehyde? Defend your choices! 35 Experiment 8 Synthesis of Aspirin Purpose If there is one experiment I could bring you into the real laboratory to attempt in person, it would be this lab. Not possible! I did find a virtual version, British A-level Chemistry, the “Aspirin Screen Test”: https://virtual.edu.rsc.org/aspirin/experiment/1 Procedure Visit the “Aspirin Screen Test” site and begin. Register formally (use your name as it shows up on my class roster) so you can save your place and your data. All 4 parts are required; you will be turning in two separate lab reports as you did for Experiment 5/Organic Acid-Base Reactions. The first lab report will be your collected data from the Aspirin Screen Test exercise—the downloaded .pdf files of your lab notebook for each of the 4 parts. The second part is a formal lab report write-up. Don’t be afraid to test things out—I learned a lot more going through this intentionally making errors! You are encouraged to repeat any level you like, to improve your score (which does affect your grade); please do, and please upload only one version of your lab notebook for each level to Canvas when you are done. I got most of the way through level 2 in Firefox, then something failed to load; switching browsers (I used Microsoft’s Edge) allowed me to finish. 36 Lab Report Download your lab notebook (pdf) after you finish each level. Upload your final version of Levels 1, 2, 3, and 4 to Canvas by next Monday evening. That’s it! Formal Lab Report About two pages typed; upload this to Canvas as a separate document by Wednesday June 16. • • • • • • Title of the Experiment Brief purpose/goals statement—2-3 sentences, summarizing the overall point of the experiment. Chemical reaction—write a balanced chemical equation for the synthesis of aspirin, drawing structures for all compounds involved. Summary of Procedure—2-3 sentences, laying out where your data came from. Conclusions—how successful was your aspirin synthesis? What proof have you that aspirin actually was (or was not) synthesized? Report the Rf values from your TLC analysis, starting material and product. Report your crude and purified aspirin mass and % yield. Discussion—end your report with a page of discussion. What did you learn from this virtual synthesis of aspirin? Give some logical reasons why you did not get 100% yield, and why you expect your recrystallized yield to be less than your crude yield. Give your opinion as to optimal reaction conditions and reagents for this experiment, discussing the relevant pros and cons—no one method is perfect. Include an answer to the following question regarding acetaminophen: The analgesic Tylenol is often taken by persons who are allergic to aspirin. Tylenol contains acetaminophen (structure shown below) as the active ingredient. How is the structure of acetaminophen similar to the structure of aspirin? How is it different? How does this relate to the body’s response to acetaminophen vs. aspirin? NHCOCH3 OH 37 (Background only!) I have included the complete on-campus/live version of the CHEM 122 Synthesis of Aspirin Experiment for a different perspective; this may be useful in writing your Formal Lab report. We are doing the virtual version, **not** this one! Synthesis of Aspirin Purpose: Aspirin will be prepared by heating salicylic acid with acetic anhydride in the presence of a catalytic amount of phosphoric or sulfuric acid according to the following equation: COOH COOH + CH3COOCOCH3 H3PO4 + CH3COOH OCOCH3 OH Salicylic acid Acetic anhydride Aspirin Acetic acid We have not discussed this reaction in class yet; the pertinent details may be found in Chapter 11 of the text. The resultant crude product will then be tested for unreacted salicylic acid using ferric chloride. Some additional tests will be performed on commercial aspirin. Background Information: Aspirin is one of the most amazing medicines known. Currently, 30,000,000 pounds are sold in the United States each year, enough for more than 200 five-grain tablets for every person in the county. It is an effective antipyretic; it reduces fever but does not lower normal body temperatures. It has analgesic (pain-reliever) properties and is effective against pains accompanying headaches, colds, flu, nervous tension, rheumatism, and arthritis. Recent evidence suggests that continues small doses over long periods of time could decrease the chances of heart problems and increase the chances of surviving a heart attack. The name aspirin comes from that of a willow, Salix spirea. In the seventeenth century, it was found that extracts of willow bark had fever reducing properties. In 1826 the active principle, salicylic acid, was isolated. By 1852 salicylic acid had been independently synthesized, and by 1874 relatively largescale production had made it available as a medicine. Although salicylic acid is an effective antipyretic, it causes severe stomach irritation in some people, and for this reason the search for a pain reliever continued in the late 1800s. Many derivatives of salicylic acid have been investigated to try and relieve the stomach the stomach irritation problems. Toward the end of the nineteenth century Felix Hofmann, working for the Bayer Company, was investigating derivatives of salicylic acid. He tested acetyl salicylic acid on his father, who suffered from arthritis. This and other tests revealed its excellent medicinal properties and decreased frequency of gastric irritation. Acetylsalicylic acid, aspirin, was first marketed in 1899 by the Bayer Company. 38 (Background only!) Procedure: Weigh 1.5 g of salicylic acid, placing it in a 125-mL Erlenmeyer flask. Then add 4 mL of acetic anhydride and 4 drops of 85% phosphoric or sulfuric acid. Measure the acetic anhydride under the hood since it is highly irritating to the nose. Stir the reaction mixture thoroughly. Heat the Erlenmeyer flask in a boiling water bath for 5 minutes, with frequent stirring. Remove the flask from the bath and stir 3 mL of water at once into the hot mixture. Continue to stir for a couple of minutes in order to destroy any excess acetic anhydride, and then continue to stir while you add 30 mL of water. At this point aspirin will begin to precipitate from the solution. Complete the precipitation by cooling the flask in an ice-water bath for about 5 minutes, with stirring. Isolate your aspirin using vacuum filtration. Using a side-armed filter flask equipped with a Buchner funnel, and attached to the vacuum outlet, rapidly pour your reaction mixture onto a piece of wet filter paper inside the Buchner funnel. Use your spatula to remove most of the crystals from your flask. Wash your aspirin crystals thoroughly with about 10 mL of water by pouring the water slowly over the crystals as you gently stir them. Distribute the crystals across the bottom of the Buchner funnel with a spatula and dry them by pulling air through the Buchner funnel for a few minutes. Gently stir the crystals frequently with your spatula so that they will all be exposed to the passing air. Weigh your dried aspirin and determine the yield, then the % yield. Recollect stoichiometry from CHEM 121—the mass aspirin expected does not equal the mass salicylic acid you began with, moles must be considered. 39 (Background only!) Product analysis: A test for unreacted salicylic acid The ferric chloride test (from Lab 4: Alcohols) is used to determine if there is any unreacted salicylic acid present in aspirin. Your aspirin and a commercial sample will be used for this test. Proceed as follows. Add about 0.1 g of salicylic acid (for comparison) to 2 mL of 1% ferric chloride solution in a test tube. Then add about 0.1 g of your aspirin to the same amount of ferric chloride in a second test tube, and finally add about 0.1 g of finely crushed commercial aspirin to 2 mL of ferric chloride solution in a third test tube. Stir each solution thoroughly. Note the color, if any, in each case. Is either your aspirin or commercial aspirin contaminated with salicylic acid? Starch binder test Commercial aspirin is only 70% to 90% acetylsalicylic acid; most of the remainder is a binder, usually starch, which holds the tablet together. To confirm that starch is the binder, dissolve some crushed commercial aspirin (the size of a pea) in a couple of mL of water, while stirring. Now add 1 drop of dilute iodine solution, and see whether the characteristic pale blue-black starch-iodine complex is formed. Acidity test Add 100 mg (an amount the size of a large pea) of your aspirin, commercial aspirin, Bufferin, and salicylic acid to 2 mL of distilled water in four separate test tubes. Stir the solutions. Use a narrowrange pH paper to determine the pH of the solutions. Add 100 mg of solid sodium bicarbonate to your aspirin solution. Is a gas formed? If so what is the gas? Record your observations. The ester test Dissolve 0.2 g of crushed commercial aspirin in 1 mL of 10% sodium hydroxide in a test tube (test the solution with litmus paper to confirm that it is basic), and heat the test tube in a boiling water bath for several minutes. To the hot solution add concentrated hydrochloric acid, stirring it in drop by drop, until the solution is just acidic (test the solution with litmus paper). Smell the contents of the test tube. Do you smell acetic acid (vinegar)? Now add several drops of ferric chloride solution. Does a colored complex form? Record your observations. Pre-Lab To be completed in your lab notebook before the start of the lab period: 1. Title of the experiment 2. A short purpose. 3. A brief summary of the procedure you will use; about one page will suffice. Do not copy the procedure verbatim from the packet! 4. Construct a Data Table similar to previous experiments—your data table should collect together the results of your product/commercial aspirin analysis, with plenty of room for observations. 40 (Background only!) Lab Report To be completed outside your lab notebook by the beginning of the next lab period: • Title of the Experiment • Brief purpose/goals statement • Chemical reactions—write a balanced chemical equation for the synthesis of aspirin, drawing structures for all compounds involved. Also include a balanced chemical equation for each of the relevant tests performed (ferric chloride, acidity test, ester hydrolysis). • Observations and data—what happened in lab, all measurements and results. A photocopy of the relevant pages from your lab notebook may be used—but select what you copy carefully. • Conclusions—how successful was your aspirin synthesis? What proof have you that aspirin actually was (or was not) synthesized? Report your final aspirin mass and % yield, showing your % yield calculation. • Discussion—end your report with a paragraph of discussion as usual. Any comments on the procedure, unusual happenings and results can be included; what went wrong, how the lab could be improved on. • Answer the following questions: 1. Why is it important to drink water immediately after taking aspirin? 2. Sodium salicylate has been used as an analgesic. Draw the structure of this compound and show how you could prepare it from salicylic acid. 3. The analgesic Tylenol is often taken by persons who are allergic to aspirin. Tylenol contains acetoaminophen (structure shown) as the active ingredient. NHCOCH3 OH Is the structure of acetoaminophen similar to the structure of aspirin? Would acetaminophen give a positive phenol test? What products would be obtained if acetaminophen were hydrolyzed in acidic aqueous solution? 4. How is unreacted acetic anhydride removed from the aspirin product? 5. What was your percent yield for the aspirin synthesis? Give some logical reasons why you did not get 100% yield.