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Arizona State University : CHM 237 : Organic Chemistry Lab I

Aspirin Synthesis Package Putting Everything Together, and More…

1. Background

• Chemical synthesis of is one of the most important things that organic chemists do • Synthesis starts with simple and readily available starting structures, and then via a series of bond breaking and bond forming chemical reactions, converts and builds these simple starting materials into new and more complex structures

1.1 A Complete Synthesis Generally Has Multiple Tasks • There is no single procedure for performing a synthesis, different syntheses require different techniques, but your simple syntheses will generally consist of the following tasks

• This synthesis will combine many of the techniques you have learned so far this semester, including recrystallization, melting point and infrared spectroscopy • This synthesis will also introduce a new concept: chemical reactions, heating and Thermal Energy • There is a lot to do this week, you will need to work quickly and efficiently.

1.2 Performing the chemical reaction The organic reaction you will perform:

In This Reaction: Two bonds are broken and Two new bonds are formed (see above) • Look at just one of the bonds that is formed as an example. • We find that we can't just make a bond (the example below has 10 electrons at the carbon indicated)

work

• We must break a bond first (or at least break the bond at the same time as making it). • Actually, it is a bit more complicated than that for this reaction, but the basic idea is an important one…. • Bond-breaking must happen first for almost all organic chemistry reactions. • Breaking bonds requires energy (the energy of the electrons must go "up") since the energy of the electrons are higher when they are not in a bond. • This is why almost all organic chemical reactions have an activation energy, i.e. an energy barrier that must be overcome.

• The rate constant of a reaction, k, is related to the size of the activation energy

• The rate constant is determined by the BALANCE between the energy that is required (Ea) and the energy that is available (RT) • The reaction rate constant increases with increasing (RT), i.e. with increasing temperature WE MUST USUALLY HEAT ORGANIC REACTIONS, BECAUSE THEY HAVE ACTIVATION ENERGIES BECAUSE

WE NEED TO BREAK BONDS, AND TO MAKE THEM GO FASTER! • The apparatus you will use to heat the reaction is simple, you will use a condenser to condense any liquids that try to escape in the heating process. • Liquid vapors formed by heating (or boiling) should condense (return to liquid) in the condenser and drip back into the reaction mixture. • Boiling, condensing with return of the solvent is called reflux.

• This reaction also uses a catalyst, an acid in this case, to make the reaction go faster

• Exactly how the catalyst increases the rate of the reaction is beyond the scope of this lab, the explanation is in the mechanism, and this is a topic that will be discussed extensively in lecture • For now, you need to know what the catalyst is and that it is a catalyst, you do not have to know how it works, yet!

1.3 Isolating the Product • Isolation of a reaction product means separating the compound we want, the reaction product, from the mixture of other chemicals inevitably present at the end of a reaction. • We can isolate a reaction product in many different ways, e.g. extraction (as we learned in the previous lab), or distillation (which we will learn later), or in this lab, we can use crystallization. • Crystallization depends upon solubility, which we now know a lot about • Solubility is given by the solubility constant (S), which decreases with decreasing temperature.

• The solubility of most organic compounds is lower in water due to the hydrophobic effect.

• The analysis of IMFs above show why aspirin is not very soluble in water as a solvent. • In this lab you will use a combination of low temperature and the hydrophobic effect to induce crystallization.

1.4 Identifying the Product • You need to make sure that the product of your reaction is the compound you expect it to be. • You can characterize your product many different ways, for example melting point, TLC Rf value or by analytical chemistry such as infrared spectroscopy or NMR spectroscopy. • You will characterize your reaction product using melting point range and IR spectroscopy.

H3C C

CH3

+ O

H O

CH3

O H3C

acid

catalyst

HO P

phosphoric acid

+ HO P

not consumed

1.5 Reaction Yield • Recall, it is always important to determine how efficient your synthesis is, in other words, does your synthesis produce the maximum number of molecules that it can? • Remember the ways that the yield of a reaction could be less than 100%: 1. Incomplete Reaction. Sometimes the reaction does not go to completion; some of the reactant remains unreacted. 2. Formation of Side-Products. Some of the reactant can sometimes undergo an unwanted side-reaction, in addition to the desired reaction, not all of the reactant makes the desired product. 3. Mechanical Losses and/or Errors. This covers many possibilities, for example, some of the product is lost when recrystallizing, or weighing, or drying or transferring, or you make an error in your experiment, you weigh an incorrect quantity of chemical… • The maximum number of moles of the product that can form is equal to the number of moles of the limiting reagent the reactant, this is the theoretical yield. • The chemical yield is the ratio of the actual number of molecules (moles) of the product you make, to the theoretical yield, or molecules, the reaction should produce:

1.6 How Synthesis is used in the Lab

• Chemical synthesis is one of the most important things that organic chemists do, They create new chemical structures with specific and important properties, such as pharmaceuticals, compounds for polymers, molecules for energy storage or for new materials, organic chemical synthesis touches almost EVERYTHING we encounter every day! • By now you are probably no longer convincingly amazed each week, however, this week….

you WILL be AMAZED!!…..

if you are paying attention that is…… • You will create a new chemical structure that will crystallize in front of your eyes! • You will have broken specific bonds in the reactants • You will have made specific bonds in the product • You will have manipulated the molecules under your control at the electron level. • And you will have done this trillions of times since you will have reacted many, many molecules! • And each of the trillions of times you will have done almost exactly the same thing to the molecules.

You will be so excited I have no idea how you will sleep the night before you do this particular lab!

2. What You Will Do 1. Pre-Lab: You must watch the online recitation (Canvas), complete the gapped notes (Section 1 of the packet), complete the Pre-Lab notes in the notebook (see Section 3), and complete the Pre-Lab activity worksheet (see Section 4). Each student must complete all of these and have them checked by the TA before starting the lab (Pre-

acid catalyst

REAGENT

REACTANT

H3C C

CH3

+ O

H O

CH3

O H3C

ASPIRIN PRODUCT "by-product"

# Moles = molecular weight

weight # Moles =

molecular weight

weight

Lab is not a group assignment). These must be in your own handwriting and words, you cannot type and paste into your gapped notes or notebook. Your handwriting should be neat and legible. Everything in your notebook must be in black or blue ink (not pencil). All errors or changes can be crossed out, initialed, and re-written. You will not be allowed to perform the lab if you have not completed all of the Pre-Lab activities. 2. In Lab: Bring all PPE to lab (long pants, goggles, closed footed shoes). You will not be able to work in the lab without them. Take careful notes in your own notebook. Each student need to collect his/her own notes, not one set of notes per group. Have the TA check and sign your notebook before leaving the lab. 3. Post-Lab: Complete the Post-Lab assignment. Each student must turn in their own completed paper copy to their TA at the end of lab (not one per group). Submit a lab report if there is one associated with this particular lab (most labs do not have an associated lab report, check the syllabus).

2.1 Synthesis of aspirin 2.1.1 Perform the Reaction

Note: Make sure that the micropipettes are set to the correct volume before you use them, and, make sure that you always use a clean pipette tip! If you are unsure about how to use the micropipettes, ask your TA! • Weigh roughly 250 mg of salicyclic acid into a 5 mL conical reaction vial. Record your exact weight. • Perform the next steps in a hood • Add 0.5 mL acetic anhydride to the vial. This volume needs to be accurate and so you will use a micropipette for this. Do not add too much acetic anhydride! • Add one drop of 85% phosphoric acid using a disposable plastic pipette (this volume does not need to be accurate). • Place a magnetic spin vane in the vial and attach an air condenser. • Place the vial in the large central hole in an aluminum block on the stirrer/hotplate and add a thermometer into one of the holes in the block. • Stir the reaction mixture gently using the magnetic stirrer and the spin vane in the reaction mixture.. • Then, slowly heat the reaction mixture in an aluminum block until the temperature of the block is ~80-100°C. Set the dial on the stirrer hotplate to 3 or 4. • You should have gentle reflux, meaning very gentle boiling, if the boiling starts to become vigorous, reduce the heat slightly. • After the solids have dissolved, continue to gently reflux the reaction mixture for another 15 minutes.

2.1.2 Isolate the Product • Remove the vial from the heat and allow it to cool to the touch. • After it has cooled enough to handle safely, but while it is still warm, remove the air condenser and add 1.5 mL of deionized water using a disposable plastic pipette (this volume does not need to be accurate). . Stir the solution until everything is in solution (the solution looks clear). • Remove the spin vane with forceps and rinse it with 2 or 3 drops of water into the reaction vial. • After the solution has cooled you should see crystals start to form. • If no crystals form, scratch the inside of the conical vial below the surface of the liquid with a clean glass rod (if two layers form, then vigorously scratch the sides of the vial with a glass stir bar, it may take multiple attempts). • Cool the solution further by placing the vial in an ice bath. • When the solution is cooling in the ice bath, setup a Hirsch funnel for filtration. • Remove the solution form the ice bath and as quickly as you can (i.e. before the solution starts to warm up again), filter in order to isolate the crystals of the product. • Rinse the vial with roughly 0.5 mL of cold water and use this water to wash the crystals on the funnel. • Dry the crystals by allowing air to be drawn through them on the filter paper for 5-10 minutes. • Dry the crystals further on a drying block until they are dry (no longer stick to the metal spatula). • Weigh the solid crystals and then crush them to make the next recrystallization step easier •Take a small quantity of the crushed crystals and put into a melting point capillary for melting point analysis.

2.1.3 Purify the Product • Purify the crude reaction product by recrystallization in a small test tube. • Put the crude product into a test tube and put the test tube in a small beaker with water on the hotplate. Add hot ethanol that is contained in a separate beaker that has also been warmed on the hotplate. • In the test tube, dissolve the crude reaction product in the minimum volume of hot ethanol. It will not require a lot of ethanol, so add slowly while constantly stirring!. The solvent will be hot, so be careful! • When all of the product has dissolved in the hot solvent, let the solution cool to room temperature and if no crystals form then scratch the inside of your container again as described above. • Cool the test tube in an ice bath to maximize crystal formation. • Remove the solution from the ice bath and as quickly as you can dry the crystals using a Hirsch funnel. When dry, weigh the crystals. Calculate the percent recovery from the recrystallization process. • Calculate the overall percent yield of the purified product in your synthesis.

2.1.4 Identify and Characterize the Product • Make sure that you have crushed your crystals! • Take a melting point range of both the crude and the recrystallized product. • Take an IR spectrum of your pure product.

characterize the product

2.2 Waste Disposal • Discard used melting point tubes in a sharps container! • Dispose of unused organic chemicals (p-aminophenol, acetic anhydride etc.) in the organic waste container in the hood. • Dispose of aqueous sample in either the acid or base waste containers as appropriate.

3. Pre-Lab and In-Lab Notebook (10 pts) 3.1 General Lab Notebook Guidelines

A lab notebook is the standard way to organize, collect, and maintain data generated in lab. A well-kept lab notebook should contain all of the information necessary for a third party to reproduce the experiment and corresponding data. The lab notebook should be bound (a composition notebook works best) without perforated pages. A “spiral” lab notebook is not acceptable, as the pages can be torn out easily. The general guidelines for setting up your lab notebook are as follows:

 Page 1: Name; Course & Semester; Contact information (email)

 Page 2-3: Table of Contents

 Page 4 to the end: See the lab packet for each experiment for the details of what to include in the pre-lab and in lab each week

Occasionally you will make a mistake while writing in a lab notebook. This is completely acceptable, science is messy and you are learning. If you make a mistake, simply cross the mistake out with a single line (regardless of the size of

the error), initial the line, and date it. This lets everyone who reads the notebook know that you made a mistake and that the piece of information is invalid. It is also important to use only a single line so that the original information can still be read. Other things NOT to do in a lab notebook include:

 Adding or editing information after the lab period has ended.

 Writing in pencil.

 Scratching out information so it is no longer legible.

 Adding or removing pages.

 Using white out.

 Falsifying data. Learning to organize and maintain a useful lab notebook is a skill that you will use in many scientific careers

3.2 Pre-Lab (5 pts)

You MUST have the following Pre-lab completed in your notebook and checked by the TA at the beginning of lab! All parts of the Pre-lab must be handwritten in ink. Include all of the following as part of your pre-lab assignment: 1. Title and date of the experiment 2. Purpose of the experiment 3. Reaction (if applicable) 4. A completed version of the Table below. Look up the molecular structure, molecular weight, melting point and MSDS information

Name Molecular Structure Molecular Weight (g/mol)

Melting

Point ( ◦ C)

MSDS (Hazards Identification)

salicyclic acid

acetic anhydride

phosphoric acid (85%)

not applicable

ethanol not applicable

acetylsalicyclic acid

The information you will need to complete this table is available from several websites, a good one is the Sigma Aldrich website (www.sigmaaldrich.com). On the Sigma Aldrich site: - Search for the compound. - The search will generate a list of different forms of the compound that the Sigma Aldrich sells. - Choose the link for a pure form of the compound (not a solution, for example), and you should be able to find the compound’s molecular structure, molecular weight, and boiling point. - Below the compound’s name, there should be a button “SDS”. Click the button to get a pdf file of the Safety Data Sheet. Scroll to Section 2.2 of the document (“Hazards Identification”) and write down the relevant information under “Hazard Statement(s)”. 5. Write in your lab notebook an answer to the following question:

- How long do you have to rinse in case of eye or skin contact with any of the chemicals you will use in this lab?

http://www.sigmaaldrich.com/

6. Complete the Table below using information in Section 2 of this packet

Waste Where to Discard

Organic Chemicals

Pipette tips

3.3 In Lab (5 pts) Your in-lab notes should adhere to the guidelines given on the previous page, i.e. it should include, as appropriate: Quantities (all weights, volumes etc. recorded)

Observations (colors, solids, precipitates etc.)

Resulting Data (e.g. melting point ranges, Rf values, IR spectral data)

Calculations (yields, recoveries etc.)

Conclusions (Did the experiment work? Based on melting point, % recovery, yield, IR data, etc.)

And your entries should be legible, the book should be clean (no spilled chemicals etc.), should use correct notebook style, be written in ink, mistakes crossed out with a line, as above.

Everything written in your lab notebook must be legible and handwritten in ink, not pencil. The book should be clean (no chemical spills etc.), should use correct notebook style, with mistakes crossed out with a line. Have your notebook checked by your TA before you leave the lab!

4. Turn-in Pre-Lab Assignment – Experiment and Objectives (10 pts) You MUST turn this paper in to your TA at the start of the LAB SESSION!

YOUR Name: ___________________________ Lab room: ________________ Partner Name: ___________________________ Lab time: _________________ TA Name: ____________________ Hood #: _________________ Give brief (1 sentence max.) responses to the following questions (1 pt each): 1. What is the name of the procedure where a mixture is heated, the liquid boils, it is condensed and drips back into the reaction vessel so that no liquid is lost?

2. Why do most reactions have an activation energy and have to be heated (circle one) because new bonds have to be made before old bonds can be broken. because old bonds have to be broken before new bonds can be made. 3. What method will you use to isolate the product in your reaction in this synthesis (circle one)? extraction crystallization distillation 4. What is the catalyst in this reaction?

5. Products that are unavoidably formed at the same time as your desired product are called?

6. Unwanted products that are formed in addition to your desired product, usually by a competing chemical reaction, are called?

7. What temperature should the aluminum block be when you are refluxing your reaction?

8. What technique will you use to purify your reaction product?

9. What two methods will you use to characterize your product, i.e. know how pure it is and what it is?

10. When should you change the tip on a micropipette?

5. Post-Lab Assignment (20 pts.) You MUST turn this paper in to your TA at the END of LAB!

YOUR Name: ___________________________ Lab room: ________________ Partner Name: ___________________________ Lab time: _________________ TA Name: ____________________ If you did not collect any data or are missing some data to complete this post-lab, then give your source of data here and give a brief explanation why you have missing data. If you use your own data you can go straight to question 1, no need to add anything here. 1. (0.5 pts.) Complete the following table.

Chemical(s)

Weight (g)

Melting Point (°C)

Starting salicyclic acid not applicable

Isolated Crude product

Isolated Recrystallized product

2. (0.5 pts.) Give the number of moles of salicyclic acid that YOU started with, show all equations WITH UNITS! (assume mass and weight are the same)

3. (0.5 pts.) Give the number of moles of acetic anhydride that YOU started with, show all equations WITH UNITS! (assume mass and weight are the same)

4. (1 pt.) Which is the LIMITING, the REACTANT or the REAGENT? 5. (1 pt.) What is the THEORETICAL YIELD of the reaction, in moles? 6. (0.5 pt.) Give the number of moles of CRUDE aspirin that YOU isolated (before recrystallization), show all equations WITH UNITS! To do this you will need to assume that all of your crude aspirin is actually aspirin, even though you know that it probably isn’t. This is the assumption that is always made when calculating yields of crude products.

7. (0.5 pt.) Give the number of moles of PURE aspirin that YOU isolated, show all equations WITH UNITS! (assume that mass and weight are the same)

8. (0.5 pt.) Calculate the percent yield of the PURE aspirin (i.e. after recrystallization). USE THE THEORETICAL YIELD and show all equations and include all units.

9. (2 pts.) The yield of your pure final product is unlikely to be 100%. Give THREE reasons for why the yield may be lower than 100% (ignore any weighing errors).

10. (1 pts.) Why did you warm the solution when performing the reaction? Give a ONE SENTENCE explanation that include the terms thermal energy and activation energy and includes the variable and the constant that determine the amount of thermal energy.

11. (2 pts.) Why was 1.5 mL of water added to the reaction mixture at the end of the reaction? Give a ONE SENTENCE explanation that includes the term hydrophobic effect.

12. (1 pts.) Why are the solutions cooled in an ice bath when crystallizing? Give a ONE SENTENCE explanation that include the term Solubility Constant (refer to the recrystallization packet from earlier in the semester).

13. (2 pts.) One problem with organic equations is that we tend to focus on what is happening to one molecule at a time, we forget that there are many, many molecules undergoing the reaction. Assume that you started with exactly 200 mg of salicylic acid in your reaction. How many MOLES of salicyclic acid is this, AND how many MOLECULES OF salicyclic acid is this? You will need to know that Avogadro's number is 6.022 x 1023 and that a mole of a substance is equal to Avogadro's number of that molecule). Give the number of molecules to 3 significant figures and do NOT USE SCIENTIFIC NOTATION, i.e. include all of the zeros in your number. After the number write down the number of zeros you included in parentheses. For example if your answer is 5.99 x 1021, then you would write it as follows: 5990000000000000000000 (19 zeros). SHOW YOUR WORK and INCLUDE ALL UNITS! (4 pts) weight of the acid = 0.2 g molecular weight = 138.1 g/mol # of moles of the acid = # of molecules of acid = 14. (4 pts.) Assign the peaks in the infrared spectrum of aspirin (below) with frequencies greater than 1500 cm-1 to specific bond vibrations AND the functional group the bond is associated with. Clearly indicate the specific bond vibration that is associated with the relevant peaks.

15. (3 pts.) Assign the peaks in the infrared spectrum of salicylic acid (below) with frequencies greater than 1500 cm-1 to specific bond vibrations and the functional group the bond is associated with. Clearly indicate the specific bond vibration that is associated with the relevant peaks.