2/27/2013 ASPIRIN. How do you decide what starting materials to use? SYNTHESIS must not involve TOXIC BYPRODUCTS that are NOT EASILY REMOVED

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Ophelia Parrish
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1 QUIZ 1 Wednesday and Thursday Lab Sections (Sections 5x, 6x and 7x) ASPIRIN Wednesday and Thursday lab sections will take the quiz as originally scheduled - Wednesday and Thursday, March 6 & 7. The quiz will cover the first three exercises (SUSB-053, SUSB-017 and SUSB-03). Monday and Tuesday Lab Sections (Sections 1x, x, 3x and 4x) Last Update: :19 PM Monday and Tuesday lab sections will take the quiz on Monday and Tuesday, March 10 & 11. The quiz will cover the three exercises performed by those sections (SUSB-017, SUSB-03 and SUSB-08) 1 SYNTESIS onducting one or more chemical REATINS using STARTING MATERIALS to produce the desired substance as a PRDUT What makes a synthesis EFFETIVE? IF IT PRDUES TE DESIRED PRDUT: from reasonable STARTING MATERIALS under practical NDITINS e.g., accessible temperature & pressure at a reasonable RATE (ATALYSTS may be helpful) with relatively high YIELD in a chemical environment that permits practical SEPARATIN F PRDUT from excess starting materials and byproducts in an ENVIRNMENTALLY RESPNSIBLE way - GREEN EMISTRY all, in a $T-EFFETIVE manner For substances that may be consumed by humans or animals, there is an additional concern: SYNTESIS must not involve TXI BYPRDUTS that are NT EASILY REMVED 4 hemical reactions rarely result in a SINGLE PRDUT. There are usually BYPRDUTS and, often, only NE reactant will be consumed, producing LEFT VER REATANTS Many reactions don t go to MPLETIN. but REATANTS and PRDUTS establish EQUILIBRIUM Reactants Products If so, reaction conditions can be chosen to PUS EQUILIBRIUM to favor PRDUTS 5 NET RESULT Must be able to separate product from reaction mixture Separation may be based on: Solubility Extraction/ rystallization Boiling Point Distillation hromatography Etc. ow do you decide what starting materials to use? 6 1

2 What are possible STARTING MATERIALS for the synthesis of ASPIRIN, 9 8 4? Does the structure of the desired product suggest a starting point for the synthesis? Aspirin 3 What MATERIALS are readily available, and inexpensive? Salicylic Acid 7 All that would be needed is a reaction that converts the group on the ring to an acetyl group 3 3 A reaction which accomplishes such a conversion is: The reaction of an alcohol or phenol with an acid anhydride 8 A reasonable synthetic pathway, then, is: 3 3 SALIYLI AID (SA) Note that AETI AETI AID ANYDRIDE (AA) is also a product The reaction of this reaction proceeds slowly* 3 3 AETI AETYL SALIYLI AID 9 AID (ASA) What are some properties of the potential REATANTS and PRDUTS? AA SA ASA MP -73 o 157 o 135 o BP 139 o 11 o DE o REATS. mg/ml 3.3 mg/ml Under what conditions should the reaction be conducted? Probably NT in WATER solution - AA reacts and SA is not very soluble Neither SA nor ASA are very soluble in water 10 ould use an RGANI SLVENT but, AETI ANYDRIDE is itself a LIQUID at room temperature. Also, Salicylic Acid is soluble in Acetic Anhydride an use AA as the REATIN MEDIUM (solvent) But Reaction is SLW in pure AETI ANYDRIDE Small amount of a STRNG AID makes reaction proceed more rapidly e.g., S 4 ( i.e., come to EQUILIBRIUM quickly) atalysis! Also, by le hatelier s principle, excess of reactant forces equilibrium towards product formation. So, 11 it is beneficial to use an excess of Acetic Anhydride IN PRE-LAB, YU WILL SW TAT:.0 g SALIYLI AID =.0 g / g / mol SA = mol = 14 mmol SA 4.0 ml AETI ANYDRIDE x 1.08 g / ml = 4.3 g / 10.1 g / mol AA = 0.04 mol = 4 mmol AA SALIYLI AID is LIMITING REAGENT Incidentally, 5 DRPS F S 4 = 5 DRPS x ~0.05 ml/drp = 0.5 ml x 1.84 g/ml = 0.46g/98g/mol = mol = 4.7 mmol (onsistent with being a atalyst) 1

What is in reaction vessel finally? INIT FINAL mmol mmol ASPIRIN 0.0 14.0 AETI ANYDRIDE 4.0 8.0 SALIYLI AID 14.0 0.0 AETI AID 0.0 14.0 SULFURI AID 4.7 4.

3mg/mL) We can add water to the reaction vessel to cause ASPIRIN to precipitate which we can then recover by filtration Some of the water will react with the excess AETI ANYDRIDE to form additional

3 mg/ml), using a small amount of water should cause the loss of very little aspirin. e.g. If 50 ml is used, 50 ml X 0.0033 g/ml = 0.165 g will be lost (out of a maximum of ~.

37 g SALIYLYI AID.37 g SA = 1.7 X 10 - mol SA 138 g / mol SA If completely converted, you should get Stoichiometery t is 1 : 1 1.7 X 10 - mol x 180 g / mol = 3.

3 What is in reaction vessel finally? INIT FINAL mmol mmol ASPIRIN AETI ANYDRIDE SALIYLI AID AETI AID SULFURI AID Want to isolate aspirin from the excess acetic anhydride, sulfuric acid and acetic acid in the reaction vessel. 13 ASPIRIN is only slightly soluble in water (3.3mg/mL) We can add water to the reaction vessel to cause ASPIRIN to precipitate which we can then recover by filtration Some of the water will react with the excess AETI ANYDRIDE to form additional acetic acid. Rest of the water will form a solution of all of the final products, insofar as they are soluble. AETI AID SULFURI AID Soluble Soluble 14 Since ASPIRIN is slightly soluble in water (3.3 mg/ml), using a small amount of water should cause the loss of very little aspirin. e.g. If 50 ml is used, 50 ml X g/ml = g will be lost (out of a maximum of ~.5 g produced) WEVER, SALIYLI AID is even less soluble (. mg/ml) in water than ASPIRIN. Therefore, any un-reacted SALIYLI AID will precipitate with the ASPIRIN 15 ALULATIN F YIELD Suppose you use.37 g SALIYLYI AID.37 g SA = 1.7 X 10 - mol SA 138 g / mol SA If completely converted, you should get Stoichiometery t is 1 : X 10 - mol x 180 g / mol = 3.10 g ASA Suppose the actual weight of your (dry) product is.49 g actual.49 weight g % YIELD =100 x = 80.3 % Theoretical 3.10 g Yield 16 SUMMARY F PREDURE Record Data & bservations in Lab Notebook Use 15 ml ERLENMEYER FLASK Weigh SALIYLI AID on top loading balance Transfer AETI ANYDRIDE using DEWIK PIPET* - IN D lean, Dry eat in a SEURE water bath -use RING and EXTENSIN LAMP Wire gauze Extension lamp lamp holder Ring ook at 100 o for 0 minutes * Be sure you know how to use this pipet! If not, ask!

Add to reaction mixture in Specified amounts Filter using VAUUM FILTRATIN apparatus Wash with SMALL AMUNT of water Save SLID!

19 Measure total amount of water used for washing 0 PREAUTINS AETI ANYDRIDE: RRSIVE, FLAMMABLE & LARYMATR N.

4 Add to reaction mixture in Specified amounts Filter using VAUUM FILTRATIN apparatus Wash with SMALL AMUNT of water Save SLID! Need PRDUT for one more exercise Make sure liquid level in flask is below water in bath. 19 Measure total amount of water used for washing 0 PREAUTINS AETI ANYDRIDE: RRSIVE, FLAMMABLE & LARYMATR N. SULFURI AID: VERY RRSIVE FERRI LRIDE: RRSIVE SALIYLI AID & ASPIRIN: IRRITANTS DN'T INALE DUST ETANL: TXI AND FLAMMABLE DISPSE F EXESS REAGENTS IN WASTE NTAINERS 1 PERFRM QUALITATIVE TESTS 1. FERRI LRIDE TEST: olor is based on complex formed by the reaction of Fe 3 with Salicylic Acid to form 1 3 Fe Fe YELLW PURPLE PERFRM QUALITATIVE TESTS FERRI LRIDE TEST: The formation of a similar complex of Fe 3 with ASPIRIN is blocked by the 3 group. 3 Fe YELLW 3 X 3. EAT TEST - SMELL WIT ARE: 3 eat 3 Vinegar 3. MELTING PINT Dry a small amount (1/4 spatula-ful) of sample to determine the melting point of the 4 product. 4

5 ne more Test Infrared Analysis of Product What do we expect? = = 5 6 Please download two supplementary pages to SUSB-08 describing the procedure for determining the IR spectrum of the product. We will actually do the IR three weeks after the synthesis during SUSB-01 p Titration of your Synthesized Aspirin SAVE PRDUT FR TE WEEK AFTER NEXT'S EXERISE!!!!!!!!! ave data sheet initialed by TA and keep it until next week when you will reweigh the aspirin to get your YIELD NEXT WEEK olorimetric Iron in Multivitamins SUSB & SUPL 005 (on Web) Do Pre-Labs 7 8 5

3/14/ EXERCISES DEAL WITH YOUR ASPIRIN SYNTHESIS ph TITRATION / IR ANALYSIS. Cathode reduction. Anode oxidation

3/14/ EXERCISES DEAL WITH YOUR ASPIRIN SYNTHESIS ph TITRATION / IR ANALYSIS. Cathode reduction. Anode oxidation // ASPIRIN PURITY BY TITRATIN EXERISES DEAL WIT YUR ASPIRIN SYNTESIS p TITRATIN / IR ANALYSIS Last Update: // : PM SUSB- Synthesis of Aspirin acetic anhydride (AA) salicylic acid (SA) acetylsalicylic acid