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Aspirin Sythesis

Aspirin Sythesis

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Published by: kramnuj on May 23, 2010
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Experiment 9- Synthesis of Organic Compounds [Aspirin] Group 7, Chem 31.1, AB2,Atienza, Von Ervy; Alcantara, Mark JunSir Kevin SisonMay 24, 2010Abstract
Organic synthesis is a branch of chemical synthesis dealing with the production of organic compoundsby organic reactions. Aspirin is one of the most widely used analgesics since its invention in 1853. The mainobjective of this experiment is to produce acetylsalicylic acid via esterification. Aspirin (wanted product) andacetic acid (by product) were produced by reacting salicylic acid with acetic anhydride and catalyzed usingphosphoric acid. After the reaction, the products were recrystallized to enhance the purity of the resultingcompound. The product was then subjected to physical and chemical tests and the results obtained wererecorded. Several methods and information regarding organic reactions learned from previous experimentswere used.
Synthesis, Acetylsalicylic acid, Salicylic acid, Esterification, Recrystallization, Suction Filtration
Organic synthesis is a special branch of chemical synthesis and is concerned with theconstruction of organic compounds via organicreactions. Organic molecules can often contain ahigher level of complexity compared to purelyinorganic compounds, so the synthesis of organiccompounds has developed into one of the mostimportant aspects of organic chemistry. In theexperiment product synthesized was acetylsalicylicacid, known as aspirin.Acetylsalicylic acid, commonly known asaspirin is used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever,and as an anti-inflammatory medication. It isstructurally related to salicylic acid. As can be seenfrom the figure in the below, salicylic acid is both aphenol and an aromatic carboxylic acid. Comparingthe two compounds, it can be observed that aspirinis an ester, formed between acetic acid and thephenol hydroxyl group of salicylic acid. Thecarboxylic acid group makes aspirin mildly acidic.Its aromatic ring causes it to be quite insoluble inwater. Aspirin can be made soluble by forming itssodium salt. Salicylic acid reacts with aceticanhydride when phosphoric acid is present as acatalyst. Once the aspirin is synthesized, it can becollected by suction filtration while the more water soluble unreacted starting materials are washedaway in the aqueous solvent.
At this point theproduct is already isolated. To purify your productfurther, it is necessary to recrystallize the crudeaspirin. 
Production of Aspirin
Two grams of salicylic acid, 5 ml aceticanhydride and 5 drops of 85% phosphoric acidwere placed in a 125-mL Erlenmeyer flask andstirred. The flask was heated in a boiling water bathfor 5 minutes. Then the flask was removed from thebath and, while still hot, 2 ml of cold water wascautiously added to it. After completedecomposition, 40 ml of water was added to it, it isthen stirred until crystals have begun forming. Themixture was cooled in an ice bath to completerecrystallization. The product was collected bysuction filtration, washed with 5 ml of cold water and then dried. The product was recrystallized from35 ml of hot water and decolorized using activatedcarbon (if the product was colored). It was thendried and weighed.
Test for the Product
a.Physical Test: The appearance, texture,color, and odor of the product wererecorded. Its melting point was alsodetermined.
b.Chemical Test: A few crystals of theproduct were dissolved in 1 ml of methanolin a test tube. One drop of 1% ferricchloride solution was added to the solution.The procedure was repeated using salicylicacid and results for both tests wererecorded.
Physical test
Appearance – crystalline
Texture fine
Color – white
Odor – vinegar-like
Melting point 135 °C (275 °F)
Chemical Test (Ferric chloride test)
Reaction with aspirin – no reaction
Reaction with salicylic acid – formed violetsolution
Aspirin is produced as a product of an acid-catalyzed or esterification reaction between salicylicacid and acetic anhydride, where the alcohol groupfrom the salicylic acid reacts with an aceticanhydride causing a chemical reaction that turnssalicylic acid's hydroxyl group into an acetyl group,(R-OH → R-OCOCH3). This yields aspirin andacetic acid as a byproduct. Small amounts of phosphoric acid are often used as a catalyst. Aceticanhydride was used since it can be easilydecomposed by the addition of water and it canalso be reused.
Reaction PathwayReaction Mechanism
Aspirin is made from a reaction oesterification between salicylic acid with aceticanhydride which is catalyzed by an acid. Themechanism is as follows. The acid protonatesacetic anhydride. The proton from the acid attacksthe carboxyl oxygen which in turn pulls the twoelectrons in one of the pi bonds. It delocalizes theelectrons and spreads them out between the twooxygen atoms. Then, the delocalized electrons, inthe presence of the hydroxyl group, rearrange insuch a manner as to create temporary bondsbetween the two reactants. The proton from thehydroxyl group attacks the positively chargedcarbon (C attached to new OH group) of theanhydride. The oxygen of the
OH group of thesalicylic acid then becomes positively charged.After that, the positive charge shifts to the oxygenatom between the two carbon atoms of theanhydride as the hydrogen atom of the
OH groupsmakes a bond with the said oxygen of theanhydride. The electrons of the
OH group of theanhydride delocalizes since there is a positivelycharged oxygen atom that must be neutralized. Asthe electrons delocalizes, the bond between thecarbon and oxygen (in the center of the anhydride)breaks, producing a protonated aspirin and anacetic acid. Finally, the deprotonated acid, beingnegatively charged, acts as a nucleophile andabstract the hydrogen of the protonated aspirin.This results to the synthesis of acetylsalicylic acidand acetic acid. Phosphoric acid, a strong acid wasadded to catalyze the reaction or to act as afacilitator to the nucleophilic acetylation of thesalicylic acid. The H
from phosphoric acidprotonates the carbonyl oxygen of acetic anhydrideto make the carbonyl groups more susceptible tonucleophilic attack.Also, the mixture was subjected to heat in a water bath in which a temperature of no higher than 80°C
was maintained. This temperature is necessary tocontrol the aspirin crystal formation and its rate of reaction. If the temperature is raised any further beyond 80°C, the aspirin might get hydrolyzed andgo back to being a salicylic acid and aceticanhydride. Finally, cold water was added to themixture to separate aspirin from the rest of the other products. This was so to decompose excess aceticanhydride and dissolve acetic acid and phosphoricacid. The aspirin is insoluble in cold water, and canbe completely isolated by filtering the chilledreaction solution. Cold water was added to thesolution and not hot for hot water will cause anincrease in the temperature of the solution therebyconverting the crude product back to the reactants.Crystal formation (white needle-like) wasobserved after the mixture was allowed to cool in anice bath for further completion of the reaction.(
: if crystal formation was slow, reduce thevolume of the solution of scratch the surface of thebeaker. These scratches would act as site of crystalformation.) After which, recrystallization was doneto separate aspirin from other crude products whichare considered impurities.
Ferric Chloride Test
Ferric chloride test was done to check thepurity of the product. Ferric chloride reacts withphenol to form an iron-phenol complex which givesthe solution a purple color. Aspirin, when mixed withferric chloride solution, did not produce a violetsolution. However, impure acetyl salicylic acid andsalicylic acid reacts with ferric chloride solution toproduce a violet coloration. This is due to thepresence of the phenol group. Since salicylic acidcontains phenolic –OH, it is suspected to form aviolet solution since its –OH group will be reactingwith the ferric chloride solution. The impure aspirinalso gives a positive result for this test for the mainimpurity in the reaction will be excess salicylic acid,which co-precipitates with the aspirin if theprocedure is done too quickly.In order to create a purer aspirin, moreacetic anhydride could be added to the reaction.This would ensure that all of the salicylic acid willreact and that it was the limiting reactant. Theunreacted acetic anhydride can then be removed byadding cold water forming an acidic solution. After the acetic anhydride is removed, a purer solution of acetylsalicylic acid should be formed.
Guide Questions and Answers:
1.What is the reaction involved in thesynthesis of Aspirin?The reaction involved in the synthesis of aspirin isreaction between salicylic acid and aceticanhydride.→Esterification - the general name for achemical reaction in which two reactants (typicallyan alcohol and an acid) form an ester as thereaction product. Esters are common in organicchemistry and biological materials, and often have acharacteristic pleasant, fruity odor. This leads totheir extensive use in the fragrance and flavor industry.2.Write the reaction pathway and mechanismfor the synthesis of Aspirin.Pathway –Mechanism –
Explain why the recrystallization of Aspirinin the water should not be heated above80°C?

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