ACETYLSALICYLIC ACID

OBJECTIVE

The purpose of this experiment is to was to prepared acetylsalicylic acid

INTRODUCTION

  +                   +

(salysilic acid)       (acetic anhydride)                    (acetysalicylic acid)       (acetic acid)

            From the chemical equation the acetysalicylic acid can be prepared by the reaction between salysilic acid and acetic anhydride.In this rection , the hydroxyl group from benzene ring was reacted with acetic acid to form ester functional group , so this reaction is referred as esterification reaction.Concentrated sulphuric acid is the catalyst in this experiment which make the reaction is complete.Crystallization process was required in this experiment because there is some impurities such as unreacted salysilic acid and acetic anhydrate presence with the acetysalicylic acid.So the process is needed to makesure there is ni impurities in the last product.

            Thus the separation of acetysalisilic acid from other materials was accomplished and the product also washed with distilled water after the crystal was formed because the water can decrease the solubity of acetysalicylic acid and dissolves the left impurities.

            Recrystallization process was formed to more purify the product.Methanol was used as solvent in order to prevent the decomposition of salicylic acid because water can make aspirin partially decompose while heating the solution.If the aspirin decompose , we cannot get the correct result for this experiment.The impurities which is salicylic acid will decompose from incomplete reaction with acetic anhydrate, so after recrystallization, there is no impurities in the last product.

RESULT AND OBSERVATION

Mass of salicyclic acid = 2.0011 g

Mass of filter paper = 0.5595 g

Mass of watch glass = 59.3232 g

Total mass = 64.9764 g – 59.3232 g – 0.5595 g

                   =5.0937 g

Mass after recrytallization = 4.4081 g

Mass of crude product =5.0937 g - 4.4081 g

                                     = 0.6856 g

C₇H₆O₃ + C₄H₆O₃               C₉H₈O₄ + CH₃COOH

Molar mass of salicylic acid = 138.121 g/mol

Mass of salicylic acid = 2.0011 g

Number of mole of salicylic acid = 2.0011 g / 138 .121

                                                    = 0.001449mol

1 mol of salicyclic acid react with 1 mol of acetic anhydride to produce 1 mol of acetylsalicylic acid

0.001449 mol of salicyclic acid react with 0.001449 mol of acetic anhydride to produce 0.001449  mol of acetylsalicylic acid

Theoretical yield of acetylsalicyclic acid = 0.001449 mol x 180.157

                                                               = 2.610 g

Percentage yield of acetylsalicyclic acid = (0.6856 g / 2.610 g) x 100%

                                                                = 26.29%

Result for ferric chloride test

Test tube A = Colourless solution change to purple solution in colour

Test tube b = colourless solution change to violet solution in colour

Test tube c = There is no change in colour which is colourless solution.

DISCUSSION

            This experiment was performed to prepared acetylsalicyclic acid . As we know acetylsalicyclic acid is a drug that is widely used as an antipyretic agent that is to reduce fever ,as an analgesic agent which is to reduce pain and as an anti-inflammatory.Chemically acetylsalicyclic acid is an ester.Esters are the products of the reaction of acids with alcohols , as shown as from the balance chemical equation below :

+            +

(salysilic acid)       (acetic anhydride)                    (acetysalicylic acid)       (acetic acid)

            We  use an acetic anhydride instead of an acetic acid because the anhydride react with water to form acetic acid. There is the formula to calculate the theoretical yield of the acetysalicyclic acid :

            From the result the theoretical yield for this experiment is 2.610 g while the actual yield is 0.6856 g .the percentage yield we get is 26.29%.There is large different percentage yield of this experiment to 100%.There maybe error occur when the temperature required for on the step of the experiment that is 50˚C , we do not maintained the temperature so the reaction do not completely react.

            There also may occur error when we cut the filter paper , the pen ink may contaminated our product so we need to make sure that we cut all the filter paper which contained the ink.While we are doing experiment we should take care of some precaution.As we know the acetic anhydride can causes severe burns and harmful to inhaled.We should wear gloves when handling the acetic anhydride solution and handle it in the fume board carefully.

The next experiment which is test of ferric chloride purity. From the result that we obtained from the experiment :

Test tube A = Colourless solution change to purple solution in colour

Test tube b = colourless solution change to violet solution in colour

Test tube c = There is no change in colour which is colourless solution.

            Ferric chloride do not react with aspirin . It will react with salicylic  acid which is used to synthesize aspirin . In this light , adding an aqueous ferric chloride solution into a sample of aspirin is a better way to see if there any unreacted salicylic acid which is not react .A purple colour indicate the unreacted salicylic acid , so a purple colour should not exhibit any color change. For test tube A and B salicylic acid was added  so the ferric chloride was reacted with the salicylic acid added while in the test tube C salisylic acid doesn’t added to the test.So there is no impurities exists in the product of the experiment.

CONCLUSION

            Acetylsalicylic acid was prepared . The actual yield we obtained from the experiment is 0.6856 g while the theoretical yield we calculated is 2.610 g.The percentage yield is 26.29%.From the ferric chloride test , we can conclude that there is no impurities in the product of the experiment.