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Preparation and Purification of Acetylsalicylic Acid

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Preparation and Purification of Acetylsalicylic Acid
Preparation and purification of acetylsalicylic acid

Results and Data treatment (A) Preparation of aspirin i) Details about the reactants
Reaction of the acetylation of salicylic acid is following

From the balanced reaction above, it can be seen that the stoichiometry between salicylic acid and acetic anhydride is 1: 1.
In this experiment, 21.7mmol of salicylic acid was used to react 6.0mL of acetic anhydride and salicylic acid was limiting reagent.
The expected amount of salicylic acid used:
21.7/1000*138.12=2.99g=3.0g
The expected amount of acetic anhydride:
21.7/1000*102.09=2.215g=2.2g
Reactants | Formula/MWt | Min. Mole Ratio | Expected amount used | Expected vol./density used | Actual amount used | Actual vol./density used | Actual mole | Actual mole ratio | Salicylic acid | C9H8O4138.12gmol-1 | 1 | 3.0g | - | 2.97g | - | 21.5mmol | 1 | Acetic anhydride | (CH3CO)2O102.09gmol-1 | 1 | 2.2g | 2.06mL/1.08gmL | 6.48g | 6.00mL/1.08gmL | 63.5mmol | 2.95 | Phosphoric acid | H3PO4 | catalyst | - | - | 5 drops | - | - | - |

ii) Yield of crude product and purified product Preparation of aspirin | Purification of aspirin | Mass of filter paper | 1.30g | Mass of filter paper | 1.17g | Mass of filter paper+ crude product | 6.13g | Mass of filter paper+ purified aspirin | 4.36g | Mass of filter paper+ residue | 1.33g | Mass of purified aspirin | 4.36-1.17=3.2g | Mass of crude product | 6.13-1.33=4.8g | | |

iii) Theoretical yield of aspirin
2.97/138.12*180.16=3.9g

iv) Percentage yield of the product
3.19/3.9*100%=82%

(B) Characterisation of aspirin I. Melting Point
The melting point of the purified product is 125.4-128.3oC which is lower than the authentic values.

II. Infrared Spectrum
The IR spectrum of the purified product is below.

According the IR spectrum table cited from internet, few peaks standing for different bonding are found. Wavenumber cm-1 | Appearance | Inference | 2871.95


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