Question

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In the synthesis of aspirin lab when 5 grams of salicylic acid is used

how much of ACETIC acid in mL should be used

how many drops of Phosphoric acid should be used?

How long should the mixture be heated?

What tempture should it be heated at?

How much DI water should be added (one mL at a time)?

Answer 1

In ths synthesis of aspirin,

for 5 gram of salicylic acid, 3 equevalent acetic acid can be use. that is 6 to 7 ml. but with acetic acid, the reaction is not favourable. because we are using a strong acid as catalyst for the preparation of aspirin (ester formation). when we use acetic acid, there is a chance of formation of water molecule in the reaction mixture. this will cause the back reaction ( hydrolysis of ester) in the presence of the strong acid catalyst, so the yield will be low. so better to use acetic anhydride (12.5 ml) instead of acetic acid.

10 drops of Phosphoric acid can be used

10 to 15 min of heating by using a boiled water bath is good

Heating by boiled water bath is prefered (95-98 0C)

50 ml of DI water can be added after completion of the reaction and cool to room temperature. the aspirine crystals will start to form. chill the mass filter it and wash with chilled water (10 ml).