Question

PRELAB EXERCISE EXPERIMENT 21 

Synthesis of Aspirin (Acetylsalicylic Acid) 

1. What is the purpose of sulfuric acid or phosphoric acid used in the acetylation reaction? Use equations to explain this purpose.

2.  The procedure calls for cautious addition of water to the reaction mixture while it is still hot. What purpose does the addition of water serve and why should the addition be done while the reaction mixture is hot? Provide an equation for the reaction involved.

3. Using the quantities of salicylic acid and acetic anhydride noted in the macroscale procedure and any other necessary data, calculate the theoretical yield in moles and grams of aspirin.

4. Describe how and why the ferric chloride test can be used to detect whether your reaction has gone to completion.

Answer 1

anhydride it cat Arswen y The purpose of sulfuric acid of phosphaic acid in the acetylation reaction is to act as a catalyet, In the esterification - heactim, it is the pheno group that reacts with -acetyl group of the acetic. to formo.aspris. The reacting catalysed in the presence of an acidic mediun. If the acid has water, then it then it deactivates acetic anhydride to water acetic acid. and the reaction does not proceed further. In the basic medium acetic anhydride forms basic acetate salt, and the reaction does not proceeds. Hence Concentrated itsa / catalyst. Then the reaction raptaly faward proceed in Isward disection with heat. PO as 1-O H + Y Conc. HS Heat Salicylic acred Acette anhydride Asprin Acetic and we is in-slight exces. The 22 Since are Cenverting Ralicylic acich to Apron Salihlic acid. must be limiting factor to get good yield economically so, acetic anhydride purpose of addition of water serves to hydrolyzed unused acetic anhydride to -acetic acid. and this reaction is fast when the mixture is still hot Stoichiometically water is -added slight excess of exces acetic al anhydriden Also the addition can be done cautiously, because the product mixture contains Concentrated Hiso which tome steam fome steam when water is added This may spit and the student may get acid burn. The weal method of water and sulfuric acid in

ولاد addition sulfuric acid is added to a large exces of water slowly from the side of the glass wall and acid burn, to avoid spit ey tto > 2 Hoy acetic acid excese acetic anhydride Loof In 32 From the reaction of formation of asprin, of Salicylic acid is converted to £ mole of asprin. >ge, the drificed yield in moles of Asprin & equivalent to noles of salicylic acid : The theoriticed yield is grams B81264 (MW) of esporin salicylic acid is producing 1.80.18 g (mw) of Asprin. 4) Here, the amount of salicy le acid must act as limiting reactant to produce aspain. economically, we have to ensure that all the salicylic acid the reaction used. Ferric ions form complex with saligeglic acid that is blue to violet in color. So, a small drop of product is required to be tested with the chloride solution in the test tube. absence of blue & violet color indicates that & wed and the all the saly salicylic acid reaction. is complete. is bees in سو The