Question

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Mustrates treat all types of ilnesses. Background Aspirin is a prodrug of salicylic acid, the actual active drug. A compound related to salicylic acid, salicin, was first isolated from willow bark in the mid 1700's, but willow-bark extract was used by the andient Greeks as a treatment for pain and fever. Salicylic acid (and many related phenols) are very hard on your Ho stomach, but when esterified, as aspirin is, they are much better tolerated. Simple esters are rapidly cleaved in vivo (Latin, "in a living thing", in your blood etc.)to generate, in this case, the free phenol. Even though aspirin has been around longer than most other drugs, it remains an important drug, especially since daily low doses он HO OH OH Salicin (in Willow) metabolism Salicylic Acid Он are now known to prevent the recurrence of heart attacks. но OH Hас acetic anhydride 102 g/mol, 1.1 g/mL "сH, "Он Acetylsalicylic acid 180 gmol Он Salicylic acid 138 g/mol cat. H3PO4 Esterification reactions are formally a condensation reaction of a carboxylic acid and an alcohol or phenol. In the example here, acetic anhydride is used as an activated form of acetic add to make the reaction easier. Acetic anhydride is used as the solvent as well as a reactant, and a small amount of concentrated phosphoric (85%) is used to promote the reaction. Phosphoric acid is not formally a "strong acid", but it almost is, and is safer than the sometimes-used sulfuric adid.

Answer 1

Question 1:

Acetic anhydride which is one of the reactants is always taken in excess. As the reaction is an equilibrium reaction we need to drive the reaction in the forward direction.

Question 2:

The molecular weight of salicilic acid is 138.12 so 3.17 gm of starting material contains 22.95 mmol

The molecular weight of the product is 180.16 g/mol

expected product is 22.95 mmol =( 22.95 X 180.16)/1000 = 4.13 gm

Answer 4.13 gm

Question 3:

Phosphoric acid is added as a catalyst to the reaction. mechanism is attached

OH ОН Н;РОД OH Mechanism OH OH H OH H* ON O O

Question 4

The water is used to hydrolise the excess acetic anhydride to acetic acid. Acetic acid is soluble in water which can be easily removed by water wash from the final reaction product

Question 5:

At the end of the reaction in order to determine the amount of free salicylic acid present in the asprin its reacted with FeCl3 solution. where FeCl3 makes a complex with Salicilic acid to give a purple solution.

Even in commercial asprin if the tablet comes in contact with moisture it will hydrolise to its starting material salicylic acid and acetic acid. In that case also FeCl3 metod is used to determine the amount of free salicylic acid