Synthesis of Aspirin Experiment Six

Therapeutic uses & contraindication Aspirin act as an analgesic, antipyretic, Anti-inflammatory also inhibit platelet aggregation & prolongs bleeding time, because of its effect on G.I.T it is contraindicated in peptic ulcer, in this case we use paracetamol . Aspirin is not given to children because is may cause raye’s syndrome. Therapeutic uses & contraindication

Aspirin (acetyl salicylic acid) is a widely used drug in modern society. Salicylic acid which is a constituent of certain plant is itself an analgesic & was originally administered as sodium salicylate, since salicylic acid has an irritating effect on the stomach, chemists thought of a modification which would retain its properties while decreasing the adverse side effects. Conversion to the ester satisfied this requirement& aspirin proved to be as effective as sodium salicylate without the irritation of phenolic compound. Aspirin however hydrolyzed to salicylic acid in the alkaline media of the intestine by esterase enzyme. Introduction :

Esterification (nucleophilic acyl substitution)

Aspirin is prepared in our lab by acetylating of salicylic acid with acetic anhydride in the presence of H2SO4 as catalyst. Esterification

Because of its low solubility in H2O it is isolated from the reaction mixture by precipitation with H2O, we pour cold water to hydrolyze acetic anhydride & complete the ppt of aspirin. Heat is produced in this reaction (exothermic reaction) Aspirin recrystallized from benzene, even though aspirin is insoluble in cold water & soluble in hot water but it is not a suitable recrystallizing solvent for Aspirin because aspirin undergoes partial hydrolysis to salicylic acid & acetic acid in hot water.

Identification of aspirin

1-Place 3 gm of salicylic acid in 100 ml E. f 1-Place 3 gm of salicylic acid in 100 ml E.f. and add with constant stirring 6 ml of acetic anhydride followed by 1 ml of conc. H2SO 2- Stir the mixture gently observing the rise in temp. to 70-80 oC. While the salicylic acid dissolves, after 15 minutes the solution cools by it self and a solid mass of aspirin forms 3-Pour 35 ml of ice-cold water over the contents of the flask to hydrolyze excess acetic anhydride and to complete the ppt of aspirin 4- Collect the crude aspirin using a Buchner funnel and wash with ice-cold water, air-dry the product and calculate the yield 5- Perform FeCl3 test on produced aspirin Procedure:

Identification test of aspirin: Ferric chloride test; The presence of phenolic group in a compound is indicated by the formation of violet iron complex when treated with ferric chloride solution Aspirin ------------► give –ve result with FeCl3 due to absence of phenolic group Salicylic acid--------► + ve result Identification test of aspirin:

Calculation:

Conclusion excellent 90-100% Very good 80-90% good 70-80% fair 60-70% poor 40-60% bad Below 40% Conclusion

Synthesis of aspirin beginning with benzene

Think What is le chatelier’s principle? Mention methods in formulation or synthesis to overcome the problem of irritability of salicylic acid to stomach? Why cold water is used in Aspirin washing? What are the methods which are used to assesse aspirin purity? List the steps used for recrystallization. What is the difference between vacuum filtration & gravity filtration? Think