Place 2.0 g of salicylic acid in a 125-ml conical flask. Add 4.0 mL d 1.08 g/mL;
ID: 636507 • Letter: P
Question
Place 2.0 g of salicylic acid in a 125-ml conical flask. Add 4.0 mL d 1.08 g/mL; 4.3 g) of acetic anhydride and 6-8 drops of 85% phosphoric acid. 3. Swirl the flask to mix all reagents, and place it in a 70 C water bath. 4, Remove the flask from the water bath and add 2 mL. of cold water drop- 5. Add 10 g of ice, and cool in an ice water bath until precipitation is com- 6. Isolate the crude product by vacuum filtration. Heat for about 10 minutes. wise, swirling the flask after each addition. plete (Z Recrystallize the product as follows: Place the crude aspirin in a 125-mL conical flask. and add 5-6 mL of ethanol. Heat the flask on a steam bath until all crystals dissolve, add 10 mL of water, and re-heat until the solu- tion is almost boiling. Remove the lask trom the steam bath, and let it cool to room temperature. 8. Cool in an ice-water bath until precipitation is complete and isolate the product by vacuum filtration. Determine the MP (literature value 138 C), and calculate the percent yield.Explanation / Answer
a. The purpose of phosphoric acid in the synthesis of aspirin is to increase the electrophilicity on the carbonyl carbon of acetic anhydride so that the O-atom of the OH group can readily attack the carbonyl carbon of acetic anhydride to achieve the corresponding acylation.
b. The purpose of adding water is to quench the acid by-products formed in the synthesis of aspirin.
c. The purpose of adding ice is to precipitate the crude aspirin (solid).
d. The purpose of adding ethanol is to dissolve the crude aspirin for the recrystallization of pure aspirin.