Synthesis of Aspirin pt 2 Flashcards
(24 cards)
synthesise acetylsalicylic acid (aspirin) by esterification of what
salicylic acid
The reaction of salicylic acid with ethanoic anhydride is what type
nucleophilic addition-elimination reaction.
what happens in the reaction
The carbonyl carbon of ethanoic anhydride undergoes nucleophilic attack by the phenolic hydroxyl group of salicylic acid.
Ethanoic anhydride is a derivative of ethanoic acid (acetic acid).
salicylic acid + ethanoic anhydride <-H2SO4->
acetylsalicylic acid + ethanoic acid
carboxylic acid derivatives react with water (a nucleophile) to
regenerate the parent carboxylic acid
alcohols and phenols can react as nucleophiles how?
with acid anhydrides and acid chlorides to produce esters.
The reaction of a phenol with ethanoic anhydride is an example of?
an acylation. An acyl group is R-C(O)-.
Molecular formula for salicylic acid
C7H6O3
(1) Place salicylic acid (0.015 mol) into
a 100 mL conical flask
(2) In the fume cupboard, carefully add ethanoic anhydride (5.0 mL). and do what
Swirl the reaction cautiously, pointing the flask away from you in the fume cupboard. AFTER 1 min VERY CAREFULLY add 5 drops of concentrated H2SO4, ONE DROP AT A TIME, swirling the
flask to mix thoroughly after the addition of EACH drop. Ensure you add the reagents in this order.
Sulphuric acid (H2SO4) is corrosive and can cause
severe burns. In case of contact with eyes or skin, rinse immediately with copious amounts of water
(3) Gently swirl the reaction mixture until
the salicylic acid begins to dissolve.
(4) Heat the reaction mixture in a water bath in the fume cupboard for 5-10 minutes while
constantly swirling the conical flask. what is the by product
ethanoic acid which can have quite a strong and pungent odour.
(5) Allow the reaction mixture to cool to room temperature. what happens as a result?
(6) The crude product should begin to crystallise from the reaction mixture. If no product
begins to crystallise, scratch the walls of the flask with a glass rod and cool the reaction
mixture slightly using an ice bath until crystallisation has occurred. (Sometimes
scratching the flask with a glass rod can help initiate crystallisation).
(7) Continue cooling the reaction mixture and slowly add water (50 mL). DO NOT add the
water before what
before crystallisation has started.
(8) how do we isolate the crude product
by vacuum filtration on a Büchner funnel.
what do we do with the crude product
(10) Slowly add saturated NaHCO3 (approximately 25 mL) to the beaker containing the
crude product. Gently swirl the solution. Stir the solution until all signs of a reaction
have ceased (listen and check pH). Some insoluble material may remain. Filter the
solution by vacuum filtration on a Büchner funnel into a clean rinsed flask.
(11) Carefully and slowly pour the filtrate into 25% HCl solution (approximately 15.0 mL)
previously placed into a clean 250 mL conical flask (some foaming will occur). Ensure
the solution is acidic using pH paper and cool the mixture using an ice bath.
CAUTION: 25% HCl is corrosive and can cause burns. In case of contact with eyes or skin,
rinse immediately with copious amounts of water and inform a demonstrator.
(12) Isolate the precipitated product by vacuum filtration on a Büchner funnel. Rinse the
product once with minimal ice-cold water, then collect the product and dry in the oven.
Record the mass of your product.
Into each of three test tubes containing 5.0 mL of water dissolve a few crystals of one
of each of the following: salicylic acid, your crude product and your precipitated product.
Add 1-2 drops of 1% iron (III) chloride solution to each tube and record your observations in the table below. what are the test results
phenol - clear, pale purple solution
salicylic acid - Pale purple solution expected
your crude product - Maybe faint or pale purple
your precipitated product - No color change or very slight yellowish tinge
why does phenol give a clear, pale purple solution
Phenol has a free OH group → reacts with Fe³⁺ to form a colored complex.
why does salicylic acid give a pale purple solution expected
→ Has a free phenol group → reacts with FeCl₃ → purple complex.
why does the crude product probably give a faint or pale purple
→ Contains mostly aspirin, but still some unreacted salicylic acid, so some phenol groups → weak positive test.
why does the precipitated product of pure aspirin give no colour change
→ Ideally contains only acetylsalicylic acid, which does not have a free phenol group → no reaction with FeCl₃.
mechanism for the reaction
