Intermediate Topic 855 of 1102 Organic Chemistry
Aspirin Synthesis
Acetylation of salicylic acid with acetic anhydride gives acetylsalicylic acid.
In-depth explanation of Aspirin Synthesis
Aspirin, acetylsalicylic acid, is made by acetylating salicylic acid with acetic anhydride in the presence of a small amount of acid catalyst such as sulfuric or phosphoric acid. The phenolic OH group of salicylic acid attacks the carbonyl of acetic anhydride, giving the ester and acetic acid as a by-product. The crude product is purified by recrystallization from ethanol and water, and its purity is checked by melting point, which is about 135 degrees Celsius for pure aspirin. A ferric chloride test shows whether unreacted salicylic acid remains.
Going deeper: Aspirin Synthesis
Key ideas: Salicylic acid reacts with acetic anhydride and a few drops of H2SO4 or H3PO4 at 50 to 60 C to give acetylsalicylic acid plus acetic acid; acetic anhydride is used because it is more reactive than acetic acid and the reaction is not reversible. Crude product is recrystallised from hot ethanol and water; purity is checked by melting point (135 C) and FeCl3 test, where free phenol gives violet colour.
Common mistakes and connections: Students use acetic acid, giving poor yield, or forget the purity test; a violet FeCl3 colour reveals unreacted salicylic acid. Another error is mis-calculating yield: 1 mol salicylic acid (138 g) gives 1 mol aspirin (180 g). Links to esterification of phenols, acid anhydrides and recrystallisation.
Visualization of Aspirin Synthesis
Salicylic acid plus acetic anhydride gives aspirin and acetic acid; molar masses allow yield calculations. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Residual salicylic acid, which contains a free phenol, gives a purple colour with iron(III) chloride, showing the product is impure.
Frequently asked questions about Aspirin Synthesis
What is Aspirin Synthesis?
Acetylation of salicylic acid with acetic anhydride gives acetylsalicylic acid.
Is Aspirin Synthesis a beginner, intermediate or advanced topic?
Aspirin Synthesis is a intermediate topic in Organic Chemistry. It builds on the vocabulary of beginner topics in this area.
What should I learn before Aspirin Synthesis?
Study these earlier topics in Organic Chemistry first: Terpenes, Steroids, Pharmaceuticals.
What comes after Aspirin Synthesis?
The next topics in Organic Chemistry are Dyes and Pigments and Petrochemicals.
Can I practise Aspirin Synthesis with quizzes?
Yes. The interactive lesson includes a self-check question on Aspirin Synthesis, and the Organic Chemistry quiz draws on every topic in this area.
Where Aspirin Synthesis fits in Organic Chemistry
Aspirin Synthesis is topic 127 of 148 in Organic Chemistry.