Green Aspirin Synthesis and Purity Testing

ISEF Category: Chemistry

Subcategory: Organic Chemistry  ·  Difficulty: Intermediate  ·  Setup: School Lab  ·  Time: 1 to 2 Months

The Hook

Aspirin is one of the most familiar drugs in the world, but the way you make it can change a lot. In this project, you can test whether citric acid can help replace harsher reagents in an aspirin synthesis. You also get to compare product quality, not just whether crystals formed. That makes this a strong chemistry project with a real sustainability angle.

What Is It?

Aspirin is made by turning salicylic acid into acetylsalicylic acid. In simple terms, you attach a small chemical group to salicylic acid so the final molecule behaves differently. The usual school-lab route uses acetic anhydride. This project asks whether acetic acid, with citric acid as a catalyst, can drive the same kind of reaction under reflux, which means heating a mixture so vapor condenses and returns to the flask.

Think of it like trying to build a model with a stubborn snap fit. The catalyst helps the pieces connect faster and more often. Your job is to see how well that greener route works, then measure how pure the aspirin is. Melting point tells you how sharp the product is, and FT-IR, short for Fourier-transform infrared spectroscopy, can help confirm which bonds are present.

Why This Is a Good Topic

This is a strong science fair topic because you can change one variable at a time, then measure both yield and purity. It connects to greener chemistry, which matters in real labs and industry. You can compare reaction conditions, catalyst amount, or heating setup without needing a university lab. You also get to practice data analysis, error checking, and spectrum interpretation.

Research Questions

• How does citric acid concentration affect aspirin yield in an acetic-acid-based synthesis?
• What is the effect of reflux setup on the melting point range of the product?
• Does longer heating improve conversion of salicylic acid to aspirin under the same starting conditions?
• To what extent does the purity of the product change when you vary the drying step before melting point measurement?
• Which catalyst amount gives the best balance of yield and melting point sharpness in this synthesis?
• How does the FT-IR spectrum of the product compare with the spectrum predicted by DFT calculations?

Basic Materials

• Salicylic acid reagent.
• Glacial or concentrated acetic acid, handled only in a supervised school lab.
• Citric acid catalyst.
• School glassware for reflux setup.
• Hot plate or heating mantle.
• Condenser and clamps.
• Thermometer or temperature probe.
• Filtration funnel and filter paper.
• Watch glasses or weighing boats.
• Digital balance with 0.01 g resolution.
• Melting point apparatus.
• FT-IR access through a school lab or shared instrument facility.
• Safety goggles, lab coat, and chemical-resistant gloves.

Advanced Materials

• Salicylic acid reagent.
• Acetic acid and catalyst set for comparative trials.
• Reflux apparatus with round-bottom flask, condenser, and heating control.
• Vacuum filtration setup.
• Melting point apparatus.
• FT-IR spectrometer.
• DFT-capable software or access to calculated spectra from published data.
• Analytical balance.
• NMR access for product confirmation if available.
• PPE and a fume hood.

Software & Tools

• Python: Organizes yield data, melting point results, and FT-IR peak comparisons.
• ImageJ: Helps if you photograph TLC plates or reaction samples for visual comparison.
• Excel: Tracks trial conditions and makes graphs for yield and purity trends.
• ChemDraw: Lets you draw the reaction and label key functional groups.
• Avogadro: Supports simple molecular modeling and DFT-related structure viewing.

Experiment Steps

1. Define the exact reaction variable you will change first, such as catalyst amount, heating setup, or reaction time.
2. Choose the response variables you will measure, then decide how yield, melting point range, and spectral matches will be recorded.
3. Plan a control synthesis that uses a known baseline route so you have a fair comparison point.
4. Design a cleanup and drying plan that stays the same for every trial so product purity does not get mixed up with workup differences.
5. Build a data table before you start, including trial labels, observations, and any instrument outputs you will need to compare.
6. Decide how you will compare your product spectrum with the predicted DFT spectrum and what counts as a good match.

Common Pitfalls

• Using an unsealed or poorly cooled reflux setup, which lets acetic acid escape and lowers reaction efficiency.
• Comparing products that were dried for different amounts of time, which can widen the melting point range and fake a purity problem.
• Changing more than one condition at once, which makes it hard to tell whether catalyst, heat, or setup caused the result.
• Reading FT-IR peaks without a clean control spectrum, which can lead you to assign the wrong functional group changes.
• Treating a low yield as proof that the chemistry failed, when poor crystallization or transfer loss may be the real cause.

What Makes This Competitive

A stronger project would not just ask whether aspirin forms. It would compare several green-chemistry conditions with careful controls and repeat trials. You could strengthen the analysis by pairing melting point data with FT-IR peak matching, percent yield, and a statistical test across conditions. A project gets much stronger when you explain why one route works better and back that claim with clean data.

Project Variations

• Compare citric acid with another food-safe acid catalyst and see which gives the sharper melting point range.
• Test different starting salicylic acid sources, such as tablet powder versus pure reagent, to study impurity effects.
• Use FT-IR peak matching alone, then compare your conclusions with melting point data to see which method is more sensitive.

Learn More

• PubChem: Look up salicylic acid, aspirin, acetic acid, and citric acid for structures, properties, and safety details in the NIH database.
• NIST Chemistry WebBook: Search for thermal and spectral reference data that can help you compare expected properties.
• PubMed: Search for review articles on aspirin synthesis, green chemistry routes, and analytical confirmation methods.
• MIT OpenCourseWare: Look for organic chemistry lectures on esterification, spectroscopy, and reaction mechanisms.
• Royal Society of Chemistry Education: Find free teaching articles and lab background on aspirin preparation and infrared spectroscopy.