1. Which method of aspirin synthesis gives the greatest yield, purity and stability?

2. = 95% Aspirin – Synthesis Synthesis using ethanoic anhydride
Synthesis using ethanoyl chloride
(optional)Synthesis from natural chemical
= 95%

3. Aspirin – Synthesis
Using acetic anhydride (ethanoic anhydride):

4. Aspirin – Synthesis
Using acetyl chloride (ethanoyl chloride):

5. New techniques:
Recrystallisation
Reflux (optional)
Chromatography

6. Aspirin –Analysis Qualitative analysis of purity: Chromatography
Melting point
Quantitative analysis:
Back titration
Iron(III) chloride – colorimetry
(optional) Comparison to pharmaceutical grade aspirin
Potential University of York visit – N.M.R analysis
Samples submitted to Loughborough Uni for chromatography and I.R. analysis

7. Aspirin – Back Titration
Theory – The aspirin is difficult to titrate directly, it is weakly acidic and some equilibria complicate direct measurement
The aspirin is instead reacted with an excess of base and then the base that is left over is titrated.
By considering how much base is left over you can work out how much aspirin was there in the first place!

8. Aspirin – Colorimetry
Theory – The amount of light a coloured compound absorbs is related to the amount of the compound present.
The main impurity in aspirin is the salicylic acid – this compound will bond to iron in alkaline solution.
By measuring the amount of salcylate ion the amount of salicylic acid can be determined as a measure of purity of your aspirin product

9. This is a blue(ish) compound formed with Iron(III)
This is the impurity in alkaline solution

10. Calibration Curve
Make up solutions of known concentration and measure absorbance
Plot calibration curve
Then measure absorbance of your own sample and determine concentration

11. Aspirin – Stability
The synthesised aspirin is subjected to a continuous stream of steam
The amount of salicylic produced after this is analysed using colorimetry

12. Aspirin – Planning
Read the articles provided to get some background about aspirin and understand the synthesis of it
Read the practical methods and familiarise yourself with the techniques
Have a think about how complex you want your project to be

13. Aspirin – Risk Assessment
The following chemicals need to be carefully risk assessed:
2-hydroxybenzoic acid
Ethanoic anhydride
(Pyridine)
Ethanoyl chloride
Sodium hydroxide 2M