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

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

Aspirin – Synthesis Using acetic anhydride (ethanoic anhydride):

Aspirin – Synthesis Using acetyl chloride (ethanoyl chloride):

New techniques: Recrystallisation Reflux (optional) Chromatography

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

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!

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

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

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

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

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

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