Negligible Difference Found Between Value of Impure and Pure Aspirin Rf

The value of the impure aspirin RfP compared with pure aspirin RfA, the difference between these two substances was only 0.64 - 0.58 =0.06, which was less than 0. 01. Because the Rf value of a compound was constant on the same plate in condition of the temperature and solvent were kept the same and the closer the value of RfP and RfA the possible these two substances were the same. So the crude product had a very high purity, which was very close to the pure aspirin.

Discussion The sample was sent to John Innes Center to analyze the purity the week after.

The John Innes Center used the ion trap mass spec to operate with a liquid chromatography system. In order to analyze the sample, it was dissolved firstly and put into a tube in order to pump into the mass spec and because the aspirin was a single chemical the solution only needed to be trickled into it. Secondly, the solvent was dried directly due to the ions were already presented in an aqueous solution.

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After that, the ions were drawn into the mass spec by the electric field. The next step was to separate the ions by mass, this was where the ion trap occurred. The graph of the mass spectrum of aspirin was attached in Appendix A.

The big peak in the spectrum in the Appendix A was a fragment. The lower peak was expected 180 due to the molecular mass of pure aspirin was 180g/mol but it appeared 178. 9, which was a negative ion chromatography.

So there had a loss of H+. In this experiment the purity of the product may due to some errors, such as product was not transferred completely from the boiling tube to the conical flask when salicylic acid reacted with ethanoic anhydride.

Reference

1. http://chemistry. about. com/od/demonstrationsexperiments/ss/aspirin. htm (Feb. 2008)
2. Synthesis of Aspirin handout from Michele Raychaudhuri. (Feb. 2008) http://chemistry.about.com/od/demonstrationsexperiments/ss/aspirin.htm