Figures index : Introducing NMR to Biomedical Laboratory Scientists through a Laboratory Exercise; Synthesis, Structure Determination and Quantization of Aspirin by Employing an 1H-NMR Bench Top Instrument : Science and Education Publishing

Figures index

World Journal of Chemical Education. 2022, 10(1), 8-19 doi:10.12691/wjce-10-1-2

Scheme 1. The Formation of acetylsalicylic acid (ASA) from salicylic acid (SA) and acetic acid anhydride

Figure 1. ¹H-NMR of ASA in d-chloroform, recorded with a 60 MHz instrument from Magritek. The resonance at 11.89 ppm is from the acid proton, the resonance around 7.5 ppm are from the aromatic protons and the resonance at 2.43 is from the methyl group

Figure 2. Spectrum 1 shows the ¹H-NMR spectra of SA, with the combined resonance from the alcohol group and the water signal at 5.29 ppm, and the resonances that originate from the aromatic hydrogen atoms in the chemical shift region of 6.73-7.95 ppm. Spectrum 2 shows the ¹H-NMR spectra of phosphoric acid catalyst (85% water) with the resonance from water at 5.73 ppm. Spectrum 3 shows the ¹H-NMR spectra of acetic acid anhydride with a resonance at 2.19 ppm from the methyl groups present. Minor impurities at 2.02 and 1.98 ppm and satellite signals from the methyl group are observable in a cut-out spectra of acetic acid anhydride in Supporting Material (figure 4). Spectrum 4 shows the ¹H-NMR spectrum of 99% d-methanol with TMS at 0.00 ppm. The resonance at 3.31 ppm originates from the non-deuterated methyl group and the resonance at 4.83 ppm is appearing from the alcohol group in methanol and water.

Figure 3. Spectrum top to bottom, show the ¹H-NMR spectra of SA (top), the crude product ASA (middle) and the final product, ASA (bottom). The cutout of the ¹H-NMR spectra includes the regions where we find the methyl group (1.6-3.00 ppm) and the aromatic region (6.6-8.5 ppm)

Figure 4. The ¹H-NMR spectrum of the final product of ASA showing the resonances with integrals that were used for quantification of the yield. The integral of the methyl resonance (2.88 ppm) was set to 3.00 and the resonances in the aromatic chemical shift region showed 4.00. In addition, the area of the methyl group in methanol (3.31 ppm, 0.28) and the water signal (4.87 ppm, 1.10) are shown

Figure S4. The ¹H-NMR spectra of acetic acid anhydride in d-methanol with 0.03 % TMS. The cutout spectra show the area of 1-5 ppm and includes resonances from impurities, solvent, and satellites

Figure S5. The¹H-NMR spectra of phosphoric acid (85%) in d-methanol with 0.03% TMS. No impurities were found

Figure S6. The¹H-NMR spectra of the crude product acetylsalicylicacid in d-methanol with 0.03% TMS

Figure S7. The ¹H-NMR spectrum of the final product, acetylsalicylicacid in d-methanol with 0.03% TMS