## 3 Results and Discussion
### Synthesis Development and Optimization
#### 3.1.2 GC-MS and NMR Analysis  
In order to confirm the ester structures and the degree of purity observed in the ATR-IR for MEPA produced with 5:1 excess of MeOH and 5 h heating time, GC-MS and NMR spectra were recorded for the commercial MEPA from Sigma Aldrich and the self-produced MEPA, and compared. Regarding GC, both commercial MEPA and PA were analyzed, and retention times of 13.880 min and 14.226 min, respectively, were observed, confirming that PA impurities would be visible and the peak well separated in the self-produced MEPA chromatogram. This would allow for identification of residual unreacted acid and impurities. Afterwards, MEPA produced in the laboratory with 5 h heating and 5:1 excess of MeOH was analyzed on the same column, and the resulting chromatogram showed that the Ester produced had a retention time of 13.883 min as expected and purity estimated around 98%. Following GC characterization, a mass spectra of the self-produced MEPA was registered to further confirm the molecular structure (Figure 5). The peak from the molecular ion was observed at 270.2 \(m/z\) with high abundance, as reported in literature for linear long-chained alkane systems [24]. From there, the cleavage of the methanol group was visible from the peak at 239 \(m/z\), corresponding to a loss of 31 of the methyl molecule (15 \(m/z\)) and alcohol atom (16 \(m/z\)). Side resonances at 241 and 242 are thought to be due to resonance forms of the methoxy group. From 227 \(m/z\) to 101 \(m/z\) several peaks distanced 14 \(m/z\) each (227, 213, 199, 185, 171, 157, 143, 129, 115, 101) show the progressive breaking of the aliphatic chain by loss of -CH\({}_{2}\) from the acid side. Hence, the overall structure of MEPA was confirmed. Figure 4: Investigation on the influence of heating time on the ester formation. PA impurities are seen decreasing and ester yield is increased for increased heating time, with a “plateau” reached after 5 h heating time. With regards to NMR results, the spectra of self-produced MEPA with 1:5 acid:alcohol ratio and 5 h heating time was fully characterized, and the structure and purity confirmed. At 3.66 ppm (a), a singlet arising from the protons of the deshielded methyl group -CH\({}_{3}\), which resonated as a singlet due to lack of neighbouring protons, was visible. The normalized area of the peak was assigned a value of 3 to correctly calculate the amount of protons in the spectra recorded. At 2.28-2.32 ppm (b), a triplet with area 2 from the -CH\({}_{2}\) in \(\alpha\)-position to the carbonyl, and a multiplet between 1.58-1.65 ppm (c) with area 2 from the -CH\({}_{2}\) in \(\beta\)-position to the carbonyl was seen. The -CH\({}_{2}\) in \(\alpha\)-position resonated as a triplet due to proximity with the two protons from the the -CH\({}_{2}\) in \(\beta\)-position, and appeared to be more de-shielded due to the neighboring carbonyl group. An intense peak corresponding to 24 hydrogen atoms resonating together was observed around 1.26 ppm (d), and was assigned to the long aliphatic chain from the fatty acid. Lastly, the -CH\({}_{3}\) group at the end of the aliphatic chain appeared as a triplet with integrated area of 3 at 0.86-0.90 ppm (e) due to strong shielding effect and distance from the carbonyl group and electro-withdrawing elements. By summing the integrated areas values of the peaks assigned, a total of 34 hydrogens were obtained, which matched the elemental composition C\({}_{17}\)H\({}_{34}\)O\({}_{2}\) of MEPA (Figure 6). No impurities were observed, thus confirming the results obtained from GC-MS spectral data. Therefore, it could be concluded that commercial MEPA had been successfully replicated in the laboratory with high purity, and new esters could be produced through the Fischer esterification procedure reported above. Figure 5: Mass chromatogram of MEPA produced in the laboratory.