The Fischer Esterification Process to Synthesize an Ester - Admission/Application Essay Example

? Lab Report College This experiment uses the Fischer esterification process to synthesize an ester (ethyl propionate). To achieve this, propionic acid is reacted with ethanol in the presence of a certain catalyst, which may be H2SO4 or equivalent. The purity of the ethyl produced Ethyl propionate is identified by use of 13C NMR, boiling point 1H NMR spectra and through its IR. The IR spectrum of the resulting Ethyl propionate had the following bonds C=0,-C-H, and R-O-‘R (ether). Moreover, the carbon NMR spectrum of the resulting ester had the same carbons in the structure of the produced Ethyl propionate. The H-NMR spectrum in the experiment indicated to have the same number of protons and retained the same position on the structure of the resulting Ethyl propionate. The result produced by the H-NMR and C-NMR was augmented with the results in the HMQC and COSY analysis. As a result, the yield was 62.23% of the ethyl propionate. After undertaking the spectroscopic analysis, it was observed that the product obtained was actually the intended Ethyl propionate, which suggests that the entire experiment was a success. Lab Report Results and discussion: Fischer esterification is obtained through a process involving nucleophilic substitution. The principle behind this action is that the carbonyl carbon has electrophilic properties while still having the dual nature of a nucleophilic element, similar to alcohols. The main purpose of the sulfuric acid catalyst is acting as a dehydrating agent in the experiment. The principle of water removal is through detachment of H-ions from the alcohol while the OH ion detaches from the propionic acid. The catalyst also prohibits any reverse reaction from occurring during the experiment; it is possible for reformation of the reactants to occur. On the other hand, ethanol’s role is to neutralize both the acids and increasing the Ethyl propionate produced in the experiment. Such yield increases by facilitating separation of the products in the mixture used in the reaction. The principle behind this action is that when the product is left in the mixture, the polarity of the washes aqueous layer increases, which facilitates better separation. Figure 2 below indicates the reaction process between ethanol and propanoic acid. Figure 1 Reaction between ethanol and propanoic acid. The electrophilic nature of the carbonyl carbon is as a result of the proton transferred from the acid to the carbonyl oxygen, which induces an attack from the ethanol’s nucleophile (oxygen atom). Moreover, an activated complex forms due to the action of the H-ion transferred from the oxonium ion to the second alcohol molecule. When the hrodoxyl groups in the activated complex protonate, they give an extra oxonium ion. Finally, the ester forms from the dehydration of the oxonium molecule after which deprotonation has to occur3. Figure 2 Mechanism of acid catalyzed Fischer esterification Simple distillation is a process through which mixtures are separated based on the difference in boiling points of the individual elements making the mixture. This may be achieved by first heating the mixture into a gas phase, and condensing the produced gases into liquid in several stages. However, the products produced under this method are impure; it is not possible to use this method for separating a mixture whose elements have close boiling points. Using Raoult’s law, it is possible to calculate and determine the composition of the vapor collected, which would be the same as the base mixer at a certain temperature and pressure. However, when two or more liquids have widely varying boiling points, in most cases, the temperatures of the vapor produced vary with similar margins such that it is possible to neglect any impurities from other elements in the mixture. Rault’s law would not be applicable in such a case, and the distillation products are considered pure. In using 1H NMR, IR, 13 NMR and GC/MS it is possible to determine the structure of the resulting Ethyl propionate. The molecular structure of the product is C2H5(C2H5COO). Considering that the carbon atoms have an odd number (5), it would be possible to have a mass charge ratio of an odd number. Figure 4 indicates the mass spectrum with a mass range below 103, with a series of ions dominating the mass spectrum (m/z = 57.1, 73, 74, 75, and 102). Figure 3 Ethyl propionate mass spectrum The molecular ion peak ([M]+) for the ester is obtained at a ratio (m/z) of 102 as seen in figure 4 Figure 5 shows the IR spectrum of Ethyl propionate. Figure 4 IR spectrum of the produced ester. An absorption peak at 1734cm-1 corresponds to a C=O (carbonyl) stretching vibration of an ester. The peak of 1185 as indicated is enough proof that an ester was formed during the esterification process. The two peaks found at 2983 and 2944cm-1 correspond to the –C-H. It was not possible to compare this peak to another peak in the spectrum considering that during the esterification process, the reaction equilibrium was maintained by converting alcohol into water. Using a sample’s IR spectrum, it might be possible to conclude that the sample was pure. As a result, figure 5 does not indicate any presence of alcohol molecules (OH), which suggests the absence of any of ethical alcohol in the ester. In addition, IR does not indicate nay presence of carboxylic acids. This implies there were no traces of propanoic acid in the ester. The product portrays the two absorptive characteristics as described above, which indicates the purity of the obtained ester. Figure indicates carbon NMR spectrum for the product, while table 1 summarizes the carbon NMR spectrum results. Figure 5 C-NMR spectrum of the produced ester Table 1 summary of the C-NMR spectrum. Predictions Actual Assignments Signal Expected Chemical Shift Range (ppm) Observed Chemical Shift (ppm) Final Chemical Shift Assignments (ppm) A 10-30 27.6 or 14.2 or 9.1 9.1 B 10-30 27.6 or 14.2 or 9.1 27.6 C 160-220 174.8 174.3 D 50-85 60.3 60.3 E 10-30 27.6 or 14.2 or 9.1 14.2 The C NMR spectrum of the ester brings out seven different types of carbon, which hare numbered A-E. A peak at any position that that corresponds to the reading 174.3ppm is a proof of carbonyl atoms in the ester, and is denoted by position (C). The down field position of this value may be valued by increased de-shielding caused by the presence of the two electronegative oxygen atoms. On the other hand, a peak at 60.3ppm corresponds to a C-O carbon, and is denoted by position D. on the other hand, all the three peaks present between 10 and 30pp are from a C-C atom. The peak observed at 27.6ppm corresponds to a carbon (B). On the other hand, a peak of 9.1ppm corresponds to carbon (A), and is far away from the C-O in the up field zone. Considering that the peaks depend on how far they are from C-O, a peak at 14.2ppm corresponds to a carbon (E). All of these peaks can be proved correct using HMQC results as indeed in figure 9. Figure 7 indicates the H-NMR spectrum and table 2 summarizes figure 7. Figure 6 H-NMR spectrum Table 2 result of H-NMR spectrum Predictions Actual Results Signal Expected chemical shift Range (ppm) Expected splitting Expected integration Observed chemical shift (ppm) Observed splitting Observed integration A 0.9-1.5 Triplet 3 1.17 Triplet 3 B 2-2.7 Quadruplet 2 2.26 Quadruplet 2 D 3.2-4.5 Quadruplet 2 4.07 Quadruplet 2 E 0.9-1.5 Triplet 3 1.07 Triplet 3 The H-NMR ester spectrum has a special peak at 1.17ppm, a peak that has to proton triplets for the carbon (A). On the other hand, the peak observed at 2.26 has three observed proton quadruplets, which correspond to carbon (B). Moreover, the peak observed at 4.07ppm has three protons quadruple that correspond to carbon (D), attached to the O atoms. Attachment to O maintains it at the down field position. The peak at 1.07ppm has two triplet protons that correspond to carbon (E). This peak manages to maintain up field considering it is far from the O atom. The COSY and HMQC assist in constructing and assigning peaks to definitive positions in the proton and carbon NMRs. Figure 8 shows all the COSY result. Figure 7: the COSY results for the ester The first spot (1) portrays coupling between the protons on carbon (A) and protons on carbon (B), while the third spot (3) indicates the same coupling. On the other hand, the second (2) and fourth (4) spots represent the coupling between protons on carbon (E) and those on carbon (D). Therefore, according to these results, it is clear that the peaks for protons on carbon (E) and (F) are properly positioned. The HMQC augment the results for C-NMR in figure 6, for the ester. Figure 9 indicates the HMQC results for pentyl acetate. Figure 8 HMQC results for the product. The position of spots (1-4) proves the correctness of peaks (A-E) carbons in figure 6. This is because the carbons connect to similar protons in figure 7. This suggests the results discussed in figure 6 are correct and accurate. In order to figure out the limiting reagents in the reaction, there is a need to calculate the number of moles of each reactant in the experiment. Figure 9 Fischer principle of esterification of Ethyl propionate with ethanol with a H2SO4 catalyst With these calculations, the number of moles of ethanol used was 0.11970, while that of propanoic acid was 0.4021 moles. The reaction was undertaken with a mole ratio of 1:1. Consequently, assuming all the ethanol reacted; the ethanol would have required 0.1970 of propanoic acid for the complete reaction. However, 0.4021 moles of propanoic acid were used in the reaction, which was more than the number of moles required. This meant that propanoic acid was used in excess in the reaction, while ethanol acted as the limiting reagent in the reaction. Considering the reaction was in a 1:1 between ethanol and propanoic acid, the reaction was expected to produce 0.1970 moles of the ester. Considering the above calculations, the theoretical mass of the ester was expected to be 20.119g. However, the actual mass of the ester obtained was 12.52g, a yield of 62.23%. The difference may have been caused by spillage of some products in the distillation process; with more care, it would be possible to obtain a higher yield. Moreover, he observed boiling point ranged between 90-100oC, while the theoretical boiling point is 98.9oC the differences may have resulted from human error in the experiment or presence of some impurities in the reactants which lowered the boiling point. Conclusion: It is possible to obtain Ethyl propionate by reacting ethanol and propanoic acid in the presence of sulphuric acid in a Fischer esterification process. This experiment managed to obtain 62.23% of the ester. After carrying out an IR spectrum on the ester, the flowing bonds were observed: C=O,-C-H and R-O-‘R (ether). Carrying out a NMR spectrum on the ester proved the carbon location of the ester as would be expected from the Ethyl propionate structure. Moreover, the H-NMR spectrum of the products indicated the same number of protons located in the same positions in the ester structure. The COSY and HMQC results augmented the results obtained under C-NMR and H-NMR. A spectroscopic test of the product (IR, GC-MS and NMR) correctly proved that the product was actually Ethyl propionate Experimental: 11.5mL of ethanol and glacial propanoic acid 30mL was poured into a 100mL round bottomed flask. 1.0mL of concentrated sulphuric acid was added to the round bottom flasks, after which a few boiling stones were added. The mixture was heated for one hour after which the heating agent was removed. A water bath was then used to speed up the cooling rate of the mixture. After cooling for some time, the mixture was poured into a separatory funnel and 50mL of water added to the mixture The reaction flask was rinsed with 10mL cold water and the rinse added to a funnel. After this, the funnel was stoppered and inverted for several minutes until the lower aqueous layer separated with upper organic layer, after which the aqueous layer was set aside for further treatment. After this, 25mL, O.5M sodium bicarbonate was poured in the funnels and the two resulting phases stirred with a stirring rod after all the carbon dioxide had escaped. The funnel was then inverted upside down and vented until there was no more carbon dioxide escaping. The lower layer was extracted after this and the extraction repeated with another 25mL, 0.5M sodium bicarbonate solution until the lower layer was extracted; the layer turned the litmus paper blue after extraction. The organic layer was then washed with 20mL, 4M sodium chloride solution. The aqueous layer was then removed and product (ester) poured into a 50mL dry flask. The anhydrous calcium chloride was used to dry the ester for 15 minutes. The ester was then decanted from the preparation beakers using CaCl2 and put into a 50mL rounded-bottomed flask. The condenser was then rinsed using acetone in removing any residual water traces from the reflux process and the simple distillation apparatus was set in place. The fraction boiling tube was collected in a 50mL round-bottomed flask. After this, mass of the product and the received flask were noted as well as the yield and the percent yield of the ester calculated. The GC, IR, C-NMR, H-NMR, COSY, and HMQC spectrums of the esters were determined Read More