Exp6report peacock - experiment 6 lab report PDF

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experiment 6 lab report...

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Diels-Alder Reaction with Maleic Anhydride and Anthracene and Recrystallizing the Product Emma Peacock CHEM 2380 – Section A6 – Desk 8 March 7, 2019 Overall Reaction

Introduction The purpose of performing this experiment is facilitate a diels-alder reaction using Anthracene as the diene and maleic anhydride as the dienophile. Diels-alder reactions have become increasingly important in a multitude of industrial applications, one example being the synthesis of steroids. The central ring of the diene, anthracene, reacts with the dienophile, maleic anhydride, to form the product, 9,10-dihydroanthracene-9,10-α,β- succinic anhydride. The highest occupied molecular orbital (HOMO) of the diene has to overlap with the lowest unoccupied molecular orbital (LUMO) of the dienophile in order for the reaction to occur. To raise the HOMO and facilitate this overlap, electron donating groups can be added to the diene in order, making it more reactive. Following this logic, to lower the LUMO, electron withdrawing groups can be added to the dienophile for the same purpose. Regiospecificity is an important aspect of this reaction, with it favors bond formation at a certain atom over all other possible alternatives. Meaning that if the starting materials are asymmetrical, only one configuration of a product is able to form. Because of this fact, it is hypothesized that a high percent yield for this reaction would result as there is only one way for it to proceed and the time allotted for the reaction was enough that it would run to completion. Following this Diels-Alder reaction, a solubility test is performed to determine the best recrystallization solvent. Once this solvent is determined, the recrystallization is performed to purify the product further. Once the purified product is produced, an IR and H NMR analysis was run on the resulting product to test the purity and chemical structure. In this reaction mechanism, the diene contributes four pi electrons, and the dienophile contributes two pi electrons in a single-step reaction to form a six membered ring with a double bond, thus there is no intermediate formation. The pi bond in maleic anhydride reacts with the carbon at the top of the central ring of anthracene, forming a carbon-carbon bond between the two species. Therefore, the pi bond at that carbon central ring of anthracene moves in between the side and central ring. The other pi bond in the central ring of anthracene reacts with the other carbon of maleic anhydride to form a second carbon-carbon bond and complete the formation of the new six membered ring as shown in the reaction mechanism drawing above. Due to the presence of an anhydride functional group on the product, there should be two sharp peaks at approximately 1780 and 1860 cm-1 because of the two carbonyl groups are expected. In addition, 4 there should be a medium broader peak at approximately 2900 cm-1 due to the formation of the aromatic, which is indicative of the C-H stretching in an aromatic compound, and there should be one peak at around 1460 cm-1 indicative of sp3 hybridized carbons. In the H NMR there are expected to be three relevant peaks at chemical shifts of approximately 7.41 for the eight aromatic hydrogens, 4.86 for the two hydrogens closest to the anhydrides, and 3.57 ppm for the two hydrogens on the newly formed ring.

Results Compound

Molecular weight (g/mol) 178.23 98.060 276.29

anthracene maleic anhydride C18H12O3

Mass (g)

Moles (mmol)

0.2498 0.1621 0.1654

Melting Point (℃)

1.400 1.600 1.500

211 - 215 51.0 - 56.0 262 - 265

Table 1. Compounds and their properties. This table shows the reactants used during experiment as well as their relevant properties. These values are used for calculations of theoretical yield, percent yield, and percent recovery. Product

Consistency

Color

C18H12O3

crystalline

white

Table 2. Characteristics of product. This table describes the consistency and color of the product, 9,10dihydroanthracene-9,10-α,β-succinic anhydride.

Theoretical Yield=0.2498 g anthracene× 0.1621 g maleic anhydride × 0.0014 mol reactant ×

Percent Yield=

1mol anthracene =0.0014 mol anthracene 178.23 g anthracene

1 mol maleic anhydride =0.0017 mol maleic anhydride 98.06 g maleic anhydride

1mol C 18 H 12 O 3 276.29 g C18 H 12 O 3 =0.0014 mol C18 H 12 O 3 × =0.3868 gC 18 H 12 O 3 1 mol reactant 1mol C 18 H 12 O 3

0.1654 g C 18 H 12 O 3 Purified Product (g) x 100= x 100=43 % Theoretical Yield (g) 0.3868 g C18 H 12 O 3

Percent Recovery =

Purified Product (g) 0.1654 g C 18 H 12 O 3 x 100= x 100=59 % 0.2790 g C 18 H 12 O 3 Crude Product (g)

Figure 1. Calculations of theoretical yield, percent yield, and percent recovery. The calculations are based on the values obtained in lab. IR Peak (cm-1) 1770.65 (double) ** 1465.90

Functional Group Anhydride Sp2 Carbons Sp2 carbon bending

**There should be peak around 1660 cm-1 for the Sp2 carbons present, and there isn’t one on my spectra. Table 3. IR Analysis. Relevant peaks and their corresponding functional groups are shown. Peak A B C D

Shift (ppm) 7.41 7.25 4.86 3.57

Splitting quintet septet quartet sextet

J (Hz) 5.4 3.0 1.8 2.4

Integration 4 4 2 2

Table 4. NMR Analysis. Relevant peaks and corresponding chemical shifts, splitting patterns, coupling constants, and integrations are shown. These values are indicated by the NMR spectrum of the product.

Figure 2. The NMR signals of the protons from 9,10-dihydroanthracene-9,10-α,β-succinic anhydride and which proton corresponds to each peak in the spectrum. See Table 4.

Discussion Questions In this experiment, a Diels-Alder reaction and subsequent purification of product was successfully performed. The reaction underwent reflux conditions for 30 minutes to ensure the reaction would reach completion. At this time, a solubility test was performed to determine the best recrystallization solvent of the option xylene, ethyl acetate, and hexane, which had to only dissolve the solid at boiling temperature, not at room temperature. The only solvent which had this characteristic was xylene. This recrystallization did purify the crude solid product because the crude mixture was off-white, whereas the “pure” product was a much more brilliant white color, indicating a successful purification. After completing this recrystallization, the pure product’s IR and NMR spectra were run. The IR spectrum contained two main peaks as tabulated above. Two corresponded to the anhydride functional group, and one corresponded to the sp2 C-H bending. These peaks were expected based on the structure of the product, and there were no peaks unexplained or extra peaks in the spectrum. In comparison to the expected IR spectrum for this product, all of the major peaks were generally the same. When compared to the IR spectra for the two starting materials, anthracene and maleic anhydride, there is one main peak that was is present in both of the starting materials and that is the sharp peak at 1465 cm-1 indicative of sp2 C-H bending. This occurs because the two starting materials do not have any sp3 hybridized carbons, whereas the product does due to the movement of pi electrons during the reaction. The NMR spectrum contained two peaks also tabulated above and labeled in the attached spectrum. The first peak occurred at a shift of 7.41 ppm and represents five aromatic hydrogens on the two outer rings. The next peak, B, has the second highest shift and represents the two hydrogens at the base of the anhydride ring, because of their proximity to the electronegative oxygens. The last peak, C, refers to the two hydrogens on either side of the middle ring. When comparing these experimental shifts to the expected literature shifts, there are also three relevant peaks, and they occur at generally the same locations with A, B, C, and D being located at shifts of 7.41, 7.25, 4.86, and 3.53 ppm respectively, indicating success in synthesizing the correct product. Also, when looking at the NMR spectra of the pure starting materials, there are also some key differences. Maleic anhydride only has one region of hydrogen density due to its symmetry. Anthracene, also a symmetrical molecule, has three regions of hydrogen density as seen on the attachment. Because the regions are very similar to the one on the pure product, the shifts are located in a very similar location as peak A is on the pure product, and there are no others. With the presence of 12 regions of hydrogen density, all of the expected peaks were present and located at a logical chemical shift, with no extras or unexplained shifts. It was hypothesized that due to the long time period left for the reaction to occur and only one possible product configuration, there would be a relatively high percent yield. The actual yield was 43% and the percent recovery was 59%. Due to these values being low, the experiment

could be improved by heating to reflux for a longer time as well as waiting a longer time for the crude product to crash out, and adding the exact amount of recrystallization solvent, rather than adding far too much, adding impurities and reducing the percent yield and recovery.

Supplemental Information

9,10-dihydroanthracene-9,10-α,β-succinic anhydride. Anthracene (0.2498 g, 1.5 mmol) and maleic anhydride (0.1621 g, 1.5 mmol) were dissolved in xylenes (3 mL) and heated to reflex. The solution was cooled and filtered via vacuum filtration and the product (9,10dihydroanthracene-9,10-α,β-succinic anhydride) was massed (0.2790 g). The recrystallization solvent (xylenes, 5 mL) was heated to boiling and the minimum amount that would fully dissolve the product was added slowly, dropwise. After the solution is slowly cooled, the crystals are obtained via vacuum filtration and the whitish-yellow crystals were massed (0.1654 g, 43%): m.p. = 262-264 ℃; IR (film) 1770, 1705, 1465 cm-1; 1H NMR (300 MHz, CDCl3) δ 7.41 (quintet, J=5.4 Hz, 4H), 7.25 (septet, J=3.0 Hz, 4H), 4.86 (q, J=1.8 Hz, 2H), 3.57 (s, J=2.4, 2).

IR Spectra

NMR Spectra...