Chem 346 Lab Report 8 e26j
This document was ed by and they confirmed that they have the permission to share it. If you are author or own the copyright of this book, please report to us by using this report form. Report 3b7i
Overview 3e4r5l
& View Chem 346 Lab Report 8 as PDF for free.
More details w3441
- Words: 4,707
- Pages: 37
Shannon Gu TA Patrick Shelton CHEM 346 12 March 2018 Multi-Step Tetraphenylnaphthalene Synthesis I.
Purpose The purpose of this lab was to convert benzaldehyde into tetraphenylnaphthalene in four
synthesis steps, to determine the yield of the products at each step, and to characterize each product using melting points, TLC, 1H NMR, and IR.
II.
Experimental Approach In the first synthesis, 0.049 mol of benzaldehyde was converted to benzoin, in a reaction
catalyzed by thiamine hydrochloride [1]. In the second synthesis, benzoin was converted to benzil via nitric acid oxidation, and the crude product was recrystallized in ethanol [1]. The third synthesis involved
reacting
benzil
with
dibenzyl
ketone
under
basic
conditions
to
create
tetraphenylcyclopentadienone [1]. Lastly, the fourth synthesis was a Diels-Alder reaction in which tetraphenylcyclopentadienone, anthranilic acid, and isopentyl nitrite reacted to form
tetraphenylnaphthalene [1]. 152 mg of crude tetraphenylnaphthalene was then recrystallized in isopropyl alcohol [1]. The yield of each synthesis product was measured, and the products were characterized using melting points, TLC, 1H NMR, and IR [1]. III.
Findings The first synthesis of benzaldehyde to benzoin yielded a highly impure product with a
percent yield of 71.2%. 3.004 g of stock benzoin was used for the second synthesis and produced benzil with a percent yield of 85.5%. From there, tetraphenylcyclopentadienone was synthesized with a percent yield of 85.7%, and crude tetraphenylnaphthalene was synthesized with a percent yield of 96.0% and recrystallized with a percent yield of 13.6%. The overall yield of tetraphenylnaphthalene prior to recrystallization was 70.3% and after recrystallization was 9.57%. Melting points, TLC, 1H NMR, and IR confirmed that each synthesis was carried out successfully.
IV.
Data and Analysis Table 1: Yields of Synthesis Products
Benzaldehyde Benzoin
Starting Amount (g) 5.194 3.004
Benzil
2.247
Reactant
Tetraphenylcyclopentadienone Crude tetraphenylnaphthalene
3.496 0.154
Product Benzoin Benzil Tetraphenylcyclopentadienone Tetraphenylnaphthalene Recrystallized tetraphenylnaphthalene
Theoretical Yield (g)
Actual Yield (g)
Percent Yield (%)
5.194 2.976
3.697 2.543
71.2* 85.5
4.070
3.489
85.7
3.933
3.775
96.0
0.154
0.021
13.6
Overall Percent Yield (%):
Pre-recrystallization:
70.3 Post-recrystallization:
9.57
*The percent yield of benzoin was not considered in the overall yield calculation due to starting the second synthesis with stock benzoin.
Calculation of theoretical yield: 1 mol benzoin
212 g
0.049 mol benzaldehyde (2 mol benzaldehyde) (1 mol benzoin) = 5.194 g benzoin 1 mol benzoin 1 mol benzil 210 g )( )( ) = 2.976 g benzil 212 g 1 mol benzoin 1 mol benzil 1 mol benzil 1 mol dienone 384 g benzil ( )( )( ) = 4.070 g tetraphenylcyclopentadienone 210 g 1 mol benzil 1 mol dienone 1 mol dienone 1 mol naph. 433 g dienone ( ) (1 mol dienone) (1 mol naph.) = 3.933 g tetraphenylnaphthalene 384 g
3.004 g benzoin ( 2.247 g 3.496 g
Table 2: Rf Values of Synthesis Products Product Benzoin Benzil
Observed Rf DCM: 0.19 DCM: 0.76
Tetraphenylcyclopentadienone
DCM: 0.93
Tetraphenylnaphthalene
50/50 hexane/acetone: 0.92
Standard Rf DCM: 0.19 DCM: 0.8 DCM: 0.93 50/50 hexane/acetone: 0.83 N/A
Table 3: Melting Points of Synthesis Products Source for Literature Values: Sigma-Aldrich Product Benzoin Benzil Tetraphenylcyclopentadienone Tetraphenylnaphthalene
Observed Melting Points (°C) 128 - 130 85.5 - 88.1 210.8 - 216.7 198.6 - 203.4
Literature Value Melting Points (°C) 134 - 138 94 - 95 217 - 220 199 - 201
Table 4: 1H NMR for Benzoin Chemical Shift (ppm)
Multiplicity
Integral (# Protons)
Coupling Constants (Hz)
0.000 1.664 2.163 4.582 5.957
Singlet Singlet Singlet Doublet Doublet
2.649 0.085 1.150 0.828 1.000
7.409
Multiplet
7.975
7.912
Doublet of Triplets
2.010
---JGJ = 6 JJG = 6 JBA = 1.2 JBC = 7.3 JCA (ortho) = 7.6 JCA (para) = 1.6 JAB = 2.2 JAC = 7
Identity TMS H2O Acetone -OH (HG) HJ
Literature Spectra Chemical Shift (ppm) ---6.120 6.090
Aromatic H (HB, HC, HD, HE, HF)
7.242 – 7.560
Aromatic H (HA)
8.024
Figure 1: Benzoin
Table 5: IR for Benzoin Wavenumber (cm-1)
Identity
1260.7 1448.3 1594.5 1675.6 3376.2
Alcohol C-O (stretch) Aromatic C=C (stretch) Aromatic C=C (stretch) Ketone C=O (stretch) O-H (stretch)
Literature Spectra Wavenumber (cm-1) 1263 1450 1595 1679 3379
Benzoin: 0.049 g of benzaldehyde was mixed with thiamine hydrochloride, ethanol, and NaOH to produce a yellow solution, which then stood in the dark for four days. After four days, my solution was the only one in the class to have a crystalline product. While the yield was fairly high (71.2%), the product was highly impure (Table 1). My product was a light yellow while pure benzoin is white, and my product also smelled distinctly of almonds which is characteristic of benzaldehyde. This product was neither recrystallized nor characterized; instead, stock benzoin was used for characterization. Benzoin’s Rf value was 0.19, the lowest of the four synthesis products (Table 2). Because benzoin is the most polar of the four synthesis products due to its hydroxyl group, it will have the highest affinity for the polar silica gel of the TLC and travel the shortest distance. Benzoin’s melting point was determined to be 128 – 130 °C, which is 4 °C lower than the literature melting point value (Table 3). Even though stock benzoin should be pure, its melting point suggests
that impurity was present. Stock benzoin may naturally have small quantities of impurities which could affect the melting point measurements. Benzoin has eight distinct proton environments. In its 1H NMR spectrum, however, there were only four distinct signals (Table 4, Appendix Figure 1). The first signal was a doublet with an integration of 0.828 and a chemical shift of 4.58 ppm; based on the multiplicity and the integration, this signal is produced by the proton on the hydroxyl group (HG) (Figure 1). It is only adjacent to one proton—the proton on the same carbon as the hydroxyl group—so based on the n+1 rule, it is a doublet (Table 4). The literature spectrum, however, places HG at a chemical shift of 6.120 ppm, and it does not have any signals that are below 6 ppm (Table 4, Appendix Figure 2). The discrepancy between the obtained spectrum and the literature spectrum can be explained by hydroxyl group protons having variable chemical shifts, ranging anywhere from 2.2-5 ppm [2]. As such, a chemical shift of 4.58 ppm would not be unreasonable for a hydroxyl group proton. The splitting between HG’s doublet peaks was 6 Hz, and because HG is adjacent to only one proton, this splitting must correspond to JGJ (Table 4). The next signal downfield was also a doublet, with an integration of 1.000 and a chemical shift of 5.96 ppm, and it corresponds to the proton on the same carbon as the hydroxyl group (HJ) (Table 4). It has a high chemical shift due to its proximity to both the hydroxyl group and the carbonyl group, which are electron-withdrawing and thus have de-shielding effects (Figure 1). Since HJ is only adjacent to HG, the coupling constant of HJ’s doublet should equal the coupling constant of HG’s doublet. As expected, the splitting between HJ’s peaks was 6 Hz, which matches JGJ (Table 4). The second-most downfield signal was a multiplet with an integration of 7.975 and centered at 7.41 ppm (Table 4). Based on literature spectra, this multiplet corresponds to protons
HB, HC, HD, HE, and HF (Table 4, Appendix Figure 2). As these protons are all aromatic, their signals would have similar chemical shifts and overlap. Within the multiplet, at least two signals can be discerned: a triplet of triplets on the left side of the multiplet and a doublet of triplets right next to it (Appendix Figure 2). Based on literature spectra, the triplet of triplets corresponds to HB due to it being split by the two protons ortho to it (HC) and the two protons meta to it (HA), while the doublet of triplets corresponds to HC due to it being split by HB and the two HA (Figure 1). The coupling constants from HB and HC were determined to be JBA = 1.2 Hz, JBC = 7.3 Hz, JCA (ortho) = 7.6 Hz, and JCA (para) = 1.6 Hz. Ortho protons have coupling constants of 6-9 Hz, meta protons have coupling constants of 2-3 Hz, and para protons have coupling constants of 0-1 Hz [3]. HB and HC are ortho to each other, and their coupling constant falls within the 6-9 Hz range (Table 4). Meanwhile, HB and HA are meta to each other, so their coupling constant is much lower as expected (Table 4). HC is also ortho to HA, making JCA = 7.6 Hz; however, it also has a smaller coupling constant of 1.6 Hz, which most likely corresponds to the HA that is para to HC (Table 4, Figure 1). The peaks in the rest of the multiplet were not clearly identified based on literature spectra, so coupling constants for HD, HE and HF were not determined. The last signal in the NMR spectrum was a doublet of triplets with an integration of 2.010 and a chemical shift of 7.91 ppm, corresponding to the aromatic protons H A (Table 4, Figure 1). HA has the highest chemical shift of the aromatic protons due to its proximity to the carbonyl group, which has a strong de-shielding effect. In addition, it is a doublet of triplets due to it being split by the two HC ortho to it as well as the HB meta to it (Figure 1). Its coupling constants were JAB = 2.2 Hz and JAC = 7 Hz, which the coupling constants determined from HB’s and HC’s signals as well as HB’s and HC’s positions relative to HA (Table 4).
As for benzoin’s IR spectrum, the key peaks were the O-H stretch at 3376.2 cm-1 as well as the C-O stretch at 1260.7 cm-1, which neither benzaldehyde nor the other synthesis products have (Table 5). Other important peaks include aromatic C=C stretches at 1448.3 cm -1 and 1594.5 cm-1, and the ketone C=O stretch at 1675.6 cm-1. The literature IR spectrum for benzoin corroborated the obtained IR spectrum (Table 5). Table 6: 1H NMR for Benzil Chemical Shift (ppm)
Multiplicity
Integral (# Protons)
Coupling Constants (Hz)
0.000 7.200
Singlet Singlet
7.678 0.077
7.517
Triplet of triplets
3.582
--JBA (ortho) = 7.4 JBC = 7.4 JBA (para) = 1.3 JCB = 7.2 JCA = 1.4 JAB = 7 JAC = 1.6
7.670 7.983
Triplet of triplets Doublet of triplets
2.000 3.738
Identity TMS CHCl3
Literature Spectra Chemical Shift (ppm) ---
H meta to ketone (HB) H para to ketone (HC) H ortho to ketone (HA)
Figure 2: Benzil
Table 7: IR for Benzil Wavenumber (cm-1)
Identity
1577.9 1591.4 1656.2 1675.1
Aromatic C=C (stretch) Aromatic C=C (stretch) Ketone C=O (stretch) Ketone C=O (stretch)
Literature Spectra Wavenumber (cm-1) 1578 1595 1658 1679
7.502 7.649 7.981
Benzil: 3.004 g of stock benzoin was reacted with nitric acid to produce benzil, which had an actual yield of 2.543 g and a percent yield of 85.5% (Table 1). The reaction was monitored with TLC until the reaction mixture only showed the presence of benzil. The reaction mixture’s benzil had a Rf of 0.76, while the benzil standard had an Rf of 0.8 (Table 2). Benzil’s Rf is higher than benzoin’s because benzil is less polar, having another carbonyl in place of the hydroxyl group on benzoin (Figure 2). After recrystallizing benzil from the reaction mixture, its melting point was determined to be 85.5 – 88.1 °C (Table 3). This melting point is around 6 °C lower than that of the literature value, suggesting that the benzil was impure (Table 3). Recrystallization should have removed most impurities from the benzil in the reaction mixture, so impurities most likely came from ethanol not being evaporated enough. After drying the benzil crystals for a longer time, however, the melting point did not increase from the original measurement. In the 1H NMR spectrum for benzil, three distinct signals were present (Table 6, Appendix Figure 5). The first signal was a triplet of triplets with an integration of 3.582 and a chemical shift of 7.52 ppm (Table 6). This signal is from the protons meta to the carbonyl group (HB), with two on each aromatic ring (Figure 2). HB’s signal is a triplet of triplets, but it was expected to be a doublet of triplets because HB is split by one HC and two HAs (Figure 2, Table 6). Based on the splitting between the peaks, HB has coupling constants of 7.4 Hz and 1.3 Hz. Since HB is ortho to both HA and HC, the 7.4 Hz coupling constant must be JBA (ortho) and JBC (Table 6). HB is also para to the other HA, so the 1.3 Hz coupling constant must be JBA (para) (Table 6). The second signal was also a triplet of triplets, and it had an integration of 2.000 and a chemical shift of 7.67 ppm (Table 6). Based on its integration, this signal must come from the two protons para to the two carbonyl groups (HC) (Table 6, Figure 2). As expected, HC’s signal is a triplet of triplet because HC is split by two HBs and two HAs (Figure 2). Its coupling constants were 7.2 Hz and 1.4 Hz,
which correspond to JCB and JCA, respectively; JCB’s value corroborated the JBC obtained from HB’s signal (Table 6). The final signal was a doublet of triplets with an integration of 3.738 and a chemical shift of 7.98 ppm, corresponding to the protons ortho to the carbonyl groups (HA) (Table 6). HA is a doublet of triplets because it is split by two HB and one HC, and it is the most de-shielded proton due to its proximity to the carbonyl group (Figure 2). Its coupling constants were determined to be JAB = 7 Hz and JAC = 1.6 Hz, which the coupling constants obtained from HB and HC (Table 6). The IR spectrum confirmed that the conversion of benzoin to benzil was successful, as it lacked a O-H peak at around 3300 cm-1 (Appendix Figure 7). Benzil’s most important IR peaks were the ketone C=O stretches at 1656.2 cm-1 and 1675.1 cm-1 (Table 7). It also contained two aromatic C=C peaks at 1577.9 cm-1 and 1591.4 cm-1 (Table 7). The literature IR spectrum for benzil ed the obtained benzil IR spectrum well (Table 7, Appendix Figure 8). Table 8: 1H NMR for Tetraphenylcyclopentadienone Chemical Shift (ppm) 0.000 1.560 2.169 6.924 7.188
Integral (# Protons)
Coupling Constants (Hz)
Singlet Singlet Singlet Doublet of Triplets
11.453 0.318 2.297
Multiplet
16.893
---JCB = 6.4 JCA = 1.8 JBC (ortho) = 6.4 JBA = 6.4 JBC (para) = 2.4
Multiplicity
3.999
TMS H2O Acetone
Literature Spectra Chemical Shift (ppm) ----
HC
6.923
CHCl3, HA, HB
7.156, 7.230
Identity
Figure 3: Tetraphenylcyclopentadienone
Table 9: IR for Tetraphenylcyclopentadienone
Peak 1 Peak 2
Wavenumber (cm-1)
Identity
1596.1 1709.8
Aromatic C=C (stretch) Ketone C=O (stretch)
Literature Spectra Wavenumber (cm-1) 1496 1710
Tetraphenylcyclopentadienone: Of the 2.976 g of benzil produced, 2.247 g was used to synthesize tetraphenylcyclopentadienone (Table 1). The theoretical yield of tetraphenylcyclopentadienone was 4.070 g while the actual yield was 3.489 g, resulting in a percent yield of 85.7% (Table 1). The reaction was carried out in a reflux apparatus; at one point the mixture was heated too quickly, causing the mixture to reflux too vigorously and making the product cover the entire inner surface of the roundbottom flask. The product was difficult to remove from the flask, and as a result, some product was lost. However, the yield was more than enough for characterization and carrying out the next synthesis. The Rf value for tetraphenylcyclopentadienone was 0.93 (Table 2). This Rf value is much higher than that of benzil’s and benzoin’s, which is expected given how nonpolar tetraphenylcyclopentadienone is compared to benzil and benzoin; tetraphenylcyclopentadienone has only one
carbonyl group and four phenyl groups (Table 2, Figure 3). The melting point was 210.8 – 216.7 °C (Table 3). While the upper value of the melting point was very close to the literature value, the range of the melting point was very wide, which may be a result of impurity from unevaporated ethanol (Table 3). The 1H NMR spectrum had two signals of interest: a doublet of triplets and a multiplet (Table 8, Appendix Figure 9). The doublet of triplets has an integration of 3.999 and a chemical shift of 6.92 ppm, and based on the literature spectrum, it comes from the ortho protons on the two phenyls closest to the carbonyl (HC) (Table 8, Figure 3). On a monosubstituted ring, protons that are ortho to the substituent tend to have the highest chemical shifts, but this trend is not observed here (Table 8). The doublet of triplets yielded coupling constants of 6.4 Hz and 1.8 Hz (Table 8). According to typical aromatic proton coupling constants [3], the 6.4 Hz must be JCB because HC is ortho to HB, and the 1.8 Hz must be JCA because HC is meta to HA (Table 8, Figure 3). Meanwhile, the multiplet has an integration of 16.983 and a chemical shift of 7.19 ppm, and its large integration indicates that it corresponds to all the remaining protons on the molecule (HA, HB) (Table 8, Figure 3). Interestingly, the literature spectrum marks all the protons on the two inner phenyl rings as identical, despite that substitution on aromatic rings produces unequal proton environments (Figure 3, Appendix Figure 10). The signals may overlap significantly, or resolution may not be high enough to discern between the protons on those phenyl groups. In addition, the integration of 16.983 is higher than the expected integration of 16, due to the CHCl 3 signal overlapping with the multiplet—the tallest peak is at 7.23, which corresponds to CHCl3 (Appendix Figure 9). Tetraphenylcyclopentadienone’s literature spectrum shows that CHCl3 specifically overlaps with HA’s signals, making coupling constants difficult to determine (Appendix Figure 10). Coupling constants can, however, be determined from HB’s peaks in the multiplet, which are
upfield from CHCl3’s peak. From HB’s signal, coupling constants were calculated as JBC (ortho) = JBA = 6.4 Hz, due to HB being ortho to both HC and HA, and JBC (para) = 2.4 Hz (Table 8). The IR spectrum for tetraphenylcyclopentadienone only contained two prominent peaks outside of the nujol mull peaks—a ketone C=O stretch at 1709.8 cm-1 and an aromatic C=C stretch at 1596.1 cm-1 (Table 9, Appendix Figure 11). While the peaks were discernible, they were not resolved well due to the tetraphenylcyclopentadienone being dilute in the nujol. The literature IR spectrum’s C=O stretch was at 1710 cm-1, which is very close to my obtained IR spectrum, but it placed the C=C stretch at 1496 cm-1 (Table 9, Appendix Figure 12). Table 10: 1H NMR for Tetraphenylnaphthalene
Multiplicity
Integral (# Protons)
Coupling Constants (Hz)
0.000 1.548
Singlet Singlet
131.74 3.610
---
6.845
Singlet
11.159
--
7.244
Multiplet
15.782
JCE = 3.4
7.393
Doublet of doublets
2.060
7.640
Doublet of doublets
2.000
Chemical Shift (ppm)
JAB (meta) = 3.4 JAB (ortho) = 6.6 JBA (meta) = 3.25 JBA (ortho) = 6.6
Identity TMS H2O Inner phenyl protons (HF, HG, HH) CHCl3, outer phenyl protons (HC, HD, HE) Aromatic ring outer protons (HA)
Literature Spectra Chemical Shift (ppm) ---
Aromatic ring inner protons (HB)
Figure 4: Tetraphenylnaphthalene
7.01 7.39 7.560 7.82
Table 11: IR for Tetraphenylnaphthalene Wavenumber (cm-1)
Identity
1442.8 1493.9 2852.7 2923.0
Aromatic C=C (stretch) Aromatic C=C (stretch) Aromatic C-H (stretch) Aromatic C-H (stretch)
Literature Spectra Wavenumber (cm-1) 1463.4 1463.4 2957.3 2957.3
Tetraphenylnaphthalene: In the final synthesis, 3.496 g of tetraphenylcyclopentadienone reacted with 1.1 molar equivalent of anthranilic acid and 3.3 molar equivalents of isopentyl nitrite to produce 3.775 g of tetraphenylnaphthalene, a percent yield of 96.0%. The lab manual originally called for 1.5 moles of isopentyl nitrite per mole of anthranilic acid [1]; however, after adding the first 1.5 moles and refluxing for 15 minutes, the reaction did not turn orange as expected. To speed up the reaction, another equivalent of isopentyl nitrite was added, and the reaction mixture began to turn orange. After isolating the crude solid, 42 mg was used for recrystallization in 25 mL of isopropyl alcohol. Crystals did not form after twenty minutes of the solution being at room temperature, and only began to form after evaporating the isopropyl alcohol with an air stream. To ensure that enough product was obtained, another 112 mg of tetraphenylnaphthalene was recrystallized. The percent yield of recovery from both recrystallizations was only 13.6% (Table 1). Considering how slow recrystallization was, recovery would have been improved if there were more time to allow crystals to form, and if less solvent were used to dissolve the tetraphenylnaphthalene. The recrystallization brought down the overall yield of the multi-step synthesis considerably: the overall yield of the crude tetraphenylnaphthalene was 70.3%, but the overall yield of recrystallized tetraphenylnaphthalene was only 9.57% (Table 1). Due to tetraphenylnaphthalene being highly nonpolar, a solvent of 50/50 hexane/acetone was used for TLC instead of DCM. There was no tetraphenylnaphthalene standard, so the
recrystallized product was compared to tetraphenylcyclopentadienone. Tetraphenylnaphthalene yielded an Rf value of 0.92, while tetraphenylcyclopentadienone had an Rf value of 0.83 (Table 2). As expected, tetraphenylnaphthalene’s Rf value is higher than that of tetraphenylcyclopentadienone, as tetraphenylnaphthalene lacks highly electronegative atoms and is thus more nonpolar. As a result, tetraphenylnaphthalene has a higher affinity for the mobile phase of the TLC and will travel further up the plate. The melting point of tetraphenylnaphthalene was 198.6 – 203.4 °C, which overlaps with the literature value of 199 – 201 °C (Table 3). While the lower and upper values for the melting point are very close to the literature values, suggesting high purity, the range of the melting point is also wide, suggesting some impurity. A different explanation for the wide range is that the temperature readings were increasing very quickly at the time the product began to melt, and thus the readings are not fully representative of the product’s true melting point. Tetraphenylnaphthalene is expected to contain eight signals in its 1H NMR spectrum, as it contains eight distinct proton environments [1]. However, only four signals were observed (Table 10, Appendix Figure 13). The most upfield signal is a singlet with an integration of 11.159 and a chemical shift of 6.84 ppm, and it corresponds to all the protons on the two inner phenyl groups (HF, HG, HH) (Table 10, Figure 4). These protons have the lowest chemical shift because they are the furthest away from the central aromatic ring (Figure 4). The signal is a singlet, which suggests that the 10 protons comprising it are identical, but the resolution may be too low to distinguish more complicated splitting patterns (Table 10). As a result, coupling constants could not be determined for those protons (Table 10). The protons on the outer phenyl groups (HC, HD, HE) comprise the next signal, a multiplet with an integration of 15.782 and a chemical shift of 7.24 ppm (Figure 4, Table 10). The integration of 15.782 is significantly higher than the integration of 10 because the signal for CHCl3 overlaps
with the phenyl protons’ signal; a large peak corresponding to CHCl3 can be seen at 7.23 ppm (Appendix Figure 13). Aside from the CHCl3 peak, only two other peaks are visible, and the splitting between them is 3.4 Hz (Table 10). Given that a coupling constant around 2-3 Hz is characteristic of meta protons, the 3.4 Hz likely corresponds to JCE (Table 10). Once again, due to low resolution, more complex splitting patterns were not observed. The final two signals are both doublet of doublets (Table 10). The upfield doublet of doublets has an integration of 2.060 and a chemical shift of 7.39 ppm, and it corresponds to the outer protons on the central aromatic ring (HA) (Table 10, Figure 4). The downfield doublet of doublets has an integration of 2.000 and a chemical shift of 7.64 ppm, and it corresponds to the more de-shielded inner protons on the central aromatic ring (HB) (Table 10, Figure 4). The two HA and two HB are adjacent to each other, so based on the n+1 rule, the expected splitting pattern would be a triplet for both HA and HB. They are doublets of doublets, however, suggesting that each HA is split by the HB ortho to it, then by the HB meta to it (Figure 4). The coupling constants derived from HA’s signal were JAB (meta) = 3.4 Hz and JAB (ortho) = 6.6 Hz, and the coupling constants from HB’s signal are expected to be very close to that; indeed, the coupling constants from HB were JBA (meta) = 3.25 Hz and JBA (ortho) = 6.6 Hz (Table 10). On an IR spectrum, a successful synthesis of tetraphenylnaphthalene would be represented by a lack of a ketone C=O stretch between 1750 cm-1 and 1650 cm-1. Indeed, the obtained IR spectrum for tetraphenylnaphthalene demonstrated no such C=O stretch (Table 11, Appendix Figure 15). The main peaks in tetraphenylnaphthalene were from the aromatic C-H stretches at 2852.7 cm-1 and 2923.0 cm-1, as well as the aromatic C=C stretches at 1442.8 cm-1 and 1493.9 cm1
(Table 11). The literature spectrum places the C-H stretch at 2957.3 cm-1 and the C=C stretch at
1463.4 cm-1, which does not align well with my obtained spectrum (Table 11, Appendix Figure
16). The differences in peaks may be due to the differences in the solvents used; the literature spectrum appears to use nujol mull, while my spectrum used DCM. Regardless, the key peaks of tetraphenylnaphthalene can be observed in both spectra (Appendix Figure 15, Appendix Figure 16).
Conclusion: In the first synthesis, 0.049 mol of benzaldehyde was converted to benzoin; however, the conversion was unsuccessful due to large amounts of unreacted benzaldehyde. 3.004 g of stock benzoin was used to initiate the second synthesis, which produced benzil with a percent yield of 85.5%. In the third synthesis, benzil was converted to tetraphenylcyclopentadienone and had a percent yield of 85.7%. In the fourth and final synthesis, tetraphenylcyclopentadienone was converted to crude tetraphenylnaphthalene, which was then recrystallized. The crude tetraphenylnaphthalene had a percent yield of 96.0%, but the recrystallized tetraphenylnaphthalene had a percent yield of only 13.6%. Thus, the overall percent yield of recrystallized tetraphenylnaphthalene was 0.855*0.857*0.96*0.136 = 9.57%. TLC and IR confirmed that each synthesis was performed correctly, with TLC showing that the synthesis products became increasingly nonpolar and IR showing the loss or gain of key functional groups between each synthesis product. Melting point measurements determined the purity of each product; each product apart from tetraphenylnaphthalene demonstrated some degree of impurity. Lastly, 1H NMR was a means to further characterize each product and confirm the completion of each synthesis step.
Sources [1] Chemistry 346 Lab Manual. (2018). [2] Overview of Chemical Shifts in H-NMR. (n.d.). Retrieved March 8, 2018, from http://www2.ups.edu/faculty/hanson/Spectroscopy/NMR/HNMRshift.htm [3] NMR Aromatic Proton Coupling. (n.d.). Retrieved March 1, 2018, from http://www.sas.upenn.edu/~genette/NMRcoupling.pdf
Appendix Figure 1: Obtained 1H NMR Spectrum for Benzoin
Appendix Figure 2: Literature 1H NMR Spectrum for Benzoin Source: Spectral Database for Organic Compounds
Appendix Figure 3: Obtained IR Spectrum for Benzoin Source: Ethan Knight, CHEM 346 AB
Appendix Figure 4: Literature IR Spectrum for Benzoin Source: Spectral Database for Organic Compounds
Appendix Figure 5: Obtained 1H NMR for Benzil
Appendix Figure 6: Literature 1H NMR Spectrum for Benzil Source: Gazi, S. & Ananthakrishnan, R. (2012). Bromodimethylsulfonium bromide (BDMS) as a Potential Candidate for Photocatalytic Selective Oxidation of Benzylic Alcohols Using Oxygen and Visible Light. The Royal Society of Chemistry, 2, 7781-7787. doi: 10.1039/C2RA20553J
Appendix Figure 7: Obtained IR Spectrum for Benzil
Appendix Figure 8: Literature IR for Benzil Source: Spectral Database for Organic Compounds
Appendix Figure 9: Obtained 1H NMR for Tetraphenylcyclopentadienone
Appendix Figure 10: Literature 1H NMR for Tetraphenylcyclopentadienone Source: Spectral Database for Organic Compounds
Appendix Figure 11: Obtained IR Spectrum for Tetraphenylcyclopentadienone
Appendix Figure 12: Literature IR Spectrum for Tetraphenylcyclopentadienone Source: Spectral Database for Organic Compounds
Appendix Figure 13: Obtained 1H NMR Spectrum for Tetraphenylnaphthalene
Appendix Figure 14: Literature 1H Spectrum for Tetraphenylnaphthalene Source: Cant, A., Roberts, L., & Greaney, M.F. (2010). Generation of benzyne from benzoic acid using C–H activation. The Royal Society of Chemistry, 46, 8671-8673. doi: 10.1039/C0CC02547J
Appendix Figure 15: Obtained IR Spectrum for Tetraphenylnaphthalene
Appendix Figure 16: Literature IR Spectrum for Tetraphenylnaphthalene Source: Shashidher, B., Bajjuri, R., & Guguloath, V. (2011). Formation and Trapping of Benzyne. Pharmaceutica Analytica Acta, 02(07). doi:10.4172/2153-2435.1000137
Purpose The purpose of this lab was to convert benzaldehyde into tetraphenylnaphthalene in four
synthesis steps, to determine the yield of the products at each step, and to characterize each product using melting points, TLC, 1H NMR, and IR.
II.
Experimental Approach In the first synthesis, 0.049 mol of benzaldehyde was converted to benzoin, in a reaction
catalyzed by thiamine hydrochloride [1]. In the second synthesis, benzoin was converted to benzil via nitric acid oxidation, and the crude product was recrystallized in ethanol [1]. The third synthesis involved
reacting
benzil
with
dibenzyl
ketone
under
basic
conditions
to
create
tetraphenylcyclopentadienone [1]. Lastly, the fourth synthesis was a Diels-Alder reaction in which tetraphenylcyclopentadienone, anthranilic acid, and isopentyl nitrite reacted to form
tetraphenylnaphthalene [1]. 152 mg of crude tetraphenylnaphthalene was then recrystallized in isopropyl alcohol [1]. The yield of each synthesis product was measured, and the products were characterized using melting points, TLC, 1H NMR, and IR [1]. III.
Findings The first synthesis of benzaldehyde to benzoin yielded a highly impure product with a
percent yield of 71.2%. 3.004 g of stock benzoin was used for the second synthesis and produced benzil with a percent yield of 85.5%. From there, tetraphenylcyclopentadienone was synthesized with a percent yield of 85.7%, and crude tetraphenylnaphthalene was synthesized with a percent yield of 96.0% and recrystallized with a percent yield of 13.6%. The overall yield of tetraphenylnaphthalene prior to recrystallization was 70.3% and after recrystallization was 9.57%. Melting points, TLC, 1H NMR, and IR confirmed that each synthesis was carried out successfully.
IV.
Data and Analysis Table 1: Yields of Synthesis Products
Benzaldehyde Benzoin
Starting Amount (g) 5.194 3.004
Benzil
2.247
Reactant
Tetraphenylcyclopentadienone Crude tetraphenylnaphthalene
3.496 0.154
Product Benzoin Benzil Tetraphenylcyclopentadienone Tetraphenylnaphthalene Recrystallized tetraphenylnaphthalene
Theoretical Yield (g)
Actual Yield (g)
Percent Yield (%)
5.194 2.976
3.697 2.543
71.2* 85.5
4.070
3.489
85.7
3.933
3.775
96.0
0.154
0.021
13.6
Overall Percent Yield (%):
Pre-recrystallization:
70.3 Post-recrystallization:
9.57
*The percent yield of benzoin was not considered in the overall yield calculation due to starting the second synthesis with stock benzoin.
Calculation of theoretical yield: 1 mol benzoin
212 g
0.049 mol benzaldehyde (2 mol benzaldehyde) (1 mol benzoin) = 5.194 g benzoin 1 mol benzoin 1 mol benzil 210 g )( )( ) = 2.976 g benzil 212 g 1 mol benzoin 1 mol benzil 1 mol benzil 1 mol dienone 384 g benzil ( )( )( ) = 4.070 g tetraphenylcyclopentadienone 210 g 1 mol benzil 1 mol dienone 1 mol dienone 1 mol naph. 433 g dienone ( ) (1 mol dienone) (1 mol naph.) = 3.933 g tetraphenylnaphthalene 384 g
3.004 g benzoin ( 2.247 g 3.496 g
Table 2: Rf Values of Synthesis Products Product Benzoin Benzil
Observed Rf DCM: 0.19 DCM: 0.76
Tetraphenylcyclopentadienone
DCM: 0.93
Tetraphenylnaphthalene
50/50 hexane/acetone: 0.92
Standard Rf DCM: 0.19 DCM: 0.8 DCM: 0.93 50/50 hexane/acetone: 0.83 N/A
Table 3: Melting Points of Synthesis Products Source for Literature Values: Sigma-Aldrich Product Benzoin Benzil Tetraphenylcyclopentadienone Tetraphenylnaphthalene
Observed Melting Points (°C) 128 - 130 85.5 - 88.1 210.8 - 216.7 198.6 - 203.4
Literature Value Melting Points (°C) 134 - 138 94 - 95 217 - 220 199 - 201
Table 4: 1H NMR for Benzoin Chemical Shift (ppm)
Multiplicity
Integral (# Protons)
Coupling Constants (Hz)
0.000 1.664 2.163 4.582 5.957
Singlet Singlet Singlet Doublet Doublet
2.649 0.085 1.150 0.828 1.000
7.409
Multiplet
7.975
7.912
Doublet of Triplets
2.010
---JGJ = 6 JJG = 6 JBA = 1.2 JBC = 7.3 JCA (ortho) = 7.6 JCA (para) = 1.6 JAB = 2.2 JAC = 7
Identity TMS H2O Acetone -OH (HG) HJ
Literature Spectra Chemical Shift (ppm) ---6.120 6.090
Aromatic H (HB, HC, HD, HE, HF)
7.242 – 7.560
Aromatic H (HA)
8.024
Figure 1: Benzoin
Table 5: IR for Benzoin Wavenumber (cm-1)
Identity
1260.7 1448.3 1594.5 1675.6 3376.2
Alcohol C-O (stretch) Aromatic C=C (stretch) Aromatic C=C (stretch) Ketone C=O (stretch) O-H (stretch)
Literature Spectra Wavenumber (cm-1) 1263 1450 1595 1679 3379
Benzoin: 0.049 g of benzaldehyde was mixed with thiamine hydrochloride, ethanol, and NaOH to produce a yellow solution, which then stood in the dark for four days. After four days, my solution was the only one in the class to have a crystalline product. While the yield was fairly high (71.2%), the product was highly impure (Table 1). My product was a light yellow while pure benzoin is white, and my product also smelled distinctly of almonds which is characteristic of benzaldehyde. This product was neither recrystallized nor characterized; instead, stock benzoin was used for characterization. Benzoin’s Rf value was 0.19, the lowest of the four synthesis products (Table 2). Because benzoin is the most polar of the four synthesis products due to its hydroxyl group, it will have the highest affinity for the polar silica gel of the TLC and travel the shortest distance. Benzoin’s melting point was determined to be 128 – 130 °C, which is 4 °C lower than the literature melting point value (Table 3). Even though stock benzoin should be pure, its melting point suggests
that impurity was present. Stock benzoin may naturally have small quantities of impurities which could affect the melting point measurements. Benzoin has eight distinct proton environments. In its 1H NMR spectrum, however, there were only four distinct signals (Table 4, Appendix Figure 1). The first signal was a doublet with an integration of 0.828 and a chemical shift of 4.58 ppm; based on the multiplicity and the integration, this signal is produced by the proton on the hydroxyl group (HG) (Figure 1). It is only adjacent to one proton—the proton on the same carbon as the hydroxyl group—so based on the n+1 rule, it is a doublet (Table 4). The literature spectrum, however, places HG at a chemical shift of 6.120 ppm, and it does not have any signals that are below 6 ppm (Table 4, Appendix Figure 2). The discrepancy between the obtained spectrum and the literature spectrum can be explained by hydroxyl group protons having variable chemical shifts, ranging anywhere from 2.2-5 ppm [2]. As such, a chemical shift of 4.58 ppm would not be unreasonable for a hydroxyl group proton. The splitting between HG’s doublet peaks was 6 Hz, and because HG is adjacent to only one proton, this splitting must correspond to JGJ (Table 4). The next signal downfield was also a doublet, with an integration of 1.000 and a chemical shift of 5.96 ppm, and it corresponds to the proton on the same carbon as the hydroxyl group (HJ) (Table 4). It has a high chemical shift due to its proximity to both the hydroxyl group and the carbonyl group, which are electron-withdrawing and thus have de-shielding effects (Figure 1). Since HJ is only adjacent to HG, the coupling constant of HJ’s doublet should equal the coupling constant of HG’s doublet. As expected, the splitting between HJ’s peaks was 6 Hz, which matches JGJ (Table 4). The second-most downfield signal was a multiplet with an integration of 7.975 and centered at 7.41 ppm (Table 4). Based on literature spectra, this multiplet corresponds to protons
HB, HC, HD, HE, and HF (Table 4, Appendix Figure 2). As these protons are all aromatic, their signals would have similar chemical shifts and overlap. Within the multiplet, at least two signals can be discerned: a triplet of triplets on the left side of the multiplet and a doublet of triplets right next to it (Appendix Figure 2). Based on literature spectra, the triplet of triplets corresponds to HB due to it being split by the two protons ortho to it (HC) and the two protons meta to it (HA), while the doublet of triplets corresponds to HC due to it being split by HB and the two HA (Figure 1). The coupling constants from HB and HC were determined to be JBA = 1.2 Hz, JBC = 7.3 Hz, JCA (ortho) = 7.6 Hz, and JCA (para) = 1.6 Hz. Ortho protons have coupling constants of 6-9 Hz, meta protons have coupling constants of 2-3 Hz, and para protons have coupling constants of 0-1 Hz [3]. HB and HC are ortho to each other, and their coupling constant falls within the 6-9 Hz range (Table 4). Meanwhile, HB and HA are meta to each other, so their coupling constant is much lower as expected (Table 4). HC is also ortho to HA, making JCA = 7.6 Hz; however, it also has a smaller coupling constant of 1.6 Hz, which most likely corresponds to the HA that is para to HC (Table 4, Figure 1). The peaks in the rest of the multiplet were not clearly identified based on literature spectra, so coupling constants for HD, HE and HF were not determined. The last signal in the NMR spectrum was a doublet of triplets with an integration of 2.010 and a chemical shift of 7.91 ppm, corresponding to the aromatic protons H A (Table 4, Figure 1). HA has the highest chemical shift of the aromatic protons due to its proximity to the carbonyl group, which has a strong de-shielding effect. In addition, it is a doublet of triplets due to it being split by the two HC ortho to it as well as the HB meta to it (Figure 1). Its coupling constants were JAB = 2.2 Hz and JAC = 7 Hz, which the coupling constants determined from HB’s and HC’s signals as well as HB’s and HC’s positions relative to HA (Table 4).
As for benzoin’s IR spectrum, the key peaks were the O-H stretch at 3376.2 cm-1 as well as the C-O stretch at 1260.7 cm-1, which neither benzaldehyde nor the other synthesis products have (Table 5). Other important peaks include aromatic C=C stretches at 1448.3 cm -1 and 1594.5 cm-1, and the ketone C=O stretch at 1675.6 cm-1. The literature IR spectrum for benzoin corroborated the obtained IR spectrum (Table 5). Table 6: 1H NMR for Benzil Chemical Shift (ppm)
Multiplicity
Integral (# Protons)
Coupling Constants (Hz)
0.000 7.200
Singlet Singlet
7.678 0.077
7.517
Triplet of triplets
3.582
--JBA (ortho) = 7.4 JBC = 7.4 JBA (para) = 1.3 JCB = 7.2 JCA = 1.4 JAB = 7 JAC = 1.6
7.670 7.983
Triplet of triplets Doublet of triplets
2.000 3.738
Identity TMS CHCl3
Literature Spectra Chemical Shift (ppm) ---
H meta to ketone (HB) H para to ketone (HC) H ortho to ketone (HA)
Figure 2: Benzil
Table 7: IR for Benzil Wavenumber (cm-1)
Identity
1577.9 1591.4 1656.2 1675.1
Aromatic C=C (stretch) Aromatic C=C (stretch) Ketone C=O (stretch) Ketone C=O (stretch)
Literature Spectra Wavenumber (cm-1) 1578 1595 1658 1679
7.502 7.649 7.981
Benzil: 3.004 g of stock benzoin was reacted with nitric acid to produce benzil, which had an actual yield of 2.543 g and a percent yield of 85.5% (Table 1). The reaction was monitored with TLC until the reaction mixture only showed the presence of benzil. The reaction mixture’s benzil had a Rf of 0.76, while the benzil standard had an Rf of 0.8 (Table 2). Benzil’s Rf is higher than benzoin’s because benzil is less polar, having another carbonyl in place of the hydroxyl group on benzoin (Figure 2). After recrystallizing benzil from the reaction mixture, its melting point was determined to be 85.5 – 88.1 °C (Table 3). This melting point is around 6 °C lower than that of the literature value, suggesting that the benzil was impure (Table 3). Recrystallization should have removed most impurities from the benzil in the reaction mixture, so impurities most likely came from ethanol not being evaporated enough. After drying the benzil crystals for a longer time, however, the melting point did not increase from the original measurement. In the 1H NMR spectrum for benzil, three distinct signals were present (Table 6, Appendix Figure 5). The first signal was a triplet of triplets with an integration of 3.582 and a chemical shift of 7.52 ppm (Table 6). This signal is from the protons meta to the carbonyl group (HB), with two on each aromatic ring (Figure 2). HB’s signal is a triplet of triplets, but it was expected to be a doublet of triplets because HB is split by one HC and two HAs (Figure 2, Table 6). Based on the splitting between the peaks, HB has coupling constants of 7.4 Hz and 1.3 Hz. Since HB is ortho to both HA and HC, the 7.4 Hz coupling constant must be JBA (ortho) and JBC (Table 6). HB is also para to the other HA, so the 1.3 Hz coupling constant must be JBA (para) (Table 6). The second signal was also a triplet of triplets, and it had an integration of 2.000 and a chemical shift of 7.67 ppm (Table 6). Based on its integration, this signal must come from the two protons para to the two carbonyl groups (HC) (Table 6, Figure 2). As expected, HC’s signal is a triplet of triplet because HC is split by two HBs and two HAs (Figure 2). Its coupling constants were 7.2 Hz and 1.4 Hz,
which correspond to JCB and JCA, respectively; JCB’s value corroborated the JBC obtained from HB’s signal (Table 6). The final signal was a doublet of triplets with an integration of 3.738 and a chemical shift of 7.98 ppm, corresponding to the protons ortho to the carbonyl groups (HA) (Table 6). HA is a doublet of triplets because it is split by two HB and one HC, and it is the most de-shielded proton due to its proximity to the carbonyl group (Figure 2). Its coupling constants were determined to be JAB = 7 Hz and JAC = 1.6 Hz, which the coupling constants obtained from HB and HC (Table 6). The IR spectrum confirmed that the conversion of benzoin to benzil was successful, as it lacked a O-H peak at around 3300 cm-1 (Appendix Figure 7). Benzil’s most important IR peaks were the ketone C=O stretches at 1656.2 cm-1 and 1675.1 cm-1 (Table 7). It also contained two aromatic C=C peaks at 1577.9 cm-1 and 1591.4 cm-1 (Table 7). The literature IR spectrum for benzil ed the obtained benzil IR spectrum well (Table 7, Appendix Figure 8). Table 8: 1H NMR for Tetraphenylcyclopentadienone Chemical Shift (ppm) 0.000 1.560 2.169 6.924 7.188
Integral (# Protons)
Coupling Constants (Hz)
Singlet Singlet Singlet Doublet of Triplets
11.453 0.318 2.297
Multiplet
16.893
---JCB = 6.4 JCA = 1.8 JBC (ortho) = 6.4 JBA = 6.4 JBC (para) = 2.4
Multiplicity
3.999
TMS H2O Acetone
Literature Spectra Chemical Shift (ppm) ----
HC
6.923
CHCl3, HA, HB
7.156, 7.230
Identity
Figure 3: Tetraphenylcyclopentadienone
Table 9: IR for Tetraphenylcyclopentadienone
Peak 1 Peak 2
Wavenumber (cm-1)
Identity
1596.1 1709.8
Aromatic C=C (stretch) Ketone C=O (stretch)
Literature Spectra Wavenumber (cm-1) 1496 1710
Tetraphenylcyclopentadienone: Of the 2.976 g of benzil produced, 2.247 g was used to synthesize tetraphenylcyclopentadienone (Table 1). The theoretical yield of tetraphenylcyclopentadienone was 4.070 g while the actual yield was 3.489 g, resulting in a percent yield of 85.7% (Table 1). The reaction was carried out in a reflux apparatus; at one point the mixture was heated too quickly, causing the mixture to reflux too vigorously and making the product cover the entire inner surface of the roundbottom flask. The product was difficult to remove from the flask, and as a result, some product was lost. However, the yield was more than enough for characterization and carrying out the next synthesis. The Rf value for tetraphenylcyclopentadienone was 0.93 (Table 2). This Rf value is much higher than that of benzil’s and benzoin’s, which is expected given how nonpolar tetraphenylcyclopentadienone is compared to benzil and benzoin; tetraphenylcyclopentadienone has only one
carbonyl group and four phenyl groups (Table 2, Figure 3). The melting point was 210.8 – 216.7 °C (Table 3). While the upper value of the melting point was very close to the literature value, the range of the melting point was very wide, which may be a result of impurity from unevaporated ethanol (Table 3). The 1H NMR spectrum had two signals of interest: a doublet of triplets and a multiplet (Table 8, Appendix Figure 9). The doublet of triplets has an integration of 3.999 and a chemical shift of 6.92 ppm, and based on the literature spectrum, it comes from the ortho protons on the two phenyls closest to the carbonyl (HC) (Table 8, Figure 3). On a monosubstituted ring, protons that are ortho to the substituent tend to have the highest chemical shifts, but this trend is not observed here (Table 8). The doublet of triplets yielded coupling constants of 6.4 Hz and 1.8 Hz (Table 8). According to typical aromatic proton coupling constants [3], the 6.4 Hz must be JCB because HC is ortho to HB, and the 1.8 Hz must be JCA because HC is meta to HA (Table 8, Figure 3). Meanwhile, the multiplet has an integration of 16.983 and a chemical shift of 7.19 ppm, and its large integration indicates that it corresponds to all the remaining protons on the molecule (HA, HB) (Table 8, Figure 3). Interestingly, the literature spectrum marks all the protons on the two inner phenyl rings as identical, despite that substitution on aromatic rings produces unequal proton environments (Figure 3, Appendix Figure 10). The signals may overlap significantly, or resolution may not be high enough to discern between the protons on those phenyl groups. In addition, the integration of 16.983 is higher than the expected integration of 16, due to the CHCl 3 signal overlapping with the multiplet—the tallest peak is at 7.23, which corresponds to CHCl3 (Appendix Figure 9). Tetraphenylcyclopentadienone’s literature spectrum shows that CHCl3 specifically overlaps with HA’s signals, making coupling constants difficult to determine (Appendix Figure 10). Coupling constants can, however, be determined from HB’s peaks in the multiplet, which are
upfield from CHCl3’s peak. From HB’s signal, coupling constants were calculated as JBC (ortho) = JBA = 6.4 Hz, due to HB being ortho to both HC and HA, and JBC (para) = 2.4 Hz (Table 8). The IR spectrum for tetraphenylcyclopentadienone only contained two prominent peaks outside of the nujol mull peaks—a ketone C=O stretch at 1709.8 cm-1 and an aromatic C=C stretch at 1596.1 cm-1 (Table 9, Appendix Figure 11). While the peaks were discernible, they were not resolved well due to the tetraphenylcyclopentadienone being dilute in the nujol. The literature IR spectrum’s C=O stretch was at 1710 cm-1, which is very close to my obtained IR spectrum, but it placed the C=C stretch at 1496 cm-1 (Table 9, Appendix Figure 12). Table 10: 1H NMR for Tetraphenylnaphthalene
Multiplicity
Integral (# Protons)
Coupling Constants (Hz)
0.000 1.548
Singlet Singlet
131.74 3.610
---
6.845
Singlet
11.159
--
7.244
Multiplet
15.782
JCE = 3.4
7.393
Doublet of doublets
2.060
7.640
Doublet of doublets
2.000
Chemical Shift (ppm)
JAB (meta) = 3.4 JAB (ortho) = 6.6 JBA (meta) = 3.25 JBA (ortho) = 6.6
Identity TMS H2O Inner phenyl protons (HF, HG, HH) CHCl3, outer phenyl protons (HC, HD, HE) Aromatic ring outer protons (HA)
Literature Spectra Chemical Shift (ppm) ---
Aromatic ring inner protons (HB)
Figure 4: Tetraphenylnaphthalene
7.01 7.39 7.560 7.82
Table 11: IR for Tetraphenylnaphthalene Wavenumber (cm-1)
Identity
1442.8 1493.9 2852.7 2923.0
Aromatic C=C (stretch) Aromatic C=C (stretch) Aromatic C-H (stretch) Aromatic C-H (stretch)
Literature Spectra Wavenumber (cm-1) 1463.4 1463.4 2957.3 2957.3
Tetraphenylnaphthalene: In the final synthesis, 3.496 g of tetraphenylcyclopentadienone reacted with 1.1 molar equivalent of anthranilic acid and 3.3 molar equivalents of isopentyl nitrite to produce 3.775 g of tetraphenylnaphthalene, a percent yield of 96.0%. The lab manual originally called for 1.5 moles of isopentyl nitrite per mole of anthranilic acid [1]; however, after adding the first 1.5 moles and refluxing for 15 minutes, the reaction did not turn orange as expected. To speed up the reaction, another equivalent of isopentyl nitrite was added, and the reaction mixture began to turn orange. After isolating the crude solid, 42 mg was used for recrystallization in 25 mL of isopropyl alcohol. Crystals did not form after twenty minutes of the solution being at room temperature, and only began to form after evaporating the isopropyl alcohol with an air stream. To ensure that enough product was obtained, another 112 mg of tetraphenylnaphthalene was recrystallized. The percent yield of recovery from both recrystallizations was only 13.6% (Table 1). Considering how slow recrystallization was, recovery would have been improved if there were more time to allow crystals to form, and if less solvent were used to dissolve the tetraphenylnaphthalene. The recrystallization brought down the overall yield of the multi-step synthesis considerably: the overall yield of the crude tetraphenylnaphthalene was 70.3%, but the overall yield of recrystallized tetraphenylnaphthalene was only 9.57% (Table 1). Due to tetraphenylnaphthalene being highly nonpolar, a solvent of 50/50 hexane/acetone was used for TLC instead of DCM. There was no tetraphenylnaphthalene standard, so the
recrystallized product was compared to tetraphenylcyclopentadienone. Tetraphenylnaphthalene yielded an Rf value of 0.92, while tetraphenylcyclopentadienone had an Rf value of 0.83 (Table 2). As expected, tetraphenylnaphthalene’s Rf value is higher than that of tetraphenylcyclopentadienone, as tetraphenylnaphthalene lacks highly electronegative atoms and is thus more nonpolar. As a result, tetraphenylnaphthalene has a higher affinity for the mobile phase of the TLC and will travel further up the plate. The melting point of tetraphenylnaphthalene was 198.6 – 203.4 °C, which overlaps with the literature value of 199 – 201 °C (Table 3). While the lower and upper values for the melting point are very close to the literature values, suggesting high purity, the range of the melting point is also wide, suggesting some impurity. A different explanation for the wide range is that the temperature readings were increasing very quickly at the time the product began to melt, and thus the readings are not fully representative of the product’s true melting point. Tetraphenylnaphthalene is expected to contain eight signals in its 1H NMR spectrum, as it contains eight distinct proton environments [1]. However, only four signals were observed (Table 10, Appendix Figure 13). The most upfield signal is a singlet with an integration of 11.159 and a chemical shift of 6.84 ppm, and it corresponds to all the protons on the two inner phenyl groups (HF, HG, HH) (Table 10, Figure 4). These protons have the lowest chemical shift because they are the furthest away from the central aromatic ring (Figure 4). The signal is a singlet, which suggests that the 10 protons comprising it are identical, but the resolution may be too low to distinguish more complicated splitting patterns (Table 10). As a result, coupling constants could not be determined for those protons (Table 10). The protons on the outer phenyl groups (HC, HD, HE) comprise the next signal, a multiplet with an integration of 15.782 and a chemical shift of 7.24 ppm (Figure 4, Table 10). The integration of 15.782 is significantly higher than the integration of 10 because the signal for CHCl3 overlaps
with the phenyl protons’ signal; a large peak corresponding to CHCl3 can be seen at 7.23 ppm (Appendix Figure 13). Aside from the CHCl3 peak, only two other peaks are visible, and the splitting between them is 3.4 Hz (Table 10). Given that a coupling constant around 2-3 Hz is characteristic of meta protons, the 3.4 Hz likely corresponds to JCE (Table 10). Once again, due to low resolution, more complex splitting patterns were not observed. The final two signals are both doublet of doublets (Table 10). The upfield doublet of doublets has an integration of 2.060 and a chemical shift of 7.39 ppm, and it corresponds to the outer protons on the central aromatic ring (HA) (Table 10, Figure 4). The downfield doublet of doublets has an integration of 2.000 and a chemical shift of 7.64 ppm, and it corresponds to the more de-shielded inner protons on the central aromatic ring (HB) (Table 10, Figure 4). The two HA and two HB are adjacent to each other, so based on the n+1 rule, the expected splitting pattern would be a triplet for both HA and HB. They are doublets of doublets, however, suggesting that each HA is split by the HB ortho to it, then by the HB meta to it (Figure 4). The coupling constants derived from HA’s signal were JAB (meta) = 3.4 Hz and JAB (ortho) = 6.6 Hz, and the coupling constants from HB’s signal are expected to be very close to that; indeed, the coupling constants from HB were JBA (meta) = 3.25 Hz and JBA (ortho) = 6.6 Hz (Table 10). On an IR spectrum, a successful synthesis of tetraphenylnaphthalene would be represented by a lack of a ketone C=O stretch between 1750 cm-1 and 1650 cm-1. Indeed, the obtained IR spectrum for tetraphenylnaphthalene demonstrated no such C=O stretch (Table 11, Appendix Figure 15). The main peaks in tetraphenylnaphthalene were from the aromatic C-H stretches at 2852.7 cm-1 and 2923.0 cm-1, as well as the aromatic C=C stretches at 1442.8 cm-1 and 1493.9 cm1
(Table 11). The literature spectrum places the C-H stretch at 2957.3 cm-1 and the C=C stretch at
1463.4 cm-1, which does not align well with my obtained spectrum (Table 11, Appendix Figure
16). The differences in peaks may be due to the differences in the solvents used; the literature spectrum appears to use nujol mull, while my spectrum used DCM. Regardless, the key peaks of tetraphenylnaphthalene can be observed in both spectra (Appendix Figure 15, Appendix Figure 16).
Conclusion: In the first synthesis, 0.049 mol of benzaldehyde was converted to benzoin; however, the conversion was unsuccessful due to large amounts of unreacted benzaldehyde. 3.004 g of stock benzoin was used to initiate the second synthesis, which produced benzil with a percent yield of 85.5%. In the third synthesis, benzil was converted to tetraphenylcyclopentadienone and had a percent yield of 85.7%. In the fourth and final synthesis, tetraphenylcyclopentadienone was converted to crude tetraphenylnaphthalene, which was then recrystallized. The crude tetraphenylnaphthalene had a percent yield of 96.0%, but the recrystallized tetraphenylnaphthalene had a percent yield of only 13.6%. Thus, the overall percent yield of recrystallized tetraphenylnaphthalene was 0.855*0.857*0.96*0.136 = 9.57%. TLC and IR confirmed that each synthesis was performed correctly, with TLC showing that the synthesis products became increasingly nonpolar and IR showing the loss or gain of key functional groups between each synthesis product. Melting point measurements determined the purity of each product; each product apart from tetraphenylnaphthalene demonstrated some degree of impurity. Lastly, 1H NMR was a means to further characterize each product and confirm the completion of each synthesis step.
Sources [1] Chemistry 346 Lab Manual. (2018). [2] Overview of Chemical Shifts in H-NMR. (n.d.). Retrieved March 8, 2018, from http://www2.ups.edu/faculty/hanson/Spectroscopy/NMR/HNMRshift.htm [3] NMR Aromatic Proton Coupling. (n.d.). Retrieved March 1, 2018, from http://www.sas.upenn.edu/~genette/NMRcoupling.pdf
Appendix Figure 1: Obtained 1H NMR Spectrum for Benzoin
Appendix Figure 2: Literature 1H NMR Spectrum for Benzoin Source: Spectral Database for Organic Compounds
Appendix Figure 3: Obtained IR Spectrum for Benzoin Source: Ethan Knight, CHEM 346 AB
Appendix Figure 4: Literature IR Spectrum for Benzoin Source: Spectral Database for Organic Compounds
Appendix Figure 5: Obtained 1H NMR for Benzil
Appendix Figure 6: Literature 1H NMR Spectrum for Benzil Source: Gazi, S. & Ananthakrishnan, R. (2012). Bromodimethylsulfonium bromide (BDMS) as a Potential Candidate for Photocatalytic Selective Oxidation of Benzylic Alcohols Using Oxygen and Visible Light. The Royal Society of Chemistry, 2, 7781-7787. doi: 10.1039/C2RA20553J
Appendix Figure 7: Obtained IR Spectrum for Benzil
Appendix Figure 8: Literature IR for Benzil Source: Spectral Database for Organic Compounds
Appendix Figure 9: Obtained 1H NMR for Tetraphenylcyclopentadienone
Appendix Figure 10: Literature 1H NMR for Tetraphenylcyclopentadienone Source: Spectral Database for Organic Compounds
Appendix Figure 11: Obtained IR Spectrum for Tetraphenylcyclopentadienone
Appendix Figure 12: Literature IR Spectrum for Tetraphenylcyclopentadienone Source: Spectral Database for Organic Compounds
Appendix Figure 13: Obtained 1H NMR Spectrum for Tetraphenylnaphthalene
Appendix Figure 14: Literature 1H Spectrum for Tetraphenylnaphthalene Source: Cant, A., Roberts, L., & Greaney, M.F. (2010). Generation of benzyne from benzoic acid using C–H activation. The Royal Society of Chemistry, 46, 8671-8673. doi: 10.1039/C0CC02547J
Appendix Figure 15: Obtained IR Spectrum for Tetraphenylnaphthalene
Appendix Figure 16: Literature IR Spectrum for Tetraphenylnaphthalene Source: Shashidher, B., Bajjuri, R., & Guguloath, V. (2011). Formation and Trapping of Benzyne. Pharmaceutica Analytica Acta, 02(07). doi:10.4172/2153-2435.1000137
Related Documents 3m3m1z
Chem 346 Lab Report 8 e26j
December 2019 43
Chem: Lab Report: Molarity 2h3e3b
November 2019 55
Chem Lab Report 2 4r726w
February 2022 0
Chem Lab Report Oxalic Acid u6c
October 2019 61
Chem Lab 5e725
October 2019 62