Evaluation Of L – Proline As A Catalyst For An Asymmetric Aldol Reaction

2273 words - 10 pages

Evaluation of L – Proline as a Catalyst for an Asymmetric Aldol Reaction

Abstract
This reaction is divided into two parts. In the first part acetone, L – proline and 4 – nitrobenzaldehyde are reacted to give (R)-4-hydroxy-4-(4-nitrophenyl)butan-2-one as the major product along with (S)-4-hydroxy-4-(4-nitrophenyl)butan-2-one. The identity of the product is confirmed by IR spectra of the product which gives peaks at 1073.94 cm-1, 1330 cm-1, 1515.05, 1600.13 cm-1, 1708.25 cm-1, 2930.82 cm-1and broad peak at 3418.10 cm-1. The mass of the product is 0.013 grams which gives a percentage yield of 29.81%. The melting point of the product is not taken due to minimal product.
In the second part ...view middle of the document...

The goal of this lab is to produce similar results.
Experimental (Materials & Methods)
Table of Reagents |
Reagent | Molecular Weight | Amount | mmol | Melting Point (℃) | Boiling Point (℃) |
L - Proline | 115.13 | 0.024 grams | 0.208 | 205 – 228 | |
DMSO | 78.13 | 4 mL | 56.316 | 19 | 189 |
Acetone | 58.08 | 1 mL | 13.619 | - 95 - -93 | 56 – 57 |
4 – nitro benzaldehyde | 151.12 | 0.060 grams | 0.397 | 103 – 106 | 299.6 ± 23 |
Ammonium Chloride sol. | 53.491 | 5 mL | | | |
Ethyl Acetate | 88.11 | 10 mL | 101.805 | - 83.6 | 77.1 |
MgSO4 | 120.37 | | | 1124 | |
CH2Cl2 | 84.93 | 4.5 mL | 70.47 | - 96.7 | 39.6 |
DMAP | 122.17 | 0.0075 grams | 0.061 | 110 - 113 | 162 |
Pyridine | 79.10 | 0.075 mL | 0.931 | - 41.6 | 115.2 |
(-) – MTPA - Cl | 252.62 | 0.125 mL | 0.400 | | 213 – 214 |
0.1 M HCl | | 2.5 mL | | | |
Sat. Bicarbonate sol | | 2.5 mL | | | |
Brine | | 2.5 mL | | | |

Reaction
1. Dissolve 24 mg of L – proline in 5 mL anhydrous DMSO/acetone (4:1) for 15 minutes.
2. To this solution add 60 mg of 4 – nitrobenzaldehyde and stir the mixture for at least 30 minutes.
Product Isolation
3. After the reaction is complete, dilute with 5 mL of saturated ammonium chloride solution and extract the product with 10 mL of ethyl acetate.
4. Dry the organic layer over MgSO4, separate the drying agent by gravity filtration and evaporate the solvent in a rotary evaporator.
Product Purification
5. Purify the product by flash chromatography using 50% petroleum ether/50% ethyl acetate as the eluting solvent. Combine the fractions containing product and evaporate the solvent.
Product Characterization
6. Record the mass of the product obtained. Obtain 1H NMR, 13C NMR and IR verification of product identity and purity, and compute the percentage yield.
Mosher Analysis
Reaction
7. Dissolve 75 mg of Aldol product in 4.5 mL anhydrous CH2Cl2 in a flame dried vial.
8. Add 7.5 mg of DMAP followed by 0.075 mL pyridine and 0.125 mL (-)-MTPA-Cl. Allow the mixture to react under nitrogen with SureSeal overnight or until TLC shows complete consumption of starting materials.
Product Isolation
9. Wash crude reaction mixture with 0.1 M HCl (2.5 mL), saturated bicarbonate solution (2.5 mL) and brine (2.5 mL).
Product Characterization
10. Determine the ratio of diastereomers by 1H NMR and from the ratio calculate the enantiomeric excess of the Aldol reaction
Results
Mass Table |
Watch glass & Product | Watch glass | Product |
41.902 grams | 41.770 grams | 0.013 grams |

Product Name (major) | (R)-4-hydroxy-4-(4-nitrophenyl)butan-2-one |
Product Molecular Mass | 209.20 grams/mol |
Limiting reagent | L – Proline (0.000208 mmol) |
Theoretical Yield | 209.20 gramsmol × 0.000208 mol = 0.0436 grams |
Percentage Yield | 0.0130.0436 gramsgrams × 100 = 29.81 % |
Melting Point | Not determined due to very little product |

Significant IR peaks (cm-1) |
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