Synthesis and Characterization of Acid via Diels-Alder Reaction

Abstract

The Diels-Alder reaction was performed between a diene, sorbyl alcohol, and a dienophile, maleicanhydride, to obtain a final product of 1,3,3a,4,5,7a-hexahydro-5-methyl-3-oxo-4-isobenzofurancarboxylic acid. The final product was a white powder which yielded 87.6 % with a melting point of 156°C – 161°C. Both the infrared and 1H-NMRspectrums were collected to further analyze and support the final product.

Introduction

The Diels-Alder reaction was introduced by both Otto Diels and Kurt Alder. This reaction is known to be the most essential transformations in organic chemistry due to the reaction allowing for selective formation of two C-C bonds and having up to four chiralcentres in a single step.

This reaction is an example of a pericyclic reaction which is done through cyclic transition states. A cycloaddition [4+2] is performed and is known to be very significant in building a six-membered rings2.

The Diels-Alder reaction is said to be very essential but there are always pros and cons. In this reaction, the diene must be able to adopt a s-cis conformation so that the two ends are close enough to react with the dienophile in which will result in a successful reaction.

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Electron withdrawing groups are attached to the dienophile and the electron donating groups are to be associated with the dienes. This is done to lower energy of the lowest unoccupied molecular orbital in the dienophile and increase the energy of the highest in which is referring to the diene, overall resulting in an overlap of orbitals.

The Infrared spectra and 1H-NMRspectra’s are used to analyze the product further.

The IR uses vibrations in order to determine the chemical composition of a product and the proton NMR uses the proton positions to figure out the structure of the product.

C6H10O + C4H2O3 → C10H12O4

[ Sorbyl alcohol + MaleicAnhydride 1,3,3a,4,5,7a-hexahydro-5-methyl-3-oxo-4-isobenzofurancarboxylic acid]

Experimental

In a 50 mL beaker, sorbyl alcohol (0.53 g) and maleicanhydride (0.52 g) were weighed and added into the beaker respectively before being mixed together using a glass stir rod for approximately 35 minutes. The final product resulted in a white powder weighing 0.92 g with a yield of 87.6 % and a melting point range of 156°C – 161°C. The product was analyzed by using an Infrared Spectroscopy. An H-NMR spectra was provided.

Results

Discussion

The product obtained from the Diels-Alder reaction of mixing both sorbyl alcohol (diene) and maleicanhydride (dienophile) was 1,3,3a,4,5,7a-hexahydro-5-methyl-3-oxo-4-isobenzofurancarboxylic acid. This reaction was found to be exothermic which was indicated by the warm touch of the beaker during the experiment. As both regents were mixed together, a yellow substance was formed then lastly, a white powdered precipitate was the end result.

The experimental melting point obtained for this product was found to be 156°C – 161°C which was close in range with the literature melting point value of 161°C1. The melting points being in agreement with one another indicates that the product was indeed pure. The percentage yield of 87.6% further coagulates that most of the product was recovered from the experiment. Dealing with a diene, sorbyl alcohol, and a dienophile, maleicanhydride, the p-orbitals perfectly overlap one another. This reaction occurs when the diene transforms into a cis conformation, thus allowing it’s two ends to get close in contact with the dienophile thus resulting in a reaction and obeying the endo-rule. The endo-rule is obeyed due to the hydroxymethyl group being able to attack the anhydride based on its cis positioning.

An infrared spectrum (IR) was obtained by utilizing the product from the experiment. Through the analysis of the IR spectra, the following functional groups were observed. The broad stretching at 3277.99 cm-1 was an indication of a hydroxyl group in which was associated with a carboxylic acid. The weak stretching at 2898.14 cm-1 was an indication that an alkane C-H was present. There were two carbonyl groups present at 1726.56 cm-1 which was indicated by a weak stretch, and at 1756.81 cm-1 which was indicated by a strong stretch. A carbon double bonded to a carbon with medium stretch was observed at 1689.12 cm-1, which was due to the bond in the 6-membered ring. And lastly, the C-H bond at 1130.15 cm-1 was indicated by carbon-hydrogen bending which was found throughout the product’s structure. The IR spectrum showed great indication that the two reagents did indeed react successfully.

An 1H-NMR spectrum was provided to further analyze the reaction. Proton NMR’s are used to identify proton signals. There were 10 protons observed within the structure. The first proton was assigned as a doublet of a doublet at 4.191-4.207 ppm. The second proton was assigned as another doublet of a doublet at 4.447-4.460 ppm. The third proton was assigned as a multiplet at 3.198-3.224 ppm. The fourth proton was assigned as a doublet of a doublet at 5.888-5.912 ppm.

The fifth proton, a doublet of triplet at 5.548-5.568 ppm. The sixth proton, a multiplet at 2.727-2.753 ppm. The seventh proton, which was the most evident proton, the methyl group of the product with 3 hydrogens, was a doublet at 1.157-1.167 ppm, in which was observed upfield. The eighth proton was assigned as a triplet at 3.159-3.174 ppm, the ninth proton was assigned as a doublet of a doublet a 3.352-3.371 ppm and lastly, the tenth proton was the most downfield and deshielded. This proton was the hydrogen of the hydroxyl group and this proton was assigned as a singlet at 6.450 ppm. The 1H-NMR spectrum accounted for all 12 hydrogens found in the product, 1,3,3a,4,5,7a-hexahydro-5-methyl-3-oxo-4-isobenzofurancarboxylic acid.

Conclusion

The Diels-Alder reaction was based on the mixture of two regents, sorbyl alcohol (diene) and maleicanhydride (dienophile), in which formed 1,3,3a,4,5,7a-hexahydro-5-methyl-3-oxo-4-isobenzofurancarboxylic acid as it’s final product. The product yielded a percentage of 87.6 % with an experimental melting point of 156°C – 161°C. Due to such high yield and the experimental melting point range agreeing with the literature value of 161°C, it is evident that the product was pure. Both the infrared spectroscopy (IR) and 1H-NMR spectrum aided in analyzing the product further to support the structure of the product’s compound. Overall, the Diels-Alder reaction was fast and performed in a single step, thus forming C-C bonds alongside four chiralcentres.

References

1. Brettle, R.; Cummings, DP.; Journal of the Chemical Society, Perkin Transaction 11977, 21:2385
2. Brocksom, Timothy John, Nakamura, Joanita, Ferreira, Maria Lúcia, & Brocksom, Ursula. (2001). The Diels-Alder reaction: an update. Journal of the Brazilian Chemical Society, 12(5), 597-622.
3. Fujimoto, H.; Sakata, K.; Origin of the endo Selectivity in the Diels–Alder Reaction between Cyclopentadiene and MaleicAnhydride, European Journal of Organic Chemistry, 2016, 25, (4275-4278), (2016).
4. Garcia, J.; Mayoral, J.; Salvatella, L.; The Source of the endo Rule in the Diels−Alder Reaction: Are Secondary Orbital Interactions Really Necessary?2005, pp 85-90

Appendix

MW sorbyl alcohol = 98.17 g/mol

MW maleicanhydride = 98.06 g/mol

Mass sorbyl alcohol = moles x MW

= (0.005 mol) x (98.17 g/mol)

= 0.4909 g

Mass maleicanhydride = moles x MW

= (0.005 mol) x (98.06 g/mol)

= 0.4903 g

Percentage yield = (mass of product obtained) / (mass sorbyl alcohol + mass maleicanhydride) x 100 %

= (0.92 g)/(0.53 g + 0.52 g) x100%

= 87.6 %