RIBAR DIELS-ALDER REACTION

Diels-Alder Reaction: Synthesis of cis-Norbornene-5,6-endo-dicarboxylic anhydride

Jessica Ribar – U14763216

TA: Boliang Dong

Lab Partner: Zoë Jones

CHM 2211.905

RIBAR DIELS-ALDER REACTION

Introduction

Diels-Alder reactions occur when a conjugate addition reaction of a conjugate diene connected to an alkene takes place. In other words, when a dienophile and a diene react with each other. This reaction then produces a cyclohexene. A simple example of a Diels-Alder reaction is the reaction between 1,3-butadiene and ethyne, which forms 1,4-cyclohexadiene. This example is shown below in figure 1.

Figure 1: Mechanism of synthesis of 2-methyl-1-butene.

The Diels-Alder reactions are stereospecific, meaning an alkene undergoes addition that forms two additional s bonds, either syn or anti addition. In Diels-Alder reactions, cis reactants give a cis product, and trans reactants get trans products. If both diene substituents obtain the same stereochemistry, then they end up on the same face. However, if they have different stereochemistry, they will end up on opposite sides of the product. [1]

The mechanism of the synthesis of Diels-Alder in this experiment is shown below in figure 2. As shown, when cyclopentadiene reacts with maleic anhydride, the product we are trying to achieve may form while it may also form the exo version of that same compound.

Figure 2: Mechanism of synthesis of cis-Norbornene-5,6-endo-dicarboxylic anhydride

RIBAR DIELS-ALDER REACTION The possible side reaction for the Diels-Alder reaction is the formation of dicyclopentadiene. This reaction is shown in figure 3.

Figure 3: Possible side reaction during the synthesis.

Experimental Procedure

Figure 3: Flow chart of experiment 2. Cracking dicyclopentadiene and performing the Diels-Alder reaction. [2] RIBAR DIELS-ALDER REACTION Chemical Tables

Dicyclopentadiene Maleic Anhydride Ethyl Acetate

Formula !"#$"% !&$%'( !&$)'% Molar Mass 132.206 g/mol 98.057g/mol 88.106 g/mol Structure

Melting 10.31 ℃ 52.56 ℃ -83.8 ℃ Point Physical Colorless crystalline solid. Colorless or white crystals with Fruity odor with bittersweet Properties Sharp unpleasant odor. pungent odor. taste. Table 1: Physical and chemical properties of the main chemicals used for experiment 2. [3]

Results

Physical Appearance Mass Collected Percent Yield Melting Point White crystals. 0.257 g 76.7 % 140-145 ℃

Calculating Theoretical Mass

" BCD EF Maleic Anhydride (MA) à 0.204> ?@× = 0.002 JKL ?@ G)." H EF

164.2 > VW MℎOKPOQRSTL ?TUU à 0.002 JKL VW× = 0.335 > VW 1 JKL VW

Actual Mass Collected

\RTL ]RQℎ ^PK_`SQ > − MTPO_ bRTL > = @JK`cQ Kd ^PK_`SQ (>)

26.02 g − 25.975 g = 0.045 g

Amount collected: 0.212 g + 0.045 g = 0.257 g

Calculating Percent Yield

@SQ`TL JKLOU 0.257 > = h 100% = 76.7% MℎOKPOQRSTL JKLOU 0.335 > RIBAR DIELS-ALDER REACTION Discussion

The amount of product obtained was converted into moles to achieve the percent yield which was 76.7 %. For this experiment, the percent yield accomplished was decent. The possible side reaction of cis-Norbornene-5,6- endo-dicarboxylic anhydride could have occurred to lower the percent yield. The simple distillation process performed was unable to produce the cyclopentadiene needed for the second part of the experiment. This problem was fixed by using product from another group’s distillation process.

The melting point obtained from the sample collected was less than the literature value by about 20 ℃ which is a pretty significant amount. This could have resulted from a few different factors. The cyclopentadiene formed could have distilled for too long which could have affected the product for the Diels-Alder reaction. The amount of cyclopentadiene used for this experiment was also much higher than instructed to add. This could have skewed the results.

Conclusion

Diels-Alder reactions are used prevalently in the scientific community. David Staple and Samuel Butcher have used Diels-Alder reactions for their research in studying RNA structures with diverse functions. The information obtained about the RNA catalyzing the C-C bond that was formed from a Diels-Alder reactions led to discoveries about the RNA itself and how it conforms to a fold of its three helicases. [4] Overall, this experiment did not produce a Diels-Alder product. This can be stated because of the significant difference in the melting points of the sample obtained and the literature value. With a better simple distillation set up and careful measurements and observations, the experiment could be successful.

References

1. “Chapter 10: Diels-Alder Reactions.” Chemistry at University of Calgary. N.p. n.d. Web. 31 Jan. 2017. 2. Weldegirma, Solomon. "Experiment 2: Acid-Base Extraction." Experimental Organic Chemistry 6 (2016): 10-11. 3. “Dicyclopentadiene, Maleic Anhydride, Ethyl Acetate CH3COOC2H5 – PubChem.” National Center for Biotechnology Information. U.S. National Library of Medicine, n.d. Web. 31 Jan. 2017. 4. Staple, David, and Samuel Butcher. “Pseudoknots: RNA Structures with Diverse Functions.” PLOS Biology. N.p,n.d. Web. 31 Jan. 2017.