Density (g/ml) Maleic anhydride s4 200 Corrosive, toxic Toluene lll Flammable

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1 Sample lab report for Experiment in Palleros (pp. 398-a00) Reaction of 9-Anthraldehyde with Maleic Anhydride via the Diels-Alder Reaction Sam P. Le January 18,2013 Purpose The purpose of this experiment was to demonstrate the utility of the Diels-Alder reaction by reacting 9-anthraldehyde with maleic anhydride to form a9-anthraldehyde-maleic anhydride adduct. The 9-anthraldehyde-maleic anhydride adduct was characterized by melting point determination, infrared (IR) spectroscopy, UV-Vis absorption spectroscopy, as well as lh NMR spectroscopy. Reagent Table [] Compound 9-anthraldehyde (9- anthracenec arboxaldehyde) Molecular weight (s/mol) Density (g/ml) Melting point ("C) r03-10s Boiling point ("C) Miscellaneous information Maleic anhydride s4 200 Corrosive, toxic Toluene lll Flammable Hexanes (mixture of isomers) 9 - anthraldehyde -maleic anhydride adduct Flammable Nujol N/A Heavy mineral oil DMSO-d r89 Deuterated Acetone t Flammable Structures, Chemical equations, and Mechanisms CI4,O +/, \ o a C,r,ls- Aldzr) U,r aleia- 1- uil,nrl*"lia^l^,x ril b, tdw',,'- o r1 6ru 4 ->^thnald"\1"- ^alo" a"l1)";/'u zdl"t W\c,l"r*ls*r Lt-twr-ta{)

2 Sample lab report for Experiment l9,{.l in Palleros (pp. 39S-a00) Procedure The experiment was conducted according to the procedure describedin Palleros, Experimental Organic Chemistry [2]. The only modification to the published procedure was the addition of a sand bath to improve heating during reflux. Data and Observations Amount of maleic anhydride used: 350 mg Amount of 9-anthraldehyde used: 250 mg Weight of 9-anthraldehyde-maleic anhydride adduct (crude): 325 mg Appearance of adduct (crude): white, powdery solid Amount of crude product used for recrystallization: 150 mg Amount of recrystallized adduct recovered: 92 mg Appearance of recrystallized adduct: colorless needles MP of recrystallized adduct: 'C IR and UV-Vis spectra of 9-anthraldehyde are attached as Figure I and2, respectively. IR, UV-Vis, and rh NMR spectra of recrystallizedg-anthraldehyde-maleic anhydride are attached as Figure 3 and 4 respectively. Calculations Calculation of theoretical yield attached as Figure 5. Percent yield : (actual yield / theoretical yield) x 100%o : (325 mg / 368 mg) x 100 :,88.3 % Percent recovery of adduct in recrystallization: (mass recovered / mass of crude used) x l00yo : (92mgl 150 mg) x 100 :61"h

3 Sample lab report for Experiment 19A.1 in Palleros (pp. 398-a00) Discussion In this experiment, the usefulness of the Diels-Alder reaction in organic synthesis was demonstrated by the reaction of 9-anthraldehyde with maleic anhydride to form a 9- anthraldehyde-maleic anhydride adduct. The Diels-Alder reaction is an example of a cycloaddition reaction and is an important reaction in organic synthesis. The usefulness of the Diels-Alder reaction arises from the fact that two carbon-carbon bonds can be formed in a single step. Consequently, large and complex molecules can be achieved in an efficient manner. The Diels-Alder reaction is also referred to as a [4+2] cycloaddition reaction because it involves the reaction of a conjugated diene, which contains 4 zr electrons, and a dienophile, which contains 2 n electrons. When a conjugated diene reacts with a dienophile, a 6-membered ring product, known as an adduct, is formed [2]. In a Diels-Alder reaction, the bonds are broken and formed simultaneously and, therefore, is a concerted reaction. While the Diels-Alder reaction proceeds readily, it is also a reversible reaction. At high temperatures, the Diels-Alder adduct decomposes into a conjugated diene and a dienophile [2]. Interestingly, the conjugated diene and dienophile formed in a retro-diels-alder reaction are not necessarily the original starting diene and dienophile in some cases [3]. The structure of the Diels-Alder adduct can be designated as endo or exo when the dienophile possesses a one or more substituents. The terms endo and exo refer to the orientation of a substituted dienophile as it approaches the diene. Endo refers to the orientation in which the substituents on the dienophile point towards the diene while exo refers to the orientation in which the substituents on the dienophile point away from the diene. In general, endo selectivity predominates due to the preferred overlap of n orbitals on the dienophile substituents with the n orbitals on the diene [2, 3]. In this experiment, the adduct of 9-anthraldehyde and maleic anhydride was synthesized using the Diels-Alder reaction. In this case, the conjugated diene was 9-anthraldehyde and the dienophile acted as the dienophile. According to the accepted mechanism of the Diels-Alder

4 Sample lab report for Experiment 19,{.1 in Palleros (pp. 398-a00) reaction, 9-anthraldehyde and maleic anhydride reacted in a concerted reaction wherein 2 carbon-carbon bonds were formed simultaneously, leading to the formation of a new 6- membered ring. As discussed above, it was expected that endo selectivity would predominate. However, due to the symmetry of both the diene and dienophile, there was no discernible preference. The Diels-Alder reaction of 9-anthraldehyde and maleic anhydride proceeded as expected. Interestingly, during the course of the reaction, the color of the reaction mixture changed from deep yellow to colorless. The initial deep yellow color was due to 9-anthraldehyde. 9- anthraldehyde is a highly conjugated compound containing three aromatic rings. Due to its high conjugation, it absorbs light in the visible spectrum, leading to its deep yellow color. However, the conjugation in 9-anthraldehyde was disrupted when it reacted with maleic anhydride. The adduct was no longer highly conjugated. As a result of the disruption in conjugation, absorbance was shifted outside of the visible spectrum, leading to a colorless substance. The change in color from deep yellow to colorless was an indication that the Diels-Alder reaction worked. 325 mg of crude product was isolated as a white powdery solid. This corresponds to 88.3 % yield. The theoretical yield calculations are shown in Figure mg of the crude product was recrystallized from a solution of toluene-hexanes according to the procedure. 92 mg of the recrystallized adduct was isolated as colorless needles. This corresponds to 6l o/o recovery. The recrystallized 9-anthraldehyde-maleic anhydride adduct was analyzed using IR, UV-Vis, and lh NMR spectroscopy. The IR and UV-Vis spectra of the adduct was compared to those of the starting material, 9-anthraldehyde. The IR and UV-Vis spectra of the starting material are shown in Figures I and2, respectively. The IR and UV-Vis spectra of the adduct are shown in Figures 3 and 4, respectively. Comparison of the IR spectra (Fig. 1 and 3) showed a significant shift in the C:O stretch on the aldehyde. This is a reasonable observation considering that the carbonyl in the product is no longer bonded to an sp2-hybidized carbon as it was in the starting material. Comparison of the UV-Vis spectra (Fig.2 and 4) showed a dramatic reduction of the peak at 400 nm in going from starting material to the adduct. This result suggests that the adduct does not absorb in the visible range as 9-anthraldehyde does. This is confirmed by the observation that the

5 Sample lab report for Experiment l9a..l in Palleros (pp. 398-a00) product isolated was colorless. The adduct was also aflalyzed,by th NMR spectroscopy using deuterated DMSO (DMSO-d6) as solvent. The NMR spectrum that was obtained agreed well with a literature spectrum [2]. The melting point range of the adduct was also determined. The melting point range of the recrystallized adduct was oc. The observed melting point range was lower and broader than the literature melting point range of 'C l2l. During the course of determining the melting point range, a color change from colorless to deep yellow was observed around 232'C. This might be due to the decomposition of the adduct to form 9-anthraldehyde via a retro-diels- Alder reaction, which explains the color change. If this was the case, the 9-anthraldehyde and maleic acid would act as impurities, thus lowering and broadening the melting point range. Overall, the reaction was easy to set up and worked as expected. The percent yield was good. There was loss of product when the product was transferred from the Hirsch funnel to the weighing paper. Due to the low humidity in the lab, static electricity also caused some of the product to stick to the sides of the funnel during transfer. Conclusion In this experiment, the Diels-Alder reaction between 9-anthraldehyde and maleic anhydride was successful. The melting point range as well as the IR, UV-Vis and NMR spectra suggest that the adduct was synthesized. The experiment was enjoyable because it demonstrated the usefulness of the Diels-Alder reaction and how easy it can be used to build large molecules. Bibliography 1. Sigma-Aldrich Catalogue (hltp/,/wyw,qismqal,etrigb,gpmlqhe{_niflfy-hln{, accessed Il18l20l3) 2. Daniel R. Palleros, Experimental Organic Chemistry (2000) 3. Francis A. Carey, Organic Chemistry, 5th ed.