Maleic Anthracene Lab Report

Abstract For the following experiment, a Diels-Alder reaction between maleic anhydride and anthracene was conducted. Reflux mechanism was used for the reaction to occur. To increase the speed of the reaction, xylene was used because of its high boiling point. After the reaction was complete, 1.08g of the off white product was obtained with a yield of 69.7%. It was not clear if a pure product had been formed because time constraints did not allow us to perform thin layer chromatography.
Introduction
The Diels-Alder reaction is a commonly used reaction in Organic Chemistry. In this reaction, an electron rich diene reacts with an electron poor dienophile and produces a new six-member ring. There are not any ionic and radical intermediates
present in this reaction. Instead, the reaction occurs through a concerted process in which bonds are broken and made simultaneously. The flow of electrons goes from a Higher Occupied Molecular Orbital (HOMO) to Lowest Unoccupied Molecular Orbital (LUMO). As the energy between HOMO and LUMO decreases, less energy is required to transfer electrons from the HOMO to the LUMO state, which allows the reaction to occur faster. Benzene rings and related aromatic rings do not go through a Diels-Alder reaction. In the case of anthracene, the reaction takes place in the middle of the ring even though the kinetic barrier is relatively high. The pi-bond allows of anthracene rings allow for the reaction to take place, after which the aromaticity of the ring gets lost. There are two ways of accelerating such slow Diels-Alder reactions. One way is to simply reflux the solution in a solvent with a high boiling point and another method that can be used is adding a Lewis acid such as aluminum chloride into the reaction. Heat can also be used when refluxing by heating the reactants and using xylene, which is a high boiling point solvent to create a relatively slow Diels-Alder reaction. The figure below illustrates the reaction of an electron rich anthracene reacting with an electron-poor maleic anhydride reacting in a Diels-Alder reaction:

Maleic Anhydride Anthracene Diels-Alder Adduct

Experimental Procedures To start this experiment, refluxing equipment was cleaned and set up.
A condenser, 100mL round bottom flask, and a drying tube were clamped near the sink so that water could be run through the condenser. 31mL of xylene, 5 boiling chips, 0.56g of maleic anhydride, and 1.02g of anthracene were mixed in the round bottom flask. A heating mantle was then used to heat the mixture and allowed to reflux for one hour. After refluxing for one hour, the product was left to cool to room temperature and then placed in an ice bath to precipitate the product. The product was vacuum filtered and an off white powdery substance was obtained. The product was then washed with two 10mL portions of pentane and left to dry for 10 minutes over the vacuum funnel. Product was left in the drawer to dry over the weekend and weighed 1.08g after drying. TLC and H-NMR was not conducted due to time
constraints.

Results
Calculations
Moles of anthracene
(1.00g anthracene )(1mol/178.23g) = 0.00561mol
For equimolar reactant:
(0.00561 mol) (98.06g/mol maleic anhydride) = 0.5502g maleic anhydride
Theoretical Yield of Product: (0.00561 mol)(276.29 g/mol product) = 1.5502g product
Actual Yield of Diels-Alder Adduct: [(1.08g obtained D.A.
Adduct) / (1.55g theoretical)]100% = 69.7%

TLC analysis (Estimated)
*Although TLC was not performed in lab due to time constraints. The table below is an estimate of Rf values for what should happen when you spot the two starting materials and the product on a TLC and run them in Methylene Chloride.
Spot Rf Value
SM (maleic anhydride) 0.81 (most non – polar, travels furthest)
SM (anthracene) 0.75 (More non polar than CP)
CP (Diels-Alder Adduct) 0.32 (Most polar, travel the least)

H-NMR Analysis of Diels Alder adduct (Back of lab manual)
PPM Integral Multiplicity Details
7.2-7.4 1 Multiplet These peaks are indicative of hydrogen’s from the benzene rings. Since there are two of them in the molecule, there are two sets of hydrogens that are similar in energy and will split each other from the other set.
4.8 1 Singlet I believe this peak is coming from the hydrogen connected to the carbon that also connects to the anhydride ring. It is deshielded by the neighboring benzene rings.
3.5 1 Singlet This peak is coming from the hydrogen attached to the anhydride. They are slightly downfield because it is close to a carbon connected to a ester
group.