The cycloaddition of a conjugated diene and a dienophile, which is drove by forming new σ-bonds from π-electrons of the diene and dienophile, which are energetically more stable than the π-bonds.
During the Diels-Alder reaction, the temperature should be kept between 60-70 ℃. Because the boiling point of the butadiene is low and do not let it vaporize. After cycloaddition, pour the reaction mixture into 50 ml water under room temperature, the product would precipitate because of the low temperature. The acid added for the hydrolysis part is very important because acids have been used to accelerate the rate of the intra-molecular Diels-Alder reaction.
The PEG 200 used in this experiment as the solvent for maleic anhydride is make the experiments more green, which is less harmful and more environmental friendly. The melting point measurement is helping us to determine what we get basically.
Compare with the IR spectra I got, the peak at 1792.62 cm-1 in the first spectra express the C=O bonds of the initial cycloaddition product, and the peak at 1697.14 cm-1 in the second IR spectra shows the C=O bonds of carboxylic acid ( RCOOH) of the final product.