Question

Why rinse with methanol?:

During a macrocyclic Synthesis experiment, propanoic acid is first refluxed. Pyrrole and benzaldehyde is then added and heated to reflux. During the work up stage, crystals should form after the mixture cools to room temperature and will be separated by filter filtration. Why is it important that the product is thoroughly washed with methanol until the washings are colorless?

Answer 1

Answer:-

As we know that Benzaldehyde is colorless liquid having a pleasant almond like odour. It is insoluble in water and soluble in methanol, ethanol and diethyl ether.

Also we know that the Pyrrole is also colorless volatile liquid that darkens upon exposure of air. It is slightly soluble in water but completely soluble in ether, methanol and ethanol.

therefore

During the macrocyclic synthesis experiment , propanoic acid is first refluxed. Pyrrole and benzaldehyde is then added and heated to reflux. During the work up stage, crystals should form after the mixture cools to room temperature and then filtered the solution and we get the crystals of macrocyclic compound having some traces of Pyrrole and benzaldehyde as a contaminated form that would be removed by thoroughly washing with methanol because both Pyrrole and benzaldehyde are soluble in methanol. Colorless washing indicates that completely removal of pyrrole which darkens upon exposure of air if it is present in the crystals then crystals becomes brown in color. That is why rinsing of crystals with methanol is important in the synthesis of  a macrocyclic compound experiment.