1. General

Review the following topics: esterfication, infrared spectroscopy, NMR spectroscopy, mass spectrometry

2. Esterification

Safety note: Concentrated sulfuric acid is very corrosive. Nitrile gloves have to be worn when transferring it.

It is very important that the benzoic acid used in this reaction is very dry. If you are not sure about it, place it under the heating lamp for 15 minutes to dry it a little more.

Do not overheat the mixture, because it will char (turn black) due to decomposition of the benzoic acid, particularly if a lot of concentrated sulfuric acid was used in the reaction. A gentle boil is enough to get the reaction going. However, the mixture has to boil and just be warm!

During the extraction, make sure that you think about first which layer contains your product. If you do not observe a phase separation, add more water. If necessary, transfer the mixture into a small separatory funnel. However, this should be avoided as much as possible since it surely will lead to loss of product.

The extraction of the organic layer should be continued until no more carbon dioxide forms. Why?

It is very important to remove the methanol from the reaction mixture, because alcohols and nitric acid form unstable alkyl nitrites.

3. Nitration

Safety note: Concentrated sulfuric acid and concentrared nitric acid are very corrosive. The mixture will be provided by lab support. Nitrile gloves have to be worn when transferring it.

The ester has to be dissolved in concentrated sulfuric acid first before the acid mixture is added.

Make sure that you cool the mixture in an ice bath. Add the acid mixture dropwise using a syringe. Why?

If you obtain an oil after you poured your reaction mixture on ice, add more ice and some water and keep mixing until the mixture solidifies.

Do not use an excessive amount of methanol (even if it is cold) to wash your crude product. You will lose significant amounts!

The crude product is recrystallized from a solvent mixture of MeOH:water = 4:1 and not 1:4!

4. Thing to think about

a. Why do you reflux the mixture in the esterification experiment?

b. Why do you use sodium bicarbonate during the work-up of the esterification mixture? Could you use sodium hydroxide as well?

c. Why do you have to control the temperature of the reaction mixture in the nitration reaction very carefully?

d. What are other methods to generate a nitronium ion?

e. What would happen if the student attempts to recrystallize the crude nitration product from a solvent mixture MeOH:water = 1:4?