1. General

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

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. It might be a good idea to acquire an infrared spectrum before the esterification is started.

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 not just be warm. A refllux ring has to be observed on the inside of the condenser. The students will use the condenser with the propylene glycol again for this experiment.

During the extraction, make sure to keep track which layer contains the 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 because it surely will lead to loss of product.

The extraction of the organic layer with sodium bicarbonate solution has to be continued until the formation of carbon dioxide ceases. Why?

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

3. Nitration

Safety note:

Concentrated sulfuric acid and concentrared nitric acid are very corrosive. The mixture (1:1) 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.

The mixture has to be cooled in an ice-bath while the acid mixture is added dropwise using a syringe. Why?

If an oil is obtained after the reaction mixture was poured over ice, more ice and some water has to be added and the mixture has to be stirred until it solidifies.

Excessive amount of methanol (even if it is cold) to wash the crude product have to be avoided because this will lead to a significant losses!

The crude product is recrystallized from a solvent mixture of MeOH:water = 4:1 and not 1:4! The compound dissolves well in pure methanol at room temperature and very poorly in water.

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?

f. The EI mass spectrum of the nitro compound exhibits a strong peak at m/z=150. Which fragment can this peak be assigned to? Why is this peak not observed in the NCI spectrum?