Preparation of Acetaminophen | Experiment 2, Lab Reports of Organic Chemistry

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Experiment 2

Preparation of Acetaminophen

p-aminophenol material used: 2.1 g

acetic anhydride: MW = material used: 2.0 mL density: 1.10 g/mL

NH 2

OH OH

NHCOCH 3

CH 3 O CH 3 C O

O

• CH 3 CO 2 H

Note: The quality of p-aminophenol is sufficient that the Norit treatment should not be necessary.

NH 2

OH

p-aminophenol: not very soluble in water

Soluble in HCl

However!

• HCl

NH 3

OH

Cl-

1. The NH 3 +^ group in not reactive in this form
2. Therefore, CH 3 CO 2 - Na +^ is added

NH 3

OH

Cl-

NH 3

OH OH

NH 2

• CH 3 CO 2 H

Cl-

• CH 3 CO 2 -^ Na+

The solubility is increased while maintaining a small amount of the free reactive amino group in equilibrium with the ammonium salt

1. Heat your reaction mixture on a hot water bath
2. Cool your reaction mixture and scratch with a glass rod, if necessary, to achieve crystallization (wait about 1 hr, use this time to work on the aspirin experiment)
3. Vacuum filter your crystals and recrystallize your acetaminophen from hot (boiling ) water using a hot plate.
4. Identify the product by its melting point and determine the yield (next week).

Recrystallization of Solids

1. Dissolve the solid in a minimum amount of hot solvent.
2. If necessary, filter the hot solution if everything doesn’t dissolve, by keeping everything hot.
3. Allow the hot solution to remain undisturbed; cool in ice water after the solution has reached room temperature.
4. Vacuum filter the solid and wash with a small amount of cold solvent.
5. Vacuum filtration is used to quantitatively remove the mother liquor which contains soluble impurities.

lec 1

Temperature

Solubility

g/100mL

Aspirin (from last week)

1. Weigh you purified aspirin and determine the yield Save a small amount for a mp determination
2. Recrystallize from ethyl acetate

Aspirin is quite soluble in ethyl acetate so it is important to use your smallest Erlenmeyer flask and a minimum of solvent. Usually, this means evaporating and concentrating the solution once all the solid has dissolved. Allow the solution to cool slowly!

3. Ferric chloride test: ferric chloride often forms colored complexes with enols and phenols. It is therefore used as a test for enols. You should test salicylic acid, your purified aspirin and your recrystallized aspirin for the presence of any enol. Only a few mg are needed for the test!
4. Take a melting point of your purified and recrystallized aspirin and run an IR spectrum of the recrystallized aspirin.

Melting point determinations:

1. Only a mg or less is needed for a melting point determination.
2. The heating rate should be 2-3 ° C per min. For a compound with a known melting point, heat quickly to within 10-15 ° quickly, then lower the heating rate accordingly to obtain the desired heating rate.
3. If the melting point of the solid is not known, the following should be followed: Heat the sample 10-15 °/min until the sample melts. Using a new sample, cool the apparatus to about 10-15 ° below the observed melting point and use a fresh sample of solid. Raise the temperature at the correct heating rate, 2-3 ° C per min.

Experiment 3

Isolation of caffeine from tea (^) N

N CH 3

CH 3

N

N

CH 3

O

O

Caffeine is a natural product produced by a variety of botanicals that constitutes about 5% of the dry weight of tea leaves. It is a stimulant and used in a variety of over the counter drugs. In this experiment we will isolate caffeine from a host of other compounds present in tea by taking advantage of the solubility of caffeine in water.

In addition to the caffeine that is water soluble, some tannins, chlorophyll and various flavonoids and other compounds are also somewhat soluble in water giving the brewed tea its characteristic color and beneficial effects.

Calcium carbonate is added to help precipitate some of the tannins.

In this experiment you will be asked to determine the % caffeine in dry tea leaves. You will use 14 g of tea or 6 tea bags (13.6g) and 200 mL of water. After brewing and filtering, you will measure the amount of water recovered. You will use the fraction of liquid recovered in your final calculation to determine how much caffeine was originally present in the tea leaves.

Molecular structure of the flavone backbone (2- phenyl-1,4-benzopyrone)

O

O

The caffeine dissolved in water will still be warm by the time it is time to extract.

DO NOT use CH 2 Cl 2 to extract until the aqueous layer is at room temperature. Methylene chloride has a low boiling point (~40 °C) and has a high vapor pressure even at room temperature. Stoppering the separatory funnel with warm water and CH 2 Cl 2 generates a closed system in which pressure can build up and cause the contents of the separatory funnel to violently erupt. Use an external ice bath to cool the tea solution to room temperature.

Do not shake the separatory funnel vigorously or you will form an emulsion!

Extraction: Suppose you allowed two immiscible liquids to come in contact with each other and and one of the liquids had a solute dissolved in it. What would happen to the solute?

How is an organic compound soluble in water recovered from an aqueous solution?

solute N N CH 3

CH 3 N

N

CH 3

O

O