3 ‫ מתוך‬1 ‫עמוד‬
9 ‫ניסוי מספר‬
Esterification Reactions.
1. Isopentyl Acetate (Banana Oil)
O
CH3COH
+
OH
O
CH3C O
Reference: Introduction to Organic Laboratory Techniques, 3rd Ed. Pavia, Lampman,
Kriz. Procedure 10; Pages 89-90.
Notes: Use a magnetic stirrer instead of boiling stones. Be extremely careful when
handling concentrated acids, especially sulfuric. In case of spills on any part of the
body wash immediately with copious amounts of water, then with a sodium
bicarbonate solution, then water again. For spills on the bench top and hood carefully
add solid sodium bicarbonate until the acid is neutralized, then clean with a wet paper
towel.
It is preferable to use an Erlenmeyer of the right size when adding aqueous sodium
bicarbonate to acid instead of adding the bicarbonate solution straight to the
separatory funnel.
2. n-Amyl Acetate
O
CH3COH
+
OH
O
CH3C O
The equilibrium constant for the esterification reaction between n-Amyl alcohol,
CH3(CH2)4OH, and acetic acid is close to unity. This experiment is designed to
illustrate one method of carrying a reaction to completion, and give you experience in
a synthetic process on a macro scale.
Introduce 0.25 mole of n-amyl alcohol and 0.27 mole of glacial acetic acid into a 250ml distilling flask containing a magnetic stirrer.
Add 3 drops of concentrated sulfuric acid (no more than 3 drops). Arrange the flask
with a Dean-Stark azeotropic trap and a reflux condenser. Reflux the mixture and
observe the formation of an aqueous layer in the side arm of the distilling flask (reflux
time, about 45 minutes). At the end of the reflux period record the volume of water
present in the side arm, and allow the contents of the flask to cool.
Transfer all the liquid from the flask and the side arm into an Erlenmeyer and add 25
ml of 5% sodium bicarbonate. Gently swirl the contents of the Erlenmeyer and add
them to a small separatory funnel. Shake the separatory funnel vigorously. Remove
the aqueous phase and test the organic phase with a piece of moist litmus paper. If the
solution is acidic, repeat the extraction with a fresh portion of bicarbonate solution.
Transfer the organic phase to an Erlenmeyer flask containing about 5 gr. of anhydrous
powdered magnesium sulfate. Stopper the flask and swirl the contents several times
over a 5 minute period. Filter into a small distilling flask, using a funnel and fluted
filter paper. Distill, collecting all material that boils over a 10º range, starting about 8º
below the literature value for the boiling point (take into account the atmospheric
pressure at the time of distillation). Determine the refractive index.
9 ‫ניסוי מספר‬
3 ‫ מתוך‬2 ‫עמוד‬
3. Methyl Benzoate
CO2H
+
CO2Me
CH3OH
Place 10 gr of benzoic acid and 25 ml of methanol in a 100 ml round-bottomed flask,
and pour 3 ml of concd. sulfuric acid slowly and carefully down the walls of the flask
and then swirl to mix the components. Add a magnetic stirrer, attach a reflux
condenser, and reflux the mixture gently for 1 hour. Cool the solution and decant it
into a separatory funnel containing 50 ml of water. Add 35 ml of CH2Cl2 using part
to rinse the original reaction flask. Shake, and drain off the water (which removes
most of the sulfuric acid and methanol). Wash with a second portion of water (25 ml)
drain, and then wash with 25 ml of 5% sodium bicarbonate to remove unreacted
benzoic acid. Shake, with frequent release of pressure, until no further reaction is
apparent; then drain off and acidify the water layer. Any benzoic acid that
precipitates is collected, dried and the amount recovered used to calculate the overall
yield. Repeat the washing with sodium bicarbonate until no precipitate forms on
acidification of the aqueous layer. Wash with water, then dry over sodium sulfate or
magnesium sulfate and filter.
Remove the solvent by distillation on a rotary evaporator or through a condenser from
a distilling flask heated on the steam bath, and collect the solvent in a receiver chilled
in ice. Decant the methyl benzoate into a 50 ml distilling flask and distill under
reduced pressure using the equipment supplied in the laboratory for this purpose.
Note both the distillation temperature and pressure and compare to literature values by
using a pressure temperature nomograph. Remember to use a “cow” distilling adapter
to be able to change receiving flasks while under low pressure. Remember also to
pre-weigh your receiving flasks to calculate the yield.
4. n-Butyl Proprionate
O
O
OH
+
OH
O
In a 250 ml round bottomed flask are placed 7.4 gr of propionic acid, 22.2 gr (28.8
ml) of n-butyl alcohol, 0.25 gr of p-toluene-sulphonic acid and 60 ml of toluene. The
flask is provided with an azeotropic Dean-Stark trap and a reflux condenser.
When the mixture is heated on a heating bath, droplets of water begin to appear in the
trap. The refluxing is continued until the liquid in the trap consists of two clear layers
(about two hours). About four ml of water are formed. The solution remaining in the
flask is washed with water, sodium bicarbonate solution, again with water, dried over
MgSO4 and the toluene is removed by distillation followed by the distillation of butyl
propionate. Isolate your compound and note the distillation temperature. Don’t
forget to add a calcium chloride trap to your distillation apparatus to prevent the
contamination of butyl propionate with moisture. Record the index of refraction of
your ester.
9 ‫ניסוי מספר‬
3 ‫ מתוך‬3 ‫עמוד‬
5. Methyl Salicylate
CO2H
OH
+
CH3OH
CO2Me
OH
Reference: Introduction to Organic Laboratory Techniques, 3rd Ed. Pavia, Lampman,
Kriz. Procedure 11; Pages 91-94. Vacuum distillation.
9 ‫ניסוי מספר‬