last updated 4/26/99
This Week's Experiment:
Preparation of an Amide: Synthesis of N,N-diethyl-m-toluamide
Safety
Precautions: This reaction is to be carried out in a hood.
Measurements of thionyl chloride and diethylamine
need to be done in the hood. Thionyl chloride is
noxious, corrosive and reacts vigorously with water. Diethylamine
is also noxious and corrosive. Place your
reaction set-up in the back half of the hood since HCl (g)
and SO2 (g) are liberated.
Waste
Disposal: Aqueous washed can be flushed down the sink with
water. Organic waste goes in nonhalogenated
organic waste bottle. Excess thionyl chloride should be cautiously added to water and discarded down the
sink with water.
1. Charge a 25 mL round bottom
flask with a spin bar, 600 mg of meta-toluic acid and 0.650 mL thionyl chloride. Complete the set-up
as shown in figure 1.
Gently reflux (~100°C) the mixture for 15
minutes.
2. Turn off the hotplate and cool the reaction
mixture to room temperature. Add 9 mL of
anhydrous diethyl ether to the reaction mixture and stir for several
minutes.
In a conical vial dissolve 1.4 mL of diethylamine
in 3.0 mL of anhydrous diethyl ether. Cap this vial and place
in ice.
Slowly add this diethylamine solution dropwise
to the room temperature reaction mixture
over a 15 minute period. Use the 1 mL plastic syringe for the
dropwise addition as shown in figure
1. Once all of the diethylamine solution has been
added, stir for an additional 5 minutes.
3.
Work-up: Add 5 mL of 10% aqueous NaOH to the reaction mixture
and continue to stir thoroughly for a 3-5
minutes. Transfer the reaction mixture to an Erlenmeyer flask
and remove the aqueous layer leaving behind the
organic layer. To the remaining organic layer,
add another 5 mL of 10% aqueous NaOH. Mix for 5 minutes and then
remove the aqueous layer.
If your organic layer is less than 10 mL, add
diethyl ether so that the volume is 10 mL.
Extract the organic layer with 5 mL of 10%
aqueous HCl. This will remove any remaining
diethylamine. Finally, wash the organic layer with 5 mL of water.
4.
Dry the organic layer over anhydrous sodium sulfate.
5.
Evaporate off the diethyl ether leaving behind the crude dark
product. Suggestion: use a warm water bath at 60°C and a stream of
air to aid the evaporation process. DO
NOT evaporate by placing directly on a hotplate.
6.
Purification by Column Chromatography:
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Push a small piece of cotton into the bottom
of a 9" Pasteur pipette. Use a stick (wood applicator) to
push the cotton in. Then add enough alumina so that the upper
level is ~ half an inch below the upper constriction in the Pasteur
pipette (see figure 2).
Obtain 6 mL of hexane in a culture tube to
be used later. To the crude product, add 10 drops of hexane.
Place a catch vial below the column.
To the column, add 1 mL of hexane. Never allow
the column to go dry. Thus once the hexane level reached the
alumina, add the crude product solution. When the solution level
in the column reaches the alumina then continuously add the remaining
hexane. Never allow the alumina to go dry during this process.
Collect all the liquid that passes through the column.
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Figure 2
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7. Evaporate off (use a warm water bath)
the hexane isolating the final product (viscous
light yellow liquid).
8. Obtain the IR. Submit your sample to your
TA.