Clean, Fast Organic Chemistry - LaborPraxis

C(O)CH 3 is an electronwithdrawing
group. Its presence
on the aryl halide makes the
aromatic ring electron-poor.
This makes the carbonbromine
bond weak, and thus,
facilitates palladium insertion.
This makes the coupling easier
than with the other two
substrates used.
Refer to Chapter 3 for more
detailed instructions on setting
up and safely securing your
HP-500 vessel, as well as
information on programming
the MARS System.
The vessel is vented by loosening the blue nut. It is then removed from the frame
and its protective sleeve. The reaction mixture is transferred from the microwave
vessel into a separatory funnel to perform an extraction. Ethyl acetate (30 mL) is
used to rinse the reaction vessel and is added to the separatory funnel along with
water (30 mL). Any solids remaining in the microwave vessel are scraped into the
funnel using a spatula. After stoppering the funnel, the solution is repeatedly
shaken and vented. The layers are then allowed to separate. The aqueous layer is
removed to an Erlenmeyer flask and the organic layer is washed with saturated
sodium chloride solution and dried over sodium sulfate. The ethyl acetate is
removed on a rotary evaporator, leaving a crystalline product. The yield of the
product is determined and the melting point compared to the literature value. The
chemical structure of the product is confirmed by IR, 1H-NMR and/or 13C-NMR
spectroscopy.
Procedure for 4-methylbiphenyl:
Reagents used:
SAFETY PRECAUTIONS:
4-Bromoacetophenone, tetrabutylammonium bromide (TBAB), and sodium
carbonate are classified as irritants.
Phenylboronic acid (366 mg, 3 mmol), 4-bromoatoluene (514 mg, 3 mmol), sodium
carbonate (945 mg, 9 mmol), palladium acetate (3 mg, 0.012 mmol), TBAB (967 mg,
3 mmol) and water (6 mL) are placed in an HP-500 Teflon ® microwave reaction vessel
containing a magnetic stir bar. NOTE: The final volume must be at least 5 mL. The
reaction vessel is inserted into a protective sleeve, fitted with a vessel top and load
disk, and then placed into the vessel frame. The pre-set torque wrench is used to
tighten the nut on top of the frame before placing it on the microwave turntable.
Note the position the vessel occupies. The reaction control vessel (position #1) is
connected to the temperature thermocouple and, if applicable, the pressure sensor.
The microwave is programmed using the ramp-to-temperature method to heat to
160 °C over a 3-minute period and then held at this temperature for 5 minutes.
The solution is then allowed to cool for 20 minutes or until it is below 50 °C before
removal from the microwave unit.
CAUTION: The vessel may still be hot to the touch.
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