My sample is Acetophenone. Experimental Procedure Reaction Design Note: Ether is
ID: 1026618 • Letter: M
Question
My sample is Acetophenone.
Experimental Procedure Reaction Design Note: Ether is extremely flammable and should be kept away from heat sources such as hotplates! Ether is also extremely volatile and should be used in a well- ventilated area. As an aid in designing your reaction, read the procedure of triphenylmethanol synthesis that is available on CANVAS. The Grignard reactions should be run on a scale of 10 millimoles (0.01 moles). Use the ketone as the limiting reagent and the phenyl magnesium bromide in excess (a usual excess is 10%). Phenyl magnesium bromide is a 3.0 M solution in ether. Use a three-neck flask for the reaction. An addition funnel and condenser should be fitted into two of the openings of the round bottom flask. The third opening should be stoppered with a rubber septum. Stir the reaction using a magnetic stir bar and stir plate. Reaction temperature can be controlled by means of an ice-bath. Water and moisture is detrimental to your reaction. All glassware for the reaction will be pre-dried in the oven. To keep water and moisture out of the reaction, the reaction could be 1) kept in a dry atmosphere, or, 2) fitted with something that will not allow moisture to enter the reaction flask. Sometimes a tube filled with drying agent or a "guard tube" is attached. A simpler method is to fill the openings with cotton wool. Assemble all glassware before obtaining chemicals. Add the ketone dissolved in at least 30 mL of anhydrous ether to the addition funnel. The phenyl magnesium bromide will be dispensed by syringe into the round bottom flask. Slowly add the ketone solution to the Grignard with stirring. The ether may begin to boil Adjust the rate of addition so that the ether does not boil too vigorously The ketone should be added slowly with stirring. Again, a perusal of the literature shows that this is typically done over the course of an hour, keeping the reaction boiling. After addition of the ketone, the mixture is allowed to stir until the ketone has reacted completely with the Grignard reagent. Allow at least an hour for this. Look for evidence of color change or precipitate as to when to stop the reaction. Further information on reaction conditions can be gleaned from a selective reading of the attached references, taken from monographs on synthesis and from journal articles. Experimental Procedure- Work-Up After the reaction is complete, the product will be a magnesium alkoxide salt. The alkoxide may be water soluble. The alkoxide can be protonated using an aqueous acid, such as 10% HzS04-Aqueous ammonium chloride, NH4Cl, is sometimes used to protonate tertiary alkoxides that may dehydrate in mineral acid solutions. Use pH paper to make sure the aqueous solution is acidic. After acidifying the reaction, extract with several portions of ether. Any residual acid in the ether layer can be neutralized by washing with saturated sodium bicarbonate. Separate the ether, dry it using an anhydrous drying agent, and remove the ether either with the forced air method or using the rotary evaporator. The product is a solid and will not be lost by rotary evaporation. If you obtain an oil, triturate with one or two mL
Explanation / Answer
Procedure for grignard reaction
To a clean dry flask fitted with a condenser and inert gas inlet was added PhMgBr (2.0 g, 1.8 ml, 11 mmol) by a syringe.
To the flask was then added acetophenone (1.20 g, 1.17 ml, 10 mmol) dissolved in 10 ml diethyl ether, in a dropwise manner. The temeprature of the reaction was controlled by slow addition.
Let the reaction run for another 1 h at room temperature.
After 1 h, cool the flask in ice-water mixture and add saturated NH4Cl (aqueous) solution to the flask.
Separate the organic diethylether and add MgSO4 to it.
Filter the organic layer to a single neck round bottom flask. Solvent is removed on a rotary evaporator.
The product is obtained as a solid.
% yield = (experimental yield/theoretical yield) x 100
Spectroscopic analysis
IR would show a broad peak at 3350 cm-1 for the O-H stretch in the product. the starting acetophenone would not have this peak and instead show a sharp strong peak at 1710 cm-1 for C=O stretch.
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