Please consider the preperation of benzoic acid: a Grignard Reaction.
Bromobenzene and diethyl ether is used in the formation of Grignard reagent. Note: procedure is listed below for reference
QUESTION:
Procedure:
* add 1.2g of magnesium and 3 crystals of iodine to RB flask and immediately assemble the dry water condenser and drying tube containing cotton and anhydrous calcium chloride to RB flask
*then add 5.2 mL bromobenzene to 5 mL of diethyl ether to seperatory funnel and turn on condenser
* add about one third of ether-bromobenzene mixture down the condenser into the RB flask by momentarily removing drying tube. Place the drying tube back as quickly as possible.
* now add 30 mL of ether to the bromobenzene-ether mixture remaining in the seperatory funnel
*to initiate reaciton, place hands under flask and gently swril
* once the reaction maintains reflux, remove hands and set the flask down on a cork ring
*maintain the vigorousness of the reaciton by continuously adding 3.5 mL portions of diluted bromobenzene-ether mixture every 30 seconds
* make sure all of the bromobenzene-ether mixture has been added
* now obtain some dry ice, CO2 (s) and transfer 50 mL of this to the reaciton mixture inside the flask
*when all the dry ice has been added, add 80 mL of 6M HCl (aq) to flask
* finally, add 100mL of solvent grade diethyl ether (not anhydrous) and carefully stir
* transfer mixture to a 250mL seperatory funnel, allow layers to seperate and discard the lower aqueous layer
*now add 20 mL of 6 M NaOH (aq) and add 100mL of deionized water to seperatory funnel containing the ether solution
* drain the lower aqueous layer into a large beaker and slowly acidify using concentrated 12M HCl (aq). Stir the mixture and add HCl (aq) until pH is about 1-2 pH units.
*cool solution in ice-water bath and collect precipitate of benzoic acid
3) In the procedure, after the reaction begins bubbling in the RB flask, you dilute the bromobenzene ether mixture with an additional 30 mL of anhydrous diethyl ether. One reason you do this is to help minimize the potential side reaction that forms biphenyl. How does the additional 30 mL of anhydrous diethyl ether minimize the formation of the biphenyl side product? (1 Mark)
