CHEM 235 Lecture Notes - Lecture 10: Benzophenone, Fume Hood, Bromobenzene

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champagnehare429

3 Dec 2016

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Document Summary

Prepare drying tube with cotton, cacl2 , cotton wool. Place 1 g magnesium turnings into 100 ml rb flask, attach drying tube to the flask, take it to the fumehood. Hold the flask 45 degree angle, flame the flask with drying tube off, put trying tube back on after flaming , allow it to cool. Insert west condenser in the rb flask, attach drying tube on top of west condenser. Pour 8 ml anhydrous diethyl ether, 4 ml bromobenzene into dry 25 ml erlenmeyer flask, add this into cooled rb flask. Prepare one ice bath and one hot bath in 2 400 ml beakers. Place one iodine crystal in reaction flask, and shake vigorously. Warm the flask with your hand, shake vigorously until cloudiness. Heat from the bottom of the flask. Disappearance and reappearance of the brown iodine color. As soon as the reaction in underway, put the rb flask in ice bath, turn on the water for condenser.

Related Questions

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

Grignard theoretical yield... also, what is the limiting reactant?

Procedure: The Claisen adapter is fitted to the neck of a 100 mL round bottom flask containing 1-2 crystals of solid iodine and 0.5 g of magnesium metal (Mg). In the side arm of the adapter, place a reflux condenser with water hoses connected, but not flowing. Insert the vacuum connecting tube into the top of the condenser. Place the glass stopper into the other joint of the connecting tube and attach a DRY piece of rubber tubing connected to a drying tube. The drying tube should have two cotton plugs and sufficient DRIERITE (anhydrous CaSO4) between them to ensure that any air getting into the system is dried by the Drierite. Place the separatory funnel in the straight arm of the adapter. Open the stopcock so there is a flow path from the funnel to the flask. Insert a second vacuum connecting tube into the top of the separatory funnel. Place the glass stopper into the other joint of the connecting tube and attach a DRY piece of rubber tubing connected to a drying tube. The drying tube should have two cotton plugs and sufficient DRIERITE (anhydrous CaSO4) between them to ensure that any air getting into the system is dried by the Drierite. Once the apparatus is assembled, use a heating mantle on medium heat to heat the flask until sublimed iodine appears on the inside walls of the flask (rosy color). Close the separatory funnel. The apparatus should now be dry enough to allow formation of the Grignard reagent to occur. After the apparatus has cooled, start the water flowing gently through the condenser. To prepare the phenylmagnesium bromide, add 5 mL of anhydrous ether to the flask (through the separatory funnel) followed by 0.5 mL of bromobenzene. Close the stopcock on the separatory funnel. After a minute or so, bubbling should occur as the reaction begins and the reaction mixture should begin to turn slightly brown. If no reaction appears to begin, warm the flask gently with your hand. When the reaction begins, add 1.5 mL of bromobenzene in 15 mL of ether, and add this solution to the separatory funnel. Slowly add the bromobenzene solution from the separatory funnel dropwise at a rate of about two drops per second. This should be a rate sufficient to keep the reaction going without further heat. There should be sufficient heat from the reaction to maintain the ether at reflux. If the reaction appears to be going too fast and the ether vapors are high on the walls of the reflux condenser, use an ice bath to cool the reaction to the point that the ether vapors are no more than one-third of the height of the reflux condenser. When all of the bromobenzene has been added, heat the reaction at reflux for about 25 minutes with a low heat heating mantle. Prepare a solution of 2.25 g of benzophenone in 10 mL of anhydrous ether (in the closed separatory funnel

Please consider the preperation of benzoic acid: a Grignard Reaction.

Bromobenzene and diethyl ether is used in the formation of Grignard reagent.

PLEASE READ PROCEDURE TO HELP ANSWER THE QUESTION:

Procedure(question is in the pic below):