The Grignard Reaction: Workup April 5 & 7, 2010

The Grignard Synthesis II
Miniscale Synthesis of Triphenylmethanol from Ethyl Benzoate,
Part 2
Organic Chemistry Lab II, Spring 2010
Dr. Milkevitch
April 5 & 7, 2010
Today’s Experiment
Complete last week’s experiment
– Grignard synthesis
React the Grignard with an ester
– Make an alcohol
Last Week
Prepared the Grignard reagent
Reacted it with ethyl benzoate
– In ether
Allowed it to sit until this week
This week:
– Workup
Isolation & purification
Procedure: Part 2
Retrieve your RB flask from the hood
Take a look at it
– Replace any lost volume with more ether
Remove the stir bar
Pure the reaction mixture into a 50 ml erlenmeyer flask that
contains 8 g of ice
Rinse the reaction flask with ~2 ml of ether and add this rinse to
the erlenmeyer with the ice
While stirring, carefully add 3M HCl dropwise to the solution
– Use a glass stir rod to break up the solid
Continue to add acid until the lower layer is just acidic to litmus
– Blue litmus turns red if the solution is acidic
Carefully pour the reaction mixture into your separatory funnel
– Leave any unreacted magnesium in the flask
Procedure, con’t
Rinse the flask with 5 ml of diethyl ether
– Add this to the separatory funnel
Reaction mixture should separate into 2 layers
Product is in the upper layer (ether layer)
Separate the layers
– Into separate erlenmeyer flasks
1)One will have ether layer
2)One will have the water layer
– Put the water layer back into the separatory funnel
Extract the water layer with 5 ml of diethyl ether
– Allow layers to separate
– Drain off the water layer into an erlenmeyer flask
Drain off the ether wash, add it to the original ether wash (#1
Now, put all the ether layers into the separatory funnel
– Extract it with 5 ml of DI H2O
Procedure, con’t
Remove the water
– Store in a beaker, set aside
Transfer the ether to a clean erlenmeyer flask
– Dry over magnesium sulfate ~10 min
Decant or gravity filter the dried solution
– Into a pre-weighed 50 ml erlenmeyer flask
Add a stir bar/boiling chip
Evaporate off ether using a hot plate
– In the hood
Should get an off-white solid
– Mixture of biphenyl and triphenylmethanol
Add 10 ml of petroleum ether
– Stir thoroughly
– Vacuum filter with a Buchner funnel
Weigh product
Do a TLC
– Plates are in the oven
– Standards are in the hood
Standards: Triphenyl methanol, biphenyl
Spot these
Also spot your compound!
Develop your plate in methylene chloride
Visualize under UV light
Submit a sample for GC analysis
Dissolve a small amount of your compound in methylene
Place in a small vial
– Vials are in the hood
– Label with your names
Your Report
Formal lab report not required
Complete experiment worksheet