1. General

Review the following topics: extraction

You will need to check out a set of glassware from the lab support. Upon receipt, immediately check for cracks and/or damage in the glassware, if the stopper and stopcock plugs fit properly and if the kit is complete. You will be held responsible for any breakage and lost equipment. Clean the glassware thoroughly when you are done and return it to the lab support at the end of your lab meeting! The students in the other lab sections will need the equipment as well. If you do not return the equipment at the end of your lab section, you will get a 10-point deduction!

It might be good to read the following papers:

Orchin, M., J. Chem. Educ. 1989, 66, 586.

Moulay, S., Chem. Educator 2003, 8, 393.

2. Experiment

Safety

1. Diethyl ether is highly flammable. It should kept away from all ignition sources.

2. Concentrated sulfuric acid, hydrochloric acid and sodium hydroxide solution are very corrosive.

3. Dry ice is very cold (T< -78 ^oC). Do not touch it with your hands.

4. All heat guns have to be removed and cannot be used after the initial heating because they can ignite the diethyl ether or any etheral solution.

For the Grignard setup and hints how to start the reaction follow the link. Make yourself familiar with the setup and the observations before you come to the lab in order to be able to repeat it in the laboratory. It is highly recommended to draw a detailed sketch of the setup in your lab notebook. The Grignard reaction will take a significant amount of time because there are a lot of little things that can go wrong.

Do not connect more than two heat guns to the same fume hood. Be aware that they are very hot after you used them. Place the noozle pointing up in the back of the hood, or on the floor to allow then to cool down.

Use the high-vacuum grease on the ground glass joints lightly. A thin film at the top part of the joint will be enough to get a good seal. The joints will become clear when you rotate the male joing inside the female joint. No grease should appear on the top or the bottom of the joint. If this happens, you will have to remove it immediately.

It is a good idea to crush the magnesium turnings inside side some weighing paper (with the Al-block) in order to have a fresh surface exposed for the reaction, which usually causes the reaction to initiate more readily. The Mg-turnings should look silvery to start with.

To prepare the etheral bromobenzene solution outside the addition funnel. Close the anhydrous ether can/bottle immediately after you are done! Transfer the solution into the addition funnel using a short-stem funnel.

To initiate the reaction, add only 5-8 mL (not more!) of the etheral bromobenzene solution to the magnesium turnings. If necessary heat the solution gently. Have an ice bath ready, in case the reaction gets out of control. Once the reaction started, add the rest of the solution so that the mixture keeps boiling. The liquid dripping into your flask is the boiling ether and not water.

Never let the reaction die down. PhMgBr is not that soluble in diethyl ether. It will precipitate and cover the magnesium surface. Why does this cause a problem?

Crushed ice is not equivalent to dry ice! The first one is solid water, while the second one is solid carbon dioxide.

NEVER, EVER THROW A LAYER AWAY AS LONG AS YOU ARE NOT 100% SURE THAT YOU ISOLATED YOUR FINAL PRODUCT!

3. Things to think about

a. Student A is running late and decides to add the bromobenzene solution faster than recommended in the procedure. In the end, he only isolates a small amount of benzoic acid. How can he rationalize the poor yield?

b. What will be the final product (after acid work-up) when you react PhMgBr with esters, ketones, nitriles, or carbon disulfide (CS₂), followed by an acidic work-up?

c. THF is generally considered a better solvent than ether for Grignard reactions. Why?