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 in the glassware, if the stopper and stopcocks fit and if the kit is complete. You will fully hold responsible for breakage and lost equipment. Clean the glassware 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.

It might be good to read the following paper: Orchin, M., J.Chem.Educ. 1989, 66, 586.

The instructor will offer an in-lab demonstration of the setup on Monday May 9,2005 at 4 pm in YH6086.

2. Experiment

Safety note: Diethyl ether is highly flammable. It should kept away from all ignition sources (hotplate, heat gun, etc).

For the Grignard setup and hints how to start the reaction follow the link. Make yourself familar 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 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 then 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 them against each other. No grease should appear on the top or the bottom of the joint.

It is a good idea to crush the magnesium turnings in order to have a fresh surface for the reaction. This will help to initiate the reaction more easily.

To prepare the etheral bromobenzene solution either mix the bromobenzene and the ether in a beaker and then pour the solution into the additional funnel, or add the ether first into the additional funnel followed by the bromobenzene and then mix well with a glass rod. Do not pour the bromobenzene in first and then the ether. Why? Close the anhydrous ether can/bottle immediately after you are done!

To initiate the reaction, add only 5-8 mL (not more!) of the etheral PhBr 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 asked for in the procedure. In the end, he only isolates a small amount of benzoic acid. How can you explain the poor yield?

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