Synthesis of Triphenylmethanol

Grignard Reaction

In this experiment you will perform what will be called the Grignard reaction in Chapter 15 of the lecture text.

In the 1^st reaction, small pieces of magnesium will actually react with alkyl and aryl halides to produce an organometallic compound. Organometallic compounds are pretty much what they sound like. They consist metal atoms bonded to the C of an organic substituent. In the case of Mg, the organometallic compound is normally written with covalent bonds. However, it has much carbanion character and is consequently a strong nucleophile and base. This type of organomagnesium compound is called a Grignard reagent after the person who discovered them.

Anions that are strong nucleophiles react with carbonyl compounds in the following manner known as Nucleophilic Addition.

This is overall called the Grignard Reaction.

For organic synthesis, it is important to have reactions that make C-C bonds. This makes it possible to connect small molecules into bigger molecules. This is why the Grignard reaction is considered an important reaction.

The phenylmagnesium bromide or Grignard reagent is not only a strong nucleophile, but it is also a strong base. They will react water long before they get a chance to react with the carbonyl.

The reaction will not work unless water is excluded through careful drying and the use of dry reagents and solvents.

The glassware must be dried in an oven. Ether will be used as a solvent. It has been distilled by the manufacturer so that it has a low amount of water in it.

Procedure Notes

• Read the entire procedure carefully.
• We will not be performing Exp. 30B. Don’t worry about it.
• Place the glassware in the oven this week. (across the hall) Remove the Teflon stopcock from the separatory funnel.
• When you heat your Mg, bromobenzene, and ether mixture be sure to use the lowest mantle setting.