Organometallics

You will be running a Grignard synthesis of a carboxylic acid from the reaction of a Grignard Reagent and carbon dioxide. See your lab text: p. 303-314. You will modify the procedure to make either p-tolyl or o-tolyl magnesium bromide from p-bromotoluene (section 01) or o-bromotoluene (section 02) and react it with carbon dioxide in the form of dry ice. Modify the procedure in your text for the synthesis of phenyl magnesium bromide as follows:

Take one-fifth of the required amounts of the bromotoluene and diethyl ether and place the mixture in a dry test tube. Add some of the magnesium metal. Scratch and break up the metal with a stirring rod to begin the reaction. Once the reaction has started, add the mixture to the ether and remaining magnesium in the round bottom flask with 10 mL of diethyl ether. Begin the slow addition of the bromotoluene/ether mixture as detailed in the lab text.

Answer the following questions:

1) Where in the nmr spectrum would you see the carboxylic acid hydrogen?

2) Why must all equipment be dry when reacting tolyl magnesium bromide with carbon dioxide? (show equations)

3) a) Explain the difference between "inverse" and "normal" addition of organometallics and substrates.

b) Which was done in this experiment? Why?

4) Write chemical equations to show all of the different methods that can be used to synthesize tertiary alcohols with Grignard reagents.

4) Write all steps in the mechanism for the reaction of an ester with a Grignard reagent.

5) What side reactions are possible during the formation of a Grignard reagent? Write structures. How were these separated from the product?

6) p-Toluic acid cannot be made from p-xylene by oxidation. Explain.

Answer questions 1, 2, 5 on page 314.