Grignard

What is the effect of stoppering the flask with a calcium chloride drying tube?

The tube prevents water from the air, or glassware from entering and touching the grignard. Water will destroy the grignard.

Why is the ether layer subsequently shaken with sulfuric acid and washed with sodium chloride?

To further remove magnesium salts, and to remove any water that may have made its way into the ether layer.

What is the point of the ether extraction?

To remove the biphenyl by product.

Describe two different techniques that are helpful when running a chemical reaction under anhydrous conditions.

1) using completely dry glassware 2) using diethyl ether to protect the R-Mg-Br by forming an ate complex

Explain triphenylmethanol from methyl benzoate.

2 molar equivalents of the grignard reagent are reacted with methyl benzoate. The two phenyl groups of the grignard add at the carbonyl compound, creating a tri-phenyl that has an OMgBr. Further treatment with hydronium ion creates the triphenylmethanol.

The method of preparation of phenyl magnesium bromide ask for using approx 1:1 molar ratio of Mg and bromobenzene. What would happen if you used two equivalents of bromobenzene and 1 equivalent of Mg?

If you used 2 equivalents of bromobenzene and only one equivalent of Mg, the Mg would bond to both Br's, and biphenyl would couple. The product would be biphenyl.

Once the reaction mixture has refluxed/sat over night, what is the point of adding sulfuric acid, ether and ice?

It promotes hydrolysis of the addition compound, the magnesium salts are converted into water-soluble neutral salts and the triphenylmethanol is pulled into the ether layer.

Triphenylmethanol can also be prepared by reacting benzophenone with phenyl magnesium bromide. How many equivalents of phenyl magnesium bromide would you need for one equivalent of benzophenone?

One. The carbonyl of the benzophenone would go through acyl addition with the phenyl magnesium bromide, and with subsequent reaction with H30+ the O will lose its negative charge, become OH and would be triphenylmethanol.

What is the nucleophile here and what is the electrophile?

The electrophile is the methyl benzoate ester, and the nucleophile is the grignard.

What is the first step of the experiment?

The first step is creating the grignard reagent by reacting an alkyl benzene (bromobenzene) with magnesium in anhydrous ether. The mixture is heated on reflux until almost no metal is visible in the bottom of the flask. The Magnesium inserts itself in between the carbon and the bromine, creating an MgBr grignard.

"Isolate the product in the usual way." What is the meaning of that sentence?

The hot solution is allowed to cool to room temperature and then is cooled on ice. Once crystals have begun to form, product is collected using vacuum filtration on a Buechner funnel. Pressed to expel any excess liquid and allowed to air dry.