The Grignard Reaction

A reaction was performed in which 0.35 mL of 2-pentanone was reacted with an excess of butyl magnesiumbromide to make 0.42 g of 4-methyl-4-octanol. Calculate the theoretical yield and percent yield for this reaction.

Theoretical yield: 0.47 g Percent yield: 89.4%

Two reactions between a Grignard reagent and a carbonyl compound are given below. Draw the main organic product for each reaction and indicate if H or H- is needed to complete each reaction. (The starting material structures are provided in the answer fields as a starting point for your drawings.)

1. H+ 2. H+

List the procedural steps, from start to finish, that are required to convert 2-butanone into 3-methyl-3-hexanol using a Grignard reagent prepared from 1-bromopropane and magnesium metal.

Dry all glassware and reagents prior to starting the experiment Add 1-bromopropane to clean magnesium Wait for reaction to turn cloudy, sonicate if necessary Add 2-butanone drowse to the grignard reagent, allowing gentle reflux Add aqueous ammonium chloride to quench the reaction Wash the reaction mixture with sodium bicarbonate and sodium chloride solutions in a separators funnel Dry over magnesium sulfate and distill with THF

The carbon-magnesium bond in a Grignard reagent is covalent and highly-polarized such that the carbon is negatively charged. Which of the following statements can be used to describe the Grignard carbanion? Select all that apply.

Grignard reagents are strong bases Grignard reagents are strong nucleophiles

Consider the reaction of a Grignard reagent prepared from 1-bromopentane and magnesium in THF solution, with 2-heptanone. Calculate the molar masses of the reactants and product.

MM of 1-bromopentane: 151.0 g/mol MM of 2-heptanone: 114.2 g/mol MM of 6-methyl-6-undecanol: 183.6 g/mol

Apparatus set up

Open to atmosphere Air condenser Screw Claisin head Keck clamp

During the preparation of a tertiary alcohol by a Grignard reaction, the reaction mixture was shaken with saturated sodium chloride solution. What is the purpose of the saturated sodium chloride solution?

Saturated sodium chloride decreases the solubility of the organic product in water.

Grignard reactions are highly exothermic and are performed in ether solvent. There is a real risk of fire during this reaction. In the case that a fire should occur in your distillation apparatus, what is the best course of action?

Smother the flames with a watch glass or beaker.

Why are ethers commonly used as a solvent for Grignard reagent preparations? Select all answers that apply.

The lone-pairs of electrons on the ether solvate the magnesium ion. Ether's high vapor pressure helps to prevent moisture from entering the reaction vessel.

The bond between carbon and magnesium is covalent, but highly polarized. Label the two sites with the appropriate partial charges.

negative positive

A ketone and a Grignard reagent react in ether solution followed by acid workup, to form a tertiary alcohol. Grignard reactions must be scrupulously dry in order to work effectively. A common method of drying glassware is to rinse with acetone prior to use. Why is rinsing with acetone not suitable for the reaction stated in the question.

Acetone is a ketone. Grignard reagents will react with acetone to make an unwanted byproduct.

A Grignard reagent was generated by reacting 1-bromobutane with magnesium metal in THF solution. Addition of 2-butanone and ammonium chloride generated the desired alcohol product. The reaction mixture was washed with sodium bicarbonate, then the THF layer was dried over magnesium sulfate. The product was distilled from THF. Identify where the waste generated by this reaction should go.

Aqueous waste: sodium bicarbonate solution Mg sulfate, Mg turnings: Mg metal, Mg sulfate Wash Acetone waste: wash acetone Glass waste: pasteur pipet THF waster: THF

Procedure

Decant dried THF solution into 25 mL round bottom flask Add boiling chips to solution in round bottom flask Grease all joints and connect flask to micro distillation apparatus Set apparatus in heating mantle and use heating tiles Adjust varian to distill THF at 60C Increase varian to cause boiling of higher boiling product Stop distillation before flask becomes dry