Experiment: Performing Of A Grignard Reaction Using Phenylmagnesium Br PDF

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Summary

Introduction, Table of Reagents, and Procedure Sections of Grignard Reaction Lab Report...

Description

Organometallic Alkylation - Grignard Reaction The purpose of this experiment is to generate an organometallic reagent in situ and to reduce a ketone starting material to a tertiary alcohol using phenylmagnesium bromide via a Grignard reaction. The Grignard reaction consists of a nucleophilic addition reaction between an organomagnesium reagent and an electrophilic carbon atom. In the nucleophilic addition to the carbonyl compound, the nucleophile donates an electron pair to the electrophilic carbon of the carbonyl compound. Consequently, the formation of a new carbon-nucleophile sigma bond pushes the carbonyl‘s pi electrons onto the oxygen. This results in the formation of an alkoxide anion. The carbonyl carbon then rehybridizes from sp2 to sp3. This is followed by the negatively charged alkoxide intermediate being protonated in order to generate a neutral alcohol product. Electrophilic species most commonly utilized for the Grignard reaction include alkyl halides, aldehydes, ketones, esters, or nitriles. This type of reaction is unique and useful in that it produces a carbon-carbon covalent bond. Grignard reagents are strongly polarized and the nucleophilic nature of these reagents derives from a negatively polarized carbon atom covalently paired with an electropositive magnesium halide moiety. Thus, commonly used Grignard reagents include alkyl chlorides, alkyl bromides, and alkyl iodides. In this experiment, an aryl bromide, bromobenzene, is used as the Grignard reagent. Because of their sensitivity to protic solvents, it is paramount that the amount of moisture the reagents are exposed to is minimized as much as possible. This type of reaction forms a racemic mixture of products as long as the new carbon-carbon bond results in the formation of a chiral carbon. Due to the symmetrical nature of triphenylmethanol, the alcohol product, this experiment’s reaction does not form a racemic mixture. This reaction is carried out via the familiar techniques of liquid-liquid extraction and recrystallization. The final product is dried through suction filtration, and then analyzed via IR spectroscopy and melting point determination.

Safety/Materials Table of Reagents

Compound Name

bromobenzene

Structure

Molecular Weight Melting/ Boiling Point (g/mol) (C)

157.02 g/mol

BP: 156C

Density

1500 kg/m³

benzophenone

182.217 g/mol

MP: 48.5C

N/A

triphenylmethanol

260.33 g/mol

MP: 162C

N/A

diethyl ether

74.12 g/mol

BP: 34.6C

713 kg/m³

2-propanol

60.1 g/mol

BP: 82.6C

786 kg/m³

sulfuric acid

98.079 g/mol

BP: 337C

1840 kg/m³

magnesium sulfate

120.366 g/mol

MP: 1124C

N/A

iodine

126.904 g/mol

MP: 113.7C

N/A

calcium chloride

110.98 g/mol

MP: 772C

N/A

sodium bicarbonate

84.007 g/mol

MP: 50C

N/A

sodium sulfate

142.04 g/mol

MP: 884C

N/A

Table of Reagents and Corresponding Safety Precautions Compound Name

Safety Precautions

bromobenzene

May cause irritation to skin and eyes, or upon inhalation or ingestion.The substance is toxic to kidneys, the nervous system, and liver.

benzophenone

May cause irritation to skin and eyes, or upon inhalation or ingestion. May be flammable at high temperatures.

triphenylmethanol

May cause irritation to skin and eyes, or upon inhalation or ingestion. Slightly flammable at high temperatures.

diethyl ether

May cause irritation to skin and eyes, or upon inhalation or ingestion. Mutagenic for mammalian somatic cells. The substance may be toxic to skin and central nervous system. Flammable.

2-propanol

May cause irritation to skin and eyes, or upon inhalation or ingestion. Known carcinogenic effects. Classified reproductive system toxin and development toxin. The substance may be toxic to kidneys, liver, skin, and central nervous system. Flammable.

sulfuric acid

May cause irritation to skin and eyes, or upon inhalation or ingestion. Known carcinogenic effects. May produce tissue damage particularly on mucous membranes of eyes, mouth, and respiratory tract. The substance may be toxic to kidneys, lungs, heart, cardiovascular system, upper respiratory tract, eyes, and teeth.

magnesium sulfate

iodine

calcium chloride

May cause irritation to skin and eyes, or upon inhalation or ingestion. May cause irritation to skin and eyes, or upon inhalation or ingestion. Eye contact can result in corneal damage or blindness. The substance is toxic to thyroid. The substance may be toxic to blood, kidneys, and liver. May cause irritation to skin and eyes, or upon inhalation or ingestion. Mutagenic for mammalian somatic cells. The substance may be toxic to heart/cardiovascular system.

sodium bicarbonate

May cause irritation to skin and eyes, or upon inhalation or ingestion.

sodium sulfate

May cause irritation to skin and eyes, or upon inhalation or ingestion.

Additional Safety Precautions Wear appropriate lab attire. Do not remove safety glasses or gloves at any time during lab. Take care to prevent spilling any compounds. Rinse skin and eyes thoroughly if contact is made as these compounds can cause severe skin or eye damage. Concentrated sulfuric acid will cause severe burns upon contact with eyes, nose, or skin. Bromobenzene and benzophenone are severely toxic when ingested. In order to prevent the inhalation of toxic fumes, ensure that the snorkel at each station is on and functioning properly. Diethyl ether and 2-propanol are highly flammable. Be sure to keep these substances away from open flames and hot surfaces. Dispose of all waste in the designated waste container.

Experimental Procedure 1. Add 1.5 g of magnesium turnings to a 10 mL round bottom flask. 2. Attach a microscale condenser fitted with a calcium chloride drying tube and seal the round bottom flask with an o-ring and cap. 3. Dissolve 600 Lof bromobenzene in 2 mL of diethyl ether in a separate 10 mL round bottom flask. 4. Add 0.5 mL of the bromobenzene/ether solution to the flask with the magnesium turnings through the top of the condenser via a syringe.

5. Add several crystals of iodine to the solution in order to initiate a reaction. 6. Begin warming the flask with your hand or in a warm water bath. 7. Once the reaction begins to boil gently, add the remaining bromobenzene/ether solution drop-wise over a 10 minute time frame. 8. Continue to warm the reaction for a further 10 minutes after all of the bromobenzene/ether solution has been added. 9. Dissolve 0.680 g of benzophenone in 2 mL of diethyl ether in a 5 mL conical vial. 10. Add this benzophenone solution drop-wise into the phenyl magnesium bromide/ether solution. 11. Warm the solution for 20 minutes once the benzophenone has been added. 12. Quench the reaction by pouring it into a 100 mL beaker containing 5 mL of 1M sulfuric acid. 13. Rinse the reaction vessel with 1 mL of water, followed by 3 mL of diethyl ether, adding the rinsings into the beaker as well. 14. Pour the contents of the beaker into a clean separatory funnel. 15. Drain off the lower aqueous layer. 16. Wash the remaining organic layer with 10 mL of 1M sodium bicarbonate. 17. Drain off the lower aqueous layer. 18. Pour the remaining organic solution into a 50 mL Erlenmeyer flask. 19. Dry the solution using sodium sulfate as the drying agent, swirling the solution until it is clear. 20. Decant the dried solution into a clean 100 mL beaker. 21. Carefully evaporate the diethyl ether by placing the snorkel right above the mouth of the beaker. 22. Once the solvent has evaporated, the crude product will crystallize in the beaker. 23. Recrystallize this crude product using a small amount of 2-propanol. 24. Collect the purified triphenylmethanol via suction filtration. 25. Determine and record the final mass and melting point range of the purified product....