Grignard Reaction PDF

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Lab Report for the Grignard reaction in Organic Chemistry...

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ccvBailey Raleigh 3/12/2018 Chem 344-09

Grignard Reaction: Synthesis of Triphenylmethanol Objective The objective of this experiment was to synthesize a Grignard reagent (phenyl magnesium bromide) from Bromobenzene and Magnesium ribbon, and use that reagent to convert benzophenone into triphenylmethanol. In this experiment, a Grignard reagent was used to convert a ketone into a tertiary alcohol. The triphenylmethanol was characterized using IR spectroscopy, NMR, and Thin Layer Chromatography. Overall Reactions: In this lab’s reaction, a Grignard reagent was synthesized (phenyl magnesium bromide) and reacted with benzophenone to form triphenylmethanol.

Mechanisms: In the reactions first step, Magnesium ribbon reacted with the organic halide to form the Grignard reagent.

Next, the Grignard reagent attacks the benzophenone. This adds another carbon-carbon bond and forms an Oxegyn anion.

Finally, Water protonates the Oxegyn anion forming the triphenylmethanol.

Stoichiometric Table: Synthesis of Grignard Reagent

Bromobenzene Magnesium

Molar mass (g/mol) 157 g/mol 24.305 g/mol

Density (g/mL) 1.5 g/mL 1.738 g/mL

Mass or volume used 0.7 mL 156 mg

mmol

Molar equivalence

6.68 mmol 6.41 mmol

1.04 1

Limiting Reagent Reaction with Ketone Molar

Density

Mass

or

mmol

Molar

Benzophenon e Grignard Reagent Limiting reagent

mass(g/mol ) 182.217 g/mol 181.31 g/mol

(g/ml) 1.11 g/mL

volume used 1.105 g

6.06 mmol

1

1.14 g/mL

1.02 mL

6.41 mmol

1.06

Procedure 1. Set up the apparatus as follows:

2. Weigh out 150 mg Magnesium ribbon. Polish and cut into small pieces. 3. Get 0.7 mL of Bromobenzene with dry centrifuge tube and add 3 mL anhydrous ether. 4. Add the bromobenzene sltn to the magnesium ribbon in 0.8 mL incriments over course of 15 mins 5. Add 0.5 mL dry ether to wash 6. Reaction should be complete in about 30 mins. Allow to return to r.t 7. Dissolve 1.09 g of Benzophenone in 2 mL dry ether. 8. Add Benzophenone into reaction in 0.5 mL increments over 15 mins. 9. Allow to come to r.t 10. Hydrolysis: Transfer to 50 mL beaker and quench with 6 mL of 6 M HCl. 11. Work-up: Transfer to separatory funnel. Draw off lower aqueous layer. Pour off ether layer. Re-extract aqueous layer with ether. 12. Dry over sodium sulfate 13. Gravity filter into side arm flask. 14. Evaporate ether under vaccum until residue remains only 15. Dissolve oil in 3 mL P.E.T to remove

equuivalence

Observations Was set up like seen on the Procedure.

156 mg Magnesium was weighed, polished and cut into pieces 0.7 ML Bromobenzene was added to 3 ml of ether When adding the Bromobenzene, the solution turned dark brown. Over time, the solution got darker and browner Waited 30 mins for the Mg to dissolve. Solution got darker and browner. 1.105 g benzophenone, dissolved with 2 ml ether. When the benzophenone was added, the solution turned deep red, like clay. As reaction cooled, the solution turned to a pink color. Was now a solid. The solid was white and smelled very good. When HCl was added, the solution fizzed and turned yellow. 2 layers formed. Saw cloudy bottom and top yellow layers. Drain off bottom, pour out ether. Re-extract aqueous with ether. Combined ether layers and dried over Sodium Sulfate -

biphenyl by-product. 16. Collect solid via vaccum filtration 17. Weigh crude and calculate yield 18. Recrystallize with hot isopropyl alcohol then vacuum filter to retrieve product. 19. Obtain NMR, TLC to characterize

Crude solid was surgary brown. 0.680 g of crude solid yielded Recrystallized with hot isopropyl alcohol and the solution turned milky brown. Pure solid was powdery white -

Results: Crude Yield : Pure Yield: % Yield: Mp range:

0.680 g 0.326 g 20.6 % 159 – 161.4 ° C

IR Spectra Assignments: Peak Stretch 3000-3500 1500-1700 650-1000 Proton NMR Peak Shif 2.2 ppm 7.4 ppm

Identification Hydroxyl Group Aromatic C-C (double) Aromatic C-H Assignment Proton #2 Proton #1

Integration 9 6

Carbon NMR Peak Shif 30 ppm 80 ppm 130 ppm 150 ppm 200 ppm

Assignment Carbon #5 Carbon #4 Carbon #3 Carbon #2 Carbon #1

Integration 3 6 6 3 1

Discussion In this reaction, a Grignard reagent was used to convert a ketone into a tertiary alcohol. When synthesizing the Grignard reagent, certain precautions were taken to ensure a successful reaction. The reaction to synthesize a Grignard reagent is extremely moisture sensitive and sluggish. Because the reaction is moisture sensitive, all glassware was ovendried before use and a drying tube was employed. Also, dry ether was used. To speed up the sluggish reaction and prevent side reactions, the magnesium ribbon was polished. The magnesium was polished to increase reactivity as polishing removes the outer layer of magnesium oxide. These precautions were taken to ensure a successful reaction. Grignard reagents cannot be purchased and must be synthesized in lab and reacted in-situ with the desired substrate. Unlike Grignard reagents, Organolithium reagents can be bought however they are very expensive to ship and pyrophoric. Based on the melting point data and spectroscopic information collected, the product that we retrieved was definitely triphenylmethanol. The melting point of the product matched that found in literature of triphenylmethanol ( 161-163 degrees Celcius). The product had a melting point slightly slower suggesting some impurities. The NMR and IR spectroscopy matched the spectroscopy found in literature. Based on these, the product was most likely triphenylmethanol....