Grignard Synthesis

GRIGNARD SYNTHESIS Syntheses of Phenylmagnesium Phenylmagnesium bromide and Triphen Triphenylmethanol ylmethanol

Group 1 Sangalang, Reymart V. V. Sucaldito, Melvir R.

Dr. Glenn Alea

INTRODUCTION

 REACTION AND MECHANISM

PROCEDURE 0.050 g of magnesium solid

2.2 mmol (0.232 ml) of bromobenzene

0.5 ml anhydrous diethyl ether

0.5 ml anhydrous diethyl ether

Phenylmagnesium bromide ( Grignard Reagent)

PROCEDURE 0.364 g of benzophenone

1.0 ml of anhydrous diethyl ether

Phenylmagnesium bromide ( Grignard Reagent)

PROCEDURE

PROCEDURE

2ml of 3M HCl

The solution was place

PROCEDURE  A - Bromobenzene B - Cospot C – Product (Ether layer) UV light as visualizing agent Solvent system: 1:5 DCM:Pet.ether  A

B

C

PROCEDURE  Aqueous layer was removed by Pasteur Pipette

Saturated NaCl Solution was added

 Anhydrous CaCl2 was added to dry

The ether extract was dried using Nitrogen gas

PROCEDURE

Slightly yellowish solid Melting Point FT-IR Analysis

Triphenylmethanol ?

RESULTS AND DISCUSSION

Phenylmagnesium bromide

RESULTS AND DISCUSSION  A - Bromobenzene B - Cospot C – Product (Ether layer) UV light as visualizing agent Solvent system: 1:5 DCM:Pet.ether  A

B

C

SPOTS

Distance of Solvent

Distance of Solute

Rf Value

 A

28 mm

18 mm

0.643

RESULTS AND DISCUSSION Weight of Test Tube w/ cap = 18.241 g Weight of Test Tube w/ cap and sample = 13.569 g

Weight of the Crude Extract = 0. 328 g

Melting Range of the Crude Extract – 43  – 47 0C Theoretical Melting Point : Triphenylmethanol – 164.2 0C Benzophenone  – 48 0C

RESULTS AND DISCUSSION  A - Benzophenone B - Cospot C  – Product UV light as visualizing agent  A

B

C

Solvent system: 1:5 DCM:Pet.ether

SPOTS

Distance of Solvent

Distance of Solute

Rf Value

 A

25 mm

8 mm

0.32

RESULTS AND DISCUSSION  A. Crude Product Pertinent Peaks

Functional Group

3454.24 cm-1 (medium)

-OH

3059.16 cm-1 (medium)

sp2 -CH

1657.18 cm -1 (strong)

-C=O

 A. Triphenylmethanol

 A. Benzophenone

Pertinent Peaks

Functional Group

Pertinent Peaks

Functional Group

3474 cm-1 (strong)

-OH stretch

3433.241 cm-1 (weak)

-OH

3087 cm-1 (medium)

sp2 -CH stretch

3050.70 cm-1 (weak)

sp2 -CH

1150 cm -1 (medium)

-C-O bending

1651.00 cm -1 (strong)

-C=O

CONCLUSION •

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The Grignard reactions are generally used by chemists due to its versatility. In this experiment, the syntheses of phenylmagnesium bromide, the Grignard reagent, and triphenylmethanol were performed.  The synthesis of Grignard reagent must take place in an inert and anhydrous solvent, ideally anhydrous diethyl ether, using bromobenzene and magnesium solid. The reaction is exothermic and must be kept closed until reaction ceases to prevent water contamination. This is the most crucial stage of the synthesis since absence of water must be maintained.  The Grignard reagent must be reacted immediately with the ketone, benzophenone, to form the alkoxide and upon acidification, the product, triphenylmethanol is formed. The product was dried, weighed and subjected to Thin Layer Chromatography.

CONCLUSION •

The mass of the crude extract is 0.328 g. The mobile phase used is 1 DCM:5 petroleum ether. The results for TLC shows that the synthesis and isolation of the desired product is unsuccessful. This is further confirmed by melting point determination, the melting range of the product was 43-47°C. The IR spectra of the product is similar with benzophenone, one of the reactants. It is concluded that the synthesis of phenylmagnesium bromide was successful and the synthesis for triphenylmethanol was not.

RECOMMENDATION •

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In performing the experiment for the synthesis of phenylmagnesium bromide, it is highly recommended to keep the system dry and free from contamination. All glasswares must be preheated at least 30 minutes to ensure dryness and cleanliness.  It is recommended to use analytic grade anhydrous diethyl ether, use proper container and proper transferring must be done to ensure water -free ether. The magnesium, bromobenzene and benzophenone must be dried also.  For the activation of magnesium, it is recommended to use iodine as activator for magnesium and indicator for the reaction so as to avoid the exposure of the mixture to air.  It is recommended to perform TLC analysis as frequent as possible to monitor the progress of the reaction and the formation of the product.

DOMO ARIGATO GOZAIMASHITA!!!!