Grignard Addition to a Ketone to Give Triphenylmethanol

Grignard Addition to a Ketone to give Triphenylmethanol

Abstract: Grignard reagents are commonly used reagents in the organic laboratory. They are very basic and must be anhydrous. The aim of this lab was to synthesize triphenylmethanol. Triphenylmethanol is a white crystalline aromatic compound, which produces an intensely yellow color in a strong acidic solution due to formation of carbocation, giving the carbon atom significant anionic character and making the Grignard reagent both a strong base and a good nucleophile.

alcohols were formed by the reaction of Grignard reagents with ketones. Triphenylmethanol was formed by reacting phenylmagnesium bromide with benzophenone. Grignard reagents are examples of organometallic compounds that can serve as carbon nucleophiles. The mass of magnesium was 18mg and the mass of benzophenone was 105mg. The crude product obtained is 117mg and the mass of Triphenylmethanol is 96 mg. The theoretical yield was calculated to be 150mg. The percent yield was calculated to be 64%. The final product of the experiment was pure Triphenylmethanol. The melting point obtained using the MEL-TEMP apparatus was 159°C. The literature melting point of the Triphenylmethanol is 162°C. The melting point was a way of determining the purity of the product. The Rf values were also calculated using a TLC plate.

Procedure:

Reaction:

D.W. Mayo, R.M. Pike, P.K. Trumper; Microscale Organic Chemistry (4th Ed.); John Wiley, New York, 2000, pps. 246-253. (5th Ed. Page 275)

Results:

Mass of Magnesium 18 mg

Mass of Benzophenone 105 mg

Mass of Culture Tube 11,444 mg

Mass of Culture Tube + Triphenylmethanol 11,532 mg

Mass of Triphenylmethanol 88 mg

Molecular Weight Triphenylmethanol 260 g/mol

Molecular Weight Benzophenone 182 g/mol

Melting Point Triphenylmethanol 160°C

Literature Melting Point Triphenylmethanol 163°C

Theoretical Yield for Triphenylmethanol 150 mg

Percent Yield for Triphenylmethanol 14 %

TLC Plate Results

Distance between Start Line and Finish Line 8.0 cm

Distance between Start Line and Benzophenone 4.7 cm

Distance between Start Line and Biphenyl 6.3 cm

Distance between Start Line and Triphenylmethanol 3.9 cm

Distance between Start Line and My Product 4.8 cm , 7.2 cm

Rf Value Benzophenone .59 cm

Rf Value Biphenyl .79 cm

Rf Value Triphenylmethanol .49 cm

Rf Value My Product .61 cm, .91 cm

Calculations:

Mass of Culture Tube +Triphenylmethanol – Mass of Culture Tube = Mass of Triphenylmethanol

= 11,529 mg – 11,444

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