Grignard Lab Report

Topics: Diethyl ether, Alcohol, Functional group Pages: 4 (1008 words) Published: April 14, 2013
Grignard Reaction: Synthesis of Triphenylmethanol

Hai Liu

TA: Ara Austin

Mondays: 11:30-2:20


In this experiment, phenylmagnesium bromide, a Grignard reagent was synthesized from bromobenzene and magnesium strips in a diethyl ether solvent. The Grignard reagent was then converted to triphenylmethanol, a tertiary alcohol with HCl. The reaction for phenylmagnesium bromide was:

The reaction for Grignard to triphenylmethanol was:

In the formation of the Grignard reagent, the limited reagent, magnesium was determined and 0.00617mol was calculated. In the second part of the experiment, a yield of 99.85% was obtained for triphenylmethanol. A melting point of 160-162°C was also determined. Additionally an IR for triphenylmethanol was taken, and all the major peaks were present. A broad peak at ~3400 cm- indicated an alcohol group present. A peak at ~3100 cm- indicating a C-H bonds in the benzene ring. A peak at ~1400-1500 cm- indicating a C=C bonds in the ring. Introduction:

In the first part of the experiment, phenylmagnesium bromide (a Grignard reagent) was prepared from reacting magnesium strips with aqueous bromobenzene in diethyl ether. The reaction is illustrated below:

The Grignard reagent formed can then behave as a base or a nucleophile due to the partial charge between the carbanion and the alkyl group. The carbanion from the phenylmagnesium bromide act as a nucleophile and under go nucleophillic addition reaction with the carbonyl group of the benzophenone forming an adduct. The adduct act as a strong base and protonate the proton from HCl with present of ether forming triphenylmethanol (a tertiary alcohol) The reaction is illustrated below:

In the presence of heat during refluxing the Grignard reagent, biphenyl impurity is formed and can be isolated with petroleum ether by extraction. The product can then be further purified through recrystallization method using hot isopropyl alcohol. This is then cooled to room...
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