Organic Chemistry Experiment 5:
Preparation of Benzoic Acid Using a
Grignard Reagent
By: --
Section: CHM 1321 (Z06)
Date Performed: Wednesday, March 18, 2020
Date Submitted:Monday, March 30, 2020
TA: Jason Crema
Introduction
, Grignard reaction is the addition of a grignard reagent (AKA organomagnesium halide)-
R-Mg-X to a ketone or aldehyde to produce a tertiary or secondary alcohol. The grignard reagent
contains a metal and an organic component. In this experiment, the grignard reagent was
produced by reacting bromobenzene (R-X) which is an organic halide with magnesium in an
anhydrous diethyl solvent. Iodine was used in this lab to activate the magnesium by making it
more reactive with bromobenzene. This reaction resulted in the reduction of magnesium, which
means the gain of electrons. Bromobenzene reacts with magnesium to form a grignard reagent
(phenylmagnesium bromide). The magnesium bromide group gets bonded to carbon, in which
the bond between the two has a higher polarity forming a stable carbanion. The carbanion (when
the negative charge is on the carbon atom) is a strong acid and a strong nucleophile (electron
donor) which allows the grignard reagent to react with compounds like carbonyl. The last step
below shows the addition of grignard reagent to a carbonyl (including aldehyde, ketone, and
ester) to form a carboxylate (a salt or ester of a carboxylic acid). After the carboxylate is
formed, an acid-base work-up is used to form benzoic acid which is a carboxylic acid. Please
refer to the mechanism below:
Preparation of Benzoic Acid Using a
Grignard Reagent
By: --
Section: CHM 1321 (Z06)
Date Performed: Wednesday, March 18, 2020
Date Submitted:Monday, March 30, 2020
TA: Jason Crema
Introduction
, Grignard reaction is the addition of a grignard reagent (AKA organomagnesium halide)-
R-Mg-X to a ketone or aldehyde to produce a tertiary or secondary alcohol. The grignard reagent
contains a metal and an organic component. In this experiment, the grignard reagent was
produced by reacting bromobenzene (R-X) which is an organic halide with magnesium in an
anhydrous diethyl solvent. Iodine was used in this lab to activate the magnesium by making it
more reactive with bromobenzene. This reaction resulted in the reduction of magnesium, which
means the gain of electrons. Bromobenzene reacts with magnesium to form a grignard reagent
(phenylmagnesium bromide). The magnesium bromide group gets bonded to carbon, in which
the bond between the two has a higher polarity forming a stable carbanion. The carbanion (when
the negative charge is on the carbon atom) is a strong acid and a strong nucleophile (electron
donor) which allows the grignard reagent to react with compounds like carbonyl. The last step
below shows the addition of grignard reagent to a carbonyl (including aldehyde, ketone, and
ester) to form a carboxylate (a salt or ester of a carboxylic acid). After the carboxylate is
formed, an acid-base work-up is used to form benzoic acid which is a carboxylic acid. Please
refer to the mechanism below:
