Jocelin Olmos
March 12, 2015
Organic Chemistry 334L
The Grignard Reaction
Abstract
The focal point of this experiment is to create a carbon-carbon bond. The Grignard Reaction,
RMgX, with a halide dioxide yields a carboxylate salt. The carboxylate salt is then converted to
the corresponding carboxylic acid upon aqueous acidic work up. Prior to the experiment we
obtained our 25mL round-bottom flask containing .36g of magnesium turnings and put it in the
oven at 110 degrees Celsius and cooled at room temperature. This was done to get rid of the
water in the container and the magnesium so it will be a better electrophile in the Grignard
reaction. We had to be extremely careful to not let too much moister in this lab experiment as to
obtain a better yield of the product. In this experiment we used two molarities for hydrochloric
acid because a strong acid in the beginning can pull off electrons and create a double bond and
water would be a good leaving group. At the end of the experiment we weigh the product and
find the melting and determine the purity of it.
Introduction
French chemist Victor Grignard discovered the utility of the Grignard reagents in 1905 and
received a Nobel Prize in Chemistry in 1912. The Grignard reagent is the development of
organometallic compounds of lithium and magnesium to synthesize alcohols. The reaction is
made using a dry anhydrous ether solvent that is needed to solvate and stabilize the Grignard
reagent as it forms. Grignard reagents can be made from primary, secondary, and tertiary halides,
as well as from aryl and vinyl halides. The most reactive of the halides are iodide, then followed
by bromides and chloride. Grignard reagents are strong nucleophiles and bases. The most useful
reaction is the addition of the Grignard reagent to the carbonyl group. The Grignard reagent first
adds to the carbonyl group to add a alkoxide ion. An addition of a dilute acid in a separate step
protonates the alkoxide to give the alcohol. The significance of the Grignard reagent to organic
chemistry is that it is one of the best methods to assemble a carbon skeleton with a strong base
and nucleophile.
Above is an example in the book regarding the Grignard reagent using a carbonyl.
Overview
The Grignard Experiment begins when we obtain the oven-dried apparatus from the instructor.
We attach the round bottom flask with the water-cooled reflux condenser and a CaCl2 filled
drying tube and we attach water lines and immediately replace the condenser and start cooling
the water, we then add one crystal of iodine through the top of the condenser. We turn on the
magnetic stirrer and it will stir the reaction vigorously. The agitated magnesium turnings provide
sufficient impetus to initiate reaction. The disappearing of the iodine color, the cloudiness in the
diethyl either and the gentle boiling of the solution indicate that the reaction has started. Once the
reaction starts the diethyl ether should boil on its own. If the boiling stops, place the flask in a
warm water bath and maintain a gentle reflux for a total reaction time of forty five to fifty
minutes. Remove from the water bath and allow cooling. While it is cooling weigh
approximately 3.0g of crushed dry ice into a 50mL beaker and slowly, but steadily pour the
solution of phenylmagnesium bromide into this beaker. Stir reaction with glass stir rod until it
sets into a gummy paste. Continue to stir until all the excess of carbon dioxide has evaporated.
Add 7.5mL of 6 M of hydrochloric acid followed by 10mL of diethyl ether to the beaker. Add
the acid very carefully. Keep checking that the pH is acidic. Transfer into a 60mL separatory
funnel. Rinse the beaker with 1 or 2mL of the diethyl ether and add this rinse to the funnel.
Shake the funnel vigorously and allow the layers to separate and set aside the aqueous lower
layer. Extract the original diethyl ether upper layer with two 5mL portions of 5% sodium
bicarbonate solution. Warm the combined extracts briefly in a sand bath to evaporate any excess
diethyl ether. Acidify the mixture to a Congo Red paper end-point by drop wise addition of
concentration hydrochloric acid with constant stirring. Isolate the precipitated benzoic acid by
vacuum filtration and wash the crude product with a few mL of cold water while on the filter.
Air dry the product until next laboratory session and weigh the dry product and calculate the
experiment yield. Determine the melting point range of the benzoic acid and compare the result
with the literature value. What went wrong with my experiment was in the beginning of the
experiment when I was adding the 25mL round bottom flask to the cool condenser I did not
properly attach them and the round bottom flask fell and broke scattering all the magnesium.
Conclusion
In conclusion the Grignard Experiment was created for a carbon-carbon bond. This experiment
was created to see how the magnesium bromide can be a strong nucleophile and yield an alcohol.