Grignard Reaction Lab Report

Any amount of H2O present would react with and therefore ruin the Grignard reagent. The negative charge on the Grignard carbon would pop a proton off of water, and the resulting hydroxide would react with MgBr2. Since all of the water and moisture was removed, the reaction should run successfully. For this experiment’s reaction, bromobenzene is turned into phenylmagnesium bromide, a Grignard reagent. Then, the Grignard reagent is reacted with benzophenone to yield a molecule with a negative charge on the oxygen. This molecule is worked up and protonated to yield triphenylmethanol.

The mixture was transferred to an ice bath to crystallize the product, after which the product was collected by vacuum filtration on a Hirsch funnel, washing the flask with small aliquots of cold xylene and pouring the solution over the crystals, allowing the vacuum to thoroughly dry the product. Additional drying was achieved by transferring the product to filter paper and pressing the crystals to remove any excess moisture. The product was then weighed and a melting point determined. A comparative TLC was run in Hexanes:Ethyl Acetate solvent against maleic anhydride to verify the purity of the

The purpose of this experiment was to synthesize the Grignard reagent, phenyl magnesium bromide, and then use the manufactured Grignard reagent to synthesize the alcohol, triphenylmethanol, by reacting with benzophenone and protonation by H3O+. The triphenylmethanol was purified by recrystallization. The melting point, Infrared Spectroscopy, 13C NMR, and 1H NMR were used to characterize and confirm the recrystallized substance was triphenylmethanol.

The mixture was heated at 120°C using an aluminum block and was stirred gently. After all of the solid dissolved, it was heated for 20 additional minutes to ensure the reaction was complete.

The reaction was then reduced with acid to protonate the carboxylate salt which yields a carboxylic acid product. By adding acid, it also dissolved any excess magnesium metal, so a liquid-liquid extraction can occur to isolate the product. A liquid-liquid extraction was used since the experiment involved a liquid solvent that removed a liquid component from the liquid mixture. A solid-liquid extraction would have been used if components were being removed from a solid by using a

The product was then suspended in 2 ml of water with a stir rod in a 50 ml Erlenmeyer flask and heated to boiling. Water was added in one milliliter increments until all the product was dissolved (18 ml added total). The saturated solution was allowed to slowly cool, and gradual white crystal formation was observed. Recrystallized product was collected once more by suction filtration with the Hirsch funnel once crystallization ceased. Collected product dried on a watch glass for a week, weighed 0.14 g (1.2 mmol), and the melting point was 139°-141°

Organometallic compounds, such as Grignard reagents, are molecules containing carbon-metal bonds and are often used to create new carbon-carbon bonds. Grignard reagents—or organomagnesims— are specifically those that have a carbon-magnesium bond.

After about 1 minute of shaking, the two layers separated. The organic layer on the top layer (consisted of ethyl acetate and naphthalene) collected for further experiment; by adding Sodium Sulfate into organic phase and filtering the Na2So4 from the solution using the wool. The dried organic layer was weighed to get its mass and the residue of Na2SO4 were rinsed with ethyl acetate under vacuum (rotary evaporator). The acid extract on the bottom layer which is a combination of benzoic acid and NaOH were collected in the 50 mL Erlenmeyer beaker for the recovery of acid.

The product obtained had a melting point of approximately 128-130 °C and a weight of .054 grams. The limiting reagent was calculated to be sodium borohydride. With the weight and limiting reagent, the percent yield was calculated to be approximately 53.33%. The IR of the product showed a peak at approximately 3311.25, which indicates the presence of an O-H bond.

For this lab, certain actions were performed to facilitate the optimal conditions for the Grignard reaction to proceed. As mentioned above, forming the Grignard reagent and the Grignard reaction must take place in dry, anhydrous conditions. This was why the glassware was initially placed in the oven to evaporate any moisture that was present on the glassware. Additionally, the magnesium used in the experiment needed to be dry too, so it was also placed in the oven to be heated. Creating a dry environment was also why the reaction vessel was covered in the septum because it helped prevent the moisture in the air from entering the reaction. Having water in the reaction vessel would destroy the Grignard reagent and hinder the Grignard reaction. Because the reaction needed to be done in dry and anhydrous conditions, diethyl ether was used as the solvent because it was aprotic meaning that the formation of phenylmagnesium bromide and the Grignard reaction would not be hindered by the protonation of water and alcohols3.

The crude product was washed by taking the reaction product in the separatory funnel and adding 23 mL of deionized H2O. The mixture was shaken and allowed to settle until layers were observable. The top layer was the desired product and approximately 25 mL of aqueous layer was extracted from the separatory funnel. Next, 25 mL of 5% NaHCO3 was added to the separatory funnel in order to neutralize the acid. This mixture was swirled, plugged with the stopper and inverted. Built-up gas was released by turning the stopcock to its opened and closed positions, releasing CO2 by-product. This was done four times in one minute intervals. The solution was allowed to settle until layers were observable. The bottom layer that contained salt, base and water was extracted from the separatory funnel. The crude product was washed again as mentioned previously.

Though the products had dissimilar melting point values, it is not enough to conclude that they are different. To be certain of the identity of the products, Infrared Spectroscopy (IR) and H- NMR were used. While IR is used to determine the functional groups present in an unknown substance through identification of covalent bonds, H-NMR is used to determine the structure of an unknown compound. The IR from both products had peaks at almost identical frequencies. The IR of both

To tube 2 and tube 3 a boiling chip is added. The two tubes are boiled to remove any residual ether. Next, the tubes are cooled to room temperature and placed into an ice bath to allow for crystallization. The solution is then removed from the solid in each tube and discarded. To tube 2 and 3 ~0.5 ml of H2O is added for recrystallization, the tubes

The Grignard reaction is an important synthetic process by which a new carbon to carbon bond is formed. Magnesium metal is first reacted with an organic halide forming the Grignard reagent. The Grignard reaction is the addition of an organomagnesium halide (Grignard reagent) to a ketone or aldehyde, to form a tertiary or secondary alcohol, respectively. For example, the reaction with formaldehyde leads to a primary alcohol. Grignard Reagents are also used in the following important reactions: The addition of an excess of a Grignard reagent to an ester or lactone gives a tertiary alcohol in which two alkyl groups are the same, and the addition of a

5.3 mL of bromobenzne and 15 mL of anhydrous ether was then placed into the separatory funnel and was shaken and vented in order to mix the solution. Half of the bromobenzene solution was added first into the round bottom flask and as soon as a color change was observed, the remaining half of the bromobenzene was added drop wise into the round bottom flask. The mixture was then refluxed on a heating mantle for 10 minutes until most of the magnesium has been consumed.