Grignard Lab Report

10 October 2016

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.

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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 temperature and facilitated with an ice bath. The purified triphenylmethanol can then be vacuum filtered and dry. The reaction mechanism for the two steps described is as followed: The purified product obtained was then tested to confirm the successful synthesizing of triphenylmethanol.

Melting point value of 160-162°C was determine, which support the correct product synthesized. Furthermore, all major functional groups were present in the IR taken for triphenylmethanol indicating a successful experiment. Procedure: All glassware used in this experiment was oven dried and sterile. A Grignard reagent was produced by reacting ~0. 15 g of magnesium metal, stir vane, 0. 80 mL of bromobenzene (0. 70 mL) and anhydrous diethyl ether (20. 0 mL) mixture in a 20-mL round-bottom flask (reflux apparatus). The apparatus was elevated from the hot plate and heated at 60°C for 15 minutes.

Brownish-gray solution was observed. The remainder bromobenzene/ether mixture was added to the round bottom flask drop-wise with additional washing of ~2. 0 mL of diethyl ether. Iodine (catalyst) was added to facilitate the reaction. Phenylmagnesium bromide was obtained upon cooling of the solution to room temperature. Benzophenone (1. 09 g) and diethyl ether (2. 0 mL) mixture was then reacted with the Grignard product for 15 minutes. Red solidified adduct was observed. Next HCl (6. 0 mL) was added drop-wise to the adduct; bilayer of triphenylmethanol and inorganic impurities was observed.

The mixture was then filtered using the reparatory funnel. The round-bottom flask was washed with additional ether (5. 0 mL) and re-extracted. Sodium sulfate was then added to dry the solution. Aqueous solution was then decanted into an Erlenmeyer flask and evaporated in a hot water bath (50°C) with air until oily solid was observed. Hot petroleum ether (3. 0 mL) was added drop-wise to dissolve the by-products and cooled to room temperature. Upon cooling, the crude was then vacuum filtered and collected. Hot Isopropyl alcohol was then added to the crude to initiate recrystallization and then vacuum filtered.

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