Grignard Reaction Lab Report

Grignard Reaction: Synthesis of Triphenylmethanol

Hai Liu

TA: Ara Austin

Mondays: 11:30-2:20

Abstract:

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
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
0.00701 mol of bromobenzene. From this a theoretical calculation of 1.12g was determined for phenylmagnesium bromide. The Grignard reagent was then furthered reacted with benzophenone and diethyl ether forming an adduct. A yield of 0.0650g of triphenylmethanol was obtained. This deviated very slightly from the theoretical calculation of 0.0651g and a near perfect 99.85% yield. Although the numbers obtained were high, these values might be slightly incorrect. During the vacuum filtration and drying of the purified crystals, some water might of still have resided in the product. This would have resulted in an excess water weight being recorded. The melting point of 160-162°C was measured from the purified product compared to the literature value of 163°C. This supported a successful synthesizing of triphenylmethanol. Additionally, all the major functional peaks were present in the IR: A broad peak at ~3400 cm- of an alcohol group, a peak at around 3100 cm- indicating a C-H bonds in the benzene ring, as well as a peak at around 1400-1500 indicating a C=C bonds in the