The Grignard Synthesis of Triphenylmethanol

Ether, Aldehyde, Grignard reaction

The purpose of this lab was to synthesize triphenylmethanol from benzophenone and bromobenzene by the formation of a Grignard compound with the reagents bromobenzene and magnesium metal. The bromobenzene was first transformed into the Grignard compound and was then reacted with the benzophenone to make the final product. The mixture was then mixed with sulfuric acid and the organic layer was extracted via a separatory funnel. The mixture was then recrystallized from methanol and was allowed to dry and the percent yield, melting point, and the IR was obtained. The mass of the product obtained was 5.45 grams and the percentage yield was determined to be 41.95%. The melting point range obtained from the final product was 89-91°C which was much lower than the literature value of 160-163°C. The peaks from the IR showed the formation of an alcohol group at 3460 wavenumbers and the presence of aromatic rings at 1600 and 1490 wavenumbers which confirms the successful formation of triphenylmethanol.

The Grignard reagent is an effective reducing agent that may be used to reduce a ketone to an alcohol. Generally, the Grignard reagent is represented by an alkyl- or aryl-magnesium halide. The nucleophilic Grignard reagent attacks an electrophilic carbon, which results in the formation of a carbon-carbon bond. Forming carbon-carbon bonds are very synthetically useful. The electrophilic carbons found within a carbonyl group are the most likely to be attacked because of their polarity. The Grignard reagent is formed by the reactions between an alkyl or aryl-halide and magnesium. The reaction proceeds via a radical electron transfer. Iodine can also be added to the reaction. The iodine lies on the magnesium and acts a catalyst to help initiate the reaction.

Scheme 1. Formation of the Grignard reagent.
The entire formation of the Grignard reagent takes place in diethyl ether. Diethyl ether prevents oxygen and carbon dioxide from...
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