What is the white precipitate that forms when benzophenone is added to a Grignard solution?

The white precipitate that forms when benzophenone is added to a Grignard reagent solution is triphenylmethanol. This is a typical result of the reaction between a Grignard reagent, which is an organomagnesium compound, and a carbonyl compound, in this case, benzophenone.

The reaction proceeds through the nucleophilic addition of the carbon atom from the Grignard reagent to the electrophilic carbon atom of the carbonyl group (C=O) in benzophenone. The overall transformation results in the conversion of the double bonded oxygen in the carbonyl group to an OH group, forming the alcohol triphenylmethanol. The process is simplified in the following reaction scheme:

RMgX + Ph_2C=O → Ph_2C(OH)R → Ph_3COH

Here, R represents the alkyl or aryl group from the Grignard reagent (RMgX) and Ph represents a phenyl group (C_6H_5-).

After the Grignard reagent attacks the carbonyl carbon, the reaction intermediate is then protonated (usually by adding an acidic work-up solution such as dilute hydrochloric acid or water) to yield the final alcohol product, triphenylmethanol. The White precipitate is this triphenylmethanol.