Question

Post-­‐Lab to Accompany the Grignard Synthesis of Triphenylmethanol You were instructed to add the bromobenzene in increments during the Grignard preparation to prevent an unwanted side reaction. What would the product of that reaction be (show structure also)? How was it removed during work-­‐up from the triphenylmethanol product?

Answer 1

The side reaction in the reaction between phenylmagnesium bromide and bromobenzene gives side product biphenyl .(impurity).When bromobenzene is added slowly to Mg/ether side rxn can be avoided.

In the experiment the impurity is removed by recrystallization,as biphenyl is much more soluble in ether(organic solvent) compared to triphenylmethanol.

Separatory funnel is used to separate the aqueous layer of the rxn containing triphenymethanol from the impurity (more soluble in organic solvent)

Procedure

After the product is formed it is soluble in ether layer so removed from separatory funnel, (after adding sulphuric acid to remove Mg salts and sodium chloride to remove water.)

Then add anhydrous sodium sulphate and swirl the funnel to remove water and extract more organic layer.Add 25 ml ligroin solution to the separated organic solution in an Erlenmeyer flask and concentrate in hot plate.Evaporate slowly to extract triphenylmethanol.