I performed the classic Grignard reagent formation leading into the preparation and purification of triphenylmethanol using phenylmagnesium bromide as my Grignard, and benzophenone as the reagent for the subsequent reaction.

In the formation of the Grignard reagent, I used Mg turnings to react with bromobenzene to produce phenylmagnesium bromide with excess bromobenzene as Mg was my limiting reagent.

In the second reaction, I reacted the Grignard reagent with benzophenone, my limiting reagent, to form an alkoxide intermediate, to which I added excess 6M HCl to protonate the intermediate to form crude triphenylmethanol.

I then performed a recrystallization of the crude triphenylmethanol (with biphenyl as a by-product) with isopropyl alcohol.

Aside from poor technique with the laboratory procedures, what can contribute to a poor yield of purified, recrystallized triphenylmethanol?

I did some searching online, and found that certain individuals mentioned a low yield being attributed to "competing side reactions", but with no further details. Is this referring to the biphenyl side-reaction between the phenylmagnesium bromide and bromobenzene, or another external factor?

  • 1
    $\begingroup$ Too little Grignard reagent. Evaporate the mother liquors of from the crystallization for more trityl alcohol and run a tlc. Formation of trityl chloride in your workup. $\endgroup$
    – user55119
    Feb 3 '19 at 2:24
  • 3
    $\begingroup$ Use a milder workup such as aq NH4Cl. 6N HCl pretty well guarantees formation of the trityl cation from trityl alcohol. $\endgroup$
    – Waylander
    Feb 3 '19 at 8:33

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