Ether One or the Other

This year we performed the synthesis of triphenylmethanol with a commercial phenylmagnesium bromide reagent. The reaction, in principle, works quite well and the reaction turns a pretty pink color on the way to completion. This year, the class was divided into three groups and each group used a different ether solvent for the reaction – diethyl ether, tetrahydrofuran, or methyl t-butylether. The goal was to determine if THF and/or MTBE was a suitable substitute for diethyl ether – the classic Grignard solvent. The students recorded their product yields on a spreadsheet that was made available as “class data.” Similar to the previous oxidation of cyclohexanol experiment, the results were compromised by impurities present in the student products. For some, the solvent was incompletely evaporated. We used the forced air method of evaporation instead of boiling water bath method because of all the ether. Many students had significant amounts of unreacted benzophenone in their products. This was most likely a result of the Grignard reagent reacting with water rather than benzophenone. Benzophenone was the limiting reagent (0.01 moles) with an excess of Grignard reagent being added (0.135 moles). A larger excess of Grignard reagent would most likely lead to a more complete reaction. All three ethers gave a similar result as far as I could tell, but they did seem to give a different look to the reaction mixture.

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