Lab 8 Conclusion Grignard Reactions Redo

Lab 8 Conclusion Grignard Reactions Redo - Synthesis of...

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Synthesis of Alcohols via Grignard Reactions Conclusion In this lab, we saw the utility of Grignard reactions in synthesizing alcohols, as we were finally able to synthesize triphenyl methanol from the given carbonyl compound, methyl benzoate, by using Grignard synthesis with bromobenzene. Specifically, the Grignard reaction to form an alcohol required two equivalents of Grignard reagent with methyl benzoate; the first equivalent eliminates the ester group and then the second equivalent allows formation of the triphenyl methanol. Through this reaction, we expected 0.223 g of triphenyl methanol, and the actual yield was relatively high though still low at 0.145 g, providing approximately 65.2% yield. We cannot expect a high yield for this somewhat convoluted reaction as it required 2 equivalents of Grignard reagent. Further, we had to scratch off the Mg quickly to prevent it from oxidizing and becoming useless in the reaction. It would be better to use fresh Mg or Mg powder, or to implement a better scratching method to transfer the Mg faster and more efficiently. We also noticed extra Mg silver at the bottom of the tube, indicating that not all the Mg reacted partially due to oxidation; we could use excess to increase the yield. Another source of lower yield is caused by adding bromobenzene too fast, which would cause biphenyl formation instead of permitting the bromobenzene reacting with Mg and ether; to better prevent this side reaction, we should add bromobenzene slower to the solution. Side reactions will lower our yield. When we added pentane to remove impurities and to help in recrystallization, the material after the ether that had evaporated off did not dissolve well in the pentane. In ideal recrystallization, the material will dissolve and then come back together to form bigger crystals. If smaller crystals formed, yield may decrease as the crystals are more likely to get through the filter paper. We
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This note was uploaded on 02/07/2012 for the course CHEM 215 taught by Professor Smith during the Spring '11 term at University of Texas at Dallas, Richardson.

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Lab 8 Conclusion Grignard Reactions Redo - Synthesis of...

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