Reduction of 9-Fluorenone Determine the molar ratio of NaBH 4 to 9-fluorenone us
ID: 1087895 • Letter: R
Question
Reduction of 9-Fluorenone
Determine the molar ratio of NaBH4 to 9-fluorenone used in the experiment. Explain why it is best to use excess NaBH4 rather than a 1:4 ratio.
Starting mass: 0.61g of 9-fluoroenone and 0.05g of sodium borohydride
Final mass: 0.43g 9-fluorenol
Chem 3450 Reduction of 9-fluorenone 1. Determine the molar ratio of NaBH4 to 9-fluorenone used in the experiment. Explain why it is best to use excess NaBH4 rather than a 1:4 ratio 2. Esters are generally unreactive with NaBH4, but are readily reactive with LiAlH4 to produce alcohols a. Explain why esters are less reactive than aldehydes or ketones to hydride b. Explain why LiAlH4 is more reactive than NaBH4 reagents c. Write structures of the organic compounds formed when LiAlH4 reacts with methyl benzoate and the reaction is worked up with aqueous acid. For the 1H NMR spectrum of 9-fluorenone, assign the peak at 7.6 based on its splitting pattern and chemical shift. Use resonance structures to differentiate the two sets of protons expected to appear as doublets. 3. 85 745 ppm 10 8, ppm For the H NMR spectrum of 9-fluorenol, there is splitting in the -OH hydrogen signal. Under what circumstances do you see OH splitting? 4. 7,65 745 ppm 5.00 ppm 2.00 ppm 10 , ppmExplanation / Answer
1. In the reduction of 9-Fluorenone with Sodium Borohydride, looking at the balanced reaction, one sees that there is a 4:1 molar ratio between fluorenone and borohydride in the reactants. This means that 1.32 mmol of sodium borohydride requires 4 x 1.32 mmol = 5.28 mmol of fluorenone to react completely. However, there are only 3.3 mmol of fluorenone present. Therefore, fluorenone is the limiting reagent and hence, excess sodium borohydride will give the best yield.
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