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  •  » Stoichiometry of borohydride reduction of benzil

#1 2008-02-05 14:57:53

orgopete
Administrator

Stoichiometry of borohydride reduction of benzil

1) What is the wt of 2.5 mmol of benzil?
answer 0.535 is it right

2) What is the wt (in grams) of 2.5 mmol of sodium borohydride?

3) What is the theoretical amount of sodium borohydride needed?

4) What is the limiting reagent?

5) What is the theoretical yield, assuming you begin with exactly 2.5 mmol of each reagents?

1) Check your calculator, 2.5 mmol x 210.1 mg/mmol = 0.525 g

2) 2.5 mmol x 38.03 mg / mmol = 0.95 g

3) Since BH4 delivers 4xHs and benzil is a diketone,
2 x benzil (mw 210) +  NaBH4 + 4ROH -> 2 pdt (mw 214) + NaB(OR)4
For two moles of benzil, one mole of NaBH4 is needed.
2.5 mmol/2 x 38.03 mg / mmol = 0.0475 g

4) Benzil because an excess of NaBH4 was used.

5) 2.5 mmol x 214.1 mg pdt / mmol = 0.535 g of pdt.

To see how a reduction transfers all four hydrogens, see http://www.curvedarrowpress.com/partd/b … dered.html

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