Lab 8 (Sodium Borohydride Reduction)

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5 Terms

1
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What is the mechanism of reduction via sodium borohydride

  1. Proton from nucleophile (NaBH4) attacks the aldehyde group 

  2. Then the BH3 will attach to the O

  3. This is then treated with water (or even better acid) to replace the BH3 with H to make it into an alcohol

<ol><li><p><span>Proton from nucleophile (NaBH<sub>4</sub>) attacks the aldehyde group&nbsp;</span></p></li><li><p><span>Then the BH<sub>3</sub> will attach to the O</span></p></li><li><p><span>This is then treated with water (or even better acid) to replace the BH<sub>3</sub> with H to make it into an alcohol</span></p></li></ol><p></p>
2
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<p></p>

2, because the acid is what protonates the oxygen, the proton from NaBH4 only attacks the carbonyl carbon

<p>2, because the acid is what protonates the oxygen, the proton from NaBH<sub>4</sub> only attacks the carbonyl carbon</p>
3
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<p>Suppose, you treated the following compound with a huge excess of sodium borohydride in methanol. What product do you expect to obtain?</p>

Suppose, you treated the following compound with a huge excess of sodium borohydride in methanol. What product do you expect to obtain?

3, because NaBH4 is not strong enough to reduce esters (need LiAlH4)

4
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In principle, how many aldehyde molecules can one molecule of NaBH4 reduce?

4, one for each proton

5
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<p>Why it is better to use 1 M aqueous NaOH solution as a solvent for NaBH4 reduction rather than pure water?</p>

Why it is better to use 1 M aqueous NaOH solution as a solvent for NaBH4 reduction rather than pure water?

4, because NaBH4 typically reacts really fast so the NaOH slows this down