Why Must Sodium Borohydride Be Added Slowly in Benzophenone Reduction?

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Discussion Overview

The discussion revolves around the reduction of benzophenone to benzhydrol using sodium borohydride, focusing on the reasons for the slow addition of sodium borohydride and the necessity of conducting the reaction in iced water. Participants also explore the subsequent steps involving the dissolution of the solid product in methanol and the addition of water.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant questions the need for slow addition of sodium borohydride, suggesting it may be to control the heat released during the reaction.
  • Another participant humorously speculates about the potential for an explosive reaction if not controlled.
  • A different participant discusses the process after the reaction, questioning the role of methanol and water in isolating the product and completing the reaction.
  • There is an assumption that water is necessary to complete the reaction and that the cloudy solution may be related to the solubility of diphenylmethanol.

Areas of Agreement / Disagreement

The discussion contains multiple viewpoints regarding the reasons for the slow addition of sodium borohydride and the role of water in the reaction, indicating that there is no consensus on these points.

Contextual Notes

Participants express various assumptions about the reaction mechanisms and the solubility of products, but these assumptions remain unverified and are not universally accepted.

ephemeral1
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Why do you have to add sodium borohydride slowly to reduce benzophenone to benzhydrol? And why do we have to place the reaction in iced water?
 
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Because you need to control the amount of heat released in the reaction. You don't want the whole thing to explode... or maybe you do. That might be a fun thing to try.
 
After we got the solid from the reaction of benzophenone with sodium borohydride, then we dissolved the solid in a minimum amount of hot methanol. Why do we add the same amount of water to get the resulting solution to a cloudy point?
 
The methanol, I assume, would isolate the (former) benzophenone, and water is needed to complete the reaction. (any acidic substance with a pKa than can protonate a diphenylmethoxide ion, really) Since diphenylmethanol has a solubility of just 0.5 g/L at room temperature, the cloudy stuff is probably that.
 

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