Why Must Sodium Borohydride Be Added Slowly in Benzophenone Reduction?

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Adding sodium borohydride slowly to benzophenone during reduction to benzhydrol is crucial for controlling the heat released in the reaction, preventing potential hazards such as explosions. The reaction is conducted in iced water to further manage temperature and ensure safety. After the reaction, the solid product is dissolved in hot methanol, and water is added to reach a cloudy point, which indicates the formation of diphenylmethanol. The addition of water is necessary to facilitate the reaction and protonate the diphenylmethoxide ion. Given the low solubility of diphenylmethanol at room temperature, the resulting cloudiness suggests the presence of this compound in the solution.
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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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