Reduction of esters to primary alcohols using LiAlH4
Description: Addition of lithium aluminum hydride to esters leads to the formation of primary alcohols (after addition of acid)
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what are the reaction conditions? is it heating under reflux?
Yes, generally esters are reduced with LiAlH4 under reflux.
What about with the cyclic ester? I am wondering about the alkoxide intermediate. Is it two separate LAH molecules, one acting at each end?
It’s not 2 separate LAH, but rather 2 separate H+ in the acid workup. If you look at the mechanism, when bond D, the one on the “leaving” oxygen, breaks, the electrons go toward the oxygen. It’s not shown, but this just makes another oxygen anion. In the case of the cyclic ester, the mechanism is the same, but if you draw it out, you’ll see that the “leaving” oxygen is just stuck at the other end of the chain. In the acid workup, the H+ protonates both ends.