Question

Why should the alkoxide ion be the one expelled instead of hydroxide?

Answer 1

Just to address the question (finally!), would you give us some context...?

Explanation:

I think you refer to the saponification reaction....i.e. the which here is the formation of a carboxylate salt from an ester under BASE hydrolysis...i.e.

`R^(1)(C=O)OR^2+HO^(-) stackrelDeltararrR^(1)(C=O)OH+""^(-)OR^2`

Now TWO products result from the first addition of hydroxide; the acid...and an alkoxide salt...but certainly given this scenario, alkoxide is a powerful base, much more powerful than hydroxide, and would have only a transient existence in aqueous solution, and proton transfer would occur to give the alcohol, and the carboxylate salt...as shown...

`R^(1)(C=O)OH+""^(-)OR^2rarrR^(1)(C=O)O^(-)+HOR^2`