# Why is sodium methanethiolate still a better nucleophile than sodium methoxide when the solvent is ethanol

I'm looking at a problem where sodium methanethiolate and sodium methoxide, both in equal amounts, are being reacted with $\ce{CH3I}$ and the solvent is ethanol.

I understand that sodium methanethiolate is a better nucleophile than sodium methoxide when the two are reacted in equal amounts with something like methyl iodide in a polar aprotic solvent. But why is sodium methanethiolate still a better nucleophile than sodium methoxide when the solvent is polar protic, like ethanol?

I thought the ethanol would reduce the nucleophilicity of both, but would do so at by different amounts, given the different electronegativity of sulfur and oxygen. If ethanol reduces the nucleophilicity of both at the same rate, why even use ethanol as a solvent in this case?

In your system the methanethiolate anion, $\ce{CH3S-}$, is a soft nucleophile while methoxide, $\ce{CH3O-}$, is a relatively hard nucleophile. You will also have ethoxide ($\ce{CH3CH2O-}$) in your system. As to the electrophile, methyl iodide, $\ce{CH3I}$: it is soft and hence it preferentially reacts with the softer nucleophile in the system, methanethiolate.