What conjugate base(s) will deprotonate water?

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Answer 1 · 2014-04-10T23:30:41

The conjugate base of any acid with a $pK_"a"$ greater than water will deprotonate water.

Here is a short $pK_"a"$ table.

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Note that $"HC≡C-H", "H"_2"N-H"$ , and $"H"_3"C-H"$ are all weaker acids than water.

The corresponding conjugate bases, $"H-C≡C:"^"-", "H"_2"N:"^"-"$ , and $"H"_3"C:"^"-"$ , are strong. They will all deprotonate water.

The conjugate base of methane $"H"_3"C:"^"-"$ is strong enough to deprotonate anything below it in the table.

Methyllithium, $"CH"_3"Li"$ , is one of the strongest bases around.

Acetylide ion ( $"H-C≡C:"^"-"$ ) is strong enough to deprotonate only an acid with a $"pK"_"a" < 25$ .

Acetate ion ( $"CH"_3"COO"^"-"$ ) is weaker still, able to deprotonate only an acid with a $pK_a < 5$ .

A more complete table of $pK_"a"$ values will give you many more conjugate bases that will deprotonate water.