How many molar equivalents of hydride does sodium borohydride contain?

1 Answer
Ernest Z.
Mar 9, 2016

1 mol of sodium borohydride contains 4 mol of hydride.

Explanation:

The borohydride reduction of an aldehyde or ketone involves the addition of two hydrogen atoms.

"RCHO"color(white)(l) stackrelcolor(blue)("1. BH"_4^"-"color(white)(m)) (→) "RCH"_2"OH"
color(white)(mmmmll)stackrelcolor(blue)("2. H"^+color(white)(m))(color(white)(m))

However, only one of the "H" atoms comes from the borohydride.

We can write the major steps as

"4RCHO" + "BH"_4^"-" → ("RCH"_2"O")_4"B"^"-"

This is where 1 mol of "BH"_4^"-" provides the 4 mol of "H"^"-".

The hydrolysis with aqueous acid provides the proton on the "OH" group.

("RCH"_2"O")_4"B"^"-" + "H"_3"O"^+ + "2H"_2"O" → "4RCH"_2"OH" + "H"_3"BO"_3

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