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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