Sodium Borohydride Reduction of 9-Fluorenone/IR Analysis of Product
April 27, 2007
Methods and Background
The purpose of the experiment was to reduce 9-fluorenone, a ketone, to 9-fluorenol, an alcohol,
using sodium borohydride and identify the product by means of melting point determination and
infrared spectroscopy analysis.
Reduction is a basic type of chemical reaction that can be defined as the gain of electrons, loss of
bonds to oxygen, gain of bonds to hydrogen, or decrease in oxidation number.
functional groups containing double bonds undergo reduction by the net addition of the elements
of one molecule of hydrogen across the π-bond, causing unsaturated compounds to become
Metal hydride reducing agents cause reduction reactions and they have different
reactivities toward specific functional groups.
For instance, lithium aluminum hydride is a very
reactive, and thus unselective, hydride donor that rapidly reduces aldehydes, ketones, carboxylic
acids, esters, and amides (even though the latter carbonyl compounds, especially amides, are not
particularly reactive due to resonance), while sodium borohydride is less reactive, and thus more
selective, reducing only aldehydes and ketones into primary and secondary alcohols,
Sodium borohydride may be used in alcoholic and aqueous solutions because it
reacts much more rapidly with the carbonyl group than with the solvent, while lithium aluminum
hydride reacts rapidly with protic solvents, so it must be used in anhydrous ethereal solvents.
The experimental reaction involves the transfer of hydride ion from borohydride ion to the
electrophilic carbonyl carbon of 9-fluorenone (the carbonyl bond is polarized because of the
electronegativity difference between oxygen and carbon, rendering the carbonyl carbon
electrophilic) with simultaneous transfer of the electron-deficient boron atom to the carbonyl
All four of the hydrogen atoms attached to boron may be transferred in this way to
produce an intermediate borate salt, which upon addition of water and acid (hydrolysis
conditions) decomposes through cleavage of the boron-oxygen bond to yield 9-fluorenol.
1 mmol of sodium borohydride can reduce 4 mmol of ketone.
Filtration is used to separate solids from liquids.
A specific type of filtration, vacuum filtration,
is used to collect crystalline solids from solvents after recrystallization or precipitation.
this technique, flowing water is used to create a vacuum, which is utilized in filtering liquid
from solid through a Büchner funnel.