The purpose of completing this laboratory experiment was to devise a method for reducing an aldehyde or ketone based on: a substrate, reagent(s), and reaction mechanisms.

1. Lindsay Meyer
Chris Devigny
Laboratory Report, Final – 8 March 2006
University of Notre Dame
CHEM 21224
Spring 2006
Title of Experiment: “Reduction of an Aldehyde or Ketone”
Purpose: The purpose of completing this laboratory experiment was to devise a method for
reducing an aldehyde or ketone based on: a substrate, reagent(s), and reaction mechanisms.
Equation:
Procedure:
Reagents were obtained: 9-fluorenone = 1.034g; sodium borohydride = 0.543g. An
initial TLC was taken for the purposes of determining reaction progress. Ether was chosen as the
solvent and added in the amount of roughly 10mL. The reaction was performed in an
Erlenmeyer, which was kept cool on ice. The mixture was mechanically stirred on high for 45
mins, with the progress being monitored every 10-15 mins. While it is likely that the reaction
did not go to completion as the “dots” never converged to signal the formation of 9-fluorenol, the
progress was notable. Due to time constraints, the reaction was halted. Weak hydrochloric acid
(3.0M) was added to the mixture to decompose the excess sodium borohydride. Water, in an
equivalent amount was also added to extract the organic product. The aqueous layer was
removed and the ether layer was Roto-vapped to collect the crude product, 9-fluorenol, which
had a distinct yellow color. An initial melting point was experimentally determined to be: 70-
72°C. Recrystallization was not performed since it would have been irrelevant and futile in
producing a product with an enhanced –OH character.
Observations/Data/Interpretations:
Mass 9-fluorenone = 1.034g
Mass sodium borohydride = 0.534g
MP1 = 70-72°C
Color = bright yellow
IR = see attached; showed a broad, but weak peak at 3209, in the –OH region. Another peak
occured at 1715, in the carbonyl region. The rest of the IR showed the aromatic stretch.
--
Stoichiometric Calculations
Number of moles start = 1.0g C13H8O * 1 mol C13H8O / 180g C13H8O = 0.0056mol C13H8O

2. Theoretical Yield = 0.0056mol C13H8O * (4mol C13H10O / 1mol C13H8O) * (178g C13H10O / 1 mol
C13H10O) = 3.95g C13H10O
Moles NaBH4 start = 0.0056mol C13H8O * 1mol NaBH4 / 4mol C13H8O) = 0.014mol NaBH4
Grams NaBH4 start = 0.014mol NaBH4 * 37.84g NaBH4 / 1mol NaBH4 = 0.5298g NaBH4
--
The melting point of the product, what was to be 9-fluorenol, was lower than the
expected value for the reagent, 9-fluorenone. A critical appraisal of the experimental techniques
showed that the correct quantities of reagents were used (see stoichiometric calculations above).
The disparity was likely introduced in the sodium borohydride, a reagent that quickly
decomposes in air. Taking reagent from a weigh boat near the balance was a poor idea, because
it had probably been saturated and rendered useless, in terms of reactivity. This explains the
melting point of the “product” – a figure that was less than the expected melting point of the
starting material. Impurities were introduced which ultimately lowered the melting point. The
“peak” we see in the –OH region, could possibly be due to residual water in the product. The
sodium borohydride was mostly to blame in this experiment in terms of error. In the future,
recalling this unfruitful experience, will serve as a helpful reminder to take care in controlling
reagents, especially those that decompose. However, the process that was used to reduce the
ketone to an alcohol was in principle correct. The methodology was sound, a good solvent was
chosen, and the measurements were correct.
The final “product” – as it was obtained from Roto-vapping off the ether solvent, was
likely mostly reagent 9-fluorenone, based on the melting points and an IR of functional groups.
The carbonyl peak was very distinct and large, whereas the alcohol peak was not distinct, and
may have been due to water. The unknown factor in this experiment was the extent to which
sodium borohydride decomposed. It seems that nearly all of it was useless, based on the amount
of –OH character seen in the IR spectrum. Repeating this experiment under much tighter
controls would prevent any future problems regarding reagent reactivity. With the developed
procedure, future attempts would most likely produce 9-fluorenol, the alcohol, in much higher
yields. This could be determined again, with an IR, and taking a melting point. The theoretical
melting point for 9-fluorenol is 152-158°C and we would expect the melting point to be slightly
under that value (to account for unavoidable impurities introduced experimentally).
Recrystallization would also be utilized, to help purify the product further. In this trial,
recrystallization was not attempted as it would not have been useful. The –OH character was so
weak, that perhaps recrystallization would have introduced additional impurities that would have
degraded the alcoholic nature of the product. Although this is debatable, it is certainly a delicate
balance and again – very unnecessary since there wasn’t a lot of physical 9-fluorenol product to
purify. Essentially, the entire procedure was one extended purification of 9-fluorenone, and
recrystallization would not have rendered any more alcohol product, from the predominating
ketone.