General
In general, we use small
scale (4/20) glassware from Aldrich and regular glassware from Fisher. Inexpensive magnetic stirrers ($115), heating
mantles ($64) and heat controls ($89) are from Laboratory Craftsmen, Inc. (www.labcraftsmen.com) Stir bars (<$1) are from Fisher
Scientific.
Reaction mixtures and
products are analyzed with a Shimadzu GC/MS QP5000. Percentages are based on uncorrected TIC.
The quantity of Clorox used
is 1.1 mole equivalent to alcohol. This
is to make up for lost of Chlorine during stirring and the chlorination of
product to chloroketone.
Glass thermometer must be
used instead of common metal digital thermometers because the metal will get
oxidized.
If available, use a crystallizing
dish (100x50) as an ice-water bath, but a 400-mL beaker will work.
The temperature may be
difficult and inaccurate to measure at the beginning because of the small
volume. Keeping temperature below 10 C
at this point should be O.K.
Low temperature minimizes
the formation of 2-chlorocyclohexane.
The purposes here are (1) to
neutralize the unreacted Clorox and acid catalyst and (2) to extract a somewhat
water soluble product from a large volume of aqueous solution.
Saturated sodium thiosulfate
is made fresh by dissolving Na2S2O3.5H2O
in water on the day of use.
When removing a drop with
pipette for testing, make sure to reach into the bottom aqueous solution. After withdrawing pipette, touch the pipette
on the side of flask to drain the drop of organic solution adhered on the
outside of pipette. Otherwise, students
may be testing the drop of organic solution.
Diethyl ether can be used
instead of MTBE during transfers and extractions.
After extraction, the
aqueous solution can be flushed down the drain as it contains only sodium
chloride and sodium sulfate in water.
The problem with distilling
a small volume of liquid is that there is an inherent significant lost of
product. Simple distillation will give a
solvent (MTBE) fraction at 53-55 C, a small in-between fraction of MTBE and
cyclohexanone and product fraction of cyclohexanone at 155-157. The yield of cyclohexanone is 80-85% with a
purity of 98-100% by GC/MS.
Rotary evaporation at 30 C
water bath gives 96% yield of cyclohexanone.
The purity by GC/MS is 95% cyclohexanone and 5% of 2-chlorocyclohexanone
and trace amounts of solvent and cyclohexanol.
Since rotary evaporators are
not generally available in large numbers in an undergraduate lab, the
distillation-suction evaporation procedure is a functional alternative. Most of the solvent is distilled at
55C. Be careful not to go above this
temperature. Stirring under aspirator suction
with gentle heat is quite efficient in removing the small amount of solvent. We use a heating mantle with no sand (sand
gets everywhere when used) to keep flask warm.
A warm water bath can be used but students will have to carefully dry
the flask each time before weighing. Most
students take two to four successive evaporations to get to no or trace solvent
condition. Student yields are 90+%
actual yield. The purity is about 95%
with impurities of cyclohexanol and 2-chlorocyclohexanone made up about
5%. There may be a trace of MTBE.