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Organic Chemistry Lab 315
Fall, 2014
DUE DATES
• Today
– At beginning of lab – Synthesis of tert-
Pentyl chloride
– At end of lab -- copy of laboratory
notebook pages for today's experiment
• Next Week
– Synthesis of Cyclohexene Report
– See my lab web site for instructions
Report Notes – Last Week
• Two important items were required (and were
included as part of the Instructions):
– Attach the distillation graphs from the Distillation
Report
– Make a comparison of the mole percent
composition as calculated from the fractional
distillation from two weeks ago and the GC peak
areas from last week.
In Lab Today
•Synthesis of cyclohexene
– The mechanism of the reaction is E1
H
H
H
OH
H
H
O H
H3PO4
H
H
H2PO4
Step 1 is an acid/base reaction
between H3PO4 (acid) and
alcohol (base) to form the
oxonium ion.
Step 2 is the dissociation of the
oxonium ion to form the
cyclohexyl carbocation and the
good leaving group, H2O.
Step 3 is the acid/base reaction
between the H-atom on the
carbocation and the base, H2O,
resulting in overall elimination.
In Lab Today
•Synthesis of cyclohexene
– The mechanism of the reaction is E1
H
H
OH
H
OH2
H
O H
H
H
H
H
H
H3PO4
H
H2O
H
H
H
H2PO4
Step 1 is an acid/base reaction
between H3PO4 (acid) and
alcohol (base) to form the
oxonium ion.
Step 2 is the dissociation of the
oxonium ion to form the
cyclohexyl carbocation and the
good leaving group, H2O.
Step 3 is the acid/base reaction
between the H-atom on the
carbocation and the base, H2O,
resulting in overall elimination.
In Lab Today
•Synthesis of cyclohexene
– The mechanism of the reaction is E1
H
H
OH
H
OH2
H
O H
H
H
H
H2O
H
H3PO4
H
H
H
+
H3O
H
H
Step 2 is the dissociation of the
oxonium ion to form the
cyclohexyl carbocation and the
good leaving group, H2O.
H2O
H
H
H2PO4
H
H
H
Step 1 is an acid/base reaction
between H3PO4 (acid) and
alcohol (base) to form the
oxonium ion.
Step 3 is the acid/base reaction
between the H-atom on the
carbocation and the base, H2O,
resulting in overall elimination.
In Lab Today
water out
water in
ice bath
• Reaction takes place within a
distilling round-bottom flask.
• Cyclohexanol and H3PO4 are
mixed, and they begin to react as
the flask is heated.
• As the products, cyclohexene
and water form, the cyclohexene
distills out of the reaction
mixture.
In Lab Today
water out
water in
ice bath
• Cyclohexene has a lower b.pt.
than cyclohexanol.
• The cyclohexanol and acid
remaining in the distilling flask
continue to react as the
equilibrium shifts because the
product cyclohexene is removed.
• The elimination reaction will
continue until all the
cyclohexanol has reacted.
In Lab Today
• The receiving flask now contains
cyclohexene with a small amount
of aqueous acid.
• Add solid NaCl, which “salts out”
the organic cyclohexene from the
aqueous phase.
• Add aqueous sodium
bicarbonate until the aqueous
layer (which one?) tests basic to
litmus.
In Lab Today
• Two phases are the upper
cyclohexene phase (with some
water and aq. base) and the
lower aqueous phase with
dissolved base and NaCl.
• Separate the phases (keeping
upper phase in funnel).
• Wash the cyclohexene layer with
water (removes ___?)
In Lab Today
• Dry cyclohexene with anhyd.
Na2SO4.
• Decant cyclohexene into clean
dry pre-weighed vial.
• No distillation.
• Take refractive index and IR.
• Store in drawer, properly labeled.
Experiment Notes
• Make sure the balance is displaying
±.001g
• Use a funnel to deliver liquids through
neck of round-bottom flasks, separatory
funnel, vial.
• You must heat the cyclohexanol/acid
mixture slowly. Never let it go above 100
deg. B.pt. cyclohexene (?_)
• This is not a distillation, but rather a
reaction that needs to get going first.
• Please clean up used pipets after doing
refractive index and IR.
Waste
• Dispose of aqueous solutions in the sink
with plenty of water.
Synthesis Report
•See the instructions on the web site for
writing a Synthesis report.
•Pay particular attention to the table on the
Report Form, which is actually a calculation
of theoretical yield.
•The phosphoric acid is a catalyst and so it
is not included in the balanced equation nor
used for determination of theoretical yield.
•Separation scheme (flow chart of
procedure for separating a pure product
from reaction by-products)
Weekly Clean-up
• McCoy
• Rockwell