experiment 4 - Experiment 4 Hydroboration-oxidation of an...

Experiment 4: Hydroboration-oxidation of an alkene
Theory & Background: The hydroboration-oxidation of alkenes to alcohols has long
fascinated organic chemists because of its synthetic usefulness and interesting mechanism.
H. C. Brown shared the 1979 Nobel prize for developing this and other boron reactions.
The reaction of borane with an unsymmetric alkene can give two regioisomeric products:
boron at the most substituted carbon (Markovnikov addition) or at the least substituted
carbon (anti-Markovnikov addition). The latter is heavily favored, providing for a regiose-
lective reaction. As long as a B-H bond remains, addition reactions to alkenes continue,
eventually affording a trialkylborane. Each addition reaction is a four-centered, four-
electron process that is extremely rapid. And, each sequential reaction is slightly more
regioselective. A GC will be taken of the product mixture at the conclusion of the ex-
periment to determine the ratio of components.
1) BH
3
•THF
2) NaOOH
OH
OH
+
Please regenerate this table in your notebook filling in any of the blanks
Reagent
Values
1-octene (98%)
ignore the 2%
1M borane in THF
a stock solution
HOOH
30% (w/w) active
3M sodium
hydroxide
120g/l
octanol
formula C
8
H
16
NA H
2
O
2
NaOH C
8
H
18
O
equiv
1.0
0.37
(1.1H- equiv)
2.2 0.67 1.0 expected
MW
density
volume
mass
mmol.
boiling
point
Glassware Set-up:
Procedure 1: Add 1-octene (150 mg, 1.0 equiv) to a dry
5.0 mL conical vial equipped with a spin vane. Attach a
Claisen adapter and a CaCl
2
drying tube. Then chill the
vial in an ice water bath (0 °C) while stirring for 5 min-
utes. Now add 1M BH
3
in THF (0.37 equiv; 1.1 hydride
equiv) with a plastic syringe and needle dropwise over 5
minutes. Remove the ice bath and stir for 30 more min-
utes. *Syringes for BH
3
additions may be shared.
Work-Up: Remove the Claisen adapter and drying tube.
Add H
2
O (5 drops) to the stirring solution slowly with a
pipet to quench any unreacted borane.
18
Techniques
Syringe use reagent transfer in air
sensitive systems
To help you preserve reagent
quality, many Aldrich and Fluka
air- and moisture-sensitive
reagents are packaged under
nitrogen or argon in crown-cap
bottles, with a 6mm diameter
hole in the crown-cap and a PTFE