Synthesis of 1-bromobutane from n-butanol via the S 2 N
TA Luke Harris
Submitted: 11/26/07 Objective: The objective of this experiment was to synthesize 1-bromobutane
(BrCH CH2CH 2H ) 2rom 3-butanol (CH CH CH CH O3). T2e me2han2sm of this
reaction is the S N mechanism.
Reaction Equations: The S 2 mecNanism is a substitution reaction in which everything
is concerted. It is an anti-addition because the nucleophile adds to the carbon with the
substituent from the opposite side of the substituent. The reason for this is that the
leaving group blocks the nucleophile from bonding, however this reaction is not
stereoselective because there are no chiral centers.
The E2 elimination reaction is also competing with the S 2 substNtution reaction
during the reaction. However, the substitution reaction should occur more than the
elimination reaction because the conditions favor the substitution reaction more than the
elimination reaction. The mechanisms for the substitution reaction and competing
elimination reaction can be found on the attached sheet.
Procedure: This experiment began with the assembly of the reflux apparatus, the
diagram of which can be found attached to this report. Then, 2.0 mL of n-butanol and 4.0
mL of 48% hydrobromic acid (HBr) were added to a 10 mL round bottom flask. The
flask was then placed in a beaker with ice until the liquid was very cold. Four black
boiling stones were added to the flask, followed by 2.0 mL of sulfuric acid (H SO ). Th2 4
flask was attached to the reflux apparatus, and allowed to reflux for approximately 40
minutes. At the end of the refluxing process, two separate layers of liquid existed in the
flask. The top layer was the desired layer, bromobutane. The desired layer was removed
with a Pasteur pipette, and placed into a 15 mL centrifuge tube. Approximately 2 mL of
water were placed into the centrifuge tube, and the liquids were mixed by sucking liquid
into and out of the Pasteur pipette repeatedly. Two layers resulted, an aqueous layer and
an organic layer. The aqueous layer (on top) was removed from the tube and placed into
a waste beaker.
Approximately 2 mL of 3M sodium hydroxide (NaOH) were then added to the
centrifuge tube, and the tube was once again mixed using the same pipette technique.
The bottom layer that resulted was removed and placed into a 20 mL beaker. Calcium
chloride (CaCl )2pellets were added to the liquid in the beaker to make it anhydrous.
The following part of the experiment was the test to determine if the experiment
was successful. 0.2 mL of n-butanol were placed in one t