lab 9 SN2 reaction.doc

5 Pages

Chemistry & Chemical Biology
Course Code
CHEM 2312

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Synthesis of 1-bromobutane from n-butanol via the S 2 N Mechanism Ross Merkin TA Luke Harris Performed: 11/12/07 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
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