Lab 5: The SN2 Reaction: 1-Bromobutane
From K. L. Williamson, Macroscale and Microscale Organic Experiments, 2nd Ed. 1994, Houghton Mifflin, Boston. p247; revised 2/22/02
Prelab Exercise: Write a detailed flow sheet/ flow chart for the isolation and purification of 1-bromobutane. Designate how each minor-product is removed from the major product and which layer holds the product in each experimental step performed.
This experiment utilizes SN2 chemistry to convert 1-butanol (n-butanol) to 1-bromobutane (n-bromobutane). The nucleophile for the reaction is Br- ions. The nucleophile in this lab is generated from an aqueous solution of sodium bromide. The sulfuric acid acts as a catalyst in converting the OH functional group of butanol, to a better leaving group (water). The by-products for this lab are 1-butene, di-n-butyl ether, and the starting alcohol (butanol). Any by-products are removed by extraction using concentrated sulfuric acid. The product can be removed from sulfuric acid, since it does not mix with H2SO4 and will remain as a separate layer.
Procedure: Synthesis of 1–Bromobutane.
Take a 25-mL round-bottomed flask. Dissolve 2.66 g of sodium bromide (solid, corrosive) in 3.0 mL of DI water and 1.60 g of 1-butanol. Add a couple of boiling chips to the round bottom flask. Cautiously, with steady swirling, add 2.2 mL (3.8 g) of concentrated sulfuric acid drop wise to the solution (conc. H2SO4 is extremely corrosive and will cause severe burns if you get any on you skin). You should notice that the NaBr will dissolve once you start to heat the reaction mixture. Reflux the reaction using a sand bath for 45 min. Make sure reactants don’t evaporate out of the condenser during the reflux (make sure that water is flowing through the condenser, throughout the reflux). [pic]
Stick a wad of glass wool on the top of the condenser to prevent vapor from escaping. As...
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