Competitive Nucleophiles Lab Report
Competitive Nucleophiles With 1-Butanol
In this experiment you will determine the nucleophile strength of bromide ion vs. chloride ion in their reaction with 1-butanol in acidic solution. The reaction is shown below. The reagents are a convenient source of HBr and HCl. The reaction is an SN2 reaction with H2O as the leaving group and Cl- and Br- as the nucleophiles. The molar amounts of Cl - and Br- are equal, so the better nucleophile will lead to more product. You will analyze the amounts of 1-bromobutane and 1-chlorobutane by GC and NMR. We will also examine the same reaction with 2-methyl-2-propanol, using a reaction carried out by the lab assistant or instructor.
Consider that the nucleophiles may be influenced by interactions with the solvent. These interactions are much more significant in protic solvents (e.g., water and alcohol) than in aprotic solvents (e.g., acetone or DMSO).
Experimental Procedure …show more content…
Assemble an apparatus for reflux using a 25-mL round-bottom flask, a reflux condenser, and a stir bar.
Using a 10-mL graduated cylinder, obtain 10.0 mL of the solvent-nucleophile mixture (NH4Br + NH4Cl + H 2SO4) which is in an Erlenmeyer flask in the hood. Pour the mixture immediately into the round bottom flask. Add 0.75 mL of 1-butanol to the round bottom flask, attach the condenser, start the water circulating and the stir bar spinning. Turn on the heating mantle and heat the mixture at gentle reflux (look for the reflux ring in the condenser) for about one hour. After the heating period, lift the round-bottom flask from the heat and allow it to cool. Do not remove the condenser until the flask is cool. You can immerse the flask in cold tap water to help it cool (do not remove the condenser). You should see an organic layer at the top of the reaction mixture. Add ~1 mL of pentane to the mixture and gently swirl the flask. The purpose of the pentane is to increase the volume of the organic layer so it's easier to
separate.
Using a Pasteur pipet, transfer most of the bottom aqueous layer to another container. Be careful to leave the organic layer in the round-bottom flask. (NOTE: If you have LOTS of solid it may be easier to transfer the top organic layer along with some of the aqueous layer to another flask instead.) Transfer the organic layer and remaining aqueous layer into a 5-mL conical vial. Allow the two layers to separate and remove the bottom aqueous layer with a pipet. Add 1 mL of water to the vial, gently shake the vial, and then remove the bottom aqueous layer. Extract the organic layer with 1-2 mL of saturated sodium bicarbonate solution and then remove the bottom aqueous layer. These steps serve to purify the organic products of leftover acid, alcohol, salts etc. Add granular anhydrous sodium sulfate to the organic layer to dry the products and cap the vial with a Teflon cap until you are ready to analyze the products by NMR and GC.
In this experiment you will determine the nucleophile strength of bromide ion vs. chloride ion in their reaction with 1-butanol in acidic solution. The reaction is shown below. The reagents are a convenient source of HBr and HCl. The reaction is an SN2 reaction with H2O as the leaving group and Cl- and Br- as the nucleophiles. The molar amounts of Cl - and Br- are equal, so the better nucleophile will lead to more product. You will analyze the amounts of 1-bromobutane and 1-chlorobutane by GC and NMR. We will also examine the same reaction with 2-methyl-2-propanol, using a reaction carried out by the lab assistant or instructor.
Consider that the nucleophiles may be influenced by interactions with the solvent. These interactions are much more significant in protic solvents (e.g., water and alcohol) than in aprotic solvents (e.g., acetone or DMSO).
Experimental Procedure …show more content…
Assemble an apparatus for reflux using a 25-mL round-bottom flask, a reflux condenser, and a stir bar.
Using a 10-mL graduated cylinder, obtain 10.0 mL of the solvent-nucleophile mixture (NH4Br + NH4Cl + H 2SO4) which is in an Erlenmeyer flask in the hood. Pour the mixture immediately into the round bottom flask. Add 0.75 mL of 1-butanol to the round bottom flask, attach the condenser, start the water circulating and the stir bar spinning. Turn on the heating mantle and heat the mixture at gentle reflux (look for the reflux ring in the condenser) for about one hour. After the heating period, lift the round-bottom flask from the heat and allow it to cool. Do not remove the condenser until the flask is cool. You can immerse the flask in cold tap water to help it cool (do not remove the condenser). You should see an organic layer at the top of the reaction mixture. Add ~1 mL of pentane to the mixture and gently swirl the flask. The purpose of the pentane is to increase the volume of the organic layer so it's easier to
separate.
Using a Pasteur pipet, transfer most of the bottom aqueous layer to another container. Be careful to leave the organic layer in the round-bottom flask. (NOTE: If you have LOTS of solid it may be easier to transfer the top organic layer along with some of the aqueous layer to another flask instead.) Transfer the organic layer and remaining aqueous layer into a 5-mL conical vial. Allow the two layers to separate and remove the bottom aqueous layer with a pipet. Add 1 mL of water to the vial, gently shake the vial, and then remove the bottom aqueous layer. Extract the organic layer with 1-2 mL of saturated sodium bicarbonate solution and then remove the bottom aqueous layer. These steps serve to purify the organic products of leftover acid, alcohol, salts etc. Add granular anhydrous sodium sulfate to the organic layer to dry the products and cap the vial with a Teflon cap until you are ready to analyze the products by NMR and GC.