Preparation of 1-Bromobutane

The mechanism is S_N2.

CAUTION: Wear gloves during the entire experiment

Bring your 100 mL RBF, wide stem funnel, and cork ring to one of the balances.

Add 17 gm. NaBr to the flask, then proceed over to the tray with the water and

1-butanol repipettors.

Add 15 mL H₂O and 10 mL 1-butanol to the flask and return to your hood workstation.

At your hood workstation, clamp the flask to the ringstand attached to your

hotplate/stirrer, add your magnetic stirring bar, and begin stirring the contents of the flask.

Bring a 50 or 100 mL beaker to the front of the lab and dispense 15 mL conc. H₂SO₄

Return to your hood workstation and S L O W L Y AND CAREFULLY the conc. H₂SO₄

to the flask.

Equip the flask with a reflux condenser and begin circulating water through it - water going in the

bottom and out the top of the condenser. ( see the figure on the next page )

Heat the flask gently (using the hot plate at a setting of about “4” ).

Continue gentle heating until the mixture begins to reflux. (liquid dripping from the condenser )

Once this is observed, continue "refluxing" the mixture for 60 minutes, controlling the

level of the vapor in the condenser so that it reaches no more than half-way up the

condenser

At the end of the 60 minute reflux period, discontinue heating

Add 700 mL of water to your 1L beaker

Once the contents of the flask ceases to bubble, remove the reflux condenser, unclamp the flask

from the ringstand and pour the contents of the flask into the Separatory funnel.

Immediately separate the lower aqueous layer from the organic layer and add it to the contents of your 1 L Beaker, WITH STIRRING. (Why is the aqueous layer on the bottom ? )

Extract the organic layer with 15 mL H₂O.

Separate the UPPER aqueous layer from the organic layer and add it to the contents

of your 1 L Beaker, WITH STIRRING.

Extract the organic layer with 15mL saturated sodium bicarbonate.

Drain the lower ORGANIC layer into a DRY 50 mL Erlenmeyer flask, and add CaCl₂ .

Swirl the flask occasionally for a period of 5 minutes. ( Why was the organic layer now on the bottom ? )

Allow the drying agent to settle and DECANT the liquid into a TARED sample bottle,

appropriately labeled. Save it in your locker for the alkyl halide tests.

Notes:

Steps 7-13: Initially, the reaction is exothermic which makes the reaction occur, but

quickly loses the energy, so the energy must be supplied by the heating

mantle in order to complete the reaction as much as possible.

Refluxing is a means of trapping the vapors of the reactants and cooling

them enough to return to the reaction flask. There, they have another

opportunity to react to form 1-bromobutane

Steps 17-20: To separate the 1-bromobutane, a series of extractions are performed. To

determine which layer is the 1-bromobutane layer, you take a test tube and add

5 mL of water to it, then remove a few drops of the bottom layer from the

separatory funnel and see if they fall through the water to the bottom. If they do,

the bottom layer is the 1-bromobutane layer or organic layer, if not, the upper

layer is the organic layer. To confirm your decision, remove a few drops of the

top layer in the separatory funnel with a pasteur pipette and place them in a dry

test tube and add 2 to 3 mL of water, dropwise, to see if it falls to the bottom.

The larger layer should be the water layer.

Step 25: Washing with water simply removes any unreacted H₂SO₄ molecules.

Step 26: Washing with saturated NAHCO₃ removes any remaining H₂SO₄.molecules.

Step 28: The water is removed by CaCl₂, as described in the propanoic acid

experiment.