Preparation of 1-Bromobutane

 

                        The mechanism is SN2.  The overall reaction is:

 

H2SO4 + NaBr + CH3CH2CH2CH2OH 6 CH3CH2CH2CH2Br + H2O + NaHSO4

 

                                                                Boiling Point 118oC                 Boiling Point 92oC

 

 

     At your hood workstation, place a hotplate/stirrer atop a ringstand .

 

    Take a  100-mL round-bottomed flask, and clamp the flask to

    the ringstand, leaving about 1 inch of room between the bottom of the flask and a

    plastic bowl, whish sits atop the hotplate/stirrer..

 

    Add 17 gm. Of NaBr, 17 mL H2O, and 10 mL 1-butanol to the flask and begin stirring the solution

    with the magnetic stirrer.

 

    Add a slurry of ice and water to the bowl beneath the flask.

 

    S L O W L Y AND CAREFULLY add 14mL conc. H2SO4 to the flask. 

 

     Remove the ice bath and replace it with a heating mantle.

 

    Add two or three boiling chips 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 jacket (see Figure on next page).

 

    Heat the flask gently (using a heating mantle setting of about 50% of capacity).

 

    Continue gentle heating until the mixture begins to reflux.

 

    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 ("drop" the heating

    mantle from beneath the condenser by lowering the metal ring( or lab jack ) holding the

    mantle to the base of the flask).

 

 

 

 

    Once the flask has air-cooled for a few minutes (3 – 5), disconnect the flask and pour the contents

     into a 125mL separatory funnel.

 

    Separate the lower aqueous layer from the organic layer and add it to a 100mL beaker

    containing 50mL H2O.  If the contents of the beaker is one miscible, single layer, add it to

    700mL H2O in a 1 L Beaker, WITH STIRRING, otherwise, consult your instructor.

 

    Extract the organic layer with 14 mL  9M H2SO4.

 

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

    Of your 1 L Beaker, WITH STIRRING.

   

    Extract the organic layer with 14 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 14mL saturated sodium bicarbonate.

 

    Drain the lower ORGANIC layer into a DRY 50 mL Erlenmeyer flask, and add 1gm. CaCl2 .

    Swirl the flask occasionally for a period of 5 minutes.

 

    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 4-8:                    The reaction, with mechanism is:

 

 

 

 

 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 23:                       Washing the organic layer with 9M H2SO4 removes any unreacted 1-butanol .

 

Step 25:                       Washing with water simply removes any unreacted 9M H2SO4 molecules. 

 

Step 26:                       Washing with saturated NAHCO3 removes any remaining 9M H2SO4.molecules.

 

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

                                    Experiment.

 

 


Che 317         Sp’2005

 

Lab Report

 

 

 

Title: Synthesis of 1-Bromobutane

 

Name:

 

Date:

 

 

Equation:

 

 

 

 

 

Table of Physical Constants

 

  Compound          M.W.          density          bp/mp

     NaBr                    102.9            -----              ---

CH3(CH2)2CH2OH      74.1           0.810            118

CH3(CH2)2CH2Br      137.0           1.275            102

 

 

CH3(CH2)2CH2OH

NaBr

CH3(CH2)2CH2Br

MW

 

 

 

Moles

 

 

 

grams

 

17

 

density

 

 

 

mL

10

 

 

 

Results: Calculate the % yield for 1-Bromobutane

 

 

 

Boiling range for your product                                                            to _________ Deg.C.