Experiment #3
Mark A. Bruder
7-16-07
T.A. Michael Hall
Alkanes: Chlorination
Introduction:
The purpose of this experiment is to determine the reactivity of hydrogen atoms
on a carbon chain using free radical chlorination. In this experiment 1-chlorobutane will
be chlorinated with the combination of sulfuryl chloride and ABCN as an initiator to
produce the chlorine radicals. The combination of 1-chlorobutane and sulfur chloride will
produce four dichlorobutane isomers. The isomers produced and their reactivity will be
analyzed by the amounts of isomers produced in the product and by gas chromatography.
Procedure:
1) Assemble the apparatus in the hood using a Thermowell Heater
2) Use a 25-mL round bottom flask fitted with a reflux condenser which will be
connected through a vacuum adapter to a 500-mL filter flask.
a. close vacuum adapter w/ cork and make sure the inlet tube does not
reach the surface of the water in the filter flask
b. make sure any water from the trap does not get sucked back into the
reaction flask
c. glass tube must not dip below the surface of the water in the trap
3) Note the differences on pg.77 of G&M fig. 2.65(b)
a. it does not use a water aspirator or house vacuum
b. Fit #7 one-hole rubber stoppers w/ a length of glass tubing about 15cm
long.
c. Tubing needs to be fire-polished on both ends and lubricate hole in
stopper with glycerin.
d. Use cloth towel to protect your hands as you insert the tubing into the
stopper and wipe off excess glycerin.
4) Add stirbar, .1g of 2,2-azobis(cyclohexanenitrile), 5mL of 1-chlorobutane and
2-mL of sulfuryl chloride and place in flask
5) Stopper and weigh. Then hook flask to reflux condenser
6) Heat solution for 20 minutes, let cool below reflux temperature and check
weight. If the weight loss is not enough continue to next step
7) Add a second .1g of 2,2-azobis(cyclohexanenitrile) and heat for another 10
minutes.
8) Weigh flask. If proper amount of weight in not lost after both heating periods,
just continue with experiment.
9) Cool reaction mixture in ice-bath, then add 15-mL of ice cold saturated to
aqueous sodium chloride (brine)
10) Transfer the resulting two-phase solution to a separatory funnel and separate
layers.
11) Wash the organic layer with 10-mL of .5 M sodium carbonate solution (don’t
forget to vent)
12) Use pH paper to determine whether the aqueous layer is basic
a. If it is not basic, wash organic layer with another 10-mL of sodium
carbonate solution until it becomes basic.
13) After washing the organic layer with brine transfer to Erlenmeyer flask and
add several scoops of anhydrous sodium sulfate
14) Swirl for 10-15 minutes during drying period ( the liquid should start to
become clear, if not add more drying agent)
15) Decant organic layer into a dry, tarred container
16) Calculate the following:
a. Theoretical yield of product
b. Amount of unreacted 1-chlorobutane
c. theoretical weight of material (product plus unreacted starting
material) expected
d. percentage yield of material recovered
17) Analyze the organic mixture directly by gas chromatography
18) From chromatography data, determine percentage composition of the mixture
of the four isomeric dichlorobutanes produced in the reaction
Main Reaction and Mechanism:
Initiation:
Formation of 2,2'-azobis[cyclohexanenitrile]
C
C
N
N
N
N
80-100 0C
N
N2 +
2
Removal of chlorine from sulfuryl chloride
Cl
O
O
N
N
Cl
+
S
+
Cl
O
O
Decomposition of sulfuryl chloride to generate sulfur dioxide and chlorine radicals
O
O
S
S
Cl
Cl
+
O
O
Removal of hydrogen from 1-chlorobutane
Cl + H
R + H
R
Cl
Removal of chlorine atom from sulfuryl chloride
O
R + Cl
S
Cl
R
Cl
O
Termination:
Cl + Cl
Cl
R + Cl
R
Cl
+ R
R
R
R
S
Cl
+
S
Cl
Cl
Preliminary Calculations:
Moles of 1-chlorobutane
5.0 mL
.886 g
1 mol
1 mL
92.57 g
=
.0479 mol 1-chlorobutane
Moles of sulfuryl chloride
2.0 mL
1.667 g
1 mol
1 mL
=
.0247 mol sulfuryl chloride
134.97 g
Mass of HCl produced
.0247 mol O2Cl2S
1 mol HCl
1 mol O2Cl2S
36.46 g
= .901 g HCl
1 mol HCl
Mass of SO2 produced
.0247 mol O2Cl2S
1 mol HCl
64.06 g
=
1 mol O2Cl2S
1 mol HCl
1.582 g SO2
90% of expected weight loss
.90(.901 g + 1.582 g) = 2.235 g
Total mass of dichlorobutane isomers produced
.0247 mol O2Cl2S
1 mol dichlorobutane
127.01 g dichlorobutane
=
1 mol O2Cl2S
1 mol dichlorobutane
3.137 g dichlorobutane
Table of Reagents:
Compound
Amounts Molecular Boiling
Used
Weight
Point
(amu)
(0C)
5.0-mL
92.57
78.4
1-chlorobutane
Melting Density
Point
(g/mL)
(0C)
-123.1
0.886
0.04768
mol
Sulfuryl Chloride
2.0-mL
134.97
69.1
-55.1
0.0247
mol
2,2’-azobis[cyclonexanenitrile]
C
C
N
N
N
N
0.1 g
244.34
114
1.667
Table of Products:
Compound
Theoretical
Yield
(grams)
Actual
Yield
(grams)
1,1-dichlorobutane
3.137
total for
all 4
isomers
Theoretical
Boiling
Point
(0C)
Theoretical
Density
(g/mL)
.22
Theoretical
Molecular
Weight
(amu)
127.01
112
1.086
1,2-dichlorobutane
.99
127.01
124
1.112
1,3-dichlorobutane
2.06
127.01
134
1.115
1,4-dichlorobutane
1.12
127.01
153.9
1.141
Data:
Apparatus
Mass of empty flask and stopper
Mass of ABCN added initially
Mass of 1-Chlorobutane
Mass of Sulfuryl Chloride
Mass of stir bar
Mass of flask, stir bar, reactants and
stopper
2nd Mass after ABCN added
Total Mass after 1st Reflux
Total Mass after 2nd Reflux
Final Mass after Reflux
Total Mass lost during Reflux
Theoretical Yield
Mass (grams)
28.82 g
.12 g
4.43 g
3.33 g
2.21g
37.90 g
37.69 g
36.28 g
35.77 g
6.87 g
2.38 g
4.49 g
Results:
Calculations:
% Recovery
Mass of dichlorobutane isomers
% Recovery = ------------------------------------- x 100
Mass of Reactants
3.14 g
% Recovery = ----------- x 100 = 46%
6.87 g
Relative Reactivity of Hydrogen Atoms:
% isomer
5.917
C1 Carbon R.R. = ------------------ = -------------- = 2.959
# C-H Bonds
2
% isomer
22.517
C2 Carbon R.R. = ----------------- = --------------- = 11.259
# C-H Bonds
2
% isomer
C3 Carbon R.R. = ----------------- =
# C-H Bonds
46.039
-------------- = 23.020
2
% isomer
C4 Carbon R.R. = ------------------ =
# C-H Bonds
25.527
-------------- = 8.509
3
Relative Reactivates:
2.959
C1 = ---------- = .3477
8.509
11.259
C2 = ---------- = 1.323
8.509
23.020
C3 = ---------- = 2.705
8.509
8.509
C4 = ---------- = 1.000
8.509
C1 :
C2: C3: C4
.3477:1.323:2.705:1.000
Observations:
The reflux apparatus was assembled and a 25-mL round bottom flask, a stir bar,
and stopper were all assembled. The flask, stir bar and stopper were weighed. .12g of
ABCN was weighted and added to the flask. 5.1-mL of 1-chlorobutane and 2.0-mL of
sulfuryl chloride were also added to the flask and everything collected was weighed. The
mixture of the ABCN, 1-chlorobutane and sulfuryl chloride was a clear solution inside
the flask. The flask was then attached to the apparatus. The amount of hydrogen chloride
and sulfur dioxide gas that will be lost during the process was pre-calculated. The precalculations determined that the reaction would be 90% complete were 2.24 g of gas had
been removed.
The reaction would be heated to bring the solution to a reflux. Once the reaction
was brought to reflux this would be allowed to occur for 20 minutes. Then the flask
would could and be massed to determine the about of gas lost. An error occurred when
the heating process only took place for 20 minutes when it should have been allowed to
heat and then reflux for 20 minutes. The initial lost of gas was only 1.41 grams. Another
.10 grams of ABCN was added and the flask was heated again. This time the flask was
heated and allowed to reflux for 15 minutes. The flask was then cooled and the amount of
gas lost was measured again. After the second reflux only 1.92 grams was lost. The flask
was then heated again; reflux began and occurred for another 15 minutes. The flask was
then cooled and the mass was taken and 2.38 grams of gas was lost.
Once the proper amount of gas was lost, the mixture was then placed in 50-mL
Erlenmeyer flask which contained 15-mL chilled sodium chloride (brine) solution. After
allowing sitting the flask formed an organic layer on the top and aqueous layer on the
bottom. This mixture was then placed in a separatory funnel. Then 10-mL of .5 M sodium
carbonate solution was used to wash the solution. The pH needed to be tested to make
sure the solution was slightly acidic. The original solution was not acidic so another 10mLs of .5 M sodium carbonate was added to the solution. The solution was re-tested and
the solution was slightly acidic. The layers were then separated. The aqueous layer was
discarded and the organic layer was drained into a 25-mL Erlenmeyer flask. Roughly 3 g
of the drying agent anhydrous sodium sulfate was placed in the flask for the drying of the
water. After 20 minutes the solution was not dry and more drying agent was placed in the
flask. After the second amount of drying agent the solution became dry. The solution was
slightly cloudy which meant it was not completely dry but enough had dried for gas
chromatography to occur. The product was decanted into another flask then weighed to
determine the mass of the product. The product was then placed in the gas
chromatography to determine the isomers of dichlorobutane.
Significant Side Reactions:
No significant side reactions occurred during this experiment.
Method of Purification:
The original solution was purified from any residual sulfuryl chloride gas be
adding .5 M sodium carbonate solution. This process had to be repeated because the
original carbonate solution did not completely remove all of the residual gas. Once the
aqueous layer was removed, the organic layer was then dried with two different doses of
anhydrous sodium sulfate. This then produced 1-chlorobutane, and the four
dichlorobutane isomers. 2.5-mLs of solution was then analyzed via gas chromatography
to determine the percent of the four dichlorobutane isomers.
Conclusion:
This experiment was performed to determine the % of the four isomers on 1chlorobutane by the process of free radical chlorination. Once the free radical
chlorination process occurs the free radical electron would be attracted to the C1 and C2
carbons. This would make those two carbon radicals less stable. This would then require
more energy to form the free radicals. Since this process takes awhile to occur the
products also take awhile to form. Since it takes awhile for the product to occur on the
first carbon this makes it the least reactive. This also makes the second carbon slightly
more reactive, the third carbon the most reactive and the fourth carbon slightly more
reactive then first carbon. The third carbon is most reactive because removing the
hydrogen atoms from that carbon allows it to become more stable and have a lower 20
radical.
Exercises:
2. In this reaction a theoretical yield was determined for how much sulfuryl chloride
should be to produce enough of the product. During the reaction some of the sulfuryl
chloride reacts with the 1-chlorobutane instead of completely reacting with the
dichlorobutane isomers. This is during the termination process and since the various
radicals combine during this process, it decreases the net radical concentration and it
decreases the rate of reaction. The termination process does completely allow all of the
sulfuryl chloride to go to the original products as determined.
9. Relative Reactivity of Hydrogen Atoms:
% isomer
5.917
C1 Carbon R.R. = ------------------ = -------------- = 2.959
# C-H Bonds
2
% isomer
22.517
C2 Carbon R.R. = ----------------- = --------------- = 11.259
# C-H Bonds
2
% isomer
C3 Carbon R.R. = ----------------- =
# C-H Bonds
46.039
-------------- = 23.020
2
% isomer
C4 Carbon R.R. = ------------------ =
# C-H Bonds
25.527
-------------- = 8.509
3
Relative Reactivates:
2.959
C1 = ---------- = .3477
8.509
11.259
C2 = ---------- = 1.323
8.509
23.020
C3 = ---------- = 2.705
8.509
8.509
C4 = ---------- = 1.000
8.509
C1 :
C2: C3: C4
.3477:1.323:2.705:1.00
Gas Chromatography Results: