CHE-3652-0BB
Experiment # 1: Chlorination of Heptane
In this experiment, we will chlorinate heptane to determine the relative reactivity of
chlorine radicals towards primary and secondary hydrogens. We will begin the chlorination
process using a condenser to maintain the reaction mixture then use fractional distillation to
separate the resulting chlorinated products. Lastly, we will analyze our product using gas
chromatography.
Reaction Mechanism
Initiation
Propagation
Termination
Table of Reagents and Solvents
Compound
Molecular
Formula
Boiling
point (oC)
Melting
point (oC)
Density
(g/mL)
Amount
Used
C7H16
C7H15Cl
Molecular
Weight
(g/mol)
100.20
134.65
Heptane
1chloroheptane
2chloroheptane
3chloroheptane
4chloroheptane
Sulfuryl
Chloride
AIBN
Sodium
Hydroxide
Sodium Sulfate
98
159 - 161
-91
-69
0.684
0.881
10 mL
N/A
C7H15Cl
134.65
146
148
0.864
N/A
C7H15Cl
134.65
144
N/A
0.864
N/A
C7H15Cl
134.65
153
N/A
0.864
N/A
SO2Cl2
134.96
69.1
-54.1
1.7
1.5 mL
C₈H₁₂N₄
NaOH
164.21
40
281.68
1390
102-105
318
0.8
2.13
0.1 g
15 mL
Na2SO4
2.66
1429
884
2.66
N/A
Organic Structures
Heptane
1-chloroheptane
2-chloroheptane
3-chloroheptane
4-chloroheptane
AIBN
Material Safety Data Sheet for Compounds
Heptane – Dangerous. Highly flammable liquid and vapor. May be fatal if swallowed and enters
airways. Causes skin irritation. May cause drowsiness or dizziness. In case of fire: Use CO2, dry
chemical, or foam for extinction. *Safety Procedures: If in EYES: Rinse cautiously with water
for at least 15 minutes. Remove contact lenses if present. If INHALED: Remove victim to fresh
air and keep at rest in a comfortable position for breathing. If not breathing, give artificial
respiration. Call Poison Control or physician if victim continues to feel unwell. If ON SKIN (or
hair): Take off all contaminated clothing immediately. Rinse skin with water/shower for at least
15 minutes. Wash contaminated clothing before reuse. Seek medical attention. If
SWALLOWED: Immediately call a Poison Control or physician. Do NOT induce vomiting.
1-chloroheptane – Warning. Flammable liquid and vapor. Keep away from heat, sparks, open
flames, hot surfaces. In case of fire: Use dry sand, dry chemical or alcohol-resistant foam to
extinguish. *Follow safety procedures as mentioned above.
2-chloroheptane – Warning. Flammable liquid and vapor. Causes skin irritation and serious eye
irritation. May cause respiratory irritation. Keep away from heat, sparks, open flames, hot
surfaces. In case of fire: Use CO2, dry chemical or alcohol-resistant foam to extinguish. *Follow
safety procedures as mentioned above.
3-chloroheptane – Warning. Flammable liquid and vapor. Causes skin irritation and serious eye
irritation. May cause respiratory irritation. Keep away from heat, sparks, open flames, hot
surfaces. In case of fire: Use CO2, dry chemical or alcohol-resistant foam to extinguish. *Follow
safety procedures as mentioned above.
4-chloroheptane – Environmental hazard. *Follow safety procedures as mentioned above.
Sulfuryl Chloride – Danger. Causes severe skin burns and eye damage. May cause respiratory
irritation. Fatal if inhaled. Reacts violently with water. Highly corrosive. *Follow safety
procedures as mentioned above.
2,2′-Azobis(2-methylpropionitrile) – Danger. Heating may cause a fire. Harmful if swallowed or
if inhaled. Harmful to aquatic life with long lasting effects. If SWALLOWED: Immediately
make victim drink water (two glasses at most), then consult a physician. *Follow the remaining
safety procedures as mentioned above.
Sodium Hydroxide – Danger. May be corrosive to metals. Causes severe skin burns and eye
damage. May cause respiratory irritation. *Follow safety procedures as mentioned above.
Sodium Sulfate – Hygroscopic. May cause skin, eye, and respiratory tract irritation. *Follow
safety procedures as mentioned above.
Experimental Procedure
1. Inside a 50mL round bottom flask, add 0.1 g of AIBN and a stir bar.
a. Make sure the flask and the inside of the condenser are completely dry.
2. Place the flask in the hood. With a pipet, add 1.5 mL of sulfuryl chloride to the flask.
3. Using a graduated cylinder, add 10 mL of heptane.
4. At the bench, set up condenser for a reflux reaction, and attach to a NaOH gas trap.
a. The glass tube must be above the NaOH solution.
5. With a thermowell, heat the reaction under reflux for 45 minutes.
6. After heating for 45 minutes, lower the thermowell, wait until it stops boiling, then add
15 mL of 5% NaOH solution carefully down the condenser into the flask.
7. Rearrange apparatus for fractional distillation, but do not add glass beads.
8. When the temperature is between 70-90° C collect the first fraction with a 25 mL
Erlenmeyer flask.
a. The first fraction contains unreacted, excess heptane, that co-distills with water.
Most of the product will be distilled around 80°C. Total volume of this first
fraction is around 8 mL. It should be discarded in the halogenated waste bottle.
9. When the temperature reaches 90° C, use a small 10 mL graduated cylinder to collect the
product fraction. Continue collecting the product fraction until you reach 99° C or a total
of 3-4 mL fraction volume has been collected.
10. With a disposable pipet, remove the lower aqueous layer from the graduated cylinder
then transfer the organic layer (product) into a vial.
11. Add sodium sulfate until product is dry then transfer it into another pre-weighed vial.
12. Record the weight of the product and analyze it using gas chromatography.
Apparatus
Calculations
Mass of Vial: 16.28319 g
Mass of Vial and Product: 16.6715 g
Actual Yield:
16.6715 g − 16.28319 g = 0.38831 g (Weight of Product)
21273
1o-chloroheptane = 197372 × 100 = 10.7781% × 0.38831 g = 0.04185 g
105291
2o-chloroheptane = 197372 × 100 = 53.3465% × 0.38831 g = 0.20718 g
Theoretical Yield:
0.684 g
1 mol Heptane
10 mL Heptane × 1 mL × 100.2 g Heptane ×
1.7 g
1 mol SO Cl
1.5 mL SO2 Cl2 × 1 mL × 134.97 g SO2 Cl2 ×
2
1 mol Chloroheptane
1 mol Heptane
2 mol Chloroheptane
2
1 mol SO2 Cl2
= 0.068263 mol Chloroheptane
= 0.037786 mol Chloroheptane
134.65 g Chloroheptane
0.037786 mol Chloroheptane × 1 mol Chloroheptane = 5.08450 g Chloroheptane
Percent Yield:
0.04185 g
1o-chloroheptane = 5.08450 g × 100 = 0.823089%
0.20718 g
2o-chloroheptane = 5.08450 g × 100 = 4.074736%
Relative Reactivity:
1o-chloroheptane =
10.7781
2o-chloroheptane =
53.3465
6H
10 H
1.79635
= 1.79635 = 1
5.33565
= 1.79635 = 2.97027
Relative Ratio: 1:3
Discussion and Conclusion
In this experiment, heptane was chlorinated to determine the relative reactivity of
chlorine radicals towards primary and secondary hydrogens. The radical chlorination reaction
was done by reflux which converted heptane to chloroheptane. The reaction produced four
different chlorinated products which were then separated using fractional distillation. To
successfully collect our product, the boiling points of the different isomers were taken into
consideration. The first fraction collected contained an excess amount of unreacted heptane and
water. The second fraction collected contained a mixture of chloroheptane products. The second
fraction was then analyzed using gas chromatography to confirm our products.
During our procedure, part of the contents contained in the round bottom flask were
accidentally spilled just as my lab partner and I were finished setting up our fractional distillation
apparatus. Our instructor was notified and helped modify our procedure to help us collect enough
product for GC analysis. For our fractional distillation, we began collecting our first fraction
around 83°C and then collected our second fraction from 90-100°C. The remainder of the
experiment was conducted as planned and we were able to successfully analyze our limited
amount of product by GC. Given the limited amount of product we were working with, we were
unable to collect the fractions correctly. This error significantly contributed to our low percent
yield of product. For the next experiment, we will be more cautious handling our equipment to
avoid this error.
Our GC showed the second product was mainly collected which is a mixture of 2 o,3 o,
and 4 o -chloroheptane products. Our calculations showed 2o-chloroheptane had a higher relative
reactivity compared to 1o-chloroheptane which tells us that 2o-chloroheptane is approximately 3
times more likely to react than 1o-chloroheptane. This is due to 2o-chloroheptane having ten
secondary hydrogens while 1o-chloroheptane only has six primary hydrogens. 2o-chloroheptane
also has more surrounding -R groups, and with these alkyl groups being more polarizable than
hydrogen atoms, they are able to donate more electron density to the electron deficient carbon
radical, thus helping to increase the overall stability of the product. 2o-chloroheptane also has a
lower C-H bond dissociation energy which allows the bond to be more readily broken for
halogenation.