CHEM 233: Organic
Laboratory I Prelab Lecture
University of Illinois at Chicago
UIC
Lab 7: Preparation of Alkyl Chlorides by Nucleophilic
Aliphatic Substitution.
alkene
E1
H
2
O
HCl
H carbocation intermediate
Cl
S
N
1 Cl alkyl chloride

Work individually for this lab. You will prepare tert -butyl chloride. The other alkyl chlorides will be provided for you.
H
3
C
H
3
C
CH
3
OH
2-methyl-2-propanol
( tert-butanol)
HCl
H
2
O
H
3
C
H
3
C
CH
3
Cl
Provided
CH
3
H
3
C
Cl product name
(IUPAC and common) yield NA substitution
(3º, 2º or 1º) b.p. (determined by reading head temperature during distillation)
AgNO
3
Precip. Test (1-3)
(1=slowest; 3=fastest)
NaI Precip. Test (1-3)
(1=slowest; 3=fastest)
University of
Illinois at Chicago
UIC © 2009, Dr. Chad L. Landrie
CHEM 233: Organic Chemistry Laboratory 1
Provided
CH
3
Cl
H
3
C
NA
Slide 2
Prelab Lecture: Lab 6

round-bottom flask ice-bath
University of
Illinois at Chicago
UIC vacuum adapter
(“drip-tip”)
1. Follow procedure in textbook, page 465.
Work individually .
2. After extraction and drying the organic layer, isolate product by simple distillation not short-path .
3. Products are volatile . Use an ice-bath to prevent product from evaporating. Also, collect product in round bottom flask attached to drip-tip to also prevent evaporation.
4. Preweigh the collection flask for easy measurement of mass at the end. Note: you will need to look up the densities of the reactants in order to calculate % yield.
5. Perform chemical tests in test-tubes.
6. **Caution: products are highly flammable!**
© 2009, Dr. Chad L. Landrie
CHEM 233: Organic Chemistry Laboratory 1
Slide 3
Prelab Lecture: Lab 6

The organic layer is washed with a saturated solution of sodium bicarbonate (NaHCO
3
) to neutralize excess HCl.
O
HO O Na sodium bicarbonate
H Cl
O
HO O H carbonic acid
+ NaCl decomposition
FYI: This equilibrium (albeit a very large K eq
) also explains why H
2
O is slightly acidic in the presence of CO
2
.
CO
2
(gas) + H
2
O
• CO
2
gas will rapidly build up pressure in a closed separatory funnel.
Vent often! TA will demonstrate proper venting technique.
• Q: Why would aqueous NaOH not be an appropriate base to neutralize excess HCl?
University of
Illinois at Chicago
UIC © 2009, Dr. Chad L. Landrie
CHEM 233: Organic Chemistry Laboratory 1
Slide 4
Prelab Lecture: Lab 6

S
N
2
S ubstitution
N ucleophilic
2 nd Order
S
N
1
S ubstitution
N ucleophilic
1 st Order
O H
1º alcohol
O H
3º alcohol
H Cl
H Cl
Cl
1º alkyl chloride
+
H
O
H
Cl
3º alkyl chloride
+
H
O
H
University of
Illinois at Chicago
UIC © 2009, Dr. Chad L. Landrie
CHEM 233: Organic Chemistry Laboratory 1
Slide 5
Prelab Lecture: Lab 6

RDS
University of
Illinois at Chicago
S
N
2
H Cl
O H protonation
H
O
H oxonium ion
+
Cl
UIC
Cl +
H
O
H
• rate = k[oxonium ion][chloride]
• rate is 2nd order/bimolecular (two reactants in RDS)
• S
N
2 = no carbocation intermediate
O H
S
N
1
H Cl protonation
H
O
H oxonium ion
RDS heterolysis
CH
3
H
3
C CH
3 carbocation intermediate
Cl
• rate = k[oxonium ion]
Cl
• rate is 1st order/unimolecular (one reactant in RDS)
• S
N
2 = carbocation intermediate
(stability: 3º>2º>>1º)
© 2009, Dr. Chad L. Landrie
CHEM 233: Organic Chemistry Laboratory 1
Slide 6
Prelab Lecture: Lab 6

N
alkene
E1
H
2
O
HCl
H carbocation intermediate
Cl
S
N
1 Cl alkyl chloride
• E1 is reversible: Markovnikoff addition of HCl to alkene regenerates carbocation intermediate.
• Since addition of chloride to carbocation is irreversible,
E1 does not interfere with S
N
1 in our experimental conditions.
University of
Illinois at Chicago
UIC © 2009, Dr. Chad L. Landrie
CHEM 233: Organic Chemistry Laboratory 1
Slide 7
Prelab Lecture: Lab 6

Cl
Lewis base
Ag
+
NO
3
-
Ag + = Lewis acid
RDS: S
N
1
CH
3
H
3
C CH
3 carbocation intermediate
+
O
O
N
O
+ AgCl
(s)
(precipitates in EtOH)
O
N
O O alkyl nitrate
• Positive test = observe AgCl precipitate in EtOH.
• Ag + is a strong enough Lewis acid (e acceptor) to remove Cl .
• As a result, carbocation intermediates are formed. Mechanism =
“S
N
1-like.”
• Therefore, reactivity of alkyl chlorides = 3º>2º>>1º.
University of
Illinois at Chicago
UIC © 2009, Dr. Chad L. Landrie
CHEM 233: Organic Chemistry Laboratory 1
Slide 8
Prelab Lecture: Lab 6

Cl
Na
+
I
–
RDS: S
N
2
I
FYI: Also known as the Finkelstein reaction.
+ NaCl
(s)
(precipitates in acetone)
• Positive test = observe NaCl precipitate in acetone.
• Na + is not a strong enough Lewis acid (e acceptor) to remove Cl .
• As a result, carbocation intermediates are not formed. Mechanism =
S
N
2.
• Therefore, reactivity of alkyl chlorides = 1º>2º>>3º.
University of
Illinois at Chicago
UIC © 2009, Dr. Chad L. Landrie
CHEM 233: Organic Chemistry Laboratory 1
Slide 9
Prelab Lecture: Lab 6

Test Solvent
Observed
Precipitate
Mechanism
Reactivity of R–X
Silver Nitrate
(AgNO
3
) ethanol AgCl S
N
1 3º>2º>>1º
Sodium Iodide
(NaI) acetone NaCl S
N
2 1º>2º>>3º
University of
Illinois at Chicago
UIC © 2009, Dr. Chad L. Landrie
CHEM 233: Organic Chemistry Laboratory 1
Slide 10
Prelab Lecture: Lab 6

• Labs 8-10 are technically challenging and can only be completed within the class time if you are adequately prepared.
• Preparation includes a thorough understanding of the background information and procedural steps before you enter the lab.
• Write a clear procedure that you intend to follow in your prelab notebook entry so that you can get to work right away on those days.
• Working within these time constraints will be good practice for the practical exam, which is also challenging.
University of
Illinois at Chicago
UIC © 2009, Dr. Chad L. Landrie
CHEM 233: Organic Chemistry Laboratory 1
Slide 11
Prelab Lecture: Lab 6