Synthesize t-Butyl (or t-Pentyl) Chloride
Note: This experiment may utilize either t-Butyl Alcohol
(m.p. 25.7oC) or t-Pentyl Alcohol (m.p. -9.5oC) as one
of the starting reactants
Text References
Slayden
Pavia
Pavia
1/17/2015
- Exp # 21
- Tech 12
- pp. 49 - 50
- pp. 172 - 174
- pp. 681 - 702
1
T-Butyl (t-Pentyl) Chloride Synthesis

1/17/2015
Today’s Experiment

Reaction of t-Butyl Alcohol (or t-Pentyl Alcohol) with
conc. HCL to form t-Butyl Chloride (or t-Pentyl
Chloride)

Three-step Sn1 Nucleophilic Substitution Reaction

This is a First Order Rate Reaction where the Rate of
Formation of t-Butyl Chloride (t-Pentyl Chloride) is
dependent only on the concentration of the Alcohol,
i.e., it is independent of the amount of acid (HCL) used

The strong acid (HCL) protonates the electron rich
hydroxyl group (nucleophile) allowing it leave as a
molecule of water

This leaves a highly electrophilic carbon atom
(positvely charged carbocation) that can be attacked
by the negatively charged chloride anion, forming the
final product
2
T-Butyl (t-Pentyl) Chloride Synthesis

1/17/2015
Today’s Experiment (Con’t)

NOTE: Rate of Formation and Limiting Reagent are
independent of each other. Thus, the Limiting Reagent
must be computed

Determine the limiting reagent and theoretical yield
from the masses & moles of the two reactants (t-Butyl
or t-Pentyl Alcohol & Conc HCl) and the stoichiometric
molar ratios

This experiment will require the student to separate
and wash (liquid/liquid Extraction) two immiscible
liquids using a separatory funnel

Several steps of the experiment generate gases
requiring care in using the separatory funnel and its
stopcock
3
T-Butyl (t-Pentyl) Chloride Synthesis
t-Butyl Alcohol
(2-Methyl-2-Propanol)
B.P.
M.P.
Density
Refractive Index
Mol Wgt
Water Solubility
-
82.4 oC
25.7 oC
0.7887 g/mL
1.3870
74.12 g/mole
Soluble
t-Butyl Chloride
(2-Chloro-2-Methyl Propane)
(507-20-0)
B.P.
M.P.
Density
Refractive Index
Mol Wgt
Water Solubility
-
50.9 oC
-26.0 oC
0.8420 g/ml
1.3857
92.5 g/mole
Sl Soluble
Conc HCl
Molecular Wgt
Molarity
Density
% Acid
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-
36.47 g/mole
12.0 moles/L
1.18 g/mL
37.3
4
T-Butyl (t-Pentyl) Chloride Synthesis
t-Pentyl Alcohol
(2-Methyl-2-Butanol
- 102.5 oC
- - 9.1 oC
- 0.8096 g/mL
- 1.4052
- 88.15 g/mole
- Soluble
B.P.
M.P.
Density
Refractive Index
Mol Wgt
Water Solubility
t-Pentyl Chloride
(2-Chloro-2-Methyl Butane)
(594-36-5)
B.P.
M.P.
Density
Refractive Index
Mol Wgt
Water Solubility
-
85.6 oC
-74.0 oC
0.8563 g/ml
1.4055
106.6 g/mole
Slightly Sol
Conc HCl
Molecular Wgt
Molarity
Density
% Acid
1/17/2015
-
36.47 g/mole
12.0 moles/L
1.18 g/mL
37.3
5
T-Butyl (t-Pentyl) Chloride Synthesis

Stoichiometric Reaction

The Mechanism
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6
T-Butyl (t-Pentyl) Chloride Synthesis

The Stoichiometric tert-Pentyl Reaction

The Mechanism
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7
T-Butyl (t-Pentyl) Chloride Synthesis

1/17/2015
Limiting Reagent Calculations

The yield (mass or moles) of the washed and dried
t-Butyl (t-Pentyl) Chloride product is compared to the
theoretical amount of product expected, which is
computed from a “Limiting Reagent” calculation using
the Stoichiometric Molar Ratio

The “Limiting Reagent” is that reactant whose mass
(on a molar equivalent basis) is totally consumed in
the reaction leaving an excess of the other reactant

The “Limiting Reagent”, thus, determines the
maximum amount of product that can be expected

The results of the “Limiting Reagent computations” are
presented in a table in the Data Report
8
T-Butyl (t-Pentyl) Chloride Synthesis

Limiting Reagent Calculations (Con’t)

Limiting Reagent Steps

Determine the mass of the alcohol to the nearest
0.001 gram.

Measure the volume of conc HCL solution to be used
to the nearest 0.1 mL

Compute the mass of the HCL from the volume,
density, and % composition (see table)

From the amounts (mass) of reactants used,
calculate the number of moles of each:
moles = mass / mol wgt

1/17/2015
Moles of HCl can also be computed directly
from the Volume and Molarity (12.0 moles/L).
If this approach is used, then back calculate the
mass of HCL from the moles
9
T-Butyl (t-Pentyl) Chloride Synthesis
1/17/2015

From the balanced reaction equation determine the
molar ratio among the reactants and products
i.e., how many moles of Alcohol react with how
many moles of HCL to give how many moles of
t-Butyl (t-Pentyl) Chloride. The ratio here is 1:1

If the ratio of moles of Alcohol to moles of HCl
actually used is greater than the stoichiometric
molar ratio, then the Alcohol is in “Excess” and HCl
is “Limiting”

If, however, the ratio of actual moles of Alcohol to
moles of HCl is less than the reaction molar ratio,
then HCl is in excess and t-Butyl (t-Pentyl) Alcohol is
“Limiting”
10
T-Butyl (t-Pentyl) Chloride Synthesis
Examples
A
+
B  C
Molar ratio A:B = 1 : 1 = 1.0
Moles actually used:
A = 0.05;
B = 0.12
Molar ratio A:B actually used: 0.05 / 0.12 = 0.42
The ratio of A:B is less than 1.00; thus A is limiting
Only 0.05 moles of the 0.12 moles of B would be
required to react with the 0.05 moles of A available
Since 0.05 < 0.12; then B is in excess, A is limiting
1/17/2015
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T-Butyl (t-Pentyl) Chloride Synthesis
Examples
(Con’t)
A
+
2B

C
Molar ratio A:B = 1 : 2 = 0.5
Moles actually used
A = 0.0069; B = 0.023
Molar ratio A:B actually used = 0.0069 / 0.023 = 0.30
The ratio A:B is less than 0.5, thus, A is limiting
Only 0.0069  2 = 0.0138 moles of B are required to
react with 0.0069 moles of A.
Since 0.0138 < 0.023:
B is in excess, A is limiting.
Any actual molar ratio less than the reaction molar
ratio indicates “B” is in Excess and “A” is Limiting.
Any actual molar ratio greater than the reaction molar
1/17/2015 ratio indicates “A” is in Excess and “B” is Limiting
12
T-Butyl (t-Pentyl) Chloride Synthesis

Examples (Con’t)

In the Friedel-Crafts alkylation of Biphenyl with t-Butyl
Chloride to form 4,4’-Di-tert-Butyl Biphenyl, 1.064 g of
Biphenyl is reacted with 2.129 g of t-Butyl Chloride. The
stoichiometric equation indicates that 2 moles of t-Butyl
Chloride react with 1 mole of Biphenyl

Determine the “Limiting Reagent” and the “Theoretical
Yield”
Amounts Actually Used
Maximum Amounts Expected
1 Biphenyl + 2 t-Butyl Chloride  1 4,4’di-tert-Butylbiphenyl + 2 HCl

1/17/2015
Mol Wgt
154.211
92.565
266.43
36.55
Mass (g)
1.064
2.129
1.838
0.504
Moles
0.0069
0.023
0.0069
0.0138
In the above example, “Biphenyl” is the limiting reagent
because 0.0069 moles is less than 0.023 / 2 = 0.0115
moles. Thus, a maximum of 0.0069 moles (1.838 g) 4,4’ditert-Butyl Biphenyl can be expected
13
T-Butyl (t-Pentyl) Chloride Synthesis

Theoretical Yield

The limiting reagent sets the maximum amount of
product that can be expected

The actual number of moles of product is the product
of the moles of Limiting reagent and the molar ratio of
product to Limiting reagent

To get the mass of product simply multiply the
expected moles of product by the molecular weight of
the product
Mass Product = Moles Limiting Reagent × Molar Ratio (Product / Reagent)× Mol Wgt Product
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14
T-Butyl (t-Pentyl) Chloride Synthesis
Elements of the Experiment


Determining the masses of the reactants (2
procedures)
• Alcohol mass is determined by weighing
• HCl mass is determined by computing mass from
volume, density and % Composition (HCl – 37.3 %)

Determining the moles of the reactants

Setting up the Stoichiometric equation

Determining the Limiting Reagent

Determining the Theoretical Yield

Mixing reagents and initiating the reaction
1/17/2015
15
T-Butyl (t-Pentyl) Chloride Synthesis

1/17/2015
Elements of the Experiment (Con’t)

Separate product from reaction mixture

Liquid/Liquid Extraction of product with H2O and
NaHCO3 to Separate & Wash the product

Drying the product with Anhydrous Sodium Sulfate
(Na2SO4)

Determining the Mass (Yield) of the Product

Computing the % yield

Determining the Refractive Index

Adjusting Refractive Index for temperature

Obtaining the Infrared Spectrum
16
T-Butyl (t-Pentyl) Chloride Synthesis
Macro Scale Procedure:


Obtain vial of t-Butyl (or t-Pentyl) Alcohol from
instructor’s desk
Note: Melting point of t-Butyl Alcohol is near room
temperature and could be solid if lab is cold.
Warm vial with hands to melt

Weigh the vial and contents; record in pre-lab

Setup cork ring on iron ring to support funnel

Transfer sample to 125 ml Separatory Funnel using a
long stem glass funnel

Reweigh the vial. In your report calculate the Mass of tButyl (or t-Pentyl) Alcohol

In your report compute the Moles of the Alcohol
1/17/2015
17
T-Butyl (t-Pentyl) Chloride Synthesis
Macro Scale Procedure (Con’t):


Add 25 mL, measured to nearest 0.1 mL, of
concentrated HCl to the separatory funnel

In your report calculate Mass of HCL
(vol(mL) * density(g/mL) * % comp (37.3))

In your report compute the moles of HCL
Note: As an alternative, the Moles of HCl can be
computed directly from the Volume and Molarity
of Conc. HCl. (Back calculate to get mass)

1/17/2015
In your report set up the Stoichiometric Equation,
determine the Limiting Reagent, and calculate the
Theoretical Yield
18
T-Butyl (t-Pentyl) Chloride Synthesis

Macro Scale Procedure (Con’t):





Stopper the funnel, firmly holding the stopper with
your finger, and gently swirl the mixture for
approximately one (1) minute
Invert the funnel and slowly open the stopcock to vent
pressure
Close stopcock; swirl the mixture again; and again
release the pressure
Repeat this process for 3-4 times until gas release is
minimized
Two layers will form in the funnel
Note: Based on the densities of the organic layer
and the aqueous layer (H20, HCl, etc.)
determine which layer is on top
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19
T-Butyl (t-Pentyl) Chloride Synthesis

Drain the aqueous reaction mixture into a large beaker

In the following steps the organic layer will be
extracted once with Water, two (2) times with Sodium
Bicarbonate (NaHCO3), and again with water
The Extraction procedure must be done in an
expeditious manner as t-Butyl (t-Pentyl) Chloride is
unstable in Water and Sodium Bicarbonate
Note: This can be one Procedure
● Retain the organic fraction in the Separatory Funnel
and the separated aqueous fraction in the waste
beaker
1/17/2015
20
T-Butyl (t-Pentyl) Chloride Synthesis
● Add 10 ml of Distilled Water to the crude product in
the separatory funnel
● Swirl the mixture for 30 seconds
● Carefully invert the funnel and slowly open the
stopcock to release any excess gas
● Close the stopcock and repeat the mixing/venting
process for about 60 seconds
● Drain the aqueous phase into the waste beaker
● Retain the organic phase (top layer) in the
separatory funnel
1/17/2015
21
T-Butyl (t-Pentyl) Chloride Synthesis
● Add 10 mL of 5% aqueous Sodium Bicarbonate
(NaHCO3) to the funnel containing the organic layer
● Note: The Sodium Bicarbonate reacts with any
aqueous acid (HCL) in the organic layer
releasing Carbon Dioxide gas
Be careful when venting the gas!
● Repeat the mixing and venting process several times
until gas is no longer being vented
● Allow the layers to separate; and drain the aqueous
layer again into the waste Erlenmeyer flask
● Repeat the washing process with a second 10 mL
portion of 5% NaHCO3
● Wash the organic layer again with 10 mL Distilled
Water
1/17/2015
22
T-Butyl (t-Pentyl) Chloride Synthesis
 After removing the aqueous layer to the waste beaker,
drain the organic layer into a 100 mL, clean, dry
beaker
 With instructors help, add Anhydrous Sodium Sulfate
to the crude product, swirling the mixture until it is
clear
Note: See p. 695-699 in Pavia for techniques on
determining dryness of sample
 Transfer the clear product into a clean, dry,
pre-weighed 50 mL Erlenmeyer flask
 Weigh the flask and contents
 Determine the mass of product by difference
 Calculate the percentage yield
 Determine the Refractive Index; Correct for
Temperature
 Obtain IR Spectrum
1/17/2015
23
T-Butyl (t-Pentyl) Chloride Synthesis

Semi-Micro Scale Procedure (Do not use this procedure
unless specifically instructed to do so by Instructor)
 Obtain vial of t-Butyl (t-Pentyl) Alcohol ( 4 mL) from
instructor’s desk
Note: Melting point of t-Butyl Alcohol is near room
temperature and could be solid if lab is cold.
Warm vial with hands to melt
 Weigh the vial and contents to nearest 0.001 g; record
in notebook
 Transfer sample to Centrifuge Tube using a long stem
glass funnel
 Reweigh the empty vial
 Calculate Mass of t-Butyl Alcohol
 Calculate Moles of t-Butyl Alcohol
1/17/2015
24
T-Butyl (t-Pentyl) Chloride Synthesis
Semi-Micro Scale Procedure (Con’t):


Add  8 mL, measured to nearest 0.1 mL, of
concentrated HCl to the Centrifuge tube

In your report calculate Mass of HCL from the Volume,
Density, % composition
Note: This calculation is different from Alcohol mass,
therefore, it is a separate procedure

Compute Moles of HCl
Note: As an alternative, the Moles of HCl can be
computed directly from the Volume and the Molarity of
Conc. HCl

In the report, setup the Stoichiometric balanced
equation

Determine the Limiting Reagent
1/17/2015
25
T-Butyl (t-Pentyl) Chloride Synthesis

Semi-Micro Scale Procedure (Con’t):
 Calculate the Theoretical Yield
Note: Each computation in the Limiting Reagent/
Theoretical Yield determination must be set up
and all calculations shown
 Screw the sealing cap onto the Centrifuge Tube and
shake the tube gently for about 10 minutes. Be sure
to unscrew the cap carefully every minute or so to
vent any gases that may form
 Two layers will form in the funnel


1/17/2015
Note: Based on the densities of the organic layer
(t-Butyl Chloride) and the aqueous layer (H20, HCl,
etc.) determine which layer is on top
Remove the Aqueous layer using a Pasteur Pipet
Place the aqueous waste in a waste beaker
26
T-Butyl (t-Pentyl) Chloride Synthesis

Semi-Micro Scale Procedure (Con’t):

The Extraction procedure that follows must be done in
an expeditious manner as t-Butyl Chloride is unstable
in Water and Sodium Bicarbonate

Extract (wash) the organic product, once with 10 mL
Distilled Water, twice with 10 mL 5% Sodium
Bicarbonate (NaHCO3) and once again with water

Be sure to vent gases carefully, especially with
NaHCO3
Note: This is one Procedure
1/17/2015

Each time, remove the Aqueous layer using a Pasteur
Pipet

Place the aqueous waste in the waste beaker
27
T-Butyl (t-Pentyl) Chloride Synthesis

Semi-Micro Scale Procedure (Con’t):

Add Anhydrous Sodium Sulfate to the crude product,
swirling the mixture until it is clear
Note: See p. 713-716 in Pavia for techniques on
determining dryness of sample
1/17/2015

Decant the clear material into clean, dry, pre-weighed
Erlenmeyer Flask

Weigh the flask and contents

Compute mass of product by difference

Compute the % yield

Determine the Refractive Index; Correct for
Temperature

Obtain IR Spectrum
28
T-Butyl (t-Pentyl) Chloride Synthesis

1/17/2015
The Report

The “Purpose” should reflect the type of reaction and
principle reactants involved. It should also reflect
introduction of any new techniques that you are to
become familiar

The “Approach” is a sequential step by step overview
of the principle procedures to be used, including
calculations, such as mass, moles, limiting reagent,
and theoretical yield determinations

It should also reflect how the results will be quantified,
such as yield and percent yield

The “Procedures” should be stated in the student’s
own words, using short, concise statements in “List”
form
29
T-Butyl (t-Pentyl) Chloride Synthesis

The Report (Con’t)

In the “Summary” section summarize the “Results”, i.e.
an overview in paragraph form of the experimental
results obtained

In the “Conclusion” section consider the following
questions:
● What was the Molar ratio of HCl to t-Butyl Alcohol
and what was the impact of this ratio on the
selection of the Limiting Reagent and the amount of
product expected?
● Provide details of the Refractive Index and IR
Spectrum analysis confirming the product obtained
was indeed t-Pentyl Chloride
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30