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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 - pp. 49 - 50Pavia - Exp # 21 - pp. 172 - 174Pavia - Tech 12 - pp. 681 - 702

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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

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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

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T-Butyl (t-Pentyl) Chloride Synthesis t-Butyl Alcohol

(2-Methyl-2-Propanol)

B.P. - 82.4 oCM.P. - 25.7 oC Density - 0.7887 g/mLRefractive Index - 1.3870Mol Wgt - 74.12 g/moleWater Solubility - Soluble

Conc HCl

Molecular Wgt - 36.47 g/moleMolarity - 12.0 moles/LDensity - 1.18 g/mL% Acid - 37.3

t-Butyl Chloride

(2-Chloro-2-Methyl Propane)

(507-20-0)

B.P. - 50.9 oC

M.P. - -26.0 oC

Density - 0.8420 g/ml

Refractive Index - 1.3857

Mol Wgt - 92.5 g/mole

Water Solubility - Sl Soluble

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T-Butyl (t-Pentyl) Chloride Synthesis t-Pentyl Chloride

(2-Chloro-2-Methyl Butane)(594-36-5)

B.P. - 85.6 oC

M.P. - -74.0 oCDensity - 0.8563 g/mlRefractive Index - 1.4055Mol Wgt - 106.6 g/moleWater Solubility - Slightly Sol

Conc HCl

Molecular Wgt - 36.47 g/moleMolarity - 12.0 moles/LDensity - 1.18 g/mL% Acid - 37.3

t-Pentyl Alcohol(2-Methyl-2-Butanol

B.P. - 102.5 oC

M.P. - - 9.1 oC Density - 0.8096 g/mLRefractive Index - 1.4052Mol Wgt - 88.15 g/moleWater Solubility - Soluble

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Stoichiometric Reaction

The Mechanism

T-Butyl (t-Pentyl) Chloride Synthesis

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The Stoichiometric tert-Pentyl Reaction

The Mechanism

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Limiting Reagent Calculations

The yield (mass or moles) of the washed and driedt-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

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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 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

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From the balanced reaction equation determine the molar ratio among the reactants and productsi.e., how many moles of Alcohol react with how many moles of HCL to give how many moles oft-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”

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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

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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 ratio indicates “A” is in Excess and “B” is Limiting

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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”

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’di-tert-Butyl Biphenyl can be expected

T-Butyl (t-Pentyl) Chloride Synthesis

Amounts Actually Used Maximum Amounts Expected

1 Biphenyl + 2 t-Butyl Chloride 1 4,4’di-tert-Butylbiphenyl + 2 HCl

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

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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

T-Butyl (t-Pentyl) Chloride Synthesis

Mass Product = Moles Limiting Reagent × Molar Ratio (Product / Reagent)×Mol Wgt Product

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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

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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

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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 t-Butyl (or t-Pentyl) Alcohol

In your report compute the Moles of the Alcohol

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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)

In your report set up the Stoichiometric Equation, determine the Limiting Reagent, and calculate the Theoretical Yield

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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 funnelNote: 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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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

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● Wash (swirl and shake) the mixture with one 10 mL portion of Distilled Water

● Hold the funnel stopper firmly in place with your thumb and gently shake to mix the contents

● Carefully invert the funnel and release any excess pressure by slowly opening the stopcock

● Close stopcock and repeat the mixing/venting process until gas is no longer being vented

● Drain the aqueous phase into the waste beaker

● Retain the organic phase (top layer) in the separatory funnel

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● 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

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After removing the aqueous layer to the waste beaker, drain the organic layer into a small (50 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

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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

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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

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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

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

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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 Each time, remove the Aqueous layer using a

Pasteur Pipet Place the aqueous waste in the waste beaker

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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

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

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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, mole, limiting reagent, and theoretical yield determinations, as well as sample cleanup and reaction verification

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

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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?

● What experimental results did you obtain to verify that the reaction produced the desired product?

T-Butyl (t-Pentyl) Chloride Synthesis