T-Butyl (t-Pentyl) Chloride Synthesis

1
T-Butyl (t-Pentyl) Chloride Synthesis

• 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

2
T-Butyl (t-Pentyl) Chloride Synthesis

• Todays 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

3
T-Butyl (t-Pentyl) Chloride Synthesis

• Todays Experiment (Cont)
• 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

4
T-Butyl (t-Pentyl) Chloride Synthesis
t-Butyl Alcohol (2-Methyl-2-Propanol
) B.P. - 82.4 oC M.P. - 25.7 oC
Density - 0.7887 g/mL Refractive
Index - 1.3870 Mol Wgt - 74.12 g/mole Water
Solubility - Soluble
t-Butyl Chloride (2-Chloro-2-Methyl
Propane) 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
Conc HCl Molecular Wgt - 36.47
g/mole Molarity - 12.0 moles/L Density - 1.18
g/mL Acid - 37.3
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T-Butyl (t-Pentyl) Chloride Synthesis
t-Pentyl Chloride (2-Chloro-2-Methyl
Butane) B.P. - 85.6 oC M.P. - -74.0
oC Density - 0.8563 g/ml Refractive Index -
1.4055 Mol Wgt - 106.6 g/mole Water
Solubility - Slightly Sol
t-Pentyl Alcohol (2-Methyl-2-Butanol B.P. -
102.5 oC M.P. - - 9.1 oC Density - 0.8096
g/mL Refractive Index - 1.4052 Mol Wgt - 88.15
g/mole Water Solubility - Soluble
Conc HCl Molecular Wgt - 36.47
g/mole Molarity - 12.0 moles/L Density - 1.18
g/mL Acid - 37.3
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T-Butyl (t-Pentyl) Chloride Synthesis

• Stoichiometric Reaction
• The Mechanism

7
T-Butyl (t-Pentyl) Chloride Synthesis

• The Stoichiometric tert-Pentyl Reaction
• The Mechanism

8
T-Butyl (t-Pentyl) Chloride Synthesis

• 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

9
T-Butyl (t-Pentyl) Chloride Synthesis

• Limiting Reagent Calculations (Cont)
• 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

10
T-Butyl (t-Pentyl) Chloride Synthesis

• 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
  11
• 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

11
T-Butyl (t-Pentyl) Chloride Synthesis

• Examples
• A B ? C
• Molar ratio AB 1 1 1.0
• Moles actually used A 0.05 B
  0.12
• Molar ratio AB actually used 0.05 / 0.12
  0.42
• The ratio of AB 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 lt 0.12 then B is in excess, A is
  limiting

12
T-Butyl (t-Pentyl) Chloride Synthesis

• Examples (Cont)
• A 2B ? C
• Molar ratio AB 1 2 0.5
• Moles actually used A 0.0069 B
  0.023
• Molar ratio AB actually used 0.0069 /
  0.023 0.30
• The ratio AB 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 lt 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

13
T-Butyl (t-Pentyl) Chloride Synthesis

• Examples (Cont)
• 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) 4,4di-tert-Butyl Biphenyl can be
  expected

14
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

15
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

16
T-Butyl (t-Pentyl) Chloride Synthesis

• Elements of the Experiment (Cont)
• 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

17
T-Butyl (t-Pentyl) Chloride Synthesis

• Macro Scale Procedure
• Obtain vial of t-Butyl (or t-Pentyl) Alcohol from
  instructors 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

18
T-Butyl (t-Pentyl) Chloride Synthesis

• Macro Scale Procedure (Cont)
• 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 HCLNote 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

19
T-Butyl (t-Pentyl) Chloride Synthesis

• Macro Scale Procedure (Cont)
• 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

20
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

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T-Butyl (t-Pentyl) Chloride Synthesis

• 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

22
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

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T-Butyl (t-Pentyl) Chloride Synthesis

• 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 clearNote 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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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 instructors 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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T-Butyl (t-Pentyl) Chloride Synthesis

• Semi-Micro Scale Procedure (Cont)
• 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

26
T-Butyl (t-Pentyl) Chloride Synthesis

• Semi-Micro Scale Procedure (Cont)
• 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 funnelNote 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

27
T-Butyl (t-Pentyl) Chloride Synthesis

• Semi-Micro Scale Procedure (Cont)
• 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

28
T-Butyl (t-Pentyl) Chloride Synthesis

• Semi-Micro Scale Procedure (Cont)
• Add Anhydrous Sodium Sulfate to the crude
  product, swirling the mixture until it is
  clearNote 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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T-Butyl (t-Pentyl) Chloride Synthesis

• 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
  students own words, using short, concise
  statements in List form

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T-Butyl (t-Pentyl) Chloride Synthesis

• The Report (Cont)
• 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?