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T-Butyl (t- Pentyl ) Chloride Synthesis

T-Butyl (t- Pentyl ) Chloride Synthesis. Synthesize t-Butyl (or t-Pentyl) Chloride Note: This experiment may utilize either t-Butyl Alcohol ( m.p . 25.7 o C) or t- Pentyl Alcohol ( m.p . -9.5 o C) as one of the starting reactants Text References

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T-Butyl (t- Pentyl ) Chloride Synthesis

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  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 • 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

  3. T-Butyl (t-Pentyl) Chloride Synthesis • 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

  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

  5. T-Butyl (t-Pentyl) Chloride Synthesis 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 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 Conc HCl Molecular Wgt - 36.47 g/mole Molarity - 12.0 moles/L Density - 1.18 g/mL % Acid - 37.3

  6. 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 (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

  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 1:1 • If the ratio of moles of Alcohol to moles of HCl actually usedis 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 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

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

  13. 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” • 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

  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 (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

  17. 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 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 (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 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 (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

  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

  21. 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

  23. 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

  24. 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

  25. 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

  26. 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 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 (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 NaHCO3Note: 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 (Con’t): • 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

  29. 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 student’s own words, using short, concise statements in “List” form

  30. 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? • What experimental results did you obtain to verify that the reaction produced the desired product?

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