Synthesis of Tert Butyl Chloride Lab Report

7. SN1 reaction- Synthesis of t-butyl Chloride

VIDEO LINK

https://www.youtube.com/watch?v=A0XvMrPfPZE

https://www.youtube.com/watch?v=YOKFQnBaVBw

DATA

Mass of tert-butanol (g)

4.011

Mass of vial (g)

10.028

Mass of vial and product (g)

13.674

Mass of product (g)

3.646

Compound

Retention time (min)

tert-butanol

 

tert-butyl chloride

 

Product

 

Test Tube

Compound

Observations

1

water

clear, no ppt

2

tert-butyl chloride

white ppt

3

product

white ppt

GC traces.

Questions: As given in the Vernier Handout.

SN1: Synthesis of tert-Butyl Chloride

Alkyl halides can be prepared from their corresponding alcohols via an acid catalyzed substitution reaction. The mechanism of these acid catalyzed substitution reactions are labeled as SN1 (substitution, nucleophilic, unimolecular) and SN2 (substitution, nucleophilic, bimolecular). Tertiary alcohols follow the SN1 route, primary alcohols follow the SN2 route, and secondary alcohols can follow either path.

Under acidic conditions, the mechanism (Figure 1) of the SN1 reaction involves rapid protonation of the alcohol, followed by the loss of water as the rate-determining step. This generates a relatively stable carbocation which is then attacked by the halide ion to form the alkyl halide. SN1 reactions are favored by tertiary alcohols because they tend to form more stable carbocations.

Figure 1 Conversion of t-butanol into t-butyl chloride by an SN1 mechanism

The product will be verified by gas chromatography by comparing the chromatograms of the starting material, tert-butyl chloride standard, and your product. Confirmation of your product, tert-butyl chloride, can also be performed by reacting the product with a solution of silver nitrate in ethanol. The tertiary alkyl halide will react by means of an SN1 mechanism with the silver nitrate to form an insoluble silver halide. The appearance of a precipitate indicates a positive result indicating the presence of a tertiary alkyl halide.

OBJECTIVES

In this experiment, you will

Synthesize tert-butyl chloride via an SN1 reaction.

Confirm the presence of a tertiary alkyl halide using the silver nitrate test.

Verify the product by gas chromatography.

MATERIALS

Part I Synthesis of tert-Butyl Chloride

25 mL graduated cylinder

two 10 mL glass vials and caps

10 mL graduated cylinder

hydrochloric acid, concentrated

50 mL beaker

tert-butanol, reagent grade

250 mL beaker

saturated sodium bicarbonate solution

125 mL Erlenmeyer flask

saturated sodium chloride solution

separatory funnel apparatus

sodium sulfate, anhydrous

glass funnel

DI water

disposable Pasteur pipets and bulb

ice

Part II Analyze by Gas Chromatography

LabQuest or computer interface

acetone

LabQuest App or Logger Pro

tert-butanol, reagent grade

Vernier Mini GC

tert-butyl chloride

1 L glass syringe

product from Part I

Kimwipes® or paper towel

 

Part III Silver Nitrate Test for Tertiary Alkyl Halides

three 13 100 test tubes

product from Part I

test tube rack

DI water

disposable Pasteur pipets and bulb

1% ethanolic silver nitrate solution

tert-butyl chloride

 

PROCEDURE

Part I Synthesis of tert-butyl chloride

1. Obtain and wear goggles. Protect your arms and hands by wearing a long-sleeve lab coat and gloves. Conduct this reaction in a fume hood.

2. Obtain 15 mL of concentrated hydrochloric acid using a graduated cylinder and carefully transfer to a 50 mL Erlenmeyer flask. CAUTION: Handle the hydrochloric acid with care. Can cause painful burns if it comes in contact with the skin.

3. Prepare an ice water bath in a 250 mL beaker and cool the flask containing the acid.

4. Set up the reaction in a separatory funnel.

Clamp the support ring onto a ring stand, place the separatory funnel into the ring, and insert a funnel.

Carefully transfer the cooled acid to the separatory funnel.

Weigh 4.0 g of tert-butanol and transfer to the separatory funnel. Record the actual mass to the nearest 0.001 g.

5. Swirl the solution in the separatory funnel for five minutes. Note: Leave the funnel uncapped as you swirl to allow the gases to escape.

6. Cap the separatory funnel, invert it, and immediately open the stopcock to release the pressure. When venting the funnel, point the tip towards the back of the fume hood and open the stopcock to release the pressure.

7. Shake the funnel for 15 minutes. Vent occasionally to prevent pressure buildup.

8. Place the funnel in the support ring and allow the solvent and aqueous layers to separate. Leave the funnel uncapped.

9. Drain the lower aqueous layer into a 125 mL Erlenmeyer flask. Be sure to label the flask as waste.

10. Prepare to wash the solution.

  1. Wash the organic layer with 30 mL of a saturated sodium bicarbonate solution. Add the sodium bicarbonate solution slowly. Swirl the funnel several times until the bubbling has stopped.
  2. Cap the funnel, invert, shake, and immediately vent.
  3. Place the uncapped funnel in the support ring and allow the layers to separate.
  4. Drain the aqueous layer into the waste beaker.

11. Repeat Step 10 with 30 mL of a saturated sodium chloride solution.

12. Prepare to dry the product.

  1. Place a pea-sized amount of anhydrous sodium sulfate in a 10 mL vial.
  2. Transfer the organic layer into the vial and swirl until clumps form.
  3. Cap the vial and wait five minutes to allow the sodium sulfate to dry the product.

13. While waiting, weigh a clean and dry 10 mL vial. Record the mass in your data table.

14. Carefully pipet the product into the clean vial and weigh. Be careful not to transfer any of the sodium sulfate. Record the mass in your data table.

15. Cap the product and save for analysis in Part II.

Part II Analyze by Gas Chromatography

16. Prepare the Vernier Mini GC for data collection:

  1. Turn on the Mini GC and connect it to the USB port on your computer or LabQuest.
  2. Choose New from the File menu of the data collection program.
  3. To bring up the Temperature-Pressure profile, tap ► in LabQuest or click Collect in Logger Pro.
  4. Set the Temperature-Pressure values to:

Start temperature

40C

Hold time

3 min

Ramp rate

5C/min

Final temperature

45C

Hold time

1 min

Total length

5.0 min

Pressure

7.0 kPa

  1. Select Done to initiate the Mini GC warm up. Continue with Step 17 during warm up.

17. Clean and flush the syringe with acetone. Important: The glass syringe and needle are fragile. Handle with care. Never pull the plunger back more than 50% of its total volume.

18. Follow the process in Step 17 to clean and flush the syringe with tert-butanol.

19. Prepare for injection and the start of data collection.

Figure 2

word image 1198

  1. Collect 0.5 L of tert-butanol for injection.
  2. The Mini GC should now have reached the correct start temperature and pressure and the LED turned to green.
  3. Insert the needle of the syringe into the injection port as shown in Figure 2.
  4. Simultaneously, depress the syringe plunger and select Collect to begin data collection. Pull the needle out of the injection port immediately.

20. While the data collection proceeds, repeat Step 17 to thoroughly clean the syringe and needle.

21. Analyze your chromatogram to determine the retention times and record your results. Store the run.

22. Repeat the necessary steps above to inject and analyze tert-butyl chloride and your product from Part I.

23. Save the file, if desired.

24. When you have completed your final data-collection run, turn off the Mini GC.

Part III Silver Nitrate Test for Tertiary Alkyl Halides

25. Set up the reaction.

  1. Obtain three 13 100 test tubes and label 13.
  2. Pipet 10 drops of distilled water into Test Tube 1.
  3. Pipet 10 drops of tert-butyl chloride into Test Tube 2
  4. Pipet 10 drops of your product into Test Tube 3.

26. Add approximately 1 mL of the 1% ethanolic silver nitrate solution to each test tube. Swirl each test tube to mix the contents. The appearence of a white precipitate indicates the presence of a 3° halide. Record your observations in the data table. Note: Avoid getting the AgNO3 solution on your skin.

27. At the end of the experiment, discard the solutions as directed by your instructor.

DATA TABLE

Part I Synthesis of tert-butyl chloride

Mass of tert-butanol (g)

 

Mass of vial (g)

 

Mass of vial and product (g)

 

Mass of product (g)

 

Part II Analyze by Gas Chromatography

Compound

Retention time
(min)

tert-butanol

 

tert-butyl chloride

 

Product

 

Part III Silver Nitrate Test for Alkyl Halides

Test tube

Compound

Observations

1

water

 

2

tert-butyl chloride

 

3

product

 

DATA ANALYSIS

1. What is the theoretical yield of tert-butyl chloride in your synthesis? What is the percent yield?

2. Why is it necessary to conduct the reaction under acidic conditions?

3. What experimental evidence proves your product is tert-butyl chloride?

4. In the reaction observed in Part III, where is the slow step?

5. Do you expect the reaction in Part III to be faster for tert-butyl chloride or 2-chloropropane and why?

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