Lab #5: Synthesis of t-Butyl Chloride
By: Lisa
Wu (Science Engagement, Supervisor Jenna Lech)
Before the lab:
· Write down the MSDS for the following chemicals: concentrated hydrochloric acid, methylpropene, t-butanol, t-butyl chloride, sodium bicarbonate, carbon dioxide gas, anhydrous calcium chloride, silver nitrate, silver chloride, nitric acid, ethanol
· It is a good idea to watch the potter videos on extraction and know the SN1 mechanism in this reaction for BOTH the synthesis of t-butyl chloride as well as the silver nitrate test for 3̊ alkyl halide and tap water
· Study the refractive index in the lab manual’s appendix section to know how to use a refractometer
Purpose: To convert tertiary alcohol, t-butanol, into an alkyl halide by reacting it with hydrochloric acid. To test the presence of the tertiary alkyl halide using the silver nitrate test.
Theory:
Substitution reactions are usually favoured under cool conditions and reactant reactivity of 3̊ > 2̊ > 1̊. In this experiment, the tertiary alcohol, butanol, acts as the nucleophile which attacks the proton of hydrochloric acid to form a very stable tertiary carbocation and water. Here, the reaction can go two ways: one, the addition of the chlorine atom can form the t-butyl chloride; and two, methylpropene side-product can form under heat and basic conditions. The purpose of this lab is to obtain the substitution product so the elimination conditions are minimized as much as possible by using cool hydrochloric acid and maintaining cool temperatures in reactions. Fortunately, methylpropene will evaporate from the reaction mixture as a gas under reaction conditions.
Using
extraction or the partitioning of chemicals between different solvents, t-butyl
chloride, an organic layer, can be easily isolated the aqueous water/HCl layer
since it is less dense than water and it will “float” on top of the aqueous
layer. The common instrument used for extraction is the separatory funnel, as
shown on the right. The silver nitrate test is used to confirm the presence of
t-butyl chloride due to its rapid reaction with silver nitrate via SN1
mechanism to produce a whitish precipitate, silver chloride.
Flowchart:
1. Obtain 13mL or 15.5g of conc. 12M HCl (aq) in a graduated cylinder and transfer to stoppered 25mL Erlenmeyer flask.
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NOTE:
Conc. HCl is extremely corrosive, use ONLY in the fumehood. Wash any spills
immediately with cold water, and neutralize with dilute sodium bicarbonate.
2. Cool solution in ice bath 5-8 degrees Celsius in fumehood.
3. Transfer acid to 250mL separatory funnel placed on a ring clamp attached to retort stand.
4. Add 5mL sample of t-butanol into unstoppered funnel. Swirl for 5 min.
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NOTE: Methylpropene
gas may be produced. It is highly flammable so no heat allowed!
5. Cloudy aqueous phase and separation of layers should be observed.
6. Shake the funnel with frequent venting to complete reaction in 20 min.
7. Drain the aqueous layer into waste beaker.
8. Wash organic layer with 10mL of cold water, then 10mL of cold 10% sodium bicarbonate with careful, frequent venting.
9. Test alkaline layer with litmus: red litmus turns blue means acidic and reaction can be continued. If blue litmus turns red (basic conditions), then another alkaline wash is required.
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NOTE: The
litmus test is to identify any trace protons left in the organic layer to
minimize production of the elimination reaction.
10. Final wash with cold water should be neutral to litmus. If not, repeat.
11. Pour t-butyl chloride layer into clean, dry 50mL Erlenmeyer flask.
12. Add anhydrous calcium chloride to cover bottom of flask, stopper flask, and swirl until a clump forms at the bottom of the flask.
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NOTE:
This was done to solidify your product immediately after extraction due to
prevent any reversible reaction from products to reactants at RT
13. Decant the excess liquid. Repeat the drying procedure; let reaction to stand stoppered 15min.
14. Decant the dry product into clean, dry, tared 25mL Erlenmeyer flask, stopper the flask and take the mass, and refractive index of the product quickly before evaporated.
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NOTE: It
is a good idea to “weigh by difference” in this case where the stopper and the
flask must be weighed before the product is obtained.
15. For silver nitrate test, place few drops of product in a small test tube to compare with same volume of water in second test tube. 2 drops of silver nitrate solution was added to both, and mix. Presence of white precipitate indicates presence of 3̊ halide. Tap water with chlorine will show cloudiness or precipitate. Dispose waste into waste beaker.
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NOTE:
Describe the differences in the results on the data sheet.
16. Submit completed data sheet and sample.
Reference: Picture of Separatory Funnel. Obtained
Background.
Obtained
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