Lab Report: Synthesis of Tert-Butyl Chloride

Categories: Chemistry

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Abstract

The objective of this laboratory experiment was to synthesize tert-butyl chloride from tert-butyl alcohol and to understand the SN1 and SN2 mechanisms involved in the reaction. The yield percentage of tert-butyl chloride was determined. The experiment successfully produced tert-butyl chloride, and the actual yield was found to be 13.23% of the theoretical yield, resulting in a percentage error of 86.78%. Qualitative chemical tests for reactivity were also performed on the synthesized product.

Introduction

Alkyl halides are compounds that have a halogen atom bonded to a saturated, sp3 hybridized carbon atom, and they can be classified based on the number of alkyl groups attached to the carbon bonded to the halogen.

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The synthesis of alkyl halides can be achieved through various mechanisms, including nucleophilic substitution. In this experiment, tert-butyl alcohol reacts with concentrated hydrochloric acid (HCl) to produce tert-butyl chloride via an SN1 reaction.

The SN1 reaction involves the formation of a carbocation intermediate and is favored by tertiary alcohols. The reaction can be represented as follows:

tert-butyl alcohol (R3COH) + HCl → tert-butyl chloride (R3CCl) + H2O

This experiment aims to synthesize tert-butyl chloride, understand the mechanisms involved in the reaction, and determine the yield percentage of tert-butyl chloride.

Methodology

Synthesis of Tert-Butyl Chloride

The following materials and chemicals were used for the experiment: tert-butyl alcohol, concentrated hydrochloric acid (HCl), separatory funnel, sodium bicarbonate solution, anhydrous calcium chloride, vial container, 250mL Erlenmeyer flask, 50mL flask, 50mL beaker, and qualitative chemical reagents (potassium iodide solution and silver nitrate solution).

The synthesis of tert-butyl chloride was performed as follows:

5mL of tert-butyl alcohol and 15mL of concentrated HCl were placed in a 125mL separatory funnel.
The mixture was gently swirled without shaking, and internal pressure was relieved by slowly opening the stopcock.
The separatory funnel was placed on a ring stand to allow the two layers to separate.
The lower aqueous layer was drained into a 250mL Erlenmeyer flask.
40mL of saturated sodium bicarbonate solution was added to the remaining organic layer in the funnel, and the previous steps were repeated.
The organic layer was transferred into a dry 50mL flask with a small amount of anhydrous calcium chloride to remove water droplets.
The liquid was decanted into a preweighed 50mL beaker, and the crude product (tert-butyl chloride) was weighed.

Qualitative Chemical Tests for Reactivity

Qualitative chemical tests were performed on both tert-butyl chloride and chlorobenzene as follows:

Four test tubes were labeled properly.
2-5 drops of synthesized tert-butyl chloride were added to two test tubes, and 2-5 drops of chlorobenzene were added to the other two test tubes.
One test tube of each compound received 1mL of potassium iodide solution, and the other two test tubes received 1mL of silver nitrate solution.
The stoppers were placed in the test tubes, and the contents were vigorously shaken.
The time it took for any precipitation to form was noted, and the differences in the results were recorded.

Data and Discussion

Data 1.1. A. Synthesis of Tert-Butyl Chloride

Chemical	Weight (g)	Molecular Weight (g/mol)	Volume (mL)	% Yield
Hydrochloric acid (HCl)	17.7	36.458	15	13.23%
Tert-butyl alcohol	3.904	74.12	5
Tert-butyl chloride (Crude Product)	0.64	92.562

Data 1.1. B. Sample Computation

Weight of the vial container = 13.65g
Weight of the crude product + vial = 14.29g
Weight of the crude product = 0.64g
Theoretical Yield = 4.8391g
Actual Yield = 0.64g
Percentage Yield = (Actual Yield / Theoretical Yield) * 100 = (0.64g / 4.8391g) * 100 ≈ 13.23%
Percentage Error = ((Theoretical Yield - Actual Yield) / Theoretical Yield) * 100 = ((4.8391g - 0.64g) / 4.8391g) * 100 ≈ 86.78%

Data 1.1. C. Chemical Reactions

The chemical reactions involved in the experiment are as follows:

t-butyl alcohol (R3COH) + HCl → t-butyl chloride (R3CCl) + H2O
NaHCO3 (aq) + HCl (aq CO2 (g)) → NaCl (aq) + H2O (l) + CO2 (g)

Qualitative Chemical Tests for Reactivity

The results of the qualitative chemical tests for reactivity are as follows:

Reagent	Reactivity	Time (seconds)
t-butyl chloride + KI	No ppt. formed, clear solution	------------
Chlorobenzene + KI	Bubbles formed	------------
t-butyl chloride + AgNO3	White ppt. formed	Right after AgNO3 was added = 0.8 s
Chlorobenzene + AgNO3	No ppt. formed	-----------

Questions

Write the complete step-wise mechanism for the reaction of t-butyl alcohol with concentrated hydrochloric acid.

The step-wise mechanism for the reaction of t-butyl alcohol with concentrated hydrochloric acid involves the following steps:

Protonation of the alcohol oxygen to form a t-butyloxonium ion.
Heterolytic cleavage of the carbon-oxygen bond to form a carbocation and a leaving group of water.
Attack of the chloride ion (Cl-) on the carbocation to form tert-butyl chloride.

What is the purpose of sodium bicarbonate solution and anhydrous calcium chloride?

Sodium bicarbonate solution is used to neutralize the acidic medium created by the addition of concentrated hydrochloric acid. It acts as a neutralizing agent and helps in removing excess acid.

Anhydrous calcium chloride is used as a drying agent to remove any remaining water droplets from the organic layer. It prevents water contamination in the final product.

What is the limiting reagent in this experiment?

The limiting reagent in this experiment is tert-butyl alcohol.

Give two observations for this experiment.

Observations for this experiment include:

On the addition of silver nitrate (AgNO3) solution, tert-butyl chloride resulted in a white precipitate forming rapidly, indicating the presence of a tertiary alkyl halide.
Chlorobenzene formed a clear solution with bubbles at the bottom when reacted with potassium iodide (KI) solution.

Explain the results of the calculated percentage yield and percentage error.

The calculated percentage yield of 13.23% indicates that the actual yield of tert-butyl chloride obtained in the experiment was 13.23% of the theoretical yield, which is 4.8391g. The low percentage yield suggests that the reaction did not produce the expected amount of product.

The percentage error of 86.78% represents the deviation of the actual yield from the theoretical yield. A high percentage error indicates that there was a significant difference between the expected and actual results, possibly due to experimental errors or incomplete reactions.

Conclusion

In this laboratory experiment, tert-butyl chloride was successfully synthesized from tert-butyl alcohol through a nucleophilic substitution (SN1) reaction with concentrated hydrochloric acid. The actual yield of tert-butyl chloride was determined to be 13.23% of the theoretical yield, resulting in a percentage error of 86.78%. Qualitative chemical tests for reactivity confirmed the presence of a tertiary alkyl halide in the synthesized product. Despite the lower than expected yield, the experiment provided valuable insights into alkyl halide synthesis and reaction mechanisms.

Recommendations

For future experiments, it is recommended to carefully monitor reaction conditions to improve yield and minimize errors. Additionally, precise measurements and thorough drying of organic layers can lead to more accurate results. Further investigation into reaction mechanisms and reactivity tests can enhance understanding and analysis of synthesized products.

References

Addison, Ault. Techniques and Experiments for Organic Chemistry 4th ed. USA: Allyn and Bacon Inc., 1983.
Basic Organic Chemistry Laboratory Manual, Institute of Chemistry, College of Arts and Sciences. University of the Philippines Los Baños. 2004.
Organic Chemistry Laboratory Manual. Institute of Chemistry. University of the Philippines Diliman. 2008.
McMurry, J. Simanek, E. Fundamentals of Organic Chemistry 5th edition. Thomson Brooks Cole. 2000.