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Title Experiment #4

Title: Nucleophilic Substitution: t-Pentyl Chloride

Date:

19

November

2020 Name: Sanampreet Sandhu

Lab Partner: Monica Lopez

Course: Chemistry 18A

Abstract This lab is designed to convert 2-methylbutan-2ol (t-pentyl alcohol) to 2-chloro-2methylbutane (t-pentyl chloride). Using the method of extraction, the organic and aqueous layers were separated. Furthermore, using a semi-microscale distillation method, the organic compound left was pure. This compound was analyzed using an Infrared Spectrometer, to ensure the substitution occurred. The observed boiling point of 86.2 ºC and Infrared Spectroscopy confirmed that the 2-chloro-2-methylbutane (t-pentyl chloride) was recovered with a 55.57∞ yield. Introduction An alcohol can be converted to an Alkyl Halide when reacted with hydrochloric acid (HCl) or Hydrobromic acid (HBr) using the substitution mechanism. In this experiment 2methylbutan-2ol (t-pentyl alcohol) was converted to 2-chloro-2-methylbutane (t-pentyl chloride), via an SN1 reaction. In order to usefully convert t-pentyl alcohol to t-pentyl chloride, hydrochloric acid (HCl) was used as a reactant. Furthermore, the separation of HCl from t-pentyl chloride takes place subsequently due to the difference in solubility and density. Using the extraction method, the t-pentyl chloride was separate from the rest of the mixture, giving a near pure organic compound. To ensure more purity, the t-pentyl chloride is then filtered using the

distillation apparatus and process. The Infrared Spectroscopy and boiling point are used ensure tpentyl chloride was usefully formed and extracted from the mixture. Table of Physical Properties Compound

MW g/mol

Amount (mL)

mp (ºC)

bp (ºC)

Density (g/cm3)

2-methylbutan-2-ol

88.15

2 mL

-12 ºC

102 ºC

0.81

2-chloro-2-methylbutane

106.59

N/A

-73 ºC

85 ºC

0.87

Hydrochloric acid

36.46

5 mL

-30 ºC

-85.05 ºC

1.2

Sodium bicarbonate

84.01

3 mL

50 ºC

100 ºC

2.2

Experimental An empty test tube was weighed, and the weight was recorded. Next, an automatic pipet was set to 1.0 mL, using this twice, 2.0 mL of 2-methylbutan-2-ol (t-pentyl alcohol) was placed into a test tube. The test tube was then weighed again once filled with t-pentyl alcohol and the weight was recorded. Next, approximately 5 mL of HCl was added to the test tube with the tpentyl alcohol. The test tube was then shook and agitated for roughly 2 minutes to ensure that the t-pentyl alcohol and HCl had mixed thoroughly. Following that, the test tube was set aside for approximately 15 minutes while the two layers began to separate. Once the aqueous layer separated and was seen at the bottom of the test tube, it was extracted using a pasture pipet. Two rinses with equal parts of sodium bicarbonate and water (3 mL each) were done during extraction. The solvent was then dried for approximately 20 minutes until the solution was clear and moved freely without clumps. Once left with a near pure organic compound, the distillation apparatus was assembled, and the solvent was moved into an 8 mL conical vial. After running

the distillation, the distillate was collected from 80-84 ºC and was weighed for analysis of the yield. The distillate and t-pentyl alcohol was then placed in an infrared Spectroscopy and the IR was used to confirm that the t-pentyl alcohol was converted to t-pentyl chloride successfully. Lastly, using a Thiel tube, the boiling point of the t-pentyl chloride and t-pentyl alcohol was measured Results Yield Weight of test tube =13.436 g Weight of test tube with alcohol=15.030 g Weight of test tube with solution=20.791 g Weight of alcohol=15.030 g−13.436 g=1.594 g Weight of acid=20.791 g−15.030 g=5.76 g Weight of t− pentyl chloride =1.071 g Determine Limiting Reagent t− pentyl alcohol 1.594 g x

1mol t− pentyl chloride =0.0 181 mol 88.15 g

hydrochloric acid 5 .00 mL x

1.18 g 1 mol hydrochloric acid =0.16 18 mol x 36.46 g 1 mL

Limiting Reagent t-pentyl alcohol Theoretical Yield 0.0181 mol t−pentyl alcohol x Percentage Yield

106.59 g =1.923 g 1mol t−pentyl alcohol

Percentage Yield=

actual yield x 10 0 theoretical yield

1.071 g x 100=55.57 % 1.923 g Infrared Spectroscopy Analysis The IR spectra for t-pentyl alcohol shows a strong wide peak at 3346.06 cm-1 which is related to the O-H functional group. There is also a strong intense peak at 2965. 62 cm-1 which corresponds to C-H stretching. There is no peak around 800 cm-1 which is typically seen in alkyl halides. Using these readings, it can be confirmed that the IR spectra is indeed for the t-pentyl alcohol. The IR spectra for t-pentyl chloride shows a strong intense peak at 2969.54 cm-1, which is related to the alkyl C-H stretching. Another strong intense peak is seen around 796.96, which is related to the C-Cl stretching seen in the molecule. There is no presence of an O-H stretch at 3600 cm-1, which concludes that the Cl was substituted for the O-H in an SN1 reaction mechanism. However, after distillation, impurities are removed, and the remaining compound is purer. The IR spectra for t-pentyl chloride distillate shows a strong intense peak at 2971.35 cm1, which is related to the alkyl C-H stretching. Another strong intense peak is seen around 797.86 cm-1, which is related to the C-Cl stretching seen in the molecule. There is no presence of an OH stretch at 3600 cm-1, which concludes that the Cl was substituted for the O-H in an SN1 reaction mechanism. The peaks are slightly more intense for the distillate, which shows that the distillation was successful in providing a purer form of the t-pentyl chloride.

Boiling Point Compound t-pentyl alcohol t-pentyl chloride

Trial 1 (ºC) 97.7 ºC 86.3 ºC

Trial 2 (ºC) 102.5 ºC 86.0 ºC

Average BP (ºC) 100.1 ºC 86.15 ºC

The observed boiling point of the t-pentyl chloride distillate was 86.3 ºC and 86.0 C, when compared to the scientific boiling point of 85ºC, the distillate is the pure form of t-pentyl chloride. Boiling Point Correction t-pentyl chloride

101300 pa x

760torr 1 atm x =759. 812torr 101325 pa 1 atm

760 torr−759.812 torr x 0.5 ºC=0.0094 10 torr Corrected Boiling Point=86. 2+0.0094=86.2094 ºC Post Lab Questions 1. Aqueous sodium bicarbonate was used to wash the crude t-pentyl chloride. a. What was the purpose of this wash? Give equations i. The purpose of this wash was to neutralize the trace amounts of HCl in the solution that is produced through the hydrolysis of the t-pentyl chloride. ii.

HCl + NaHCO 3 → H 2 CO 3+ NaCl

b. Why would it be undesirable to wash the crude halide with aqueous sodium hydroxide? i. This would be undesirable because hydroxide ions are considered a strong nucleophile and will react with the t-pentyl chloride in an elimination reaction, forming 2-methylbut-1-ene. Using a weaker nucleophile such as sodium bicarbonate is best for this experiment. 2. Some 2-methylbut-2-ene may be produced in the reaction as a by-product. Give a mechanism for its production

a. 3. How is unreacted t-pentyl alcohol removed in this experiment? Look up the solubility of the alcohol and the alkyl halide in water and report a. The unreacted t-pentyl alcohol is removed using the sodium bicarbonate as this neutralizes the pH, which soaks up the remaining HCl. Using equal waters of water in the wash and shaking the mixture allows the t-pentyl alcohol to mix with the water. This happens because t-pentyl alcohol is soluble in water while alkyl halides are not soluble in water. The hydrogen bonding between the t-pentyl alcohol and water allows the alcohol to become part of the aqueous layer and leaves the t-pentyl chloride in the organic layer

4. Why must the alkyl halide product be dried carefully with anhydrous sodium sulfate before the distillation? a. The alkyl halide must be dried to ensure that all of the water is removed from the mixture. This is extremely important because at high temperatures water and organic solvents form compounds and the water cannot be distilled out of the compound. Instead, under heat, the water could potentially react with the t-pentyl chloride though nucleophilic substitution, ruining the work done in the experiment. Therefore, to ensure the purest form of the compound is distilled, the compound must be thoroughly dried. 5. Show the stepwise mechanism for the synthesis of t-pentyl chloride from t-pentyl alcohol and hydrochloric acid showing the flow of electrons

a.

Data...