Preparation and SN1 Reactivity of 2-Bromobutane

Introduction
The overall goal of this experiment is to understand and be familiar with SN1 reactivity. We also learned how to prepare 2-Bromobutane by learning how to distill and extract this product from its organic layer. Finally, another goal was to specifically understand the relative reactivity of alkyl halides under SN1 conditions by reacting the alkyl halide and silver nitrate in ethanol.
Results and Discussion

The Overall Reaction
The proposed mechanism experimental procedure to prepare the 2-Bromobutane you must fill a 100 mL round bottom flask with 20 mL of 12M sulfuric acid and 7. 4 mL of 2-butanol. Then add 8. 0 g of ammonium bromide along with a magnetic stir bar. Then attach the flask to the apparatus, which is mounted on a Thermowell over a stirrer and a condenser attached to it, along with the thermometer in the flask. Then the mixture was heated at 90oC then kept at the range of 90oC-100oC for 30 minutes.
When that is completed add 20 mL of water into the flask to perform a simple distillation to collect the distillate in a graduated cylinder, keep doing this until there is no more 2-Bromobutane collected. Use a Pasteur pipette to draw off the organic layer to another container. Add the potassium carbonate to allow the liquid to dry by swirling it. Once this is completed the reactivity of alkyl halides under SN1 conditions was tested. Adding two drops of our product and the other different compounds into different test tubes along with 1mL of ethanolic silver nitrate reagent.
We are comparing these by seeing how they react and if there is no reaction after 5 minutes we will place the test tubes in a beaker of water that is heated at a temperature of 70oC-80oC and observe what happens.
Experimental Stoichiometry

Compound
Molecular Weight
Quantity
Moles

2-Butanol
74. 122 g/mol
7. 41 mL (6. 01 g)
0. 081

Sulfuric Acid
98. 079 g/mol
20. 1 mL
0. 242

Ammonium Bromide
97. 94 g/mol
8. 02 g
0. 082

The limiting reagent is the 2-Butanol.
Yield Data

Product Name
2-Bromobutane

Molecular Weight
137. 02 g/mol

Boiling Point Range
89°C-91°C

Theoretical Yield (Moles)
0. 081 moles

Theoretical Yield (grams)
11. 09 grams

Actual Yield (grams)
6. 84 grams

Actual Yield (moles)
0. 05 moles

Percent Yield
62%

NMR Table Signal

*
Chemical Shift (ppm)
Multiplicity
Integration

A
4. 1 ppm
Sextet
1

B
1. 85 ppm
Pentet
2

C
1. 7 ppm
Doublet
3

D
1. 05 ppm
Triplet
3

Reactivity of Alkyl Halides

Compound
Room Temperature
Heating

1-Bromobutane
After 30 seconds, the mixture was a cloudy whitish color but no precipitate formed
After 5 minutes, it changed into a yellow color with precipitate formed.

2-Bromobutane
After 30 seconds, the mixture was a light yellowish color and a precipitate formed instantly.
Not Heated

2-Bromo-2-methylpropane
After 30 seconds, the mixture was yellow and a precipitate formed instantly.
Not Heated

Compound
Room Temperature
Heating

1-Chlorobutane
After 30 seconds, the mixture was clear.
After 5 minutes, the color changed slightly to white and lightly cloudy.

2-Bromobutane
After 30 seconds, the mixture was a white cloudy color and formed a precipitate instantly.
Not Heated

2-Iodobutane
After 30 seconds, the mixture was yellow and precipitated instantly.
Not Heated

Conclusion
In conclusion, the SN1 reaction of 2-Bromobutane was performed. According to the Yield Data table, when the actual yield and theoretical yield are calculated we can get the percent yield, which was 62%. At least this number was higher than 50%; I can understand how this could have happened. When I was drying the reagent with potassium carbonate, prior to that I had put the other pellets, which were calcium chloride on accident.
This probably affected my percent yield also with the fact that the temperature was not well maintained it kept fluctuating under 90OC. According to the reactivity of alkyl halides, the results of these tables can conclude the theories of the conditions of SN1 reactions. The first table states that the tertiary carbocation is more stable which allows this reaction to perform faster than second and primary structured carbocations. Then the second table can conclude that iodine is the best leaving group because it is a much weaker base than the bromide ion and chloride ion causing it to react faster.