Question

Please answer the below for SN2 reaction of 1-butanol in the presence of sulfuric acid and sodium bromide to produce 1-bromobutane and SN1 reaction of 2-methyl-2-butanol in the presence of hydrochloric acid to produce 2-chloro-2-methylbutane

1.     Explain how the amount of sample injected onto a column affects the separation of a two-component mixture in gas chromatography?

2.     What effect would each of the following have on the retention times in gas chromatography?

a.     increase the column temperature

b.     increase the flow rate of the carrier gas

c.     use a more polar column

3.A student neglected to add sulfuric acid to the reaction mixture in an SN2 reaction of 1-butanol in the presence of sulfuric acid and sodium bromide to produce 1-bromobutane.What is the expected outcome? Explain.

4.     A possible side product from the experiment is dibutyl ether. Where in the procedure is this compound removed?

5.     Explain where the alkenyl side products are removed in the experimental procedure.

Answer 1

For the Sn2 reaction of primary alvohol 1-butanol to 1-bromobutane and the Sn1 reaction of tertiary alcohol 2-methyl-2-butanol to 2-methyl-2-chlorbutane,

1. When the amount of sample injected into the column is large, we see broad peaks and peak overlap. Whereas, the peaks becomes sharp and separated from one another when small amounts of sample is injected in to the column.

2. Effect of factors on the retention times,

a. Increase in the column temperature : Increasing the column temperature would elute the components out of the column quickly without any retention or low retention on the column. therefore the retention times observed would be much low.

b. Increase in the flow rate of the carrier gas : Again the components does not get much time to separate on the column with increasing the carrier gas flow rate. The components are pushed out of the column quickly. Therefore the retention time would be decreased.

c. Use of more polar column : This would increase the retention time of more polar componentd on the column (like-like interaction). Whereas, the retention times for non-polar components would decrease.

3. The addition of sulfuric acid is to make the poor leaving group -OH to a good leaving group -OH2+. This facilitates the loss of leaving group during the Sn2 reaction. If the student neglected to add sulfuric acid in the reaction mixture, the rate of Sn2 reaction would decrease considerably as now poor leaving group does not leave easily and reaction is thus less favoured to proceed.

4. Dibutyl ether formed as a side product in the reaction is removed by distillation.

5. The E2 elimination reaction of the alcohol yields alkenyl side products which are removed from the reaction by boiling off the reaction mixture. The alkenyl side products are low boiling compounds.