Experiments 7/8: Williamson-Ether Synthesis via Refluxing & Short-Path Distillation

Question 1

see lots of questions in Lab 7 quiz Nick + Uria for diagrams

Answer 1

diagrams

Question 2

The reaction of 1-bromobutane with sodium ethoxide affords the product 1-ethoxybutane. What is the effect of doubling the concentration of both sodium ethoxide and 1-bromobutane on the rate of the reaction?

Answer 2

The rate increases by a factor of 4.

Question 3

! If 4.60 mL of 1-bromobutane are used, how many moles of 1-bromobutane are used?

sodium ethoxide: D = 0.868 g/mL and MW = 68.05 g/mol
1-bromobutane: D = 1.27 g/mL and MW = 137.02 g/mol

Answer 3

42.6 mmol

Question 4

If 10.0 mL of prepared 21% (by weight) sodium ethoxide solution is used, how many mmol of sodium ethoxide are reacted?

sodium ethoxide: D = 0.868 g/mL and MW = 68.05 g/mol
1-bromobutane: D = 1.27 g/mL and MW = 137.02 g/mol

Answer 4

26.7 mmol

Question 5

! The reaction of 1-bromobutane with sodium ethoxide affords the product 1-ethoxybutane. What is the effect of doubling the concentration of sodium ethoxide on the rate of the reaction?

Answer 5

The rate increases by a factor of 2.

Question 6

Using your knowledge of reaction mechanisms, determine which of the following statements is not true?
Good leaving groups are often weak bases with strong conjugate acids.
Equilibrium favors the products of the nucleophilic substitution when the leaving group is a stronger base than the nucleophile.

Answer 6

Equilibrium favors the products of the nucleophilic substitution when the leaving group is a stronger base than the nucleophile.

Question 7

What is the electrophile of the reaction between sodium ethoxide and 1-bromobutane?

Answer 7

1-bromobutane

Question 8

During the work up of the williamson-ether synthesis reaction, diethyl ether is washed with brine solution. What is the purpose of this wash?

Answer 8

It is to “predry” the diethyl ether. It helps remove traces of water in the ether.

Question 9

What is the reaction mechanism for the Williamson-ether synthesis reaction between sodium ethoxide and 1-bromobutane?

Answer 9

Sn2

Question 10

! Reaction rates are affected by the type of solvent that is used. Which of the following solvents is not a polar protic solvent?
CH3OH
CH3CN
CH3COOH
H2O

Answer 10

CH3CN

Question 11

During the work up of the reaction, diethyl ether is used for the extraction process. Which of the following statements is true about the extraction. (Which layer is the diethyl ether in and why?)

Answer 11

Diethyl ether will be the top layer because it is less dense than water.

Question 12

A precipitate is formed during the Williamson-ether synthesis reaction between sodium ethoxide and 1-bromobutane. What is the likely precipitate and how is it completely removed from the reaction mixture?

Answer 12

The precipitate is sodium bromide and it dissolve sin the aqueous layer during quenching and is removed during the extraction work-up.

Question 13

! Ethanol was used as the solvent and diethyl ether was used in the extraction work-up between sodium ethoxide & 1-bromobutane (Williamson-ether synthesis). If everything worked as it was supposed to, what will be distilled today? What compound will be collected as the first distillate?

Answer 13

Diethyl ether and 1-ethoxybutane will be distilled. Diethyl ether will be the first distillate.

NOT residual sodium ethoxide and 1-ethoxybutane will be distilled. 1-ethoxybutane will be the first distillate.

Question 14

! When is it appropriate to use a short path distillation set-up and how does a short path distillation differ from a simple distillation set-up?

Answer 14

A short path distillation can be done when the liquids have very different boiling points and it differs in that there is no condenser used in a short path distillation.

Question 15

! A reflux condenser was used during the reaction. What was the purpose of using a reflux condenser?

Answer 15

to prevent the ethanol solvent from boiling off

NOT to provide a larger surface area on which the reaction would occur

Question 16

! Which of the following situations would contribute to a lower yield of product?

Answer 16

Both a & c would both contribute to a lower yield

a — sodium ethoxide solution reacts with water in the air or solvents, instead of 1-bromobutane

Question 17

see Q5 of Lab Quiz 8

In the molecule of 1-ethoxybutane, which proton will be the most downfield in the 1H NMR?

Answer 17

hydrogen right next to the O on the ethyl substitutent

Question 18

What was the purpose of adding brine to the ether layer as a final wash in the last step of the extraction work up?

Answer 18

to remove any residual water in the ether layer, further drying the organic layer

Question 19

! The first step in the work-up was to add both water and ether to the reaction mixture of sodium ethoxide & 1-bromobutane, then to transfer the mixture to a separatory funnel, and then to drain off the aqueous layer. Which of the following species were in the water layer?

Answer 19

residual sodium ethoxide, sodium ions & bromide ions

NOT sodium ions & bromide ions only

Question 20

What is the purpose of performing NMR spectroscopy on the product of the Williamson ether synthesis?

Answer 20

all of the above

Question 21

! For the Williamson ether synthesis, 25 mL of 21% (by weight) sodium ethoxide solution is used. The density of the solution is 0.868 g/mL and the molar mass of sodium ethoxide is 68.05 g/mol. How many moles of sodium ethoxide were used?

Answer 21

67 mmols NOT 320 mmols

Question 22

The first step in the work up was to add both water and ether to the reaction mixture, to transfer the mixture to a separatory funnel, and then to drain off the aqueous layer. Which of the following species were in the organic layer? Consider the possibility that the reaction did not go to completion.

Answer 22

1-bromobutane & 1-ethoxybutane

Question 23

What was the purpose of adding brine to the ether layer as a final wash in the last step of the extraction work up?

Answer 23

to remove any residual water in the ether layer, further drying the organic layer

Question 24

A reflux condenser was used during the reaction. What was the purpose of using a reflux condenser?

Answer 24

to prevent the ethanol solvent from boiling off

Question 25

! Why are deuterated solvents used in NMR spectroscopy?!

Answer 25

deuterated solvents do not contain protons so they do not have an NMR signal that could interfere with your compound’s NMR signal

Question 26

What is the nucleophile in the Williamson ether synthesis involving sodium ethoxide and 1-bromobutane?

Answer 26

(sodium) ethoxide