Question

HCl (12 M, 3.5 equiv) он CI tert-amyl alcohol tert-amyl chloride

a) After the reaction is completed, the reaction mixture is transfered to a separatory funnel. The layers are separated and the organic layer is washed with each of the following: an equal amount of saturand NaCl, satured NaHCO3, deionized H2O, and again with saturated NaCl. This is an example of a "basic" work-up. Illustrate what is being neutralized in this work up using a balanced equation. (2 Marks)

b) The base used is NaHCO3. This base can be dangerous in a liquid-liquid extraction due to the formation of CO2 (g) as a by-product. NaOH does not produce a gas by-product. Why is NaHCO3 used as the base instead of NaOH? As part of your answer illustrate what would happen if NaOH was used with a balanced equation. (2 Marks)

c) Explain, step-by-step, how you will “wash” the organic layer once with each of the following: sat NaCl, sat. NaHCO3, deionized H2O and sat NaCl. State which layer is the top and which layer is the bottom. (2 Marks)

Answer 1

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Washing with a saturated solution of NaCl helps to remove the trace amount of water present in the organic layer. This happens because a concentrated salt solution always wants to become dilute.

Second wash with NaHCO3 removes the excess amount of HCl present in the solution.

canbonic aid 2

Third wash with deionized water removes all traces of ions (acidic and basic) as it contains no minerals. Again washed with saturated NaCl makes the organic layer completely water free.

b) Sodium bicarbonate is a weak base and it can react only with strong acid. So it reacts with the excess HCl but not with the product formed.

But, NaOH is a very strong base. It react with the alkyl halide formed in the reaction substituting the chloride with hydroxide and thereby reverse the reaction.

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c) Which layer will be in the bottom and which will be on the top , it depends on the density of the organic solvent used. For instance, ethylacetate has lower density than water, so it is always the top layer, whereas chloroform or dichloromethane has higher density than water, so they are bottom layer.