Question

The reaction took place with t-pentyl alcohol and HCL to produce t-pentyl chloride. Aqueous sodium bicarbonate was used to wash the crude t-pentyl chloride (a) What was the purpose of this wash? Give equations. (b) Why would it be undesirable to wash the crude halide with aqueous sodium hydroxide?

Answer 1

The reaction between t-pentyl alcohol and HCl is an sn1 reaction to give t-pentyl chloride . the OH group is replaced by Cl.

a) During the work up, the excess HCl remaining unreacted is washed off by using a weak base like sodium bicarbonate . Sodium bicarbonate is weak base and does not produce enough OH- ions to react with the product t-pentyl chloride to give back alcohol.

b) It is not advisable to use NaOH to wash of the excess HCl, as it is a strong base and the further reaction of t-pentyl chloride occurs in the presence of aqueous NaOH to give a mixture of t-butanol and alkene(through elimnation).