So we did a preparation of t-pentyl Chloride experiment in class the other day using t-pentyl alcohol, HCL, Aqueous sodium Bicarbonate, and calcium chloride as the drying agent.
Little confused on a few of these questions
Aqueous sodium bicarbonate was used to wash the crude t-pentyl chloride, what was the purpose of this wash (show reactions) and why would it be undesirable to was with aqueous sodium hydroxide instead?
NaHCO3 is used to get rid of the excess HCl used in the experiment.
You don't use NaOH because t-pentyl chloride + NaOH ==> the alcohol so you undo what you've done.
The purpose of washing the crude t-pentyl chloride with aqueous sodium bicarbonate is to neutralize any acidic impurities present in the solution. The reaction that occurs during this wash is as follows:
t-Pentyl chloride (acidic impurity) + Sodium bicarbonate (base) → t-Pentyl chloride + Sodium chloride + Carbon dioxide + Water
By adding aqueous sodium bicarbonate, any remaining hydrochloric acid (HCl), which is a byproduct of the reaction between t-pentyl alcohol and HCl, will react with sodium bicarbonate to form carbon dioxide gas, water, sodium chloride, and the desired t-pentyl chloride.
It would be undesirable to wash with aqueous sodium hydroxide (NaOH) instead of sodium bicarbonate for a couple of reasons. Firstly, the presence of hydroxide ions from sodium hydroxide can cause the t-pentyl chloride to undergo an elimination reaction, leading to the formation of alkene products. This is known as the E2 (elimination, bimolecular) reaction. Secondly, sodium hydroxide is a strong base, and it can react with the t-pentyl chloride to form undesirable side products. Therefore, sodium bicarbonate is preferred as it is a weaker base and does not promote elimination reactions or unwanted side reactions.
The purpose of washing the crude t-pentyl chloride with aqueous sodium bicarbonate is to remove any remaining traces of hydrochloric acid (HCl) and neutralize any acidic impurities. Here's the reaction that occurs:
t-pentyl chloride + sodium bicarbonate (aqueous) → t-pentyl chloride + carbon dioxide + water
The sodium bicarbonate (NaHCO3) reacts with the remaining HCl in the crude t-pentyl chloride to form carbon dioxide (CO2), water (H2O), and sodium chloride (NaCl). This reaction helps remove acidic impurities.
Now, let's address the second part of your question. Why would it be undesirable to wash with aqueous sodium hydroxide instead? Well, sodium hydroxide (NaOH) is a strong base, and using it to wash the crude t-pentyl chloride would result in a different reaction:
t-pentyl chloride + sodium hydroxide (aqueous) → t-pentyl chloride + water + sodium chloride
In this case, the sodium hydroxide would simply neutralize any residual acid, but it won't remove it. Additionally, using a strong base like sodium hydroxide can lead to the formation of unwanted by-products or side reactions.
So, in summary, using aqueous sodium bicarbonate is preferred for washing the crude t-pentyl chloride because it not only neutralizes any remaining HCl but also removes acidic impurities more effectively.