HCl is added to t-pentyl alcohol in a vial to synthesize t-pentyl chloride. t-pentyl chloride separates on top and the bottom layer is discarded. Sodium bicarbonate is then used to wash the crude t-pentyl chloride. What is the purpose of this wash and why would it be bad to wash with sodium hydroxide?
The NaHCO3 wash is to remove the excess HCl that was added initially. Would washing with NaOH reform the alcohol?
NaOH is a strong base, so it would likely act as a nucleophile and attack the halide making it undergo an elimination reaction, forming an undesired compound.
The purpose of washing the crude t-pentyl chloride with sodium bicarbonate is to neutralize any remaining traces of hydrochloric acid (HCl) that may be present in the product. This helps to remove any acidic impurities and improve the purity of the t-pentyl chloride.
Sodium bicarbonate (NaHCO3), also known as baking soda, is a weak base. When it comes into contact with an acid like HCl, it reacts to form carbon dioxide gas (CO2), water (H2O), and sodium chloride (NaCl). This reaction helps in neutralizing the acidic impurities:
2HCl + NaHCO3 -> CO2 + H2O + NaCl
On the other hand, washing with sodium hydroxide (NaOH) instead of sodium bicarbonate would not be ideal in this scenario. Sodium hydroxide is a strong base and can react with t-pentyl chloride to form an alkoxide salt. This reaction is called an elimination reaction or a dehydrohalogenation reaction and leads to the formation of alkenes:
ROH + NaOH -> RO- + Na+ + H2O
RO- -> R + H2O
In this case, using sodium hydroxide for washing the crude t-pentyl chloride could result in the unwanted formation of alkenes and thus lead to a decrease in the yield and purity of t-pentyl chloride.
Therefore, sodium bicarbonate is preferred over sodium hydroxide for washing the crude t-pentyl chloride in order to neutralize any remaining hydrochloric acid without causing undesirable side reactions.