Aqueous sodium bicarbonate was used to wash the crude n-butyl bromide. What was the purpose of this wash? Give equations. Why would it be undesirable to wash the crude halide with aqueous sodium hydroxide?
You have not stated how you made the butylbromide. I take it the product is in a solvent?
If you made the product using a PBr3 bromination of butyl alcohol then a small scale work up is to pour the mixture onto iced water and extract with a solvent. The aqueuos phase will become very acidic (phosphoric acid and HBr) and some of this acidity transfers to the aqueous phase. The washing with bicarbonate will then remove the acid from the aqueous phase. It will also remove traces of bromine (slight yellow colour) in the product as well. Bromine can be a by-product of the reaction.
If you use NaOH some of the butyl bromide will be converted to butyl alcohol.
Well, glad you asked! The purpose of washing the crude n-butyl bromide with aqueous sodium bicarbonate is to remove any acidic impurities. Sodium bicarbonate (NaHCO3) is a basic compound that reacts with acidic substances, converting them into water-soluble salts. Here's the balanced equation for the reaction:
n-butyl bromide + sodium bicarbonate -> sodium bromide + water + carbon dioxide
Now, why is aqueous sodium hydroxide not desirable for washing the crude halide? Well, sodium hydroxide (NaOH) is a strong base and can react with n-butyl bromide to form an alcohol and sodium bromide. However, this reaction is relatively slow and can lead to significant side reactions, such as the formation of unsaturated compounds. So, it's better to stick with sodium bicarbonate to ensure a cleaner and safer process.
The purpose of washing the crude n-butyl bromide with aqueous sodium bicarbonate is to remove any remaining acidic impurities. During the reaction to synthesize n-butyl bromide, there may be traces of acidic impurities such as hydrobromic acid (which may be present due to side reactions or incomplete conversion). By using aqueous sodium bicarbonate, any acidic impurities will react with the sodium bicarbonate to form a salt and water.
The equation for the reaction between n-butyl bromide and sodium bicarbonate is as follows:
n-C4H9Br + NaHCO3 → n-C4H9OH + NaBr + CO2
Here, n-butyl bromide reacts with sodium bicarbonate to form n-butanol (n-C4H9OH), sodium bromide (NaBr), and carbon dioxide (CO2).
It would be undesirable to wash the crude halide with aqueous sodium hydroxide (NaOH) because n-butyl bromide is an alkyl halide, and alkyl halides can react with strong bases like sodium hydroxide to undergo elimination reactions. This can result in the formation of alkenes through a mechanism called the E2 elimination. Washing with aqueous sodium hydroxide could lead to the formation of unwanted alkenes in the final product.
The purpose of washing the crude n-butyl bromide with aqueous sodium bicarbonate is to remove any acidic impurities that may be present. Sodium bicarbonate (NaHCO3) is a basic compound that can react with acidic impurities, such as leftover hydrobromic acid (HBr), to form carbon dioxide gas (CO2), water (H2O), and a salt.
The reaction equation for the reaction between NaHCO3 and HBr is as follows:
NaHCO3 + HBr -> CO2 + H2O + NaBr
By washing the crude n-butyl bromide with aqueous sodium bicarbonate, any remnants of HBr or other acidic impurities react with the sodium bicarbonate to form CO2 gas, which bubbles out of the solution, leaving behind purified n-butyl bromide.
On the other hand, washing with aqueous sodium hydroxide (NaOH) would not be desirable because it is a strong base and may react with n-butyl bromide. The reaction between NaOH and n-butyl bromide would produce sodium bromide (NaBr) and n-butanol, which is an unwanted side product. Therefore, it is preferable to use a weaker base like sodium bicarbonate to selectively remove acidic impurities without reacting with the desired n-butyl bromide.