Question

Sketch the mechanism for the nuceophilic
substitution reaction of NaSH with 1-
bromopropane​

Answer 1

Answer:

If a halogenoalkane is heated under reflux with a solution of sodium or potassium hydroxide, the halogen is replaced by -OH and an alcohol is produced. Heating under reflux means heating with a condenser placed vertically in the flask to prevent loss of volatile substances from the mixture.

The solvent is usually a 50/50 mixture of ethanol and water, because everything will dissolve in that. The halogenoalkane is insoluble in water. If you used water alone as the solvent, the halogenoalkane and the sodium hydroxide solution wouldn't mix and the reaction could only happen where the two layers met.

For example, using 1-bromopropane as a typical primary halogenoalkane:

You could write the full equation rather than the ionic one, but it slightly obscures what's going on:

The bromine (or other halogen) in the halogenoalkane is simply replaced by an -OH group - hence a substitution reaction. In this example, propan-1-ol is formed.

The mechanism

Here is the mechanism for the reaction involving bromoethane:

This is an example of nucleophilic substitution.

Because the mechanism involves collision between two species in the slow step (in this case, the only step) of the reaction, it is known as an SN2 reaction.