Understanding Alcohol as a Solvent in Halogenoalkane Reactions

[Kyoma]

Homework Statement

When a halogenoalkane reacts with aqueous sodium hydroxide under reflux conditions, an alcohol is formed.

However, when the same halogenoalkane reacts with ALCOHOLIC sodium hydroxide under reflux, an alkene is formed (It is an elimination reaction).

Now, the problem is why does a change in solvent result in different products being formed?

2. The attempt at a solution
Alcohol is a non-polar solvent while water is a polar solvent. But how does that reason link to the question asked?

 

[nate808]

it is important to understand the properties of different solvents and how they can affect chemical reactions. In this case, the change in solvent is resulting in different products being formed because of the solvents' ability to stabilize different reaction intermediates.

In the first scenario, where aqueous sodium hydroxide is used as the solvent, the polar nature of water allows for the formation of a stable intermediate, known as an oxonium ion. This intermediate can then undergo a nucleophilic substitution reaction, resulting in the formation of an alcohol.

However, in the second scenario, where alcoholic sodium hydroxide is used as the solvent, the non-polar nature of the alcohol does not allow for the formation of the oxonium ion intermediate. Instead, the reaction proceeds through an elimination mechanism, where a hydrogen atom is removed from the halogenoalkane, resulting in the formation of an alkene.

This difference in reaction mechanism is due to the different stabilizing effects of the solvents on the reaction intermediates. In general, polar solvents tend to stabilize charged intermediates, while non-polar solvents tend to stabilize neutral intermediates.

It is also worth noting that the strength of the base (in this case, sodium hydroxide) can also play a role in determining the reaction mechanism. A stronger base will favor elimination reactions, while a weaker base will favor substitution reactions.

In conclusion, the change in solvent results in different products being formed due to the different stabilizing effects on the reaction intermediates. Understanding the properties of different solvents is crucial in predicting and controlling the outcome of chemical reactions.