The reaction between methyl salicylate and sodium hydroxide is a saponification reaction, which is a type of chemical reaction that occurs when an ester reacts with a base to form an alcohol and a salt. In this case, methyl salicylate, which is an ester, reacts with sodium hydroxide, which is a base, to form methanol, which is an alcohol, and sodium salicylate, which is a salt.

The overall reaction can be represented by the following equation:

C7H6O3CH3 + NaOH → CH3OH + C7H5O3Na

The reaction proceeds through a nucleophilic substitution mechanism, in which the hydroxide ion from sodium hydroxide attacks the carbonyl carbon of methyl salicylate, breaking the ester bond and forming a tetrahedral intermediate. This intermediate then collapses, expelling methanol and forming sodium salicylate.

Saponification reactions are commonly used in the production of soap, as they can be used to convert fats and oils, which are esters, into soap, which is a salt of a fatty acid.