Write down the reaction equations for the formation of simple and complex esters

Write down the reaction equations for the formation of simple and complex esters in the interaction of β-hydroxybutyric acid with methyl alcohol.

Explanation of the solution:
1st reaction – obtaining an ester by reacting β-hydroxybutyric acid with methyl alcohol. In this case, the esterification reaction takes place with the participation of the carboxyl group of β-hydroxybutyric acid.
2nd reaction – the reaction of formation of a simple ester of β-hydroxybutyric acid with methyl alcohol, by reacting the hydroxo group of β-hydroxybutyric acid with the hydroxo group of methyl alcohol, followed by the elimination of a water molecule.