Question

How does sulfuric acid catalyze the preparation of esters?

Answer 1

Because it is very hygroscopic.

Explanation:

It litterally tears out `H_2O` combinations out of substances that do not even contain water, as long as it contains `H`'s and `O`'s. That's why sulfuric acid is so dangerous, as it rips away these `H`'s and `O`'s from all organic material, like skin...
As you might know, esterization is the combination of a alkanoic acid (`R_1-COOH`) with an alcohol (`R_2-OH`), where the `R`'s are the stuff that's attached to it.

It goes like this:

`R_1-COOH+R_2-OHrightleftharpoonsR_1-COO-R_2+H_2O`

This is an equilibrium reaction. If you remove one of the reaction products (in this case water) the reaction will shift to the right.

Note: in this view, sulfuric acid is not really a catalyst, because it changes (becomes more diluted) in the process.