The hydroxyl oxygen is protonated,thus creating a good leaving group. 一H H+ ROH R- OR OR :OR +HO protonated ester ester This leaves with assistance from the neighboring hydroxyl oxygen. The cation remaining is resonance stabilized,and deprotonation yields the desired ester. The overall mechanism is quite long,but both steps have been seen before(acid catalyzed addition to a carbonyl; acid catalyzed dehydration),and so should not be viewed as difficult,or as new work to learn Ch20 Carboxylic Acids (landscape) Page 20 Ch20 Carboxylic Acids (landscape) Page 20 The hydroxyl oxygen is protonated, thus creating a good leaving group. This leaves with assistance from the neighboring hydroxyl oxygen. The cation remaining is resonance stabilized, and deprotonation yields the desired ester. The overall mechanism is quite long, but both steps have been seen before (acid catalyzed addition to a carbonyl; acid catalyzed dehydration), and so should not be viewed as difficult, or as new work to learn