Lactic acid is a chemical compound that plays a role in various biochemical processes and was first isolated in 1780 by the Swedish chemist Carl Wilhelm Scheele. Lactic acid is a carboxylic acid with the chemical formula C2H4OHCOOH. It has a hydroxyl group adjacent to the carboxyl group, making it an alpha hydroxy acid (AHA).
In solution, it can lose a proton from the carboxyl group, producing the lactate ion CH3CH(OH)COO−. Compared to acetic acid, its pKa is 1 unit less, meaning lactic acid deprotonates ten times more easily than acetic acid does. This higher acidity is the consequence of the intramolecular hydrogen bridge between the α-hydroxyl and the carboxylate group, making the latter less capable of strongly attracting its proton.