Protonation is the addition of a proton to an atom, molecule, or ion. Protonation is different from hydrogenation in that during protonation a change in charge of the protonated species occurs, while the charge is unaffected during hydrogenation.
Protonation occurs in many catalytic reactions. Both protonation and deprotonation occur in most acid-base reaction. When a species is either protonated or depronated, its mass and charge change, plus its chemical properties are altered. For example, protonation may change the optical properties, hydrophobicity, or reactivity of a substance. Protonation is usually a reversible chemical reaction.
- An example is the formation of the ammonium group where NH4+ is formed by protonation of ammonia NH3
- Water may be protonated by sulfuric acid:
H2SO4 + H2O ⇌ H3O+ + HSO-4