protontransferreaction

Proton transfer reaction refers to a chemical process in which a proton (H+) is transferred from a donor species, typically an acid, to an acceptor base. It is a central concept in Brønsted–Lowry acid–base theory, and its feasibility is governed by the relative acid strengths of the conjugate acids involved, commonly described by pKa values in the reaction solvent.

In aqueous solution, proton transfer reactions can be exemplified by HCl reacting with water to form Cl− and hydronium: HCl + H2O → Cl− + H3O+. More generally, a proton moves from an acid AH to a base B when AH is a stronger acid than BH, yielding A− and BH+. The choice of solvent greatly influences both the thermodynamics and the kinetics of the transfer.

Kinetics are affected by solvent structure and hydrogen-bonding networks. In water, protons can move rapidly via the Grotthuss mechanism, effectively relaying a proton through successive hydrogen bonds. In nonaqueous media, transfers can be slower and more dependent on direct encounters between donor and acceptor or on solvation dynamics.

Proton transfer reactions are fundamental to many processes, including enzyme catalysis, metabolic pathways, and acid–base neutralization. They also play a key role in proton transport chains across membranes and in buffering systems that maintain pH. In analytical chemistry, proton-transfer reaction mass spectrometry (PTR-MS) uses hydronium ions to protonate volatile analytes, enabling their detection by mass spectrometry. Related concepts include proton-coupled electron transfer and various forms of acid–base catalysis.