Catalytic Kinetics and Thermodynamics of Galactose Isomerization to Tagatose With a Homogeneous Triethylamine Catalyst

ABSTRACT Catalytic isomerization of galactose to produce tagatose has garnered significant attention due to the pressing need for low‐calorie sweeteners. However, there is no detailed kinetic or thermodynamic framework describing the catalytic isomerization of galactose to tagatose. To fill the gap, this study demonstrates a reversible galactose–tagatose–talose network, as parallel irreversible degradation was modeled and experimentally validated across 40–100°C with triethylamine (Et 3 N) as a homogenous base catalyst in aqueous solution. Time‐resolved concentration profiles were accurately fitted by a pseudo–first‐order model, yielding activation energies ( E a ) of 50.6 kJ mol −1 for galactose to tagatose and 73.1 kJ mol −1 for tagatose to talose, respectively. The corresponding equilibrium constants ( K ( galactose to tagatose ) = 0.6–0.99, K ( tagatose to talose ) = 0.04–0.25) increased with reaction temperature, consistent with an endothermic and entropy‐driven reaction. Thermodynamic analysis gave the standard enthalpy changes () of 7.9 kJ mol −1 and the standard entropy changes () of 21 J mol −1 K −1 for the galactose to tagatose reaction equilibrium. Although isomerization towards tagatose accelerated with reaction temperature, degradation became increasingly competitive as k ( galactose to byproducts ) rose from 2.78 × 10 −5 min −1 (40°C) to 2.02 × 10 −4 min −1 (100°C), resulting in declining tagatose selectivity at extended times.