Large eddy simulation is used to investigate the reactive scalar transport in a confined jet reactor at high Reynolds and Schmidt numbers. Numerical simulations are performed for a fast neutralization reaction of acid and base supported by experimental data. Based on detailed planar laser-induced fluorescence measurements, a simple conditional micromixing model for infinitely fast chemistry is developed and successfully applied to the jet mixer configuration. Results obtained for the reactive scalar transport are in excellent agreement with measurements, whereas established micromixing approaches based on the eddy dissipation model, multi environment model, and presumed probability density function with infinetly fast chemistry models indicate discrepancies in the determination of micromixing rate and product concentration.