This work presents numerical simulations of a turbulent piloted jet diffusion flame at two Reynolds numbers. Methane partially premixed with air (25% vol. CH4, 75% vol. air) serves as fuel. The focus is on the investigation of different chemical reaction mechanisms using the Monte Carlo PDF method. This approach has proven to be suitable for the representation of finite-rate chemistry. Hence, a conventionally reduced four step mechanism and a description via two-dimensional manifolds are used as chemical mechanisms. Turbulence is modeled with an eddy-viscosity model. Results shown as first and second moments of velocity are compared with LDV measurements. Species concentrations are compared to data obtained from Raman/Rayleigh/LIF spectroscopy. Even for the flame being close to extinction at high Reynolds number a stable solution can be obtained and the essential features of the flame are well reproduced. The major species and temperature are well predicted whereas the minor species like CO require a more complex chemistry as given by the four step mechanism.