<p>This <?tk 2?> paper the mass and thermal transfer in a system of infinite vertically parallel plates under the influence of a first order chemical reaction has been investigated. This study provides a novel contribution by integrating Casson fluid dynamics, MHD effects, and chemical reaction mechanisms within a multifluid framework, offering new theoretical and practical insights into complex fluid systems. By using regular perturbation techniques, we solve the nonlinear coupled mathematical model, applying appropriate restrictions. The purpose of this study is to investigate how Casson fluid, a non-Newtonian fluid model, behaves when subjected to magnetic fields and interacts with other immiscible fluids (Pattnaik et al. in Math. Problems Eng. 2022:2227811, 2022. 10.1155/2022/2227811). The incompressible fluids, is assumed, fluid have different viscosities and thermal conductivities, and their transport properties are considered constant. We match the separate solutions using appropriate matching conditions. The study analysis explores how various parameters affect heat and mass transfer, presenting the results graphically. We found that both the thermal &amp; the mass Grashof numbers increase the flow. Regardless of the presence of a first-order chemical reaction. While viscous dissipation, viscosity, width and conductivity ratio promote the flow, the first-order chemical reaction parameter tends to suppress it in both regions. Effect of thermal expansion and concentration expansion enhances the fluid molecules as a results flow increases, Due to presence of Lorentz effect by the variation of Hartmann number flow decreases as like chemical reaction parameter effect (Tinker et al. in Proceed. Inst. Mech. Eng., Part N: J Nanomater., Nanoeng. Nanosyst. 236:19–30, 2022).</p>