A nonlinear problem of hydrochemical Marangoni convection and mass transfer across the liquid-liquid interface in the presence of an interfacial chemical second-order reaction has been considered, Basic parameters for convective flows and concentration fields have been found using the finite amplitude stability method for weakly nonlinear structures. The diffusion flux of a surface-inert component across the interface under hydrochemical convection has been calculated. Correlations between the Sherwood number and Marangoni number as well as other physicochemical and regime parameters have been obtained.