Montmorillonite was employed as a heterogeneous catalyst in the condensation of o-tert-butylaniline with paraformaldehyde for its significant confinement effect on the selective synthesis of 4,4'-diamino3,3'-dibutyl-diphenyl methane (4,4'-MBTBA). Due to the appropriate d-spacing which is larger than the molecular size of 4,4'-MBTBA but smaller than that of 4,4'-(4-amino-5-tert-buty1-1,3-phenylene) bis(methylene)bis(2-tert-butylaniline) (PBMBA), montmorillonite favored the production of 4,4'-MBTBA, comparing with HY, P/SBA-15 and PW/C catalysts. In addition, with the decrease of the d-spacing of montmorillonite, the formation of PBMBA was inhibited and the selectivity of 4,4'-MBTBA became more and more remarkable, which verified the confinement effect as a tool for selectivity orientation on the heterogeneous synthesis of 4,4'-MBTBA over montmorillonite catalysts. When paraformaldehyde was used as starting material and the ratio of o-tert-butylaniline to paraformaldehyde was as low as 4:1, the yield of 4,4'-MBTBA reached 83.9% with butyl acetate as solvent, reaction temperature of 130 degrees C and catalyst loading of 0.18g. (C) 2010 Elsevier B.V. All rights reserved.