A novel and efficient solvent-free and heterogeneous method for the synthesis of primary, secondary and bis-N-acylsulfonamides using metal hydrogen sulfate catalysts - Massah, Ahmad Reza; Asadi, Beheshteh; Hoseinpour, Mahdieh; Molseghi, Azadeh; Kalbasi, Roozbeh Javad; Javaherian Naghash, Hamid (Tetrahedron, 2009)