Following the search for new and effective methods for promoting reactions rapidly and under green and mild conditions, ionic liquids (ILs) were interesting suggestions which widely used in synthetic methods. Br?nsted acidic ionic liquids are an important class of ILs. They have been used as catalysts and/or media instead of inorganic acids in many conventional acid-catalyzed reactions. Since the key property of Br?nsted acidic ILs is their Br?nsted acidity and there is a special relationship between their structure, acidic strength and performance, in this project the properties and performance of two Br?nsted acidic ILs N- methyl-2-pyrrolidonum hydrogensulfate ([H-NMP] HSO 4 ) and Morpholinium hydrogensulfate ([Hmor] HSO 4 ) were studied. The Hammett acidic scale and pK a values were calculated for both acidic ILs and the relationship of acidity and structure was discussed. The obtained results showed a remarkably high acidic strength for [H-NMP]HSO 4 in compared with [Hmor]HSO 4 . Further investigations were carried out by synthesis of other acidic ionic liquids [H-NMP]H 2 PO 4 , [H-NMP] NO 3 and [H-HMP]Cl and was evaluated their acidic scale by Hammett method. A significantly poor acidity was observed for these acidic ILs compared with [HNMP]HSO 4 . Therefore, the IL [H-NMP]HSO 4 was employed as an efficient proton source in the preparation of diazonium salts from corresponding aniline derivatives at room temperature and desired results were obtained. The diazonium salts were prepared in aqueous media and at room temperature without phenol formation as by-product. We also studied the stability of these aryldiazonium salts prepared using [H-NMP]HSO 4 at room and low (0 o C) temperature and found a considerable stability for that salts stored at 0 o C temperature for long period. In continuation, these obtained aryldiazonium salts were treated with azide and iodide ions and the corresponding aryl azide and aryl iodide products obtained in high yields. In order to investigate the catalytic performance of these acidic ionic liquids, acid-catalyzed multicomponent reactions of synthesis of some heterocyclic compounds were carried out. The bioactive compounds of aryl 14 H -dibenzo[a,j]xanthenes were synthesized in the presence of [H-NMP]HSO 4 under solvent-free conditions at 120 o C and [Hmor]HSO 4 catalyzed three-component condensation reaction of preparation of 3,4-dihydropyrimidine-2(1 H )-one derivatives under solvent-free conditions at 110 o C.
