[TBP]2SO4 ionic liquid catalyst for 4MCR of pyridazinoindazole, indazolophthalazine and pyrazolophthalazine derivatives.Tetrabutyl phosphonium sulfate ([TBP]2SO4), as novel room-temperature ionic liquid (RTIL), was synthesized by a simple cost-effective method, characterized by 1H, 13C, 31P NMR and FT-IR spectrophotometry. 
TBP
[TBP]2SO4 ionic liquid catalyst for 4MCR of pyridazinoindazole, indazolophthalazine and pyrazolophthalazine derivatives.Tetrabutyl phosphonium sulfate ([TBP]2SO4), as novel room-temperature ionic liquid (RTIL), was synthesized by a simple cost-effective method, characterized by 1H, 13C, 31P NMR and FT-IR spectrophotometry. 
1H
[TBP]2SO4 ionic liquid catalyst for 4MCR of pyridazinoindazole, indazolophthalazine and pyrazolophthalazine derivatives.Tetrabutyl phosphonium sulfate ([TBP]2SO4), as novel room-temperature ionic liquid (RTIL), was synthesized by a simple cost-effective method, characterized by 1H, 13C, 31P NMR and FT-IR spectrophotometry. 
13C
[TBP]2SO4 ionic liquid catalyst for 4MCR of pyridazinoindazole, indazolophthalazine and pyrazolophthalazine derivatives.Tetrabutyl phosphonium sulfate ([TBP]2SO4), as novel room-temperature ionic liquid (RTIL), was synthesized by a simple cost-effective method, characterized by 1H, 13C, 31P NMR and FT-IR spectrophotometry. 
31P NMR
[TBP]2SO4 ionic liquid catalyst for 4MCR of pyridazinoindazole, indazolophthalazine and pyrazolophthalazine derivatives.Tetrabutyl phosphonium sulfate ([TBP]2SO4), as novel room-temperature ionic liquid (RTIL), was synthesized by a simple cost-effective method, characterized by 1H, 13C, 31P NMR and FT-IR spectrophotometry. 
FT-IR spectrophotometry