Study On Nitration (Nitrolysis) In The Presence Of Br(?)nsted Acidic Ionic Liquids

Synthesis of nitro aromatic compounds using ionic liquids (ILs) as green solvents and/or catalysts is a hot spot in the study of nitration at present days. Series of Bransted acidic ionic liquids were synthesized and characterized, such as [CaprolactamJX, [SO₃H(CH-2)4Mim]X, [SO₃H(CH₂)₄Pyr]X, [COOHCH₂Mim]X, and [COOHCH₂Pyr]X(X^-= pTSO^-, HSO₄^-, CF₃COO^-, BF₄^-, NO₃^-), and also a kind of Bransted acidic ionic salt based on Keggin heteropolyoxotungstate anion, [SO₃H(CH₂)₄Mim]_nH_3-nPMo₁₂O₄₀(n=1, 2, 3). Using these compounds as catalysts, nitration of simple aromatics has been studied in the system of NO₂/air, HNO₃/Ac₂O, HNO₃ (67%) in the absence of organic solvent. The yields and selectivities of the reaction were investigated. The results showed that:Under the condition of stepped rising of temperature, NO₂/air nitration of toluene catalyzed by [CaprolactamjpTSO achieved a good yield of mononitrotoluene(61.4%). And nitration of toluene in IL-HNO₃/Ac₂O system gave stoichiometry yield of mononitro product.The rate of nitration of toluene was slow in IL-HNO₃ (67%) system. In the presence of ionic liquid in catalytic amount, mol ratio of toluene to nitric acid being 1:1, reacting for 12h at 70℃, the reaction gave a yield of mononitro products about 40% and the ratio of ortho- to para-isomers about 1.0-1.2. But catalyzed by Keggin heteropolyoxotungstate anion based Br(?)nsted acidic ionic salt [SO₃H(CH₂)₄Mim]_nH_3-nPMo₁₂O₄₀(n=1, 2, 3), nitration of toluene in HNO₃(67%) gave improved yields. For example, catalyzed by [SO₃H(CH₂)₄Mim]H₂PMo₁₂O₄₀, mol ratio of toluene to nitric acid being 1:3, mol ratio of catalyst to toluene being 1:10, reacting for 10h at 50℃, the reaction gave a yield of mononitro products about 84.9% and the ratio of ortho- to para-isomers about 1.21.In addition, in the presence of ionic liquid, cyclonite (RDX) was synthesized by direct nitrolysis of hexamethylenetetramine with HNO₃ (95%) with the yield increased. Three types of ionic liquids adopted in the reaction, such as [HMimjX, [(CH₂)₄SO₃HMim]X, and [(CH₂)₄SO₃HPyr]X (X^-= pTSO^-, NO₃^-, CF₃COO^-), all showed good catalytic activities. Compared with the system without ionic liquid, the yield of RDX was improved by 4-9% in the presence of ionic liquids.