Green Synthesis of TMETN Using Ionic Liquid [Btem-SO3H][NO3] as a Nitrating Agent

Abstract

In this study, a novel sulfonic acid-functionalized ionic liquid N,N,N-triethyl-4-sulfobutan-1-aminium nitrate ([Btem-SO₃H][NO₃]) was synthesized as a nitrating agent. The cation and anion of [Btem-SO₃H][NO₃], respectively, provide an acidic environment and a nitro source, enabling green nitration of TMETN (Trimethylolethane trinitrate). It was found that [Btem-SO₃H][NO₃] exhibited good thermal stability up to 170 °C. The acidity of [Btem-SO₃H][NO₃] increases with a decrease in the water content. When the water content is lower than 9%, the nitration efficiency remains unchanged. The [Btem-SO₃H][NO₃] system exhibited a ΔT_ad of 57.62 °C and an MTSR of 30.54 °C, which are significantly lower than 88.15 and 36.96 °C of the fuming HNO₃ system. Under optimized conditions, a TMETN yield of 95% was achieved, and the ionic liquid maintained ideal activity after five recycling cycles, outperforming fuming nitric acid (89% yield, poor recyclability). Mechanism analysis showed that the reaction of [Btem-SO₃H][NO₃] with Ac₂O to form acetyl nitrate (CH₃COONO₂) is a key step in the entire nitration reaction. These findings demonstrate that [Btem-SO₃H][NO₃] reduces waste acid emissions and improves thermal safety and reusability while maintaining high nitration efficiency, providing a promising strategy for replacing traditional nitric acid systems and achieving green and sustainable synthesis of nitrate esters.