Synthesis of Hexanitrostilbene (HNS) using a Kenics Static Mixer

Abstract

Previous work on a Shipp−Kaplan type synthesis of hexanitrostilbene (HNS) using a Kenics static mixer (ref1, from Chemineer Ltd., Cranmer Road, West Meadows, Derby DE21 6XT, UK; www.chemineer.com) has been extended by using a larger mixer (9.5 mm vs 4.75 mm OD), enabling the scale to be increased from 2.5 g to 25 g of trinitrotoluene (TNT) for the same mixing time (<4 min). Various conditions for the after-reaction period (2 h) have been explored on the basis of previous work with a batch reactor, including (i) no pH control, (ii) pH control using aqueous H2SO4 and NaOH solutions, and (iii) pH control using aqueous RNH3Cl and RNH2 solutions. Other parameters that have been varied are the ratio of NaOCl to TNT (0.5−1.2) and the concentration of both reactants. The yields of crude HNS that have been achieved, whilst not outstanding, are an improvement over the conventional batch process. It has been demonstrated that the yield and selectivity of the HNS synthesis can be considerably increased if, during the after-reaction period, the reaction conditions are pH controlled. The yield and selectivity are also significantly enhanced by using more dilute reaction solutions.