Study On Nitration Of Phenols In Microemulsions

Microemulsions are normally formed spontaneously by surfactants, co-surfactants, oil and water in appropriate proportions, which are usually isotropic transparent or translucent system with low viscosity and are thermodynamically stable. Microemulsions have been widely used as chemical reaction media in which the problem of incompatibility between reactants can be overcome and reaction between polar and non-polar reactants can be greatly speed up. In recent years microemulsions were found to be effective in inducing orientation of reagents at oil/water interface so that selective organic reactions can be realized.This thesis aimed to enhance the selectivity of nitration of phenol by utilizing the orientation of reagents at oil/water interface in microemulsion systems. First of all, a monophase microemulsion was prepared with Triton X-100 as surfactant, and the nitration of phenols by concentrated nitric acid in the systems was studied. The influence of the mass fraction of nitric acid, oil/water volume ratio, reaction temperature and other factors on the reaction conversion and selectivity was examined. It was found that the nitration reaction has a high ortho-selectivity, and a high conversion could be achieved.Due to strongly corrosive and volatile, concentrated nitric acid is replaced by dilute inorganic acid (such as sulfuric acid) and nitrate for the selective nitration of phenol. The effects of surfactant concentration, oil/water ratio and oil chain length in the microemulsion, together with the reaction time and reaction temperature on conversion and selectivity of nitration were investigated. An optimal condition was obtained under which the phenol in the microemulsion systems could be completely converted, and an ortho-selectivity as high as 90% can be achieved.In addition, the nitration of phenol in other microemulsion systems was carried out. It was found that in middle-phase microemulsion system with same surfactant, co-surfactant and oil phase, the ortho-selectivity was poor, although the concentration of surfactant reduced greatly. In a monophase microemulsion where the oil (heptane) phase was replaced by an ionic liquid, high ortho-selectivity of nitration of phenol can be achieved. Keywords: microemulsion, nitration, surfactant, selectivity...