Aromatic nitration at high sulphuric acid strengths

The nitration of aromatic compounds has been performed on an industrial scale since the turn of the century. The rapid development of nitroaromatics as explosives and their use today in the dye industry and as intermediates in organic syntheses makes nitration an important, large scale process. The importance of nitration as a model electrophilic aromatic substitution reaction for the investigation of electronic effects in organic molecules led to it being studied in great depth in the homogeneous phase. Until recently, however, there was a sparse amount of information on the industrially significant two-phase reaction with mixed sulphuric and nitric acids and little attempt had been made to apply the results of kinetic experiments in a single phase to the phenomena observed in two phase batch and continuous nitration plants. In the last few years, however, much progress has been made arid a better understanding of the processes involved in these systems is now possible. The rates of nitration in a miniature stirred batch reactor and stirred cell containing pure toluene and chlorobenzene have been successfully interpreted on the basis of Danckwerts' Surface Renewal Theory of mass transfer. Many of the factors which affect the rate in these systems have been investigated and suitable rate equations tested experimentally. Despite the progress, however, the results obtained are not totally conclusive and several anomalous features have become apparent. The object of this work is to account for these features and hence try to substantiate the Theory of Danckwerts as applied by Cox and Strachan to the nitration of aromatics in two-phase systems.