Abstract
This review highlights the state of the art in the field of continuous flow nitration with miniaturized devices. Although nitration has been one of the oldest and most important unit reactions, the advent of miniaturized devices has paved the way for new opportunities to reconsider the conventional approach for exothermic and selectivity sensitive nitration reactions. Four different approaches to flow nitration with microreactors are presented herein and discussed in view of their advantages, limitations and applicability of the information towards scale-up. Selected recent patents that disclose scale-up methodologies for continuous flow nitration are also briefly reviewed.
Highlights
Nitration of aromatics is one of the oldest and industrially most important reactions
Among the earliest reports are those of Faraday nitrating benzene, the synthesis of nitrobenzene by Mitscherlich [2] using benzene and fuming nitric acid, and the use of mixed acids for aromatic nitration by Mansfield [3]
We provide a guideline that helps to quickly decide under which conditions it is worthwhile to conduct continuous flow nitration from a practical point of view
Summary
Nitration of aromatics is one of the oldest and industrially most important reactions. Nitrations with undiluted nitric acid generate water that leads to the dilution of the nitric acid, so that the concentration of the nitronium ions and the reaction rates are reduced. It gives a lower selectivity due to the oxidation of the aromatic substrate. This approach is not considered economically feasible, so that most nitrations are carried out with the cheapest nitrating agent i.e., a mixture of nitric and sulfuric acids If they are used in excess, both of them are usually treated by neutralization, by feeding the weak nitric acid to an absorption tower, or recovered from the spent acid.
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