Nitration of nitronaphthalene to dinitronaphthalene

As Pascal [20a] reports, the reaction is carried on in the following way. The nitrator is fed with 1150 kg of a nitrating mixture of the composition  

After all the nitronaphthalene has been added, the temperature is raised to 55°C within one hour, and then cooled to 40°C. The dinitronaphthalene solidifies in the form of granules. 

The nitrator contents are drawn off to the filter tank (1) (Fig. 110). The tank is lead-lined and equipped with a ventilating pipe for conducting away nitrogen oxide. Filtration is most effective with a 20-cm layer of coarse-grained dinitronaphthalene as a filter material, placed between perforated plates of sheet aluminium. 

The water content in washed dinitronaphthalene is 25% the product is dried in dryers, which may be of various construction, until the content of water falls to 0.5%. 

The two-stage nitration of naphthalene to dinitronaphthalene requires more complex plant and is more labour consuming nevertheless it is more economic than single stage nitration, since the product obtained is of higher purity, more easily freed from acid, and the consumption of nitric acid is lower. 

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Fig. 110. Flow sheet of the nitration of nitronaphthalene to dinitronaphthalene (Pascal [20a]).

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