Side reactions in the nitration of naphthalene

Nitration of naphthalene, and higher stages of the nitration (e g. trinitration) in particular, are accompanied by oxidation reactions which are manifested by the evolution of large quantities of nitrogen oxides. 

As a result nitrophthalic acids are formed, namely nitro- and dinitro-phthalic  

Since under the conditions of the above reaction partial decarboxylation may take place, nitrobenzoic acids may also be formed  

In addition nitronaphthols are obtained, which may be formed either by direct oxidation or through isomerization of nitronaphthalenes to nitrosonaphthol or its derivatives  

It has been found that such reactions can occur under the influence of fuming sulphuric acid, at 40-50°C. Nitrosonaphthol may then by oxidized to nitronaph-thol. Moreover, picric acid may be formed during the nitration processes. 

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