Diazotization of \(2,4-\) dinitroaniline in aqueous solution is accompanied by some conversion to phenols in which a nitro group is replaced by a hydroxy group. Give a reasonable mechanism for this reaction.

First, let's draw the structure of 2,4-dinitroaniline: ``` NO2 NH2 | | H - C-C - C-C - H | | H - C-C - C-N - O2 | NO2 ``` 2,4-dinitroaniline has an amino (NH2) group and is substituted with two nitro (NO2) groups on the benzene ring.

During diazotization, the primary amine group (NH2) is converted into a diazonium salt (N2+). The reaction takes place in the presence of nitrous acid (HNO2) and an acid like hydrochloric acid (HCl). The chemical equation for the reaction is: 2,4-dinitroaniline + HNO2 + HCl → 2,4-dinitroaniline diazonium salt + H2O ``` H NO2 HNO2(HCl) Cl | ----- | H - C-C -N2+ - - - C-C - H | | | H - C-C - C=N - - - O2 | | NO2 H ```

This step will involve demonstrating how one of the nitro groups undergoes a substitution reaction to be replaced with a hydroxy (OH) group as part of the phenol. 1. The electron-rich diazonium nitrogen from the diazonium salt initiates the reaction by attracting a nitro group to get electron density from the diazonium salt N2+. ``` Cl X NO2 | | | H -C-C-N2+-C-C-H | | | H -C-C-W-C-N=O | | NO2 H ``` 2. As a result, one of the NO2 groups leaves as a leaving group with the diazonium salt N2+, and the carbon position previously occupied by the NO2 groups gains a positive charge. ``` Cl NO2 | | H -C-C+-C-C-H | | H -C-C Y-C-N=O | | NO2 H ``` 3. The remaining pair of electrons on the central carbon reacts with water or another nucleophile, resulting in the addition of a hydroxy group (OH) and the formation of a phenol compound. ``` Cl | H -C-C -C-C-H | | H -C-C -C-C-N=O | | NO2 OH ``` The final product is a phenol where one of the nitro groups has been replaced with a hydroxy group.