Chlorodinitrobenzene, hydrolysis

In industrial practice, hydrolysis of chlorodinitrobenzene is now the main method of producing dinitrophenol. The reaction proceeds as follows ... 

Towards the end of this operation a sample should be taken and diluted with water to test whether hydrolysis is complete. A completely hydrolysed product will go into solution. Otherwise chlorodinitrobenzene will collect as an oil. 

Dry dinitrophenol prepared by hydrolysis of chlorodinitrobenzene usually melts at 110-111 °C. Its impurities come from the chlorodinitrobenzene, which may contain unhydrolysed admixtures (such as m- chloronitrobenzene, dichlorodinitro-benzene isomers, m- dinitrobenzene). 

Picric acid is produced either by nitrating phenol or by nitrating dinitrophenol prepared by hydrolysis of chlorodinitrobenzene. 

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