2.4- Dinitrophenyl ethers, from phenols

Dissolve 1 g. (or 0 01 mol) of the phenol in a solution of 0-40 g. of sodium hydroxide in 5 ml. of water. Add the resulting solution to 2-Og. of 2 4-dinitrochlorobenzene dissolved in 30 ml. of 95 per cent, ethanol add more alcohol, if necessary, to effect solution. Heat the solution under reflux on a water bath until the colour (usually red) is discharged and a copious precipitate of sodium chloride appears (30-60 minutes). Dilute the reaction mixture with an equal volume of water, filter off the precipitated 2 4-dinitrophenyl ether, wash with water, and recrystallise from alcohol. 

If the other product from the hydrolysis is phenol, the procedures described in Section 5.1 are applied to the preparation of the derivatives, particularly those which permit a very sensitive analysis. Perfluorinated acyl derivatives and 2,4-dinitrophenyl-, 2,6-dinitro-4-trifluoromethylphenyl and pentafluorophenyl ethers are frequently used [482], when concentrations of 0.01—0.1 ppb of the insecticide in water can be determined. 

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