PREPARATIONS 263 into 2,4-dinitroaniline (III). Similarly it reacts with one molecular equivalent of hydrazine to give 2,4-dinitrophenylhydrazine (IV). Required: Chloro- 2,4-dinitrobenzene, 10 g.; hydrazine hydrate, 8 ml. (64% w/w); dioxan,* 50 ml. Dissolve 10 g. of chloro- 2,4-dinitrobenzenefin 50 ml. of dioxan in a 250 ml. conical flask. Dilute 8 ml. of hydrazine hydrate with an equal volume of water and add this slowly with shaking to the dioxan solution, keeping the temperature between 20° and 25°. Heat under reflux for 10 minutes to complete the reaction and then add 5 ml. of ethanol and heat again for 5 minutes. Cool and filter off the orange 2,4-dinitrophenylhydra-zine. Recrystallise the dry product from ethyl acetate: m.p. 200° (decomp.). Yield, 7 g. Preparation of 2,4-Dinitrophenylhydrazones. 2,4-Dinitrophenyl-hydrazine is much more reactive than phenylhydrazine towards aldehydes and ketones: consequently a compound having a carbonyl group of low reactivity may often readily give a 2,4-dinitrophenylhydrazone, although the unsubsti-
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