Hydrogen fluoride
The potassium salt of dinitromethanide, KCH(NO2)2, was first prepared by Villiers in 1884 by reduction of bromodinitromethane. Hydrogen fluoride and the potassium salt of dinitromethane react in diethyl ether to form dinitromethane. Free dinitromethane was previously understood to be a pale, yellow oil that decomposed rapidly at ambient temperatures.