Prepn by reduction of dinitrodurene: Smith, Org. Synth. vol. 10, 40 (1930); Smith, Dobrovolny, J. Am. Chem. Soc. 48, 1420 (1926); by condensation of 2,3-diketopentane with itself in presence of alkalies: von Pechmann, Ber. 21, 1420 (1888); by the action of alkalies on 3,3-dichloropentan-2-one: Faworsky, J. Prakt. Chem. [2] 51, 538 (1895).