Fifty-six grams (0.25 mole) of benzil monohydrazone [Org. Syntheses, 15, 62 (1935)] (Note
1) is mixed in a
mortar with
81 g. (0.38 mole) of yellow mercuric oxide and
35 g. of anhydrous calcium sulfate (Note
2). The mixture is introduced into a
1-l. three-necked flask fitted with a
stirrer, a
condenser, and a
thermometer. The flask is placed in a
water bath,
200 ml. of dry thiophene-free benzene is added, and the suspension is stirred at 25–35° (thermometer in solution) for 4 hours (Note
3) and (Note
4). The reaction mixture is filtered through a
fine-grained filter paper, with slight suction, and the residue is washed with dry
benzene until the washings are colorless.
The
benzene solution of the diazo compound is poured into a
separatory funnel protected with a drying tube and connected to a
125-ml. Claisen distilling flask provided with a
condenser set for downward distillation and arranged so that it can be heated in a
bath of Wood's metal. The temperature of the metal bath being maintained at 100–110°, the
benzene solution is dropped slowly into the hot flask. Under these conditions, the
benzene is removed by distillation and the diazo compound is transformed into
diphenylketene. The residue is distilled under reduced pressure in an atmosphere of
nitrogen, and the fraction boiling at
115–125° at 3–4 mm. (Note
5) is collected. The yield is
31 g. (
64%) of a product which, on redistillation, yields
28 g. of
diphenylketene boiling at
119–121° at 3.5 mm. (
58%).