Anhydrous benzene (ca. 200 ml.) (Note
1) is poured into a
calibrated, 500-ml., standard-taper dropping funnel equipped with a gas-inlet tube containing a fritted-glass filter; the dropping funnel is stoppered and weighed accurately. The funnel is protected with a
calcium chloride tube, and
15–20 g. of phosgene is introduced at room temperature over a period of
ca. 1 hour; this quantity corresponds to an increase in volume of 12–16 ml. (Note
2). The calcium chloride tube is removed, and the funnel is immediately restoppered and reweighed (Note
3). The amount of
imidazole corresponding to the increase in weight observed (
e.g.,
16.55 g., 0.167 mole, of phosgene) is calculated on the basis of a phosgene:imidazole molar ratio of 1:4 (Note
4). The funnel is placed on a
1-l., three-necked, round-bottomed flask, that contains a solution of the
imidazole (here, 45.60 g., 0.669 mole) in
500 ml. of anhydrous tetrahydrofuran (Note
5) and is equipped with a
sealed mechanical stirrer and a calcium chloride tube. The flask is cooled with cold water, and the solution of
phosgene in
benzene is added with stirring from the dropping funnel over a period of 15–30 minutes. The reaction mixture is stirred for an additional 15 minutes and then allowed to stand for 1 hour at room temperature. The precipitate of
imidazolium chloride is removed by suction filtration with exclusion of atmospheric moisture by the use of a
standard-taper fritted-glass filter funnel (Note
6). The filtrate is evaporated to dryness under reduced pressure on a
water bath at 40–50° (Note
7). The yield of colorless crystalline
1,1'-carbonyldiimidazole is
80–94% (here,
24.8 g.;
91%). The product obtained in this way sinters at 110° and melts between
112° and 117° (here,
114–115°). This material can be used without further purification for most reactions,
e.g., ester, peptide, and aldehyde syntheses
2 (Note
8). The purity of a product of m.p.
113–117° was 98±2%.
3 The quality and yield of
1,1'-carbonyldiimidazole are not reduced when the scale is doubled.