A 1000-mL (Note
1),
multinecked flask is provided with an
efficient stirrer, vented outlet,
thermometer, and
250-mL dropping funnel. The flask is surrounded by an
ice–water bath and charged with
62.5 mL (68.4 g, 0.53 mol) of quinoline,
250 mL of dichloromethane,
55 g (0.55 mol) of finely powdered calcium carbonate, and 250 mL of water. The mixture is stirred vigorously, cooled to 10°C, and maintained at 10–15°C as a solution of
37.5 mL (56.5 g, 0.49 mol) of thiophosgene (Note
2) in
120 mL of dichloromethane is added over 15 min. There is very little exotherm or foaming. The cooling bath is removed and the reaction mixture is stirred vigorously at ambient temperature overnight. The reaction is then filtered through a bed of filter aid. The layers are separated and the aqueous layer is extracted with
50 mL of dichloromethane. The combined organic layers are washed twice with
150 mL of 2 N hydrochloric acid (Note
3), then with 150 mL of water, and dried over anhydrous
magnesium sulfate. Concentration under reduced pressure gives
95–103 g of crude material (Note
4). This is dissolved with heating in
400 mL of cyclohexane,
decolorizing carbon is added, and the mixture is filtered through a bed of filter aid. The filtrate is heated under reflux for 2 hr (Note
5) and allowed to cool with stirring (Note
6). The resulting solid is isolated by filtration, washed with
cyclohexane, and dried in a
vacuum oven at 40°C to give
78–83 g (
84–89%) of
o-isothiocyanato-(E)-cinnamaldehyde as cream crystals, mp
77–79°C (Note
7).