Tetrahydrofuran (36 g., 0.5 mole) (Note
1) is added to a mixture of
potassium iodide (332 g., 2 moles),
85% orthophosphoric acid (231 g., 135 ml., 2 moles), and
phosphoric anhydride (65 g.) (Note
2), (Note
3), and (Note
4) in a
1-l. three-necked flask equipped with a
sealed mechanical stirrer, a
reflux condenser, and a
thermometer. The mixture is stirred and heated at its reflux temperature for 3 hours, during which time a dense oil separates from the acid layer. The stirred mixture is cooled to room temperature, and 150 ml. of water and
250 ml. of ether are added (Note
5). The
ether layer is separated, decolorized with dilute aqueous
sodium thiosulfate solution, washed with cold saturated
sodium chloride solution, and dried over anhydrous
sodium sulfate. The
ether is removed by distillation on a
steam bath, and the residue is distilled under reduced pressure from a
modified Claisen flask. The portion boiling at
108–110°/10 mm. is collected. The yield of colorless
1,4-diiodobutane (
nD20 1.615;
d420 2.300) (Note
6) is
143–149 g. (
92–96%).