Two hundred grams (1.72 moles) of freshly distilled dry n-caproic acid (Note
1) is placed in a
1-l. flask with
300 g. (96 cc., 1.88 moles) of bromine which has been dried by washing once with
200 cc. of concentrated sulfuric acid (Note
2). A
3-cc. portion of phosphorus trichloride is cautiously added and the flask connected to a
reflux condenser (Note
3), the top of which is connected with a trap and
absorption bottle containing water. The mixture is then heated in a water or
oil bath to 65–70°, at which temperature the reaction commences and
hydrogen bromide is given off smoothly. After five to six hours, the
bromine has all reacted (Note
4). Towards the end of the reaction, the temperature is allowed to rise to about 100°. The contents of the flask are now distilled under diminished pressure (Note
5). The fraction boiling at
132–140°/15 mm. is collected and weighs
280–298 g. (
83–89 per cent of the theoretical amount).