- Provide a 1 -litre three-necked flask with a dropping funnel carrying a calcium chloride guard-tube, a mechanical stirrer and a thermometer reaching almost to the bottom of the flask, and cool the flask in a mixture of ice and salt.
- Place in the flask 182 g (132ml, 1.5 mol) of allyl bromide (1) and 250ml of dry carbon tetrachloride, and introduce 255 g (80 ml, 1.6 mol) of dry bromine into the dropping funnel.
- Set the stirrer in motion and when the temperature has fallen to — 5 °C, drop the bromine in slowly at such a rate that the temperature does not rise above °C (about 90 minutes).
- Allow the orange-coloured solution (the colour is due to a slight excess of bromine) to warm to room temperature with constant stirring (about 30 minutes) and then remove the solvent under reduced pressure on a rotary evaporator.
- Distil the residue under reduced pressure; the residual carbon tetrachloride passes over first, followed by 1,2,3-tribromopropane at 92-93 °C/10mmHg or 100-103 °C/18mmHg as an almost colourless liquid. The yield is 400 g (95%).
Notes to keep in mind:
1. The allyl bromide should be dried over
anhydrous calcium chloride and redistilled; the fraction, b.p. 69-72 °C, is
collected for use in this preparation.
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