Submitted by Herbert S. Rhinesmith
Checked by Reynold C. Fuson and W. E. Ross.
1. Procedure
In a
2-l. three-necked, round-bottomed flask, equipped with a
mechanical stirrer (Note
1),
dropping funnel, and
Friedrichs condenser1 (Note
2), are placed
200 g. (1.7 moles) of fumaric acid (Note
3) and 400 g. of water (Note
4). The materials are thoroughly mixed until the
fumaric acid has been completely wet by the water. The resulting thick, viscous mass is then stirred vigorously (Note
5) and brought to boiling by heating on a
wire gauze with a Bunsen flame (Note
6).
Two hundred and seventy-six grams (94.3 cc., 1.7 moles) of bromine (Note
7) is now added as rapidly as possible through the dropping funnel, the rate of addition being so controlled that the Friedrichs condenser is continuously about half full of the refluxing liquid (Note
8). This operation takes about one hour (Note
9). After about
100 g. of bromine has been added, the
dibromosuccinic acid forms rapidly and separates in tiny white needles. At the completion of the reaction there should be a slight excess of
bromine, as indicated by the red color of the solution. Occasionally
5–10 g. of bromine has to be added at this point to ensure an excess.
The reaction flask is now surrounded with ice water and cooled to 10°, with stirring. The product is then collected on a
large Büchner funnel, and washed with cold water to remove the
bromine liquor. The filtrate may be discarded, as it contains only impurities. The material is dried overnight at room temperature and need not be recrystallized; the yield is
343–400 g. (
72–84 per cent of the theoretical amount).
2. Notes
1. A heavy stirrer with as large a paddle as possible is used, in order to rotate the mass of crystals formed during the course of the reaction. A
mercury seal is unnecessary, but it is advisable to have the stirrer bearing extend beneath the surface of the liquid.
2. Glass connections or
rubber stoppers should be used throughout, as
corks are rapidly disintegrated by the hot
bromine.
5. Vigorous stirring is essential to obtain good yields.
6. It is necessary to keep the reaction mixture boiling throughout the entire course of the reaction. During the addition of the
bromine, however, the size of the flame should be reduced considerably, because the reaction is exothermic.
7. The apparatus should be set up under a
hood, or the top of the condenser connected to a
gas absorption trap for the removal of
bromine vapor, small amounts of which escape continually under the conditions of the experiment.
8. By this procedure most of the unchanged
bromine is washed back into the flask, so that the amount escaping from the top of the condenser is kept at a minimum.
9. If the
bromine is added over a much longer period of time, the yield is materially decreased.
3. Discussion
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