Submitted by C. Ernst Redemann and Carl Niemann.
Checked by Lee Irvin Smith, R. T. Arnold, and Iver Lerohl.
1. Procedure
In a
1-l. round-bottomed flask are placed
66 g. (0.33 mole) of d-glucose monohydrate (Note
1) and
302 g. of 95% acetic anhydride (280 ml., 2.81 moles). To this mixture 3 small drops of concentrated
sulfuric acid are added
from a medicine dropper (Note
2). The
glucose is kept in partial suspension by shaking the flask with a swirling motion; the reaction starts almost immediately. If the temperature of the mixture approaches the boiling point, the flask is momentarily immersed in a pan of cold water. Within 10–15 minutes nearly all the
glucose will have dissolved and the temperature of the reaction mixture will have risen nearly to 100°. The flask is loosely stoppered and is heated on a
steam bath for 2 hours. Then about
200 ml. of mixed acetic acid and
acetic anhydride is removed by distillation under reduced pressure (Note
3).
Sixty-five grams
(60 ml., 0.64 mole) of acetic anhydride is added to the warm, viscous, light-yellow syrup; the mixture is warmed slightly and is mixed by imparting a swirling motion to the flask until the solution is homogeneous. The flask is then fitted with a
two-holed rubber stopper bearing an
inlet tube and an exit tube, the former reaching within 5 mm. of the bottom. Dry
hydrogen bromide is passed into the mixture, while it is cooled in an
ice bath, until the gain in weight is 140–160 g. (Note
4). The flask is then sealed with a rubber stopper and allowed to stand at 5° overnight.
The
hydrogen bromide,
acetic acid, and
acetic anhydride are then removed from the straw-yellow solution by distillation under reduced pressure; a
water bath whose temperature does not exceed 60° should be used to heat the mixture (Note
5). During the distillation the solution becomes slightly darker. When no further distillate comes over, or when the residue crystallizes, distillation is stopped,
250–300 ml. of dry isopropyl ether is added (Note
6), and the flask is warmed carefully on a water bath to hasten solution of the product (Note
7). The hot solution is transferred to a
1-l. Erlenmeyer flask and is cooled rapidly, with cold water, to about 45°. The mixture is then allowed to cool slowly to room temperature and is finally placed in a refrigerator at 5° for 2 or more hours. The
acetobromoglucose is collected on a
Büchner funnel, pressed into a firm cake, and washed with about
50 ml. of dry isopropyl ether. The white crystalline material, after being dried under reduced pressure over
calcium (or sodium) hydroxide, weighs
110–120 g. (
80–87%) (Note
8).
2. Notes
2. If any uncertainty exists about the size of the drops, it is better to add 2 drops at first and then to wait at least 10 minutes before adding the third drop. If too much
sulfuric acid is added the reaction may become so vigorous that it cannot be controlled.
3. The lowest pressure attainable with a good aspirator is satisfactory. The
acetic acid may be removed rapidly at bath temperatures up to 100°. Two hundred milliliters of distillate is collected in about 35 minutes. Complete removal of the
acetic acid is not necessary; the only purpose of removing it is to decrease the amount of
hydrogen bromide required.
5. This distillation is best conducted in the following manner: The
hydrogen bromide is removed as completely as possible at a bath temperature of 40–50° under the pressure attainable with a good aspirator; this requires about 1 hour. The bath temperature is then slowly increased to 50–60° over a period of about 30 minutes, during which time considerable
acetic acid and
acetic anhydride are removed. The receiver is then emptied and the system is connected to a
mechanical pump capable of maintaining a pressure of less than 5 mm. By keeping the temperature of the bath at 55–60°, sufficient
acetic acid and anhydride are removed in 30–45 minutes. The mechanical pump must be adequately protected; the vapors should be passed through a trap cooled in
carbon dioxide-
ethanol, then through a
12- to 16-in. tower of flake
sodium hydroxide, before they enter the pump. A somewhat higher bath temperature can be used with a good aspirator alone, but this will produce much darkening of the reaction mixture and will give a less desirable product.
7. Heating to effect solution should be as brief as possible. The water bath should be at a temperature near the boiling point, and the flask should be immersed for only short periods of time. The flask should be shaken continuously during this process.
8. The product, m.p.
87–88°, is satisfactory for most purposes. A single recrystallization from
isopropyl ether gives a product having a melting point of
88–89°.
The product is best stored in a vacuum desiccator.
3. Discussion
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