Checked by Homer Adkins and E. Leon Foreman.
1. Procedure
In a
1-l. round-bottomed flask, equipped with a
mechanical stirrer and cooled in an
ice-salt bath, is placed
275 g. (250 ml., approximately 1 mole) of 15% sodium hydroxide solution. This is cooled to −10° (Note
1), and
115 g. (105 ml., approximately 1 mole) of 30% hydrogen peroxide which has been similarly cooled is added in one portion. The heat of reaction causes the temperature to rise markedly. When the temperature has again dropped to −10°,
75 g. (0.5 mole) of phthalic anhydride which has been pulverized to pass a 40-mesh sieve is added as quickly as possible while the contents are stirred vigorously in the freezing mixture (Note
2) and (Note
3). As soon as all the anhydride has dissolved,
250 ml. (0.5 mole) of 20% sulfuric acid which has been previously cooled to −10°, but not frozen (Note
4), is added.
The acid solution is filtered without suction through glass wool into a
2-l. separatory funnel and extracted once with
500 ml. of ether, then three times with 250-ml. portions of the same solvent. The combined
ether extracts are shaken out with three
150-ml. portions of 40% ammonium sulfate solution and dried for 24 hours, preferably in a
refrigerator, over
50 g. of anhydrous sodium sulfate.
If the
ether is evaporated under reduced pressure (Note
5), crystalline
monoperphthalic acid is obtained. It is more convenient, however, to use the
ether solution directly (Note
6). Its peracid content is determined by adding to
2 ml. of the solution 30 ml. of 20% potassium iodide solution and titrating the
iodine after 10 minutes with 0.05
N thiosulfate solution. The yield is
60–65 g. (
65–70% based on the
phthalic anhydride) (Note
7).
2. Notes
1. If the solutions are cooled to −10°, little
oxygen is evolved and the yields of peracid are good. If the reaction is carried out at 0°, a large amount of
oxygen is evolved and the yields are poor.
2. Commercial
phthalic anhydride may be used directly. If excessive decomposition occurs, however, the anhydride should be purified by distillation under reduced pressure.
3. The anhydride is added in large portions or, better, in one portion.
4. The decisive factor in the success of this preparation is the time interval between the addition of the anhydride and the acidification of the reaction mixture. All the anhydride should dissolve, but prolonged stirring results in excessive
oxygen evolution. The quicker the anhydride dissolves, and the smaller the
oxygen evolution, the better the yield of the peracid. Hence, stirring must be vigorous.
5. If crystalline
monoperphthalic acid is desired, it may be prepared conveniently as follows: The dried ether solution is placed in a distilling flask equipped with a
capillary tube connected with a drying tube, and the flask is connected with the
water pump. The
ether is evaporated at the pressure thus obtained without the application of heat (ice will form on the flask) to a thin syrup (approximately 150 ml.). The syrup is transferred to an
evaporating dish and the flask rinsed with a small amount of dry
ether, the washings being added to the syrup. The remainder of the ether is then evaporated in a
vacuum desiccator over concentrated
sulfuric acid. For good results in this preparation the drying must be very thorough, for only 1% of water in the
ether solution will be more than sufficient to destroy the entire amount of peracid.
6. If
ether is not suitable for the oxidation reactions in which the peracid is to be used, the material can be dissolved in another solvent after removal of the
ether. An excellent solvent for
monoperphthalic acid oxidations is
dioxane, and a solution of the peracid in
dioxane is readily prepared by adding
dioxane to the dried
ether extract and then removing the
ether under reduced pressure at 15°. The
dioxane must be peroxide-free.
1
7. As originally submitted, this preparation was on one-fifth the scale indicated here. However, the checkers have had no difficulty with the larger-scale preparation.
It has been reported
2 that an
86% yield of
monoperphthalic acid results when a single
ether extraction is employed. In the modified procedure, 40% alkali was employed, and crushed ice was added directly for cooling.
3. Discussion
Copyright © 1921-2002, Organic Syntheses, Inc. All Rights Reserved