Org. Synth. 1940, 20, 70
DOI: 10.15227/orgsyn.020.0070
MONOPERPHTHALIC ACID
[Phthalic monoperacid]
Submitted by Horst Böhme
Checked by Homer Adkins and E. Leon Foreman.
1. Procedure
Caution! Reactions and subsequent operations involving peracids and peroxy compounds should be run behind a safety shield. For relatively fast reactions, the rate of addition of the peroxy compound should be slow enough so that it reacts rapidly and no significant unreacted excess is allowed to build up. The reaction mixture should be stirred efficiently while the peroxy compound is being added, and cooling should generally be provided since many reactions of peroxy compounds are exothermic. New or unfamiliar reactions, particularly those run at elevated temperatures, should be run first on a small scale. Reaction products should never be recovered from the final reaction mixture by distillation until all residual active oxygen compounds (including unreacted peroxy compounds) have been destroyed. Decomposition of active oxygen compounds may be accomplished by the procedure described in Korach, M.; Nielsen, D. R.; Rideout, W. H. Org. Synth. 1962, 42, 50 (Org. Synth. 1973, Coll. Vol. 5, 414). [Note added January 2011].
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.
17.
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
Monoperphthalic acid has been prepared by hydrolysis of
phthalyl peroxide with
sodium hydroxide3 and by shaking
phthalic anhydride with excess alkaline
peroxide solution.
3 The method described here is a modification of the latter process.
4
This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
Monoperphthalic acid
Phthalic monoperacid
sulfuric acid (7664-93-9)
ether (60-29-7)
sodium hydroxide (1310-73-2)
sodium sulfate (7757-82-6)
oxygen (7782-44-7)
potassium iodide (7681-11-0)
phthalic anhydride (85-44-9)
iodine (7553-56-2)
hydrogen peroxide,
peroxide (7722-84-1)
thiosulfate
ammonium sulfate (7783-20-2)
dioxane (123-91-1)
phthalyl peroxide
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