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Org. Synth. 1962, 42, 77
DOI: 10.15227/orgsyn.042.0077
MONOPERPHTHALIC ACID
[Phthalic monoperoxy acid]
Submitted by George B. Payne1
Checked by K. Nagarajan and John D. Roberts.
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 a solution of 62 g. (0.5 mole) of sodium carbonate monohydrate in 250 ml. of water. This is cooled to 0°, and 69 g. (63 ml., 0.6 mole) of 30% hydrogen peroxide (Note 1) is added in one portion. With the temperature at −5 to 0°, 74 g. (0.5 mole) of phthalic anhydride (Note 1) which has been pulverized to pass a 14-mesh sieve is added (Note 2).
The reaction mixture is stirred vigorously at −5 to 0° for 30 minutes, then the resulting solution or suspension (Note 3) is poured into a 2-l. separatory funnel, shaken with 350 ml. of ether (Note 4), and carefully acidified with an ice-cold solution of 30 ml. of concentrated sulfuric acid in 150 ml. of water. The liberated monoperphthalic acid is extracted into the ether and removed completely from the water by extraction with two more 150-ml. portions of ether. The combined ether extracts are washed with two 200-ml. portions of 40% ammonium sulfate solution and dried overnight in a refrigerator over 50 g. of anhydrous magnesium sulfate.
The peracid content is determined by adding 30 ml. of 20% potassium iodide solution to 2 ml. of the peracid solution and, after 10 minutes, titrating the liberated iodine with 0.1 N thiosulfate. The yield is 71–78 g. (78–86% based on phthalic anhydride).
If crystalline monoperphthalic acid is desired, it may be prepared as described earlier.2
2. Notes
1. Commercial phthalic anhydride and hydrogen peroxide, both of reagent grade, are used.
2. Fieser and Fieser3 recommend that the phthalic acid be recrystallized from benzene rather than pulverized.
3. The sodium salt of monoperphthalic acid may precipitate during the reaction.
4. The ether may be used, along with a small amount of cold water, to effect a quantitative transfer of the suspension from reaction vessel to separatory funnel.
3. Discussion
Monoperphthalic acid has been prepared by hydrolysis of phthalyl peroxide with sodium hydroxide,4 by reaction of phthalic anhydride with excess alkaline peroxide solution,5 by reaction of phthalic anhydride with hydrogen peroxide,6 and by stirring phthalic anhydride with mildly alkaline peroxide.7 The method described here is a slight modification of the last procedure.
The methods of preparation, properties, analysis, and safe handling of monoperphthalic acid have been reviewed.8
4. Merits of Preparation
The Böhme procedure2,5 for preparing perphthalic acid from phthalic anhydride and hydrogen peroxide is sensitive to slight variations in the experimental conditions.6,7 The present method gives reproducible yields with quite short reaction times.

References and Notes
  1. Shell Development Company, Emeryville, Calif.
  2. H. Böhme, org. Syntheses, Coll. Vol. 3, 619 (1955).
  3. L. F. Fieser and M. Fieser, Reagents for Org. Synthesis, 1, 820 (1967).
  4. A. Baeyer and V. Villiger, Ber., 34, 764 (1901).
  5. H. Böhme, Ber., 70, 379 (1937); G. B. Bachman and D. E. Cooper, J. Org. Chem., 9, 307 (1944).
  6. E. E. Royals and L. L. Harrell, Jr., J. Am. Chem. Soc., 77, 3405 (1955).
  7. G. B. Payne, J. Org. Chem., 24, 1354 (1959).
  8. D. Swern, "Organic Peroxides," Vol. I, Wiley-Interscience, New York, 1970, p. 424, 489.

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

Monoperphthalic acid

Phthalic monoperoxy acid

sodium salt of monoperphthalic acid

sulfuric acid (7664-93-9)

Benzene (71-43-2)

ether (60-29-7)

sodium hydroxide (1310-73-2)

potassium iodide (7681-11-0)

phthalic anhydride (85-44-9)

iodine (7553-56-2)

hydrogen peroxide (7722-84-1)

ammonium sulfate (7783-20-2)

phthalic acid (88-99-3)

magnesium sulfate (7487-88-9)

phthalyl peroxide

sodium carbonate monohydrate (5968-11-6)