[3851-95-4] · C4H4O5 · Peroxymaleic Acid · (MW 132.08)
(electrophilic reagent capable of reacting with many functional groups; delivers oxygen to alkenes and amines2)
Alternate Names: permaleic acid; PMA.
Solubility: sol CH2Cl2, CHCl3 and water.
Form Supplied in: not available commercially.
Analysis of Reagent Purity: assay using iodometry.3
Preparative Methods: (a) to a cooled (0 °C) and stirred mixture of 90% Hydrogen Peroxide (caution!) (11.6 g, 0.34 mol) and CH2Cl2 (150 mL) is added in one batch 39.2 g (0.4 mol) of freshly crushed Maleic Anhydride. When the major portion of the anhydride has reacted, the reaction mixture is heated to reflux.2 (b) 0.1 mol of 88% H2O2, 0.13 mol of maleic anhydride, CHCl3 (19.5 mL), and DMF (0.5 mL) are stirred at 20 °C for 1.5 h to give the reagent, essentially free from H2O2.4
Handling, Storage, and Precautions: reasonably stable in CH2Cl2 solution, decomposing to the extent of 5% in 6 h at rt. Since peroxy acids are potentially explosive, care is required while carrying out the reactions; during workup, test for peroxides before solvent removal. This reagent should be handled in a fume hood.
Simple acyclic ketones and cyclic ketones having seven or more carbon atoms in the ring do not undergo facile Baeyer-Villiger reaction with normal peroxy acids like m-Chloroperbenzoic Acid; only PMA and Trifluoroperacetic Acid (TFPAA) are useful for this reaction. Although PMA is not as powerful an oxidizing agent as TFPAA, its reactivity is adequate. When TFPAA is used, an inorganic buffer reagent has to be added; when PMA is used there is no need for such a buffer reagent.2
Baeyer-Villiger reaction of the ketone (1) furnishes the ester (2) (eq 1).2 Oxidation of the diketone (3) furnishes the lactone (4) in 77% yield; the reaction was performed on a 1.0 mol scale.5 Baeyer-Villiger reaction of the ketone (5) furnished in 93% yield the acetate (6).6 Ketone (7) gave the acetate (8) in 90% yield;7 this oxidation cannot be carried out with m-CPBA.
Cyclododecanone has been oxidized to the lactone (9) (eq 2).8 The reaction has been carried out on the 250 g scale. In this case, PMA satisfactory for the Baeyer-Villiger reaction was prepared with 30% H2O2 by using enough Acetic Anhydride to react with the water present.
It has been observed that reaction of maleic anhydride with 86% H2O2 in CH2Cl2 is incomplete even at reflux temperature. PMA prepared by method (b) above reacted rapidly (15-30 min) with a slight excess of cyclohexanone at 35-40 °C to provide hexanolide in 90-100% yield.4
Aromatic primary amines (10) and (12) have been oxidized by PMA to the nitro compounds (11)2 and (13)9 in yields of 40% and 61%, respectively. The nitro compound (11) cannot be prepared from (10) using TFPAA.2
Alkenes which are not electron rich can be epoxidized by PMA; 1-octene and methyl methacrylate have been epoxidized in 80% and 74% yields.2 Adenine 1-oxide nucleotides have been prepared by oxidation of natural compounds in 75-80% yields with PMA in aqueous solution at neutral pH.10
A. Somasekar Rao & H. Rama Mohan
Indian Institute of Chemical Technology, Hyderabad, India