Peroxycarboximidic acids

An interesting method for the hydrolysis of nitriles to amides involves two redox processes with H2O2 and a peroxycarboximidic acid (236) intermediate stage, as shown in equation 84. The mechanism of hydrolysis was established for acetonitrile and benzonitrile... 

Presumably, peroxycarboximidic acid (26) is formed by the reaction of carbodiimides and hydrogen peroxide. This is eventually converted to the urea derivative during epoxidation after transfer of oxygen to the substrate. 

Scheme 5.9 shows a possible mechanism for this epoxidation reaction. First, H202 reacts with a base site on the HT surface to form a HOO species, which attacks a nitrile to generate peroxycarboximidic acid as an active intermediate oxidant. The oxygen of the peroxycarboximidic acid is transferred to an olefin molecule. Interestingly, the resulting amide can be further employed for the epoxidation of olefins in the presence of a HT catalyst [44b]. 

Reaction of aliphatic carbodiimides with 98 % H2O2 produces peroxycarboximidic acid 712, which can be used to oxidize arenes to arene oxides. ... 

When the unsaturated tertiary amine, pitprofen (179 R = H) is treated with MCPBA the reaction takes place selectively at the mwe nucleophilic nitrogen to furnish the corresponding amine oxide with the alkene moiety intact. In contrast, peroxycarboximidic acid, prepared in situ from acetonitrile/H202. reacts selectively with the alkene moiety of the ester (179 R = Me equation 65). The sterically hindered nitrogen of (179) is able to react with peroxy acids which have a low steric demand, but not with peroxy-caiixrximidic acids which have a large steric demand. 

Arene oxides. The reaction of this carbodiimide (supplier Aldrich) with hydrogen peroxide generates a peroxycarboximidic acid (1) (c/ Payne s reagent 6, 455-456). In combination with acetic acid, 1 converts phenanthrene into the 9,10-oxide (28% yield) and pyrene into the 4,5-oxide (27% yield). Some other carbodiimides can be used in this reaction. ... 

The modification of cyano groups during the N-oxidation of cyanopyri-dines (p. 198) produces different results according to the position of the cyano group. Thus, with hydrogen peroxide at pH 7 5-8, picolinonitrile gives picolinamide 1-oxide (70 per cent), nicotinonitrile forms nicotinamide 1-oxide (44 per cent) and isonicotinonitrile yields isonicotinamide (45 per cent) with only 4 per cent of the oxide. The first result is ascribed to intramolecular oxidation by the peroxycarboximidic acid, the second to similar intermolecular oxidation. The small proportion of 1-oxide from the 4-isomer may be due merely to deactivation by the 4-substituent . ... 

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