Kinetics and Mechanism of Oxidation of Anilines by Hydrogen Peroxide As Catalyzed by Methylrhenium Trioxide

Article abstract of DOI:10.1021/jo00110a042

The oxidation of anilines by hydrogen peroxide in methanol is catalyzed by methylrhenium trioxide, CH3ReO3.The major product of the oxidation of aniline at room temperature is nitrosobenzene.For 4-substituted N,N-dimethylanilines, the N-oxide is the only product.The rate constants for the oxidation of 4-substituted N,N-dimethylanilines follow a linear Hammett relationship with ρ = -1.19.The rate constants for the reaction between CH3Re(O)2(O2), referred to as A, and 4-XC6H4-NMe2 are as follows: 4-Me, 24.5; 4-H, 18.4; 4-F, 12.7; 4-Br, 8.7; and 4-NO2, 1.0 L mol^-1 s^-1.This shows that electron-withdrawing substituents inhibit the reaction.The corresponding rate constant for the oxidation of aniline is 2.04 +/- 0.11 L mol^-1 s^-1, whereas it is 178 +/- 11 L mol^-1 s^-1 for the oxidation of N-phenylhydroxylamine to nitrosobenzene.A mechanism has been assigned on the basis of the kinetics and product yields.The data are consistent with the attack of the nucleophilic nitrogen atom on one of the peroxidic oxygen atom of A.The kinetics of the reaction of CH3ReO3 and hydrogen peroxide in methanol were also investigated.The formation of the 1:1 peroxide compound A is characterized by an equilibrium constant K₁ = 261 +/- 6 L mol^-1.The equilibration occurs rapidly: k¹ = 1150 +/- 60 L mol^-1 s^-1 and k_-1 = 4.4 +/- 0.4 s^-1 at 25.0 deg C.The bisperoxide compound, CH3Re(O)(O2)2(H2O), B, forms more slowly.The rate constant is k₂ = 308 +/- 16 L mol^-1 s^-1, and the equilibrium constant is K₂ = 814 +/- 14 L mol^-1 at 25.0 deg C in methanol.B reacts with the anilines, but much more slowly than A.