Mechanistic investigation of oxidation of aromatic anils by isonicotinium dichromate in acidic medium. A kinetic study

Abstract

Under identical experimental conditions the kinetics of oxidation of aromatic anils to benzaldehyde and nitrosobenzene, by isonicotinium dichromate, has been studied in aqueous acetic acid medium. The low dielectric constant of the medium facilitates the reactivity. Ionic strength has no significant effect on the conversion. The added Mn(II) decreases the rate of the reaction. The added acrylonitrile has no effect on the reaction rate indicating the absence of free radical mechanism. Highly negative DS # values indicate a structured transition state. The deviation of Hammett plot is noted and a concave downward curve is obtained for the anils with substituents in the aniline moiety. The observed break in the log k obs versus r is attributed to the change in the transition state whereas the linear plot is observed for the substituents in the benzaldehyde moiety. A suitable mechanism has been proposed. Graphical AbstractMechanistic investigation of oxidation of aromatic anils by isonicotinium dichromate in acidic medium. A kinetic study.

Oxidation of Aromatic Anils by Sodium Perborate in Aqueous Acetic Acid Medium

“…Since the electron releasing substituents also retard the rate of the reaction, the rate-determining step proceeds with the development of negative charge on the nitrogen atom of anil. It is to be noted that this kind of transition state has been suggested in the oxidation of anil by INDC 18 . Ramalingam and Jayanthi 18 have established the order dependence with respect to the reactants and other kinetic parameters of anils (substitution only in aniline moiety).…”

“…Anils were prepared 18 by refluxing equimolar quantities of benzaldehyde and aniline (Sigma Aldrich) in ethanol for ca. 2-3 h. The resulting solution was cooled and poured into cold water.…”

Kinetic Investigation of Oxidation of Aromatic Anils by Potassium Peroxymonosulfate in Aqueous Acidic Medium

“…It is to be noted that this kind of transition state has been suggested in the oxidation of sulfides by pyridinium chlorochromate (PCC) [47] and pyridinium dichromate (PDC) [48] and anil by isonicotinium dichromate (INDC) [36]. Gurunathan et al [36] have established the order dependence with respect to the reactants and other kinetic parameters of anils (substitution only in the aniline moiety).…”

“…Gurunathan et al [36] have established the order dependence with respect to the reactants and other kinetic parameters of anils (substitution only in the aniline moiety). The formation of oxalatochromate species is reported as the intermediate of the reaction since oxalic acid is used as a catalyst.…”

“…It is therefore possible to get several reaction constants for different substituents in one of the two rings. The kinetics and mechanism of oxidation of some substituted anils, using several oxidants, have been reported . A literature survey reveals that no report is available on the kinetics of oxidation of meta‐ and parasubstituted aromatic anils with PPMS; hence it is worthwhile to do research on the kinetics and mechanism of oxidation of anils by PPMS.…”