Structure–Reactivity Correlation in the Oxidation of Substituted Benzaldehydes by Pyridinium Bromochromate

Abstract

Oxidation of 36 monosubstituted benzaldehydes by pyridinium bromochromate (PBC) in dimethyl sulfoxide (DMSO), leads to the formation of corresponding benzoic acids. The reaction is first order with respect to both PBC and aldehydes. The reaction is promoted by hydrogen ions; the hydrogen–ion dependence has the form kobs = a + b[H+]. The oxidation of [2H]benzaldehyde (PhCDO) exhibited a substantial primary kinetic isotope effect. The reaction was studied in 19 different organic solvents and the effect of solvent was analysed using Taft's and Swain's multi-parametric equations. The rates of oxidation of para- and meta-substituted benzaldehydes showed excellent correlation in terms of Charton's triparametric LDR equation, whereas the oxidation of ortho-substituted benzaldehydes were correlated well with the tetraperametric LDRS equation. The oxidation of para-substituted benzaldehydes is more susceptible to the delocalized effect than is that of ortho- and meta-substituted compounds, which display a greater dependence on the field effect. The positive value of η suggests the presence of an electron-deficient reaction centre in the rate-determining step. The reaction is subjected to steric acceleration by the ortho-substituents. A suitable mechanism has been proposed.

Kinetics and Mechanism of Oxidation of Aliphatic Secondary Alcohols by Benzimidazolium Fluorochromate in Dimethyl Sulphoxide Solvent

“…The correlation 29 within the activation parameters like enthalpies and entropies 29 of the ten secondary alcohols oxidation was not satisfactory (r 2 = 0.9391), indicating that the compensation effect was not operative in this reaction 30 . The correlativity was in accordance with the Exnerʼs criterion [31][32] .…”

“…85% of the data 29 . Both β and α played relatively minor roles 29 . Solvent effect data were analyzed in relation to Swain's equation 35 (10), which included the cation and anion solvating 36,37 conception of the solvent.…”

Oxidation Kinetics of some Lower Oxyacids of Phosphorus by Picolinium Chlorochromate: Determination of Reactive Reducing Species

“…Picolinium chlorochromate (PICC) is also one of such compounds used for the oxidation of primary and secondary alcohols [6]. We have been interested in the kinetic and mechanistic aspects of the oxidation by complexed Cr(VI) species and several studies on halochromates including that of PICC, have already been reported from our group [7][8][9][10]. Further, the lower oxyacids are reported to exist in two tautomeric forms [11][12], and it is of interest to determine the nature and species of the oxy-acid acid that is involved in the oxidation process.…”

Kinetics and Mechanism of the Oxidation of DL-Methionine by Tetrakis(Pyridine)silver Dichromate

“…One of such compounds is tetrakis(pyridine)silver dichromate reported by Firozabadi et al 2 . We have been interested in the kinetic and mechanistic aspects of the oxidation by complex salts of Cr(VI) and several studies have already been reported from our laboratory [3][4][5][6] . It is, known however, that mode of oxidation depends upon the nature of counter-ion attached to the chromium anion.…”