Substituent effects in cooxidation: Cr(VI) – oxalic acid – sulfoxides systems

Abstract

The kinetics of cooxidation of several substituted phenyl methyl sulfoxides and oxalic acid with Cr(V1) have been carried out in the presence of perchloric acid. The reaction is first order each in sulfoxide, oxalic acid, Cr(VI), and H'. The products of oxidation are sulfones and carbon dioxide. Electron-releasing groups in the phenyl ring accelerate the rate while electron-withdrawing groups retard it. The Hammett correlation yields a reaction constant of -0.927 +-0.08 ( r = 0.994) at 313 K. Addition of aluminium nitrate prevents the occurrence of cooxidation. Based on the kinetic information a suitable mechanism has been proposed. Diary1 sulfoxides behave in an analogous manner in the cooxidation.C. SRINIVASAN, P. PANDARAKUTTY JEGATHEESAN, S. RAJAGOPAL et N. ARUMUGAM. Can. J. Chem. 65, 2421Chem. 65, (1987.Operant en presence d'acide perchlorique, on a mesure les cinetiques de cooxydation de l'acide oxalique et de plusieurs phenyl methyl sulfoxydes substitues par le Cr(V1). La reaction est du premier ordre en sulfoxyde, en acide oxalique, en Cr(V1) et en H +.Les produits d'oxydation sont les sulfones et le dioxyde de carbone. La presence sur le noyau phenyle de groupements ~lectrodonneurs provoque une augmentation de la vitesse de la reaction alors que les groupements electroaffinitaires la diminue.A 313 K, la correlation de Hamrnett conduit i une constante de reaction de -0,927 + 0,08 (r = 0,994). L'addition de nitrate d'aluminium empkche la reaction de se produire. Sur la base des informations cinetiques, on propose un mecanisme approprie. Les sulfoxydes de diaryles se cornportent d'une fason similaire lors de cooxydations.[Traduit par la revue] Introduction A dramatic rate acceleration was observed by Hasan and RoEek (I) in the Cr(V1) oxidation of a mixture of isopropanol and oxalic acid compared to the Cr(V1) oxidations of either of the above substrates. They attributed this rate acceleration to the phenomenon called cooxidation wherein both substrates undergo oxidation simultaneously. On the other hand, oxalic acid acts as a catalyst in the Cr(V1) oxidations of iodide (2) and ferroin (3). Recently the mechanisms of oxidation of alkyl aryl sulfoxides (4) and diaryl sulfoxides (5) by Cr(V1) have been reported and therefore the study of the influence of oxalic acid on the rates of Cr(V1) oxidation of sulfoxides will be of particular interest. In this paper we wish to report the salient features of the Cr(V1) oxidation of sulfoxides in the presence of oxalic acid.

Mechanism of oxidation of aryl methyl sulfoxides with sodium hypochlorite catalyzed by (salen)MnIII complexes

“…Substituent effect studies can give an insight into the mechanism of [(salen)Mn v O] + oxidation of organic sulfoxides. The observed ρ-value of −2.57 ± 0.09 is close to the ρ-values found for the oxidation of substituted phenyl methyl sulfoxides by potassium bromate [32] (ρ = −2.05) and by chloramine-T [33] (ρ = −2.02). These reactions were characterized as proceeding through an electrophilic attack by a halogen ion on the sulfur centre of the sulfoxide in the rate-determining step.…”

“…: (i) a rate-determining electrophilic attack of the oxidant on the sulfur of the sulfoxide [10,[32][33][34][35][36]; (ii) a single electron transfer from the sulfoxide to the metal ion in the rate-limiting step [37][38][39]; and (iii) a nucleophilic attack of the oxidant on the sulfoxide in the ratedetermining step [3,40,41], have been reported so far for the oxygenation of organic sulfoxides. In the present investigation, let us consider how the oxygen atom is actually transferred from the oxo species to the sulfoxide in the rate-limiting step.…”

“…In the Lewis acid catalyzed permanganate oxidation of sulfoxides [42] (ρ = −2.18), nucleophilic attack of sulfur atom on the metal centre or on the oxygen atom of the permanganate ion has been proposed. However, in the oxidation of phenyl methyl sulfoxides by dioxiranes [34] (ρ = −0.76), gemdialkylperoxonium ion [35] (ρ = −0.83), Cr(VI)-oxalic acid [36] (ρ = −0.93), methyltrioxorhenium(VII) catalyzed H 2 O 2 [43] (ρ = −0.65), and oxo(phosphine)ruthenium(IV) complexes [44] (ρ = −0.42), although low ρ-values have been observed, an S N 2 mechanism has been postulated. In the present study, since the observed ρ-value is high, similar to the ρ-value (−2.44) observed for PhIO oxidation of sulfoxides catalyzed by (salen)Mn III complexes [10] and log k 2 values are better correlated with σ p than σ + /σ + , one may anticipate an S N 2 mechanism involving the ratedetermining electrophilic attack of the oxidant on the sulfur of the sulfoxide.…”

Spectral Evidence for the One-Step Three-Electron Oxidation of Phenylsufinylacetic Acid and Oxalic Acid by Cr(VI)

“…Such complex formation between the oxidant and oxalic acid is indispensable for co-oxidation to occur [17]. In the present case too, addition of oxalic acid to Cr(VI) leads to a substantial hyperchromic shift at 263 nm and 351 nm in the UV-vis spectra of Cr(VI) (Figure 4(b)) which indicates the involvement of Cr(VI) in complex formation.…”

“…Srinivasan et al [17] reported the co-oxidation of phenylmethyl sulfoxides and oxalic acid with Cr(VI) and designed the mechanism for the reaction which also highlights the substituent effect. Das et al [18] monitored the micellar effect on the cooxidation of dimethyl sulfoxide and oxalic acid by Cr(VI) considering it as a probe for three-electron transfer in a single step.…”