Mechanistic study on the oxidation of (phenylthio)acetic acids by oxo(salen)manganese(V) complexes and the reactivity–selectivity principle

Chellamani, Arunachalam; Sengu, Paramasivan

doi:10.1016/j.molcata.2007.12.004

Cited by 9 publications

(9 citation statements)

References 56 publications

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“…It has been shown that addition of ligand oxide to the salen complex does not alter neither the λ max value nor the optical density. Similar results are observed during the oxidations of PMAAs by oxo(salen) Mn(V) complexes [64] and oxovanadium(IV)-salen. [37,39] In contradiction, addition of ligand oxide such as TPPO, PicNO, and PyO to the solution of [oxo(salen) chromium(V)] + ion [13,14] during sulfoxidation gives rise to an immediate color change from dark greenish black to emerald green, a significant red shift in the λ max and increase in absorbance in the absorption maxima.…”

Section: Spectral Observationsupporting

confidence: 82%

Impact of added ligand oxides in the sulfoxidation of phenylmercaptoacetic acids with oxovanadium(IV)‐salen complexes

Kavitha¹,

Subramaniam

2023

J of Physical Organic Chem

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The mechanistic aspects covering the effect of added ligand oxides, picoline N-oxide (PicNO), pyridine N-oxide (PyNO), and triphenyl phosphine oxide (TPPO) on the selective sulfoxidation of phenylmercaptoacetic acids to PSAA by H 2 O 2 catalyzed by oxovanadium(IV)-salen complexes have been studied spectrophotometrically in 100% acetonitrile medium. Hydroperoxovanadium(V)-salen is the reactive species in this sulfoxidation.The rate of sulfoxidation is found to be enhanced significantly by increasing the concentrations of PMAA, salen, and H 2 O 2 . The ascertained order of reactivity among the oxovanadium(IV)-salen complexes is 5,5 0dimethyl > unsubstituted salen > 5,5 0 -dichloro. The reaction is found to be impeded by the addition of ligand oxide and introduction of substituents in PMAA. The observed order of rate retardation among ligand oxides is TPPO < PyNO < PicNO. Downward Hammett plot obtained has been rationalized by change in rate-determining step from coordination of PMAA to active species for electron-withdrawing substituents to transfer of oxygen to PMAA for electron-donating substituents within the same mechanism.

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Section: Spectral Observationsupporting

confidence: 82%

Impact of added ligand oxides in the sulfoxidation of phenylmercaptoacetic acids with oxovanadium(IV)‐salen complexes

Kavitha¹,

Subramaniam

2023

J of Physical Organic Chem

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“…The range of [ 3 C*] PTA,corr /[ 3 C*] SYR,corr is 0.27–0.88 with a mean value of 0.45. A ratio less than 1 might be explained by the higher oxidation potential of PTA (1.47 V vs SHE, estimated using the Marcus equation) than SYR (∼1.17 V vs SHE), , suggesting that PTA can miss weakly oxidizing triplets that are captured by SYR. This is consistent with the PTA having a much lower rate constant than SYR with the weakly oxidizing 2-acetonaphthone triplet (Figure S8 and Table S3).…”

Section: Resultsmentioning

confidence: 99%

Evaluation of Probes to Measure Oxidizing Organic Triplet Excited States in Aerosol Liquid Water

Worland

Tran

et al. 2023

Environ. Sci. Technol.

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Oxidizing triplet excited states of organic matter ( 3 C*) drive numerous reactions in fog/cloud drops and aerosol liquid water (ALW). Quantifying oxidizing triplet concentrations in ALW is difficult because 3 C* probe loss can be inhibited by the high levels of dissolved organic matter (DOM) and copper in particle water, leading to an underestimate of triplet concentrations. In addition, illuminated ALW contains high concentrations of singlet molecular oxygen ( 1 O 2 *), which can interfere with 3 C* probes. Our overarching goal is to find a triplet probe that has low inhibition by DOM and Cu(II) and low sensitivity to 1 O 2 *. To this end, we tested 12 potential probes from a variety of compound classes. Some probes are strongly inhibited by DOM, while others react rapidly with 1 O 2 *. One of the probe candidates, (phenylthiol)acetic acid (PTA), seems well suited for ALW conditions, with mild inhibition and fast rate constants with triplets, but it also has weaknesses, including a pH-dependent reactivity. We evaluated the performance of both PTA and syringol (SYR) as triplet probes in aqueous extracts of particulate matter. While PTA is less sensitive to inhibition than SYR, it results in lower triplet concentrations, possibly because it is less reactive with weakly oxidizing triplets.

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“…Sulfur cation radical then undergoes several fast steps including oxygen transfer (OT) from the oxo function of the complex to PSAA and decarboxylation from PSAA moiety by a, b-cleavage leading to the formation of the products, methyl phenyl sulfone and CO 2 for PSAAs having electronreleasing groups. It is pertinent to mention here that on the basis of the observed linear correlation of log k 2 and E red , SET mechanism has been proposed for the sulfoxidation of PTAA [33] and sulfides [31,68] by oxo(salen)Mn(V) complexes, and oxidation of anilines by oxo(salen)Cr(V) + [47] and oxo(salen)iron(IV) [23] complexes.…”

Section: Discussionmentioning

confidence: 99%

“…Additive like 4-phenylpyridine N-oxide (4-PPNO) facilitates faster reaction rates, higher epoxide yields and improved enantio-selectivity [61][62][63][64][65][66][67] in the Mn(III) salen mediated reactions. On the other hand in the epoxidation of olefins [53] and in the oxidation of aryl methyl sulfides [29,68], aryl phenyl sulfides [30,69], sulfoxides [31,32] and arylthioacetic acids [33] by oxo(salen)manganese(V) complexes, the added LOs have no appreciable effect on the reaction rate.…”

Section: Discussionmentioning

confidence: 99%

“…Although, a large number of reports on the reactivity of oxo metal complexes with nitrogen bases as additives [23][24][25][26][27] have appeared in the literature only little interest has been paid by using ligand oxides as additives in these reactions. Even in majority of cases where ligand oxides are used as additive, no effect is observed in epoxidation [28] and sulfoxidation reactions [29][30][31][32][33]. Further, there was no detailed mechanistic study on the oxidation of phenylsulfinylacetic acid (PSAA) except our recent publications on the proximal effects of nitrogen bases with oxo(salen)Cr(V) + ion [34] and Cr(VI) oxidation of PSAA [35] mediated by cetyltrimethylammonium bromide [36], oxalic acid [37] and picolinic acid [38], though PSAA is a versatile synthetic agent used for the synthesis of antibiotics [39] and various organic compounds [40][41][42][43][44].…”

Section: Introductionmentioning

confidence: 99%

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Electrophilic and nucleophilic pathways in ligand oxide mediated reactions of phenylsulfinylacetic acids with oxo(salen)chromium(V) complexes

Subramaniam¹,

Devi

Anbarasan³

2016

Polyhedron

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a b s t r a c tThe mechanism of oxidative decarboxylation of phenylsulfinylacetic acids (PSAA) by oxo(salen)Cr(V) + ion in the presence of ligand oxides has been studied spectrophotometrically in acetonitrile medium. Addition of ligand oxides (LO) causes a red shift in the k max values of oxo(salen) complexes and an increase in absorbance with the concentration of LO along with a clear isobestic point. The reaction shows first-order dependence on oxo(salen)-chromium(V) + ion and fractional-order dependence on PSAA and ligand oxide. Michaelis-Menten kinetics without kinetic saturation was observed for the reaction. The order of reactivity among the ligand oxides is picoline N-oxide > pyridine N-oxide > triphenylphosphine oxide. The low catalytic activity of TPPO was rationalized. Both electron-withdrawing and electrondonating substituents in the phenyl ring of PSAA facilitate the reaction rate. The Hammett plots are non-linear upward type with negative q value for electron-donating substituents, (q À = À0.740 to À4.10) and positive q value for electron-withdrawing substituents (q + = +0.057 to +0.886). Non-linear Hammett plot is explained by two possible mechanistic scenarios, electrophilic and nucleophilic attack of oxo(salen)chromium(V) + -LO adduct on PSAA as the substituent in PSAA is changed from electrondonating to electron-withdrawing. The linearity in the log k vs. E ox plot confirms single-electron transfer (SET) mechanism for PSAAs with electron-donating substituents.

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Mechanistic study on the oxidation of (phenylthio)acetic acids by oxo(salen)manganese(V) complexes and the reactivity–selectivity principle

Cited by 9 publications

References 56 publications

Impact of added ligand oxides in the sulfoxidation of phenylmercaptoacetic acids with oxovanadium(IV)‐salen complexes

Impact of added ligand oxides in the sulfoxidation of phenylmercaptoacetic acids with oxovanadium(IV)‐salen complexes

Evaluation of Probes to Measure Oxidizing Organic Triplet Excited States in Aerosol Liquid Water

Electrophilic and nucleophilic pathways in ligand oxide mediated reactions of phenylsulfinylacetic acids with oxo(salen)chromium(V) complexes

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