3959-08-8Relevant academic research and scientific papers
COMPOSITES, METHODS AND USES THEREOF
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Page/Page column 28, (2021/06/04)
The present invention relates, in general terms, to methods of catalysing a reaction, including the steps of contacting a chemical entity comprising a sulphide moiety with a composite and an oxidant. The composite acts as a heterogeneous catalyst to oxidise the sulphide moiety. The present invention also relates to composites, methods of synthesising the composites and its use as a catalyst thereof.
Competitive behavior of nitrogen based axial ligands in the oxovanadium(IV)-salen catalyzed sulfoxidation of phenylmercaptoacetic acid
Kavitha, C.,Subramaniam, P.
, (2020/08/10)
The sulfoxidation of twelve phenylmercaptoacetic acids (PMAA) by H2O2 catalyzed by three oxovanadium(IV)-salen complexes, having varied substituents on PMAA and salen with regard to their position, size and inductive effect, has been performed spectrophotometrically in 100percent acetonitrile medium. Three nitrogen bases (NB), pyridine (Py), imidazole (ImH) and 1-methylimidazole (MeIm), were used as axial ligands. It has been found that the rate of sulfoxidation is not only tuned by the substituents on PMAA and salen, but it is also varied by the addition of nitrogen bases. The observed order of retardation found among the different nitrogen bases is ImH > MeIm > Py. The rate of reaction decreases with the increase in concentration of the NB axial ligands. The strongly binding ImH shows the least reactivity. Hydroperoxovanadium(V)-salen has been proposed as the sole active oxidizing species. A detailed mechanistic study reveals that the low rate constant values in the presence of the nitrogen base is due to the existence of competition of NB with H2O2 and PMAA during the formation of active species and the coordination of PMAA with active species, respectively. Both electron donating and electron withdrawing substituents on PMAA retard the sulfoxidation rate significantly. The Hammett correlation between the rate constants and substituent constants shows a non-linear concave downward curve which is explained by the existence of two different rate determining steps within the same mechanism; coordination of PMAA with the active species for electron withdrawing substituents and transfer of oxygen to PMAA for electron donating substituents. All the experimental observations are explained by proposing a suitable mechanism.
Alteration of electronic effect causes change in rate determining step: Oxovanadium(IV)–salen catalyzed sulfoxidation of phenylmercaptoacetic acids by hydrogen peroxide
Kavitha,Subramaniam
, (2019/11/13)
Sulfoxidation of a series of phenylmercaptoacetic acids (PMAA) by hydrogen peroxide catalysed by oxovanadium(IV)–salen complexes has been carried out spectrophotometrically in 100% acetonitrile medium. The formation and involvement of hydroperoxovanadium(
Fe3O4?BNPs?SiO2-SO3H as a highly chemoselective heterogeneous magnetic nanocatalyst for the oxidation of sulfides to sulfoxides or sulfones
Ghanbari Kermanshahi, Mohammad,Bahrami, Kiumars
, p. 36103 - 36112 (2019/11/20)
To achieve green chemistry goals and also to reduce the cost of catalysts as well as to avoid producing toxic wastes and show the importance of separation and recycling of catalysts from the reaction medium, in this work, we describe the preparation and characterization of magnetic acidic boehmite nanoparticles as a heterogeneous catalyst, which is called Fe3O4?BNPs?SiO2-SO3H. This catalyst works efficiently in the selective oxidation of sulfides to sulfoxides or sulfones in the presence of H2O2 as a green oxidant. It can easily be separated from the reaction medium by using an external magnet and it was recycled 6 times without loss of magnetic catalytic properties.
Tungstate supported mesoporous silica SBA-15 with imidazolium framework as a hybrid nanocatalyst for selective oxidation of sulfides in the presence of hydrogen peroxide
Sedrpoushan, Alireza,Hosseini-Eshbala, Fereshteh,Mohanazadeh, Farajollah,Heydari, Masoud
, (2017/09/07)
In this work, a new heterogeneous catalyst (SBA-15/Im/WO4 2?) was prepared, and then its performance in the oxidation of organic sulfides was studied (using 30% H2O2 as green oxidant under neutral reaction conditions). This organic–inorganic hybrid mesoporous material was characterized by various techniques, such as FT-IR, inductively coupled plasma, X-ray powder diffraction, high-resolution-transmission electron microscopy, N2 adsorption–desorption and thermogravimetric analysis. The catalyst was also applied to the selective oxidation of various sulfides. The hybrid catalyst was easily recovered, and was very stable and retained good activity for at least five successive runs without any additional activation. Moreover, there was no remarkable decrease in the activity and selectivity of the catalyst. The products could be easily isolated by just removing the solvent after filtering the catalyst. The yields of the catalytic productions through this catalyst were in the range from 75% to 97%.
Influence of sulfur groups on carboxylic acid strengths
Boschmann, Erwin,Miller, Roger D.
, p. 2617 - 2619 (2018/04/30)
The relative acid strength for a series of monocarboxylic acids of the general formula R–X–(CH2)n–COOH and related dicarboxylic acids of the general formula HOOC–(CH2)n–X–(CH2)n–COOH, where R = Ph or Me, X = CH2, –S– –SO– or –SO2–; and n = 1 or 2 as appropriate; have been studied as a function of X. It is found that sulfur containing acids have lower pKa values than the corresponding carbon analogues, that the pKa is highest for the thioacids and lowest for the sulfonyl acids, that the pKas increase as n increases, and that for the dicarboxylic acid systems only the thio members show a significant reduction in pKa (2) – pKa (1) differences upon changing n from 1 to 2.
Electrophilic and nucleophilic pathways in ligand oxide mediated reactions of phenylsulfinylacetic acids with oxo(salen)chromium(V) complexes
Subramaniam,Sugirtha Devi,Anbarasan
, p. 164 - 173 (2016/06/06)
The 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 λmax 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 electron-donating substituents in the phenyl ring of PSAA facilitate the reaction rate. The Hammett plots are non-linear upward type with negative ρ value for electron-donating substituents, (ρ- = -0.740 to -4.10) and positive ρ value for electron-withdrawing substituents (ρ+ = +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 electron-donating to electron-withdrawing. The linearity in the log k vs. Eox plot confirms single-electron transfer (SET) mechanism for PSAAs with electron-donating substituents.
Modulation of catalytic activity by ligand oxides in the sulfoxidation of phenylmercaptoacetic acids by oxo(salen)chromium(V) complexes
Subramaniam,Anbarasan,Sugirtha Devi,Ramdass
, p. 14 - 22 (2016/09/07)
Mechanism of sulfoxidation of eleven para-substituted phenyl mercaptoacetic acids (PMAAs) by three oxo(salen)chromium(V)+PF6?complexes in the presence of different ligand oxides (LOs) such as triphenylphosphine oxide, pyridine N-oxide and 4-picoline N-oxide have been studied spectrophotometrically in 100% acetonitrile medium. Spectral and kinetic profiles establish the formation of adduct, O[dbnd]Cr(V)(salen)+-LO as the reactive intermediate in the catalytic cycle. The rate of sulfoxidation is found to be enhanced significantly by the addition of LOs and introduction of substituent in PMAA and salen complex. Both electron releasing and electron withdrawing substituents in the substrate and oxidant facilitate the rate of sulfoxidation. Correlation with Hammett constants yields a non-linear concave upward curve. Based on the experimental results and substituent effects two different mechanisms, a direct oxygen atom transfer (DOT) for PMAAs with electron withdrawing substituents and a single electron transfer for PMAAs with electron donating substituents have been postulated.
A paradigm shift in rate determining step from single electron transfer between phenylsulfinylacetic acids and iron(III) polypyridyl complexes to nucleophilic attack of water to the produced sulfoxide radical cation: a non-linear Hammett
Subramaniam, Perumal,Janet Sylvia Jaba Rose, Jebamoney,Jeevi Esther Rathinakumari, Rajasingh
, p. 496 - 504 (2016/09/21)
Mechanism of oxidative decarboxylation of phenylsulfinylacetic acids (PSAAs) by iron(III) polypyridyl complexes in aqueous acetonitrile medium has been investigated spectrophotometrically. An initial intermediate formation between PSAA and [Fe(NN)3]3+ is confirmed from the observed Michaelis–Menten kinetics and fractional order dependence on PSAA. Significant rate retardation with concentration of [Fe(NN)3]3+ is rationalized on the basis of coordination of a water molecule at the carbon atom adjacent to the ring nitrogen of the metal polypyridyl complexes by nucleophilic attack at higher concentrations. Electron-withdrawing and electron-releasing substituents in PSAA facilitate the reaction and Hammett correlation gives an upward ‘V’ shaped curve. The apparent upward curvature is rationalized based on the change in the rate determining step from electron transfer to nucleophilic attack, by changing the substituents from electron-releasing to electron-withdrawing groups. Electron-releasing substituents in PSAA accelerate the electron transfer from PSAA to the complex and also stabilize the intermediate through resonance interaction leading to negative reaction constants (ρ). Conversely, electron-withdrawing groups, while retarding the electron transfer exert an accelerating effect on the nucleophilic attack of H2O which leading to low magnitude of ρ+ compared to high ρ? values of electron-releasing groups. Marcus theory is applied, and a fair agreement is seen with the experimental values. Copyright
Picolinic acid promoted oxidative decarboxylation of phenylsulfinylacetic acid by Cr(VI)
Subramaniam, Perumal,Selvi, Natesan Thamil
, p. 137 - 146 (2016/02/12)
The kinetics and mechanism of picolinic acid promoted reaction of phenylsulfinylacetic acid (PSAA) with Cr(VI) was carried out in aqueous acetonitrile medium under pseudo first order conditions. The reaction follows Michaelis-Menten type of kinetics with respect to PSAA. The catalytic activity by picolinic acid can be interpreted on the basis of the formation of a highly active oxidizing species, Cr(VI)-PA complex. The mechanism involves the formation of a termolecular complex, Cr(VI)-PA-PSAA by the nucleophilic attack of the sulfur atom of PSAA on chromium of Cr(VI)-PA complex in an equilibrium step followed by ligand coupling in a slow step. Electron releasing substituents in the phenyl ring of PSAA accelerate while electron withdrawing groups retard the reaction rate. The overall rate constants for the para- and meta-substituted PSAAs are found to correlate excellently with Hammett ó constants with a very low reaction constant, ρ.
