Oxidation Of Benzoin Research Articles

Synthesis, Electrochemistry, and Oxygen-Atom Transfer Reactions of Dioxotungsten(VI) and -molybdenum(VI) Complexes with N2O2 and N2S2 Tetradentate Ligands

A series of N2O2 tetradentate ligands with a range of substituents attached to the nitrogen atoms have been prepared (H2Ln) (n = 1–9). Treatment of these ligands and the N2S2 tetradentate ligand H2L10 with [WO2Cl2(DME)] (DME = 1,2-dimethoxyethane) in the presence of triethylamine leads to the formation of cis-dioxotungsten(VI) complexes [WO2(Ln)] (n = 1–10). Reaction of the N2O2 tetradentate ligands H2Ln (n = 1, 3–7) with ammonium molybdate tetrahydrate and dilute hydrochloric acid gives the corresponding molybdenum(VI) analogs [MoO2(Ln)] (n = 1, 3–7). These compounds have been spectroscopically characterized and the molecular structures of [WO2(Ln)] (n = 1, 2, 9) and [MoO2(L5)] have been established by X-ray diffraction analysis. These high-valent compounds participate in oxygen-atom transfer reactions and can catalyze the oxidation of benzoin with dimethyl sulfoxide. The complex [WO2(L10)], which contains an S-donor ligand, has lower reduction potential and higher reactivity toward oxo-transfer reactions than analogous tungsten complexes having N2O2 ligands. The kinetics of these catalytic processes along with the structure and electrochemistry of these dioxotungsten and -molybdenum complexes are described and compared.

ORGANOPHOSPHOROUS CHEMISTRY: SELECTIVE TRANSFORMATION OF BENZOIN TO BENZIL, DESYL BROMIDE, OR BENZYL PHENYL KETONE

Reaction of benzoin with dibromotriphenylphosphorane under various conditions has been closely investigated. Benzoin was selectively converted to desyl bromide by treatment with dibromotriphenylphosphorane in the presence of triethylamine, while benzyl phenyl ketone was formed in the presence of an excess amount of triphenylphosphine. On the other hand, benzoin was effectively oxidized to bend by treatment with only bromine. The mechanism of producing these was also proposed. Desyl bromide was formed from the reaction of benzoin with dibromotriphenylphosphorane as a primary product and converted to benzyl phenyl ketone via the Perkow reaction, and benzil was formed by the oxidation of benzoin by bromine. When triethylamine or triphenylphosphine was used as an added base, these bases trapped free bromine, and the oxidation product, benzil, was formed in low yield. In the presence of triphenylphosphine as a base, the Perkow reaction of desyl bromide proceeded smoothly to give benzyl phenyl ketone preferentially, while in the presence of triethylamine, replacement of the hydroxy group to bromide occurred mainly.

Solid State Oxidation of Benzoins on Alumina-Supported Copper(ii) Sulfate under Microwave Irradiation†

Benzoins are rapidly oxidised to benzils in high yields by the solid reagent system copper(II) sulfate–alumina, under the influence of microwaves.

Cis-Dioxo-tungsten(VI) and -molybdenum(VI) complexes with N2O2 tetradentate ligands: synthesis, structure, electrochemistry and oxo-transfer properties

Treatment of [WO2Cl2(dme)] with N2O2 tetradentate ligands [H2Ln (n = 1–7)] in the presence of 2 equivalents of triethylamine gave the corresponding dioxotungsten(VI) complexes [WO2Ln] (n = 1–7). The molybdenum counterparts [MoO2Ln] (n = 1–4) were prepared in good yield by treating ammonium molybdate tetrahydrate with the respective ligands and dilute hydrochloric acid. The molecular structures of four of these complexes, namely [WO2Ln] (n = 1, 5 or 6) and [MoO2L2], as determined by single crystal X-ray analysis, revealed that the metal centre exhibits distorted octahedral co-ordination with cis-dioxo ligands. These high-valent oxo complexes are active toward oxygen atom transfer reactions and can catalyse the oxidation of benzoin with dmso. Their reactivity and electrochemical properties are discussed and compared.

Oxidation of benzoin with anchored vanadyl and molybdenyl catalysts

The organic polymer and alumina anchored vanadyl and molybdenyl complexes were found to be effective for the oxidation of benzoin with tert-butylhydroperoxide as oxidant. With some of the catalysts only benzil was formed, whereas with others three products, benzil, methyl benzoate and benzoic acid, were formed. The anchored molybdenum complexes were observed to be better catalysts than anchored vanadium complexes for the oxidation of benzoin. With the organic polymer anchored MoO 2 (salphen) catalyst, 89% of benzoin to benzil was formed. The effect of ligand, metal and support on the catalytic activity for the oxidation of benzoin has been studied.

Preparation of Methylammonium Chlorochromate Adsorbed on Alumina and Its Use in the Oxidation of Benzoins

Preparation of Methylammonium Chlorochromate Adsorbed on Alumina and Its Use in the Oxidation of Benzoins

Preparation of Methylammonium Chlorochromate Adsorbed on Alumina and Its Use in the Oxidation of Benzoins

Preparation of Methylammonium Chlorochromate Adsorbed on Alumina and Its Use in the Oxidation of Benzoins

Oxidation of Benzoins with Pyridine N-oxide-SbCl5 (1:1) Complexes.

When a mixture of a few benzoins and a pyridine N-oxide- SbCl5 (1 : 1) complex (Complex A) was boiled in nitromethane, the corresponding benzils were obtained in various yields dependent upon the kinds of substituents in each reactant. The yield of benzil becames higher by adding some tertiary amines. In this reaction, tribenzylamine is a good accelerator to promote it.When Complex A, 4-picoline N-oxide-SbCl5 (1 : 1) complex (Complex B) and 4-nitro-pyridine-SbCl5 (1 : 1) complex (Complex C) were used as the oxidant of benzoin, the order of the reaction rate was as follows : Complex C>Complex A>Complex BThe oxidation of benzoin with these pyridine N-oxide - SbCl5 (1 : 1) complexes seems to proceed according to the following there processes ; i) the oxidation by pyridine oxide-SbCl5 (1 : 1) complexes themselves ii) the oxidation by α-OSbCl4 pyridines and iii) the oxidation by the mixure of pyridine N-oxides and antimony (III) chloride.

Benzoin Oxidation at Extreme Temperature by Bis (1,2-benzenedithiolato)dioxotungstate(VI) Complex: A Model Study for Hyperthermostable Tungsten Oxidoreductases

Abstract The oxidation of benzoin by (NEt4)2[MVIO2(S2C6H4)2] (M = W (1) and Mo (2)) (S2C6H4 = 1,2-benzenedithiolate) was studied to clarify the role of tungsten ions in hyperthermostable enzymes. The reaction was analyzed by saturation kinetics, primary isotope effects of kH/kD, and the high temperture reaction at 100 °C. The rate constants were also compared with those of the selenolato analogs.

Kinetics and mechanism of oxidation of benzoin by polymer-supported N-bromo-sulphonamide

The oxidation of benzoin by polymer-supported N-bromo-sulphonamide in acetonitrile and in the presence of sulphuric acid has been studied. The reaction is first order with respect to N-bromosulphonamide and hydrogen ion concentration. The rate law and a probable mechanism, involving generation of reactive bromonium ion, are discussed.

Oxidation of benzoin to benzil and of p-substituted benzyl alcohol to the corresponding benzaldehyde catalyzed by iron(II) thiolate complexes. A proposed reaction mechanism

The catalytic p-benzoquinone or air oxidation of benzoin to benzil was carried out in the presence of [Fe II(S 2- o-xyl) 2] 2- ( o-xyl = o-xylene-α, α′-dithiolate) or [Fe II(S- t-Bu) 4] 2- in a ratio [benzoin]/[catalyst] = 20/1 in DMF at 25 °C. Under such mild reaction conditions, the Fe(II) thiolate complex exhibited high catalytic activity. In the reaction catalyzed by [Fe II(S 2- o-xyl) 2] 2-, 64% and 93% of benzoin was oxidized to benzil in 25 h by air and p-benzoquinone, respectively. In the air oxidation of benzyl alcohol catalyzed by [Fe II(S 2- o-xyl) 2] 2-, benzaldehyde was formed specifically without formation of benzoic acid. Furthermore, p-substituent effect (Cl > H > OMe) was found in the catalytic air oxidation of p-substituted benzyl alcohol. The catalytic oxidation is first order with respect to each of substrate and the catalyst at initial stage. A reaction mechanism was proposed and the rate-determining step is at the release of the methine hydrogen as a proton which is based on the kinetic isotope effect (k H/k D was 4.3 by p-benzoquinone oxidation and 5.0 by air oxidation, respectively) and p-substituent effect of substrate in the presence of [Fe II(S 2- o-xyl) 2] 2-.

Air oxidation of p-substituted benzoin to the corresponding benzil catalyzed by Fe(II)-cysteine peptide complexes

The Fe(II)-cysteine-containing peptide complexes were found exhibit catalytic activity for air oxidation of benzoin to benzil and methyl DL-mandelate to methyl benzoylformate. In the presence of [Fe(Z-cys-Gly-Val-OMe)4] 2−, the rates of catalytic air- oxidation of p-substituted benzoin indicate a trend, Br > H > CH 3 > MeO, and the isotope effect k H/k D was 3.4. The indicates that the methine hydrogen of benzoin is released as a proton in the rate determining step. Furthermore, solvent effect was found, in a non-polar solvent, e.g. 1,2-dimethoxyethane (DME), a chelating bidentate cys-peptide complex, [Fe(Z- cys-Pro-Leu-cys-Gly-Val-OMe) 2] 2−' shows higher catalytic activity than that of a non- chelating cys-peptide complex, [Fe(Z-cys-Gly-Val-OMe) 4] 2−. This is explained by the contribution of intramolecular NH---S hydrogen bonds since such hydrogen bonds stabilize the Fe(III) state which is the active species during the oxidation.

Catalytic oxidation of benzoin and p-substituted benzhydrol by p-benzoquinone or air in the presence of [Fe II(SPh) 4] 2− and [Fe II(SePh) 4] 2−

[Fe II(SPh) 4] 2− ( 1) and [Fe II(SePh) 4] 2− ( 2) exhibit high catalytic activity in the oxidation of benzoin with p-benzoquinone or air and of p-substituted benzhydrol with air under mild conditions (1 atm, 25 °C). p-Substitution of benzhydrols shows a trend in the oxidation rate: 4-Cl>H>4-OMe. Furthermore, the observed isotope effect of k H/ k D = 4.0 (catalyzed by [Fe(Sph) 4] 2− ( 1)) and 3.3 (catalyzed by [Fe(SePh) 4] 2− ( 2)) in the p-benzoquinone oxidation of benzoin indicates that the methine hydrogen of benzoin and benzhydrol is released as a proton in the rate-determining step.

O-atom transfer biomimetic oxidation of benzoin in the presence of monooxomolybdenum(IV) thiolate complexes

Novel catalytically active monooxomolybdenum(IV) species containing four thiolate ligands obtainable in solution by NaBH4 reduction of [MovO(SC6H5)4]−, [MovO(Z-cys-Val-OMe)4]−, (Z=benzyloxycarbonyl), or [MovO(S2C6H4)2]− perform the pyridine-N-oxide oxidation of benzoin in N,N-dimethylformamide at 30 °C. The order of catalytic activity is [MovO(Z-cys-Val-OMe)4]− > [MovO(S2C6H4)2]− > [MovO(SC6H5)4]− ([benzoin]/[oxidant]/[catalyst]= 20/20/1), while the oxidation by air under the same catalytic conditions gives a different order, [MovO(Z-cys-Val-OMe)4]−> [MovO(SC6H5)4]− >[MovO(S2C6H4)2]−. During the catalytic cycle in the amine-N-oxide oxidation, two intermediate species, [MoIVOL4]2− and [MoVIO2L4]2−, were detected by 1H NMR, while in the air oxidation an unidentified Mo(VT) species is involved.

Catalytic mechanism for the biomimetic oxidation of benzoin by p-benzoquinone in the presence of {Fe4S4} complexes with bulky arenethiolate or cysteine-containing tripeptide ligands

Catalytic oxidation of benzoin to benzil by p-benzoquinone in the presence of [PPh4]2[Fe4S4(tipbt)4](tipbt = 2,4,6-triisopropylbenzenethiolate) obeys first-order kinetics in the concentrations of benzoin and the catalyst. The observed rate constant was found to depend on the bulkiness of the thiolate or the peptide ligand of [Fe4S4(SR)4]2–. A complex with a bulky peptide, [Fe4S4(Z-CysS-Pro-Val-OMe)4]2–(Z = benzyloxycarbonyl, CysS = S-deprotonated cysteinate), had an activity five times higher than that of [Fe4S4(Z-CysS-Pro-Gly-OMe)4]2–. para-Substitution of benzoin indicated a trend in the oxidation rate: 4-Cl > H, 4-OMe. It is proposed that the methine hydrogen of benzoin is released as a proton in the rate-determining step. This is supported by the isotope effect (kH/kD 2.5:1) on the oxidation rate of α-C-deuteriated benzoin. An increase in the relative permittivity of the solvent results in an increase in the rate constant, indicating a polar transition state.

Polymeric oxidizing reagents based on polyacrylamides: Effect of the nature and extent of crosslinking on reactivity

AbstractAcrylamide was copolymerized with N,N′‐methylene‐bis‐acrylamide (NNMBA), tetraethyl‐eneglycol diacrylate (TEGDA), and divinyl benzene (DVB) in different proportions to afford crosslinked polyacrylamides with varying nature and extent of crosslinking. These insoluble polymers were functionalized with the N‐bromoamide function and the reactivity of the resulting polymeric N‐bromoamide was investigated under different conditions. The capacities of the reagents varied from 6.7 mequiv / g for the linear polymeric reagent to 1.1 mequiv / g for the 15% DVB‐crosslinked reagent. Oxidation of benzoin to benzil was used as the model reaction. Investigation of the reaction under different conditions of solvent and varying molar excess revealed a significant influence of the nature and extent of crosslinking in deciding the extent of reaction. In the case of NNMBA‐crosslinked reagents, the reactivity increased up to 10% crosslinking and then decreased. The reactivity of the reagents increased up to 15% crosslinking in the case of TEGDA‐crosslinked ones and for DVB‐crosslinked reagents the reactivity decreased with crosslinking. The polarity of the crosslinking agent and its molar percentage on the polymeric reagent (crosslink density) are factors affecting the solvent compatibility, which in turn, is decisive in the facilitation of the reactions.

Kinetics and mecahnism of oxidation of benzoins by peroxydisulfate catalyzed by Ag(I)

The kinetics of Ag(I) catalyzed oxidation of benzoin and four substituted benzoins by peroxydisulfate have been investigated in 30 vol. % acetic acid-water mixture at constant ionic strength. The parameters of Arrhenius and transition state theories have been computed. The rate laws are explained on the basis of a free radical mechanism.

Catalytic air and amine N-oxide oxidation of p-substituted benzoin by molybdenum(VI) complexes. Identification of the deactivation process by dioxygen

The catalytic oxidation of benzoin and two p-substituted benzoins, e.g. 4,4′-dimethoxy- and 4,4′-dichloro derivatives, by dioxygen or pyridine N-oxide, in the presence of [MoO2(cysS-OMe)2](cysS-OMe = S-deprotonated cysteinate methyl ester) and [MoO2(S2CNEt2)2] was studied kinetically. The catalytic oxidation rates indicate a trend, MeO > H > Cl, which is related to the ease in apparent hydride release from the C–H group of benzoin derivatives. The stoicheiometric oxidation indicates a similar oxo-transfer reactivity of the above complexes towards the three p-substituted benzoins. Only one 18O atom from [18O] dioxygen was found in one of the benzil carbonyl groups. The catalytic dioxygen oxidation by [MoO2(S2CNEt2)2] suffers from deactivation through the formation of [MoVO(S2CNEt2)2] formed by a one-electron-transfer reaction from [MoIVO(S2CNEt2)2] to dioxygen.

Oxidative reactivity of (NEt 4) [Mo v(SR) 4] complexes: catalytic oxidation of benzoin by proton and electron transfer

The biomimetic anion complex, [Mo vO(SC 6H 5) 4] −, exhibits catalytic oxidation activity in the reaction with benzoin in the presence of air, pyridine- N-oxide or p-benzoquinone under mild conditions. A redox cycle, [Mo vO(SC 6H 5) 4] −/[Mo IVO(SC 6H 5) 4] 2−, predominates in air and p-benzoquinone oxidations, while [Mo VIO 2(SC 6H 5) 4] 2−/[Mo IVO(SC 6H 5) 4] 2− is the preferred catalytic cycle in pyridine- N-oxide oxidation. [Mo VO(2,4,6-trimethylbenzenethiolato) 4] − and [Mo VO(2,4,6-triisopropylbenzenethiolato) 4] − also exhibit catalytic activity in similar oxidations.

Mn11-thiophenolate and -selenophenolate complexes as catalyst in air oxidation of benzoin, benzaldehyde and hydrazobenzene

Catalytic air oxidation of benzoin to benzil in N,N-dimethylformamide (DMF) occurred in the presence of [Mn(SePh)4]2- or [Mn(SPh)4]2- (with conversion of 70% and 45%, respectively ([complex]/[benzoin] =1/20, 50 h, 20 °C)). Similar oxidation of other substrates, e.g. hydrazobenzene, benzaldehyde, and benzhydrol, was also found.