Organotin–oxotungstate coordination polymer: An efficient catalyst for the selective oxidation of amines

The organometallic coordination polymer [(nBu₃Sn)₂WO₄] catalyzed the selective oxidation of secondary and primary amines to nitrones and oximes, respectively. The catalyst was found to be reusable for five catalytic cycles without any appreciable loss in activity. Under the optimized reaction conditions [4 mol% catalyst, 3–4 equiv of hydrogen peroxide (30 wt%, aqueous solution), methanol as the solvent, r.t.], the corresponding nitrones and oximes were obtained with good efficiency.     

Silica aerogel–iron oxide nanocomposites: recoverable catalysts for the oxidation of alcohols with hydrogen peroxide

Various aerogels of silica gel doped with Fe₂O₃ were prepared by sol–gel method. They were calcined to produce nanoparticle solids. The nanosized mixed oxides were active in the oxidation of alcohols and produced carbonyl compounds in very good to excellent yields using hydrogen peroxide.     

Silica/A153–SO3H: An efficient catalyst for the Baeyer–Villiger oxidation of cyclic ketones with hydrogen peroxide

Silica/A153–SO₃H was prepared and characterized by FT–IR, TG and SEM. It proved to be an efficient and recyclable heterogeneous catalyst in the Baeyer–Villiger (BV) oxidation of cyclic ketones with H₂O₂ as an oxidant. Catalysts with different silica particle sizes were also made comparisons in terms of catalytic effect.     

Green and efficient oxidation of benzylic alcohols with hydrogen peroxide catalyzed by an inorganic–organic hybrid catalyst

Inorganic–organic hybrid catalysts 1-POM(M) were prepared by electrostatic interaction between transition metal-substituted polyoxometalates, {[PW₁₁MO₃₉]^4? [M?=?Cr(III), Fe(III)], [PW₁₁MO₃₉]^5?, [M?=?Mn(II), Co(II), Ni(II), Cu(II), Zn(II)], [PW₁₁VO₄₀]^4?}, and branched organic polyammonium, (tris[2-(dimethylammonium)ethyl]-1,3,5-benzenetricarboxylate), and characterized by elemental analyses, UV–vis and FT IR spectroscopic techniques, XRD, SEM, and Thermogravimetric-Differential thermogravimetric analyses. The hybrid material 1-POM(Zn) was an efficient and selective heterogeneous catalyst in the oxidation of benzylic alcohols to their corresponding carbonyl compounds with hydrogen peroxide. The catalyst was reused several times without significant loss of catalytic activity.     

Dirhodium caprolactamate and tert-butyl hydro- peroxide – a universal system for selective oxidations

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Characterization of a titanium(IV)–porphyrin complex as a highly sensitive and selective reagent for the determination of hydrogen peroxide: a computational chemistry approach and a critical review

The Ti–TPyP reagent, i.e. an acidic aqueous solution of the oxo[5,10,15,20-tetra(4-pyridyl)porphyrinato] titanium(IV) complex, TiO(tpyp), was developed as a highly sensitive and selective spectrophotometric reagent for determination of traces of hydrogen peroxide. Using this reagent, determination of hydrogen peroxide was performed by flow-injection analysis with a detection limit of 0.5 pmol per test. The method was actually applied to determination of several constituents of foods, human blood, and urine mediated by appropriate oxidase enzymes. The reaction specificity of the TiO(tpyp) complex for hydrogen peroxide was clarified from the viewpoint of the reaction mechanisms and molecular orbitals based on ab initio calculations. The results provided a well-grounded argument for determination of hydrogen peroxide using the Ti–TPyP reagent experimentally. This review deals with characterization of the high sensitivity and reaction specificity of the Ti–TPyP reagent for determination of hydrogen peroxide, to prove its reliability in analytical applications. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Pt-Sn/γ-Al2O3-catalyzed highly efficient direct synthesis of secondary and tertiary amines and imines

Versatile syntheses of secondary and tertiary amines by highly efficient direct N‐alkylation of primary and secondary amines with alcohols or by deaminative self‐coupling of primary amines have been successfully realized by means of a heterogeneous bimetallic Pt–Sn/γ‐Al₂O₃ catalyst (0.5 wt % Pt, Pt/Sn molar ratio=1:3) through a borrowing‐hydrogen strategy. In the presence of oxygen, imines were also efficiently prepared from the tandem reactions of amines with alcohols or between two primary amines. The proposed mechanism reveals that an alcohol or amine substrate is initially dehydrogenated to an aldehyde/ketone or NH‐imine with concomitant formation of a [PtSn] hydride. Condensation of the aldehyde/ketone species or deamination of the NH‐imine intermediate with another molecule of amine forms an N‐substituted imine which is then reduced to a new amine product by the in‐situ generated [PtSn] hydride under a nitrogen atmosphere or remains unchanged as the final product under an oxygen atmosphere. The Pt–Sn/γ‐Al₂O₃ catalyst can be easily recycled without Pt metal leaching and has exhibited very high catalytic activity toward a wide range of amine and alcohol substrates, which suggests potential for application in the direct production of secondary and tertiary amines and N‐substituted imines.     

Selective oxidation of sulfides to sulfoxides with cyanuric chloride and urea–hydrogen peroxide adduct

Although a number of methods have been developed for the selective oxidation of sulfides to sulfoxides, the need remains for alternative efficient, reliable strategies that can be generally applied to various sulfides and that use readily available reagents under mild reaction conditions. Herein, we report the use of urea–hydrogen peroxide adduct (UHP) and cyanuric chloride in CH₃CN at room temperature to convert sulfides to sulfoxides in excellent yields. In particular, this protocol produced sulfoxides with aromatic rings bearing electron-withdrawing groups in excellent yields.     

Copper–Schiff base complex catalyzed oxidation of sulfides with hydrogen peroxide

A straightforward, efficient, and selective oxidation of sulfide to sulfoxide with 30% H₂O₂ catalyzed by copper(II)–Schiff base complex is described. The reactions proceed under mild conditions in acetonitrile at room temperature to provide a variety of aryl and alkyl sulfoxides in excellent yield.     

Triruthenium carbonyl complexes containing bidentate pyridine–alkoxide ligands for highly efficient oxidation of primary and secondary alcohols

Reactions of substituted pyridylalkanol 6-CH₃PyCH₂CH(OH)R (R = Ph (L¹H), R = 4-CH₃C₆H₄ (L²H), R = 4-OCH₃C₆H₄ (L³H), R = 4-ClC₆H₄ (L⁴H), R = 4-BrC₆H₄ (L⁵H), R = 4-CF₃C₆H₄ (L⁶H)) with Ru₃(CO)₁₂ in refluxing tetrahydrofuran afforded the corresponding ruthenium carbonyl complexes [6-CH₃PyCH₂CHRO]₂Ru₃(CO)₈ (R = Ph ( 1a ), R = 4-CH₃C₆H₄ ( 1b ), R = 4-OCH₃C₆H₄ ( 1c ), R = 4-ClC₆H₄ ( 1d ), R = 4-BrC₆H₄ ( 1e ), R = 4-CF₃C₆H₄ ( 1f )) in good yields. These ruthenium complexes were well characterized using elemental analysis and Fourier transform infrared and NMR spectroscopies. Furthermore, their crystal structures were determined using single-crystal X-ray diffraction analysis. Complexes 1a – 1f were found to be highly active toward oxidation of a wide range of primary and secondary alcohols to corresponding aldehydes and ketones within 5 minutes in the presence of N-methylmorpholine-N-oxide as oxidant.     

A rationale of the Baeyer-Villiger oxidation of cyclohexanone to ε-caprolactone with hydrogen peroxide: unprecedented evidence for a radical mechanism controlling reactivity

We demonstrate, for the first time, in the Baeyer-Villiger oxidation of cyclohexanone with aqueous hydrogen peroxide under conditions aimed at obtaining ε-caprolactone, that a thermally activated radical reaction leads to the concurrent formation of adipic acid, even when a stoichiometric amount of the oxidant is used. In fact, ε-caprolactone is the primary reaction product, but it is more reactive than cyclohexanone, and quickly undergoes consecutive transformations. When titanium silicalite-1 (TS-1) is used as a catalyst, the high concentration of hydroxy radicals within its pores accelerates the reaction rates, and the consecutive formation of adipic acid (and of lighter diacids as well) becomes largely kinetically preferred. The proper choice of the solvent, which also may act as a radical scavenger, both without catalyst and with TS-1, is a powerful tool for controlling the rates of the various reactions involved.     

Granulated copper oxide nano-catalyst: a novel and efficient catalyst for C–N cross-coupling of amines with iodobenzene

Abstract  

Nano-structured CuO granules catalyze the C–N cross-coupling of amines with iodobenzene in excellent yields. The reaction is simple, efficient, and operates in air under ligand-free conditions.     

Ruthenium(III) chloride-catalyzed efficient protocol for ethyl diazoacetate insertion into the N–H bond of secondary amines

Ruthenium(III) chloride (1 mol%) alone can catalyze the insertion of ethyl diazoacetate into N–H bonds of various structurally and electronically diverse secondary cyclic amines under solvent-free conditions to afford the corresponding glycine esters in good yields under ambient conditions. Reactions with various aliphatic primary and aromatic amines examined, however, were unsuccessful.     

Computer modeling of radical polymerization in the butadiene–hydrogen peroxide– isopropyl alcohol system

The structure of the initiating complex in the radical polymerization of butadienes initiated by hydrogen peroxide was refined by quantum-chemical and molecular-dynamics calculations. The role of singlet–triplet transitions in the hydrogen peroxide molecule during initiation of the polymerization was identified.     

Ruthenium(III) chloride-catalyzed efficient protocol for ethyl diazoacetate insertion into the N–H bond of secondary amines

Ruthenium(III) chloride (1 mol%) alone can catalyze the insertion of ethyl diazoacetate into N–H bonds of various structurally and electronically diverse secondary cyclic amines under solvent-free conditions to afford the corresponding glycine esters in good yields under ambient conditions. Reactions with various aliphatic primary and aromatic amines examined, however, were unsuccessful. Correspondence: Dr. Srinivas R. Adapa, Indian Institute of Chemical Technology, Hyderabad 500 007, India.     

Intramolecular hydrogen bonding-assisted cyclocondensation of α-diazoketones with various amines: a strategy for highly efficient Wolff 1,2,3-triazole synthesis

A catalytic and highly efficient Wolff's cyclocondensation of α-diazoketones with aromatic and aliphatic amines has been realized for the first time by utilizing the strategy of an intramolecular hydrogen bonding-activating carbonyl group. This approach successfully solved the challenging problem of poor condensation efficiency in Wolff 1,2,3-triazole synthesis, and constitutes a powerful method for the synthesis of highly functionalized 1,2,3-triazoles.     

Reactions of acyl phosphonates with organoaluminum reagents: a new method for the synthesis of secondary and tertiary α-hydroxy phosphonates

The reactions of organoaluminum reagents (trimethylaluminum, triethylaluminum, etc.) with aryl and alkyl acyl phosphonates, which lead to the formation of α-hydroxy phosphonates in moderate to good yields, are reported. This method provides easy access to secondary and tertiary α-hydroxy phosphonates depending on the reaction conditions. The reactions of triethylaluminum with a series of acyl phosphonates at 0 °C gave the secondary α-hydroxy phosphonates, while at −100 °C they afford the tertiary α-hydroxy phosphonates.