2,6-Dicarboxypyridinium chlorochromate: an efficient and selective reagent for the oxidation of thiols to disulfides and sulfides to sulfoxides

2,6-Dicarboxypyridinium chlorochromate (2,6-DCPCC) was found to be an efficient reagent for the conversion of thiols to disulfides and sulfides to sulfoxides under neutral and anhydrous conditions in good to excellent yields. Selective oxidation of thiols in the presence of sulfides at room temperature is also observed with this reagent.     

Phospho sulfonic acid as an efficient and recyclable solid acid catalyst for the solvent-free preparation of acylals

Phospho sulfonic acid (PSA) acts as a highly effective and reusable catalyst for the chemo-selective protection of aldehydes with acetic anhydride under solvent-free conditions. The desirable features of this new catalytic methodology include its sustainability, effectiveness in the absence of solvent, a facile work-up procedure, and economic viability. PSA is fully characterized by Fourier transform infrared spectroscopy, wide-angle X-ray scattering analysis, and scanning electron microscopy with energy dispersive X-ray spectroscopy. The catalyst can be reused several times without significant loss of activity. In addition, no chromatographic separations are needed to obtain the desired products.     

Nitric acid in the presence of supported P2O5 on silica gel: an efficient and novel reagent for oxidation of sulfides to the corresponding sulfoxides

This paper describes an efficient and easy method for oxidation of sulfides 1 to their corresponding sulfoxides 2 with nitric acid in the presence of supported P₂O₅ on silica gel under solvent-free conditions in high yields.     

Mn(III)-porphyrin/graphene oxide nanocomposite as an efficient catalyst for the aerobic oxidation of hydrocarbons

In this study, manganese porphyrin was grafted on the surface of graphene oxide nanosheets via covalent bonding to produce a heterogeneous catalyst. The prepared nanocomposite was characterized using X-ray diffraction, UV–vis spectroscopy, scanning electron microscopy, Fourier transform infrared, and thermogravimetric analysis. Atomic absorption spectroscopy was also used to determine the amount of the loaded catalyst. The catalytic efficiency of the immobilized Mn-porphyrin was investigated for the aerobic oxidation of alkenes and saturated alkanes in acetone under mild reaction conditions. The prepared heterogenized catalyst displays superior catalytic performance as compared to the homogeneous catalyst. Moreover, the excellent turnover number (more than 31,767) achieved for the oxidation of styrene indicates the high longevity of the supported catalyst. The catalyst structure is preserved well after the oxidation reaction and is simply reused at least five times, without any significant loss of the catalytic efficiency.     

Xanthan sulfuric acid: An efficient and biodegradable solid acid catalyst for the synthesis of bis(indolyl)methanes under solvent-free conditions

Xanthan sulfuric acid (XSA) is found to be an efficient catalyst for the electrophilic substitution reaction of indole with aromatic aldehydes to afford the corresponding bis(indolyl)methanes at room temperature under solvent-free conditions. The catalyst was characterized for the first time with the help of powder XRD, SEM–EDX and DSC–TGA. The attractive features of this green, new methodology are excellent yield of products, clean reaction profile, reusability of the catalyst, energy sustainable protocol, simple experimental and easier work-up procedures.     

Brønsted acidic ionic liquid as an efficient and reusable catalyst for one-pot synthesis of 1-amidoalkyl 2-naphthols under solvent-free conditions

A mild and efficient method has been developed for the preparation of amidoalkyl naphthols from condensation of aldehydes with amides or urea and 2-naphthol in the presence of a catalytic amount of Brønsted acidic ionic liquid ([TEBSA][HSO₄]) under thermal solvent-free conditions. High yields, short reaction time, easy work-up and reusability of the catalyst are advantages of this procedure.     

Ferric nitrate in the presence of catalytic amounts of KBr or NaBr: an efficient and homoselective catalytic media for the selective oxidation of sulfides to sulfoxides

Abstract  A mild, efficient, and highly selective oxidation method of sulfides to sulfoxides using Fe(NO₃)₃·9H₂O and catalytic amounts of KBr or NaBr in the presence of wet SiO₂ (50% w/w) has been developed. A variety of aliphatic and aromatic sulfides were selectively oxidized at room temperature in good to excellent yields. Graphical abstract        

Ru/C催化5-羟甲基糠醛选择氧化高效合成2,5-呋喃二甲醛

在活性炭负载金属钌(Ru/C)催化剂上实现了5-羟甲基糠醛的高效选择氧化.以甲苯为反应溶剂,在383 K和2.0 MPa O₂的反应条件下,2,5-呋喃二甲醛(DFF)收率高达95.8%.与活性炭负载的具有相似粒径的Pt,Rh,Pd,Au等其它贵金属催化剂相比,Ru/C具有更加优良的活性和DFF选择性.同时Ru/C催化剂结构稳定,具有良好的重复使用性能.在相似的反应条件下,采用水代替甲苯作为溶剂,同时添加少量水滑石固体碱,可便捷地将主要产物从DFF调变为5-甲酰基-2-呋喃甲酸或2,5-呋喃二甲酸,显示出Ru/C催化剂在控制5-羟甲基糠醛选择氧化反应产物方面的优异性能.     

Zinc polyoxometalate on activated carbon: an efficient catalyst for selective oxidation of alcohols with hydrogen peroxide

[PW₁₁ZnO₃₉]^5? was immobilized on activated carbon and characterized using Fourier transform infrared, X‐ray diffraction, Brunauer–Emmett–Teller and elemental analysis techniques. Effective oxidation of various alcohols with hydrogen peroxide was performed in the presence of this catalyst. Easy separation of the catalyst from the reaction mixture, cheapness, high activity and selectivity, stability as well as retained activity in subsequent catalytic cycles make this supported catalyst suitable for small‐scale synthesis. Copyright © 2015 John Wiley & Sons, Ltd.     

Copper perchlorate hexahydrate: a highly efficient catalyst for the cyanosilylation of aldehydes

Cu(ClO₄)₂·6H₂O has been found to be an efficient catalyst for cyanosilylation reaction of aldehydes in THF at room temperature with low catalytic loading (1.0 mol%) in short reaction time (mostly within 10 min). Copyright © 2008 John Wiley & Sons, Ltd.     

One‐pot synthesis of magnetic palladium–NiFe2O4–graphene oxide composite: an efficient and recyclable catalyst for Heck reaction

A magnetically separable NiFe₂O₄@GO–Pd composite (GO = graphene oxide) was successfully prepared by a facile one‐pot hydrothermal strategy. This new kind of hybrid material was fully characterized using powder X‐ray diffraction, Raman spectroscopy, X‐ray photoelectron spectroscopy, transmission electron microscopy and vibrating sample magnetometry. Structural characterizations confirmed the formation of NiFe₂O₄ and Pd nanocrystals, and the close anchoring between nanoparticles and GO sheets. Additionally, the as‐prepared NiFe₂O₄@GO–Pd nanocomposite was effectively employed in the palladium‐catalyzed Heck reaction in an ethanol–water system as a green solvent. The catalyst was completely recoverable with the simple application of an external magnetic field and with no obvious loss of catalytic activity even after six repeated cycles. Copyright © 2016 John Wiley & Sons, Ltd.     

A TEMPO-like nitroxide combined with an alkyl-substituted pyridine: An efficient catalytic system for the selective oxidation of alcohols with iodine

An efficient method for the oxidation of alcohols to aldehydes or ketones in a two-phase CH₂Cl₂/NaHCO₃ (aq.) system, using iodine and catalytic amounts of 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxyl and 2,4,6-trimethylpyridine, was developed. The performance of the method was demonstrated by the selective oxidation of 37 variously substituted alcohols in ≥90% yield, including the gram-scale synthesis of the important chemical 2,5-diformylfuran from biomass-derived 5-hydroxylmethylfurfural.     

An ionic liquid based on a cyclic guanidinium cation is an efficient medium for the selective oxidation of benzyl alcohols

A novel room temperature ionic liquid (RTIL) has been prepared containing a cyclic hexaalkylguanidinium cation. The selective oxidation of a series of substituted benzyl alcohols has been carried out in it, with sodium hypochlorite as the oxidant. The RTIL acts as both phase transfer catalyst (PTC) and solvent. The ionic liquid could be recycled after extraction of the benzaldehyde product with ether.     

Pd(l‐proline)2 complex: an efficient catalyst for Suzuki–Miyaura coupling reaction in neat water

An efficient catalytic system for Suzuki–Miyaura coupling reactions in neat water has been developed by using a water‐soluble Pd(l ‐proline)₂ catalyst. Under the optimized conditions, various biaryl compounds were obtained in good to excellent yields and a wide range of functional groups on the tested substrates were well tolerated. The catalytic system could be reused at least six times with no significant loss in its activity. Copyright © 2014 John Wiley & Sons, Ltd.     

Iron fluoride: the most efficient catalyst for one-pot synthesis of 4H-pyrimido[2,1-b]benzothiazoles under solvent-free conditions

A new iron fluoride assisted convenient and efficient strategy for the preparation of 4H-pyrimido[2,1-b]benzothiazoles derivatives in solvent-free media is described. The reactions can be performed at low-catalyst loadings with excellent functional group tolerance. The catalyst can be readily recovered and reused for next reaction for at least three runs without any significant impact on the yields of the products. The easy recovery of the catalyst and high yield of the products make the protocol attractive, sustainable, and economic.     

Solid-supported Pd(0): an efficient heterogeneous catalyst for aerobic oxidation of benzyl alcohols into aldehydes and ketones

Solid-supported nano- and microparticles of Pd(0) (SS-Pd) were used as heterogeneous catalysts for aerobic oxidation of benzyl alcohols. Primary and secondary benzyl alcohols gave the corresponding products in good yields. In addition, the catalysts could be reused up to five runs without significant loss of activities.     

Melamine trisulfonic acid:A new,efficient and recyclable catalyst for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones/thiones in the absence of solvent

Melamine trisulfonic acid(MTSA) can be used as an efficient and recyclable catalyst for the promotion of the synthesis of 3,4- dihydropyrimidin-2(1H)-ones/thiones(DHPMs) in the absence of solvent.All reactions were performed at 80℃in good to high yields.     

Silica supported sodium hydrogen sulfate(NaHSO4/SiO2): A mild and efficient reusable catalyst for the synthesis of aryl-14-H-dibenzo[a,j]xanthenes under solvent-free conditions

A simple and efficient procedure for the preparation of aryl-14-H-dibenzo[a,j]xanthenes by a one-pot condensation reaction of 2-naphthol and aryl aldehydes,in the presence of silica supported sodium hydrogen sulfate(NaHSO_4/SiO_2)as a catalyst and in the absence of solvent has been developed.The present method offers several advantages such as excellent yields,short reaction time (10-30 min),mild condition,simple work-up,and the use of a cheap and environmentally friendly catalyst with remarkable reusability.     

SiO2-NHC-Cu(I): an efficient and reusable catalyst for [3+2] cycloaddition of organic azides and terminal alkynes under solvent-free reaction conditions at room temperature

A novel SiO₂-NHC-Cu(I) 3b was developed and used as a highly efficient catalyst for [3+2] cycloaddition of organic azides and terminal alkynes. In the presence of SiO₂-NHC-Cu(I) 3b (1 mol %), the reactions of terminal alkynes with organic azides underwent smoothly to generate the corresponding regiospecific 1,4-disubstituted 1,2,3-triazoles in excellent yields under solvent-free reaction conditions at room temperature. Furthermore, catalyst 3b was quantitatively recovered from the reaction mixture by a simple filtration and reused for 10 cycles without loss of its activity.