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Chemoselective Reduction of Aromatic Nitro and Azo Compounds in Ionic Liquids Using Zinc and Ammonium Salts.
Abstract
Nitroarenes were chemoselectively reduced to the corresponding amines using zinc and aqueous ammonium salts in ionic liquids as a safe and recyclable reaction medium. Our results specify the effect of ammonium salts in the process; the combination of Zn/NH4Cl in [bmim][PF6] or Zn/HCO2NH4 in [bmim][BF4] were the suitable conditions for the reduction of nitroarenes. Azobenzenes were also smoothly reduced to hydrazobenzenes with Zn/HCO2NH4 (aq.) in recyclable [bmim][BF4] without any over reduction to the corresponding anilines.
... It is usually a salt of quaternary ammonium, phosphonium compound, and crown ether, etc. [31]. By using a simple phase-transfer (PT) catalyst, a diversity of liquid-liquid and liquid-solid reactions such as quats, Crown ethers, ionic liquids [35], polyethylene glycol-400 [32][33][34][35] etc. have been intensified and selective, permitting ionic species to be transmitted from aqueous part to organic part. ...
... It is usually a salt of quaternary ammonium, phosphonium compound, and crown ether, etc. [31]. By using a simple phase-transfer (PT) catalyst, a diversity of liquid-liquid and liquid-solid reactions such as quats, Crown ethers, ionic liquids [35], polyethylene glycol-400 [32][33][34][35] etc. have been intensified and selective, permitting ionic species to be transmitted from aqueous part to organic part. ...
In this article, a chemoselective reduction process of various aldehydes to their corresponding alcohols is described. An aqueous solution of various aromatic and allylic aldehydes was treated with NaBH4 and tetrabutylammonium iodide as a phase transfer catalyst by choosing appropriate concentrations to give their respective alcohols in good to moderate yield. This methodology offered several advantages, including simple environmentally benign experimental procedure, good yields, short reaction time, and no toxic by-product. DOI: http://dx.doi.org/10.17807/orbital.v13i4.1576
... Aromatic amino compounds are important organic industrial raw materials which are widely used as key intermediates in dye, pharmaceutical, herbicide, agrochemical and pesticide industry [1]. Classical methods for the synthesis of amines have involved amination of aryl halides using palladium catalysts in the presence of toxic phosphine ligands [2], amination of various groups (H, F, Cl, Br, I, OH, etc.) via the corresponding diazonium salts [3] and catalytic or non-catalytic reduction of nitroarenes [4][5][6][7][8][9][10][11][12][13]. However, the selective reduction of aromatic nitro compounds is the best route to obtain industrially important aryl amines. ...
... There are several reports in the literature for the reduction of the nitro aryl compounds, these include metal/acid reduction [4,5], catalytic hydrogenation [6][7][8], electrolytic reduction [9], homogeneous catalytic transfer hydrogenation [10] catalytic transfer hydrogenation [11][12][13], etc. However, each of these methods suffers from different drawbacks [14]: metal/acid system are readily inactivated and less selectivity and acid brings severe corrosion to the equipment; catalytic hydrogenation employs a higher reaction pressure which may bring great danger; homogeneous or heterogeneous catalytic transfer hydrogenation could perform well only in the existence of expensive metals such as palladium, platinum, and ruthenium, and separation of the target product is difficult. ...
In this paper, we report the green synthesis of the Cu/Fe3O4 nanoparticles using Silybum marianum L. seeds extract and their application as magnetically separable nanocatalyst for the reduction of nitroarenes. Our method is clean, nontoxic and environment friendly. The synthesized nanocatalyst is characterized by XRD, TEM, EDS and UV-visible techniques. UV-visible spectroscopy is used to monitor the kinetics of the Cu/Fe3O4 nanoparticles formation. The results from Fourier transform infrared spectroscopy showed that the C=O and C-O groups in the plant seeds extract played a critical role in capping the nanoparticles. The expected reaction mechanism in the formation of nanoparticles is also reported. The catalyst is recoverable by magnetic decantation and could be reused several times without significant loss in catalytic activity.
... The industrial production of Aazo is achieved by the azo-coupling reaction between a diazonium salt and an electron-rich arene, in which stoichiometric amounts of nitrite salts are used, therefore generating large amounts of dangerous wastes of diazonium salts in this process [17][18][19]. Other methods, including the oxidation of anilines by transition metals, the reduction of nitroaromatics by stoichiometric amounts of metals, and the rearrangement of aromatic azoxy compounds, have also been developed for the synthesis of Aazo [20][21][22][23][24][25]. However, these conventional procedures generally require harsh reaction conditions or a long reaction time. ...
A Schiff-base modified Pt nano-catalyst was prepared via one-pot aldimine condensation and then impregnation-reduction of a platinum precursor, in which the Pt nanoparticles (NPs) with an average size of 2.3 nm were highly dispersed on the support. The as-prepared catalyst exhibited excellent activity and selectivity in the hydrogenation coupling synthesis of aromatic azo compounds from nitroaromatic under mild conditions. The strong metal–support interaction derived from the coordination of nitrogen sites on Schiff-base to Pt NPs enables stabilizing the Pt NPs and achieving the catalytic recyclability. The scheme can also tolerate various functional groups and offer an efficient method for the green synthesis of aromatic azo compounds.
... The aliphatic and aromatic amines diazotization reaction is a common method to prepare azoic dyes by using a different of nitrosating agents under strong acids such as silica sulfuric acid [22], sulfanilic acid [23], p-toluene sulfonic acid [24], potassium hydrogen sulfate [25], nano sized iron-promoted [26], and ammonium salts [27]. The azo coupling is carried out at low temperature (0e5 C) in the presence of nucleophilic coupling compounds. ...
Novel family of azoic dyes pyrazolone based were prepared by an efficient and rapid methodology through diazotization reaction of different pyrazolone amine derivatives, in the presence of acidic ionic liquid supported on silica-coated magnetite nanoparticles as acidic catalyst at room temperature and under solvent-free conditions.
The attractive advantages of the present process include short reaction times, milder and cleaner conditions, higher purity and yields, easy isolation of products, easier work-up procedure and lower generation of waste or pollutions. This catalyst was easily separated by an external magnet and the recovered catalyst was reused several times without any significant loss of activity. Therefore, this method provides improved protocol over the existing methods.
... 4-Isoxazoline 5daa underwent reductive cleavage of the N-O bond successfully in the present of zinc powder and NH 4 Cl at 75 C, affording allylic alcohol 6 in a yield of 75%. 8,21 Besides, it was found that Co 2 (CO) 8 catalyzed rearrangement of 4-isoxazoline 5raa could occur in MeCN, giving enamide 7 in 52% yield, instead of ring contraction product acylaziridines. 22 While the mechanism for Co 2 (CO) 8 catalyzed rearrangement is not clear at present, further examination of the rearrangement reaction conditions and mechanism will be carried out in due course. ...
A [3 + 2] cycloaddition of indanone-derived nitrones and alkynes under mild conditions is developed, allowing facile synthesis of spirocyclicindenyl isoxazolines with structural diversity. The sequential protocol of generated in situ ketonitrone from unsaturated ketones and N-alkylhydroxylamines is also achieved successfully, affording the desired products in considerable yield with moderate to good diastereoselectivity. Moreover, the spirocyclic product can be conveniently transformed into indenyl-based allylic alcohol and enamide.
... It is in consistent with previous literatures. 7,28 In heterogeneous systems, it is demonstrated that there are four steps in the reduction of aromatic nitro compounds: (i) absorption of hydrogen, (ii) absorption of aromatic nitro compounds to the metal surfaces, (iii) electron transfer mediated by metal surfaces from BH 4 À to aromatic nitro compounds. ...
Synthesis of CuO nanoparticles using peel of Musa balbisiana and its application in reduction of nitro aryl compounds are reported here. CuO nanoparticles were characterized by using XRD, XPS, PL, SEM and TEM technique. In XRD analysis, significant peaks appeared at 18.3, 24.4, 33.6, 34.6, 35.2, 38.2 and 42.7 respectively. The BET surface area and total pore volume of CuO was found to be 7.479 m2/g and 0.1259 m3/g respectively. The generated CuO nanoparticles exhibited inter planar lattice fringes spacing of 0.16 nm. SEM images indicate the formation of flower like CuO architecture. The hierarchical CuO architecture is found to be made up of nanosheets which were self assembled to form flower like nanostructure. The synthesized CuO nanoparticles show efficient catalytic activity in reduction of nitro aryl compounds to corresponding amino compounds with high yield of conversion (74-96%). The reaction was carried out in a greener solvent i.e. water. The catalyst was found to be active for several runs. It was further confirmed by several experimental evidences
... 18 Selecting the proper reductant for nitro groups that would work efficiently in complex biological systems constitutes a great challenge. Such reductants as palladium-on-carbon, 19 or Raney nickel, 20 sodium hydrosulfite, 21 tin(II) chloride, 22 iron in acidic and alkaline media, 23 titanium(III) chloride, 24 zinc, 25 and samarium 26 are used in laboratory organic synthesis to obtain aromatic amines. However, it appears that the choice of a proper reductant that might be applied in biological systems may be based on metal complexes which can act as artificial enzymes. ...
A novel and effective method is presented for modulating the stability of 2-Pyridinyl Thermolabile Protecting Groups (2-Py TPGs) in the "chemical switch" approach. The main advantage of the discussed approach is the possibility of changing the nucleophilic character of pyridine nitrogen using different switchable factors, which results in an increase or decrease in the thermal deprotection rate. One of the factors is transformation of a nitro into an amine group via reduction with a low-valent titanium in mild conditions. The usefulness of our approach is corroborated using 3'-O-acetyl nucleosides as model compounds. Their stability in various solvents and temperatures before and after reduction is also examined. Pyridine N-oxide and pH are other factors responsible for the nucleophilicity and stability of 2-Py TPG in thermal deprotection. Protonation of 4-amino 2-Py TPG is demonstrated by 1H-15N HMBC and HSQC NMR analysis.
... The reduction of nitro-compounds is one of the important and well accessible strategies for amine syntheses. The different catalytic reduction methods using metal-based catalysts [5][6][7], electrolytic reductions [8], homogeneous/heterogeneous catalytic hydrogenation [9,10] are largely utilized. Nevertheless, the utilization of these metals has several shortcomings, such as the use of costly metals, environmentally hazardous reagents, difficulties to recover homogeneous catalysts, and corrosion to the equipment. ...
A highly efcient nitrogen-doped carbon sheet-like material (NCS) is developed via simple pyrolysis of β-cyclodextrin
and urea at diferent temperatures. The efect of the pyrolysis temperature (500–800 °C) on the nitrogen species present
in the catalysts is thoroughly studied. These nitrogen species formed by the pyrolysis are proven to be the active sites for
chemical conversion. These catalysts containing a significant amount of nitrogen with a high degree of defects display
excellent catalytic activity towards the reduction of nitro compounds. The effect of solvents, reaction time, and temperature
in nitrobenzene reduction reaction is also studied. This protocol can be easily utilized industrially due to its several excellent
features such as short reaction time, use of green solvent, column chromatography free, and applicable to the gram scale.
Besides, after the reaction, the NCS catalyst can be easily recovered and reused up to five runs without significant loss on
its catalytic activity.
... However, the remaining amine-containing aromatic by products in these processes poses environmental and health risks. As a result, many strategies have been developed for reducing the nitro substrates including metal/acid reduction [27][28][29], catalytic hydrogenation [30], hydrogenation at homogeneous catalytic transition [31], and hydrogenation at heterogeneous catalytic transfer [32,33]. Nonetheless, these processes have some significant disadvantages; for instance, metal/acid system has shown poor selectivity and it is ecologically hazardous; besides, catalytic hydrogenation is not favored duo to applying H 2 gas at high temperature, and it is not feasible to retrieve the homogeneous or heterogeneous catalysis after the reaction [34,35]. ...
Nitro-aromatic pollution in industrial waste streams threat wellbeing of water resources. This study investigates the performance of a copper-based nano catalyst to reduce nitro-aromatic compounds in aqueous solution. Anchoring Cu NPs within the nano spaces of a fibrous silicate with high surface area, and simple accessibility of active sites were successfully established by a facile approach to produce a novel nanocatalyst (DFNS/PEI/Cu). DFNS displayed different properties such as dandelion-like shape, high surface area, and simple availability of active sites. Immobilization of the Cu NPs on DFNS nanospheres not only prevented their aggregation, but also considerably improved the availability of the catalytic active sites. The DFNS/PEI/Cu nanocatalyst demonstrated great catalytic activities for the reduction of nitro compounds under green conditions. Our findings show fibrous DFNS and Cu NPs as a helpful platform for the fabrication of noble metal-based affordable nanocatalyst for many catalytic applications.
Graphic Abstract
DFNS/PEI/Cu nanocatalyst as a new adsorbents for the reduction of nitro compounds
... In general, selective reduction of nitroarenes to aromatic amines has served as one of the most constantly used methods in both industry and laboratory (Kabalka and Varma 1991;Ullmann 2012;Blaser et al. 2001;Nishimura 2001;Arnold et al. 2008;Nugent 2010). Conventionally employed methods require the use of stoichiometric amounts of iron (Chandrappa et al. 2010;Desai et al. 2001;Gamble et al. 2007) or other metals (Kelly and Lipshutz 2014;Khan et al. 2003;Mahdavi and Tamami 2005;Basu et al. 2000;Ankner and Hilmersson 2007) in combination with large excess of various proton sources, and thus generate huge amounts of wastes. Nowadays, transition-metal catalyzed hydrogenation of aromatic nitro compounds to aromatic amines has been considered as a potential alternative and significant progress has been made (Nishimura 2001;Orlandi et al. 2018;Jagadeesh et al. 2013;Wang et al. 2010;Corma et al. 2008). ...
A novel protocol for chemoselective reduction of aromatic nitro compounds to aromatic amines has been established. The metal-free reduction goes through a hydrogen transfer process. Various easily reducible functional groups can be well tolerated under the optimized reaction conditions.
... There have been several studies on improving the catalytic performance and selectivity for selective reduction of aryl nitro compounds to anilines [8] as well as N-formylation of anilines with various formylating agents [9][10][11][12][13][14][15][16][17]. Conventionally, stoichiometric amounts of metallic reagents is used for the reduction of nitroarenes, such as iron [18,19], tin [20], zinc [21,22] in the presence of an acid, Raney nickel-based systems [23,24], and hydrogen gas as reducing agent [25][26][27][28]. Although convenient, the major concern with these systems is stoichiometric amount of metallic reagents which are not environmentally benign, use of fiery hydrogen gas under drastic conditions of high pressure and temperature, difficulties in handling H 2 gas on an industrial scale, and/or poor selectivity of the reaction process in multi-reducible functional nitroarenes. ...
Palladium nanoparticles (~ 1–3 nm, 0.4 wt% Pd) were uniformly distributed over the surface of fibrous silica nanospheres (KCC-1) modified via aminopropyltriethoxysilane using a fast and cost-effective palladium (II) chloride reduction process. The Pd nanoparticles (Pd NPs) distribution over the ensuing catalyst Pd/KCC-1-NH2 showed much more uniform distribution, and smaller size compared with the tedious hydrothermal reduction method. The morphological, chemical, and size analyses of Pd/KCC-1-NH2 by BET, UV–Vis spectra, XRD, HR-TEM, EDS and XPS analysis revealed that the succeeding material consist of a distinct fibrous silica nanospheres support adorn with Pd NPs. The resultant nanocatalyst was tested for the one-step reductive aminoformylation of aromatic nitro compounds using formic acid. A wide range of substituted nitroarenes including electron withdrawing, releasing, sterically hindered and multifunctional groups have been converted to corresponding aryl formamide in quantitative yields (yields up to 98%) at moderate temperature (70 °C). Optimization study has proved that the 6 equivalent of formic acid is required and toluene was found to be the better solvent. The established practice is beneficial due to the use of formic acid as H2 source and formylating agent, easiness in handling of the catalyst and simple workup procedure with efficient catalyst reusability.
Graphic abstract
... Amines serve as versatile intermediates in the synthesis of pharmaceuticals, polymers, pesticides, explosives, fibers, dyes and cosmetics [2e4]. The traditional method of the reduction of nitro compounds required the use of stoichiometric amount of metal under acidic conditions, thus generated a large amount of waste [5,6]. In contrast to the traditional method, the catalytic hydrogenation of nitro compounds has received a great interest due to its high efficiency, high selectivity and more environmental-friendly. ...
The hydrogenation of nitro compounds into amines is of great importance both from academic and industrial points. In this study, graphene oxide was simultaneously decorated by Fe3O4 and Pd nanoparticles to generate magnetic C-Fe3O4-Pd catalyst, which showed high catalytic activity towards the transfer hydrogenation of nitro compounds by the use of NaBH4 as the hydrogen donor at room temperature. Aniline was produced in a high yield of 99% after 30 min at 25 degrees C. A wide variety of substituted nitroarenes with other reducible groups were also successfully converted into the corresponding amines with high yields. Kinetic studies revealed the active energy of the transfer hydrogenation of nitrobenzene was 31.1 kJ mol(-1). One of the main reasons of the high catalytic activity of the C-Fe3O4-Pd catalyst was due to the fact that the catalyst showed high ability to absorb the substrate on its surface. The transfer hydrogenation of nitrobenzene was confirmed to proceed via azobenzene as the intermediate. More importantly, the catalyst was very stable without the loss of its catalytic activity.
Chemoselective reduction of nitro group in polyfunctional nitrophenyl 2-oxobut-3-enyl Cglycopyranosides to the respective aminophenyl 2-oxobut-3-enyl glycopyranosides with SnCl2·2H2O under ultrasonic vibration in good yields was achieved successfully. Other potentially reducible groups such as carbonyl, ester, azide, tosyl, alkenic substituents were unaffected during reaction. The 2′-nitrophenyl-2-oxobut-3-enyl glycopyranosides as reduction substrates gave 2-quinolinemethyl glycopyranosides via reduction followed by intramolecular cyclocondensation reactions. These β-C-glycopyranosides hold great promise in medicinal chemistry.
The catalytic properties of phosphate rocks (natural phosphates: NP) and their role as a catalyst or catalyst support were discussed in the light of the versatility and potential of phosphate‐based catalysts. NP have both acidic and/or basic properties, structure flexibility, capacity to disperse a catalytic active phase (e.g. metal salts), and low cost. Thus, NP have been studied as catalytic materials in several chemical processes, in particular in organic synthesis, with interesting catalytic efficiency. This chapter is dedicated to the study of NP in several application in organic chemistry such as condensation, cross‐coupling, alkylation reactions, hydration of aromatic nitriles, hydrogenation, reduction, reforming of methane, etc.
The chemoselective transfer hydrogenation of nitroarenes into anilines was investigated using immobilized iron metal containing ionic liquid (ImmFe-IL) as a versatile heterogeneous catalyst. The present protocol has high atom efficiency with excellent chemosectivity and regioselectivity. Selective reduction of the nitro group was observed in the presence of other reducing functional groups such as nitrile, ketone, acid, amide, ester, halogens, hydroxyl, olefin, and heterocycles. The developed protocol is also highly selective toward conversion of dinitroarenes into nitroanilines. The present catalytic system uses environmentally benign ethylene glycol as a solvent which is inexpensive, easily available, nontoxic, nonvolatile, nonflammable, thermally stable, and biodegradable. The catalyst was reused up to four consecutive cycles with high activity and selectivity. The fresh catalyst and recycle catalyst was well characterized by XPS analysis.
N-Arylhydroxylamines were prepared in high yields through chemoselective reduction of the corresponding aromatic nitro compounds under ultrasound (59 kHz) at room temperature using a convenient Zn/HCOONH4/CH 3CN system. This method was highly efficient, environmentally benign, especially simple and practical.
A fundamental reduction reaction, nitrobenzene to aniline in SnCl2 and hydrochloric acid, was investigated by density functional theory (DFT) calculations. First, the change of SnCl2 SnCl42− Cl4SnH− was discussed, and the reaction path of SnCl42− + H3O+ Cl4SnH− + H2O was obtained. Starting from nitrobenzene, six elementary processes were found so as to arrive at the protonated aniline. The hydride ion from Cl4SnH− is connected always to the cationic nitrogen, and the proton is always to oxygens. An intermediate PhN+H2OH was obtained, which is isomerized to the para OH adduct protonated imine via the Bamberger rearrangement. This species may undergo the H− acceptance at the sp2 N+H2 center. In the nitrobenzene reduction, the proton enhances the electrophilicity of the nitrogen center, which makes the hydride shift ready. NH bonds are formed, and NO bonds are cleaved both by the proton attach and subsequent H2O elimination and by the formal [1,5] OH shift. Copyright
Reduction of nitrobenzenes to prepare anilines is an important process. The progress of the selenium-catalyzed of nitrobenzenes with CO/H2O to prepare anilines is reviewed in detail. The process of selenium-catalyzed reduction with CO/H2O from high pressure reaction to atmospheric reaction is introduced. It is pointed out that the selenium-catalyzed reduction of nitrobenzenes with CO/H2O to prepare anilines in atmosphere is a convenient and environmentally benign method.
Ionic liquids (ILs) have been used in numerous applications in chemistry. Wet ILs constitute a new class of solvents with their own new and interesting properties. The properties of ILs are significantly influenced by the addition of water and also affect reaction rates and selectivity. IL/water mixing makes it easy to control the properties of the solution and the formation of these ionic liquid mixtures increases synthetic flexibility. In this review, mixtures of IL/water solvent system promoted organic reactions have been described and the results are compared with other solvent systems. In many cases IL/water combinations were superior compared to conventional organic solvents and biphasic IL/organic co-solvent media with respect to catalytic performance as well as to catalyst separation and recycling.
Simple ion exchange of the chloride anion of an ionic-liquid-functionalized magnetic nanoparticle with [PdCl4]2− provided a highly water-dispersible and magnetically separable palladium catalyst that exhibited excellent activity toward transfer hydrogenation reactions in water as a solvent. The catalyst demonstrated outstanding performance in aqueous-phase transfer hydrogenation of various nitroarenes in a highly chemo- and regioselective manner by using HCOONH4 as a low-cost, green, and easily available hydrogen donor. Also, by using only 0.25 mol % of the catalyst and formic acid as both a hydrogen donor and formylating agent, the catalyst showed excellent activity in the one-pot, direct synthesis of N-arylformamides from nitroarenes in water as a solvent. Notably, owing to the presence of a hydrophilic ionic liquid on the surface of silica-coated iron oxide nanoparticles, the catalyst showed highly stable dispersion in water, as evidenced by the zeta potential and extremely low affinity to the organic phase. These features make this catalyst system suitable for an efficient double-separation strategy (successive extraction/final magnetic separation). The recovered aqueous phase containing the catalyst can be simply and efficiently reused in eight runs without a decrease in activity and can be easily separated from the aqueous phase at the end of the process by applying an external magnetic field.
Herein, we report a novel well-defined diamino Mo3S4-based catalyst system for the reduction of nitroarenes and azo compounds to the corresponding anilines with silanes as reducing agents. This catalytic protocol provides a facile route to access aromatic amines under mild conditions in good to excellent yields. Notably, even anilines functionalized with other potentially reducible moieties are obtained with high selectivity. The new chemoselective catalyst of formula [Mo3S4Cl3(dmen)3](BF4) (dmen: N,N′-dimethylethylenediamine) is conveniently synthesized through coordination of the diamine ligand to the incomplete Mo3S4 cubane-type cluster core in a one-pot two-step procedure. The crystal structure of the [Mo3S4Cl3(dmen)3]+ cation confirms the formation of a single isomer in which the chlorine atom lies trans to the bridging sulfur atom to afford a C3 symmetry complex with intrinsic backbone chirality. The structure is preserved in solution, as evidenced by multinuclear NMR spectroscopy and electrospray-ionization mass spectrometric techniques.
A direct amidation of aldehydes or benzyl amines with azobenzenes through TBHP-mediated N=N double bond cleavage of azobenzenes has been developed. A series of amide compounds with a wide range of functionalities were obtained with moderate to good yields. To the best of our knowledge, it is the first example for the N=N double bond cleavage of azobenzenes used in synthesizing amide compounds.
[1314-15-4] O2Pt (MW 227.08) InChI = 1S/2O.PtInChIKey = YKIOKAURTKXMSB-UHFFFAOYSA-N(catalyst for hydrogenation of various functional groups with minimal hydrogenolysis problems; used as dehydrogenation catalyst; used for selective oxidation of primary alcohols)Alternate Name: Adams’ catalyst.Solubility: insol most organic solvents.Form Supplied in: dark brown solid, usually hydrated with 2 or more mol of H2O.Analysis of Reagent Purity: elemental analysis.Handling, Storage, and Precautions: no precaution is necessary with the oxide, but after exposure to H2 the Pt black must be handled as a pyrophoric reagent; the general precautions for handling hydrogenation catalysts should be followed; during filtration the filter cake must not be allowed to go dry; if a filter aid is necessary, a cellulose-based material should be used if catalyst recovery is desired.
This work deals with selective reduction of aromatic nitro compounds to corresponding symmetrical substituted azo compounds using nitrogen-doped TiO2 nanoparticles as photocatalyst in the presence of a catalytic amount of formic acid. Various azo compounds containing additional reducible substituents including halogens, and carboxyl and phenol functions have been synthesized in a single step by use of this catalyst. The conversion was reasonably fast, clean, and high yielding at room temperature. A mechanism of formation for the azo compounds is proposed. The behavior of the N/TiO2 catalyst is of particular interest because this is the first time, as far as we know, that formation of azo compounds has been catalyzed by an N-doped TiO2 photocatalyst. Nitrogen-doped TiO2 was prepared by a simple modified sol–gel process with urea as nitrogen source. The catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy, and transmission electron microscopy. The chemical nature of N was identified by XPS as N–Ti–O in the anatase TiO2 lattice.
The binary composite ionic liquid mixtures composed of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) and 1-butyl-3-methylimidazolium acetate ([bmim][Ac]) were studied and used in electroreduction of nitrobenzene for the first time. 1H NMR and Fourier transform infrared (FTIR) spectroscopy were carried out to acquire a deep understanding of the interaction of binary ionic liquids, and UV/Vis spectroscopy was used to study the interaction between the mixture of ionic liquids and nitrobenzene. It was found that chemical shifts of all protons were changed and significant changes in the anion IR bands were induced, and the UV maximum absorption wavelength and absorbance of nitrobenzene in binary ionic liquids were different from those in the neat ionic liquid. The electrochemical reduction behavior of nitrobenzene in binary composite ionic liquids on platinum electrode was studied by cyclic voltammetry, in situ Fourier transform infrared spectroscopy, and constant potential electrolysis. Results indicated that the reduction of nitrobenzene in binary composite ionic liquids demonstrated higher current densities with a more positive potential, and the product (azobenzene) showed higher yield and selectivity in the composite ionic liquids than in the neat ionic liquids; the concentrations of water in the binary mixtures of ionic liquids had great effect on the electrochemical behavior of nitrobenzene. In the end, the mechanism of reduction of nitrobenzene in binary mixtures of ionic liquids was discussed.
A newly developed protocol for the reduction of nitroarenes using thiourea as the hydrogen source is described. The method is simple, inexpensive and easily applicable to the preparation of a variety of substituted anilines with high yields and selectivity. In contrast to traditional hydrogenation methods, this chemistry does not require a catalyst, elaborated work-up procedures, or the use of high-pressure equipment. Make me an amine: A new protocol for the chemoselective reduction of nitroarenes to primary amines is disclosed. Thiourea was used as an efficient reducing agent for the reduction of various nitroarenes with satisfactory yields (24examples, 34-97% yield). Reduction-sensitive functional groups including nitriles and ketones were unaffected. This chemistry is mild and free of transition-metal catalysts.
A convenient, environmentally benign, and highly efficient protocol for the preparation of N-aryl-hydroxylamines from the corresponding nitroarenes in a Zn/HCOONH 4 /CH 3 CN system under ultrasound is described. The advantages of the present method include high chemoselectivity, simple and practical work-up procedure and high yield.
Some benzimidazole derivatives were designed and screened via molecular docking. Six compounds which obtained high scores were selected for synthesis and all compounds were characterized by 1H- and 13C-NMR, and HR-ESI-MS. Subsequently, these compounds were evaluated for their inhibitory activities on thrombin. Compound 5a (IC50 3.11 nm) showed a better activity than the reference argatroban (IC50 9.88 nm). These results, along with related molecular model studies, indicated that 5a could be a potential thrombin inhibitor for further research. This article is protected by copyright. All rights reserved.
Magnetic hydroxyapatite (HAP) supported Pd nanoparticles (γ-Fe2O3@HAP-Pd) were used for the transfer hydrogenation of nitro compounds with HCOONH4 as hydrogen donors. Aniline was produced in an excellent yield (>99%) in water at 25 °C with 6 equiv. HCOONH4. This process is suitable to a wide range of nitro compounds with excellent yields for most cases. Both the HAP support and the Pd nanoparticles showed a synergistic effect on the transfer hydrogenation of nitro compounds. Furthermore, the γ-Fe2O3@HAP-Pd catalyst was stable.
The reduction of the nitro group represents a powerful and widely used transformation that allows to introducing an amino group in the molecule. New synthetic strategies for complex functionalized molecular architectures are deeply needed, including highly efficient and selective nitro reduction methods, tolerant of a diverse array of functional moieties and protecting groups. Since chiral amino groups are ubiquitous in a variety of bioactive molecules such as alkaloids, natural products, drugs and medical agents, the development of reliable catalytic methodologies for the nitro group reduction is attracting an increasing interest also in the preparation of enantiomerically pure amines. In this context, the modern reduction methods should be chemoselective and respectful of the stereochemical integrity of the stereogenic elements of the molecule. The review will offer an overview of the different possible methodologies available for this fundamental transformation, with a special attention on the most recent contributions in the field: hydrogenations, metal dissolving and hydride transfer reductions, catalytic transfer hydrogenations and metal-free reductions. The main advantages or limitations for the proposed methods will be briefly discussed, highlighting in some cases the most important features of the presented reduction methodologies from an industrial point of view.
Sustainable development demands an environmentally friendly and efficient method for the hydrogenation of organic molecules, including the hydrogenation of functionalized nitroarenes. In this study, a highly active and selective metal–organic framework‐supported palladium catalyst was prepared for the catalytic hydrogenation of nitroarenes. High selectivity (>99%) and excellent yield (98%) of aniline were realized after 2 hours in ethanol under hydrogen (1 atm) at room temperature. The reductions were successfully carried out in the presence of a wide range of other reducible functional groups. More importantly, the catalyst was very stable without the loss of its catalytic activity after five cycles. A kind of metal–organic framework‐supported Pd catalyst was used for hydrogenation of nitroarenes under ambient conditions (1 atm H2, room temperature), which displayed excellent catalytic activity for the hydrogenation of various nitroarenes.
The high atom-economical and eco-benign nature of hydrogenation reactions make them much more superior to conventional reduction and transfer hydrogenation. Herein, a convenient and highly selective hydrogenation reaction of azoarenes using molecular hydrogen to access diverse hydrazoarenes is reported. The present catalytic method is general and operationally simple, and it operates under exceedingly mild conditions (room temperature and 1 atm of hydrogen pressure). The reusability of catalysts used in this method is also successfully demonstrated.
P, Se-codoped g-C3N4 (PSeCN) nanosheet was in situ prepared by facile thermal polymerization of melamine, phosphonitrilic chloride trimer, and selenium black powder as the precursors. It was found as a suitable support for the immobilization of silver nanoparticles (Ag NPs). The prepared nanocatalyst was fully characterized via standard analysis methods including EDX, ICP-OES, XRD, FT-IR, SEM, TEM, and BET. This PSeCN/Ag nanocatalyst with a higher specific surface area compared with CN, showed excellent catalytic activity towards the reduction of several nitroaromatic compounds using sodium borohydride (NaBH4) in short reaction times with high efficiency and good selectivity in water as a green solvent. Significantly, the above-mentioned nanocomposite could be reused six times without appreciable loss of its catalytic activity.
A visible-light-promoted transfer hydrogenation of azobenzenes has been developed. In the presence of B2pin2 and upon visible-light irradiation, the reactions proceeded smoothly in methanol at ambient temperature. The azobenzenes with diverse functional groups have been reduced to the corresponding hydrazobenzenes with a yield of up to 96%. Preliminary mechanistic studies indicated that the hydrogen atom comes from the solvent and the transformation is achieved through a radical pathway.
Water is an essential substance for life on earth and for all living things. Plants and animals need almost pure water to live; if it is contaminated with harmful chemicals and micro organisms, it will be impossible for them to survive. This study has tried to investigate the performance of catalyst to reduce nitro-aromatic combinations in the attendance of NaBH4 solution duo to the hydrogen source. TEMPO@FeNi3/DFNS–laccase MNPs was prepared, and its features were reviewed using SEM, TEM, XRD, TGA, VSM, AFM, and FTIR. Then, its strength as a nanocatalyst for removal of nitro-aromatic combinations was tested in contact time, initial concentration, the effects of pH and nanocatalyst amount was study. The results of this research proved that TEMPO@FeNi3/DFNS–laccase MNPs has a good return in removal of nitro-aromatic combinations, as its easy synthesis and reliable recovery.
A highly versatile and flexible copper nanoparticle (Cu(0) NPs) catalytic system has been developed for the controlled and selective transfer hydrogenation of nitroarene.
Interestingly, the final catalytic product is strongly dependent on the nature of the hydrogen donor source. The yield of nitrobenzene reduction to aniline increased from 20% to an almost quantitative yield over a range of alcohols, diols and aminoalcohols. In glycerol at 130 °C aniline was isolated in 93% yield. In ethanolamine, the reaction was conveniently performed at a lower temperature (55 °C) and gave selectively substituted azobenzene (92% yield). Experimental studies provide support for a reaction pathway in which the Cu(0) NPs catalysed transfer hydrogenation of nitrobenzene to aniline proceeds via the condensation route. The high chemoselectivity of both protocols has been proved in experiments on a panel of variously substituted nitroarenes. Enabling technologies, microwaves and ultrasound, used both separately and in combination, have successfully increased the reaction rate and reaction yield.
We report a reinterpretation of the reduction of 4-nitrophenol catalyzed by silver nanoparticles. Mass spectrometry and UV-vis spectroscopy measurements support the existence of 4-nitrosophenol as a stable reaction intermediate. We propose that dissolved oxygen is consumed – both by oxidizing 4-nitrosophenol (an intermediate) and re-oxidising the reduced catalyst surface – resulting in the commonly observed ‘induction period’ in the reaction kinetics. Upon complete consumption of dissolved oxygen, subsequent reduction to 4-aminophenol can occur. A complete kinetic analysis including modelling is presented, conceptually fitting data from recent reports in the literature as well as fitting data from our own experiments.
Hydrazines represent a class of compounds with high interest due to their applicability as versatile starting materials in many important transformations. Herein, we report a synthetic approach to hydrazine derivatives...
Reduction of Fe(II)EDTA[single bond]NO as well as Fe(III)EDTA is the main process for simultaneous removing nitric oxide and sulfur dioxide with Fe(II)EDTA solution. In this paper, iron powder was proposed to reduce the Fe(II)EDTA[single bond]NO. The mechanism and kinetics of Fe(II)EDTA[single bond]NO reduction by Fe powder were studied with respect to the Fe(II)EDTA[single bond]NO concentration, pH value, and temperature. The experimental results indicated that the bonded NO was converted to ammonium. Fe(II)EDTA[single bond]NO reduction by Fe powder was a first-order reaction concerning Fe(II)EDTA[single bond]NO. The reaction rate increased with the decrease of pH value as well as the increase of temperature. In addition, the energy of activation (Ea) and the entropy of activation (ΔS‡) of the Fe(II)EDTA[single bond]NO reduction by Fe powder were 23.229 kJ mol⁻¹ and −215.251 J K⁻¹ mol⁻¹, respectively. Finally, the simultaneous reduction of Fe(III)EDTA and Fe(II)EDTA[single bond]NO by Fe powder was investigated. The results showed that Fe(III)EDTA reduction was restricted by Fe(II)EDTA[single bond]NO, and Fe(III)EDTA had little effect on the reduction of Fe(II)EDTA[single bond]NO. Besides, the reduction of Fe(II)EDTA[single bond]NO was the determining step in the whole process of Fe(II)EDTA regeneration. These findings can provide constructive instruction for the NO removal in industrial applications with mixed Fe(II)EDTA and Fe powder system.
ABSTRACT
A mild, environmentally friendly method for reduction of aromatic nitro compounds to the
corresponding amines is reported, using polymethylhydrosiloxane, PMHS, in the presence of
catalytic tetrabutylammonium fluoride, TBAF. A range of aromatic nitro compounds such as
(m-Nitroaniline 1a and p-Nitroaniline 2a) have been converted efficiently to the corresponding
aromatic amines: 1,3-diaminobenzene (1b), and 1,4-diaminobenzene (2b) with > 61% yield.
KEY WORDS: Reduction, PMHS, TBAF, aromatic, nitro compounds.
An improved and practical method was reported here for accessing 3',4',5'-trifluoro-[1,1'-biphenyl]-2-amine (1), a key intermediate for Fluxapyroxad. The overall yield for the preparation of 1 was 73%, with a purity of 99.88%, after a three-step process. More importantly, this process was an improvement in the manufacture of biphenyl compounds by Suzuki-Miyaura coupling, which enabled catalyst loading as low as 0.04 mol%. This method could provide an economic and environment-friendly process leading to extensive prospects in industrial applications.
Reduction of nitrobenzene by excess organic electron donor, 12, affords diphenylhydrazine in a reaction where azobenzene oxide and azobenzene are likely intermediates. No cleavage of the N-N σ-bond is seen under photoactivation conditions, whereas traces are seen under thermal activation. Hydrazone derivatives were prepared to explore the cleavage of N-N σ-bonds; the results show that a low-lying LUMO assists the transition state for accepting an electron, and the stabilisation that the potential fragments from N-N bond cleavage afford to the fragments is important in determining whether cleavage is observed.
A method for [3 + 2] cycloaddition of oxaziridines with alkynes to form 4-isoxazolines via visible-light photoredox catalysis is described. This method is a greener, atom-economical reaction that tolerates various functional groups and provides good to excellent yield. Moreover, the cyclization products can be conveniently converted into tetrasubstituted allylic alcohols and enamines. A mechanistic study suggests that the reaction involves photoredox-catalyzed in situ generation of a nitrone from the oxaziridine by SET.
A new, powerful and recyclable copper catalyst were prepared by heterogenization of copper chloride using of Fe3O4 nano particles modified with citric acid as a linker. This system can catalyze reduction of nitroaren compound to aniline derivatives in the presence of Sodium borohydride as a reduction agent in moderate to good yields. In addition, easy separation and recoverable with an external permanent magnet is the dominant properties of this catalyst (Cu2+-CA@Fe3O4).
Regeneration of Fe(II)EDTA, converting Fe(III)-EDTA and Fe(II)EDTA-NO to Fe(II)EDTA, is the key process in a wet flue gas denitrification technology with Fe(II)EDTA solution. In this paper, Zn powder was first employed as a reductant to reduce Fe(II)EDTA-NO. The stoichiometry and kinetics of Fe(II)EDTA-NO reduction by Zn powder were investigated with respect to Zn powder concentration, pH value, and temperature. The effect of the particle size of the Zn powder on Fe(II)EDTA-NO reduction was also investigated. The experimental results indicated that Fe(II)EDTA-NO reduction rate increased with the decrease of pH value and elevated temperature, and small particle size is beneficial to Fe(II)EDTA NO reduction. Fe(II)EDTA-NO reduction with Zn powder showed a pseudo-second-order reaction concerning Fe(II)EDTA-NO. In addition, the energy of activation (Ea) and the entropy of activation (ΔS‡) of the Fe(II)EDTA-NO reduction with Zn powder were estimated to be 19.853 kJ mol⁻¹ and −135.557 J K⁻¹ mol⁻¹, respectively. Finally, the simultaneous reduction of Fe(III)EDTA and Fe(II)EDTA-NO with Zn powder was investigated. Results showed that Zn powder had better performance on simultaneous Fe(III)EDTA and Fe(II)EDTA-NO reduction as compared to the earlier related research. These fundamental researches can offer valuable guidance for industrial denitrification using mixed Fe(II)EDTA and Zn powder system.
A novel continuous flow method for the methoxylation of chloronitrobenzenes was developed. The reaction went smoothly and high yields were achieved under the optimized conditions. Furthermore, up to 76% yield of azoxybenzenes were obtained from the corresponding nitrobenzenes in the presence of NaOH in continuous flow. Compared to batch conditions, the reaction time was significantly shortened, and the chemical waste was reduced obviously. © 2017 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
In this research, Ni/ZSM-5/KIT-6, Ni/H-ZSM-5/KIT-6, Pd/ZSM-5/KIT-6 and Pd/H-ZSM-5/KIT-6 were synthesised for first time as mesoporous zeolites by hydrothermal method. Physical and chemical properties of the prepared catalysts were characterized by XRD, BET, FT-IR, 27Al-NMR, SEM, TEM, XPS, DRS-UV, ICP and AAS techniques. These four mesoporous zeolites were used as acid-metal bifunctional heterogeneous catalysts as hydride donors in the reduction of nitroaromatic compounds. In these reactions, NaBH4 was used a reducing agent. The reaction was carried out at room temperature in aqueous medium. To increase of the catalytic activity of the synthesized mesoporous zeolite, various conditions such as the effect of type of nanoparticles, the ratio of reactants and the amount of catalyst on reaction performance were studied. Finally under the optimized conditions, different nitroaromatic compounds were reduced within 2-20 min. The reaction progress followed by thin layer chromatography (TLC) and the products were analyzed by FT-IR, 1H-NMR and 13C-NMR methods. In all cases, the products were achieved in a good yield, high selectivity, without any side-product. The used catalysts in the reaction could be easily reusable and no signficant changes were seen in their selectivity, catalytic activity, morphology as well as their structures. High yield, short reaction time in room temperature, no side-product, easy reusabaility of catalysts and low amounts of catalyst and NaBH4, are some of the advantages of these catalysts, Thes reactions are in agreement with green chemistry due to use H2O as a green solvent.
A metal-free synthesis of bifunctionalized indole derivatives was developed through a novel TBHP/TBAI-mediated oxidative coupling of C2,C3-unsubstituted indoles with arylsulfonyl hydrazide. With C3-methyl substituted indoles the reaction underwent diazotization process, affording 2-sulfonyldiazenyl-1H-indoles. The former simultaneously established C−S and C−N bonds through selective sulfonylation and diazotization of indole framework, enabling a mild and practical access to polyfunctionalized indoles with good to excellent yields.
Ionic liquids are salts that are liquid at low temperature (<100 °C) which represent a new class of solvents with nonmolecular, ionic character. Even though the first representative has been known since 1914, ionic liquids have only been investigated as solvents for transition metal catalysis in the past ten years. Publications to date show that replacing an organic solvent by an ionic liquid can lead to remarkable improvements in well‐known processes. Ionic liquids form biphasic systems with many organic product mixtures. This gives rise to the possibility of a multiphase reaction procedure with easy isolation and recovery of homogeneous catalysts. In addition, ionic liquids have practically no vapor pressure which facilitates product separation by distillation. There are also indications that switching from a normal organic solvent to an ionic liquid can lead to novel and unusual chemical reactivity. This opens up a wide field for future investigations into this new class of solvents in catalytic applications.
The ionic liquid 1‐n‐butyl‐3‐methylimidazolium hexafluorophosphate (bmim PF6) (6 ) has been studied as catalyst medium for biphasic homogeneous hydrogenations of sorbic acid (1 ). As catalyst we used the Cp*‐ruthenium‐complex [Cp*Ru(η⁴‐CH3—CHCH—CHCH—COOH) (CF3SO3)] which efficiently enables the stereoselective hydrogenation of sorbic acid leading to the formation of cis‐3‐hexenoic acid (3 ) in selectivities of up to 90% with turnover frequencies of up to 1100 h—1. Compared to other biphasic systems the hydrogenation in bmim PF6 proceeds with enhanced activity. The kinetics can be described with a Michaelis Menten‐equation, and the activation energy for the whole process was determined to be E A = 78 ± 5 kJ/mol.
Diels–Alder reactions in neutral ionic liquids (such as 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, and 1-butyl-3-methyl-imidazolium lactate) are reported. Rate enhancements and selectivities similar to those of reactions performed in lithium perchlorate–diethyl ether mixtures have been observed. As the ionic liquids used have no measurable vapour pressure, are thermally robust, will tolerate impurities such as water, and are recyclable, it is envisaged that these systems could be used on an industrial scale.
Ionic liquids are salts that are liquid at low temperature (<100°C) which represent a new class of solvents with nonmolecular, ionic character. Even though the first representative has been known since 1914, ionic liquids have only been investigated as solvents for transition metal catalysis in the past ten years. Publications to date show that replacing an organic solvent by an ionic liquid can lead to remarkable improvements in well-known processes. Ionic liquids form biphasic systems with many organic product mixtures. This gives rise to the possibility of a multiphase reaction procedure with easy isolation and recovery of homogeneous catalysts. In addition, ionic liquids have practically no vapor pressure which facilitates product separation by distillation. There are also indications that switching from a normal organic solvent to an ionic liquid can lead to novel and unusual chemical reactivity. This opens up a wide field for future investigations into this new class of solvents in catalytic applications.
The first report of the use of indium metal and allyl bromide for the allylation of aldehydes and ketones in ionic liquids is given in this paper. The homoallylic alcohol products are obtained in high yields on reaction at room temperature using stoichiometric quantities of indium. Initial results gained using a catalytic system of indium, manganese and TMSCl are also reported. The effect of ionic liquid solvents on the stereochemical selectivity of allylation of 2-methoxycyclohexanone and benzoin methyl ether has been investigated, showing a higher selectivity towards the chelation-controlled mechanism in ionic liquids than in conventional solvents such as water and THF. Using tetraallyltin as the allylating agent, the same reaction occurs with modest improvements in stereoselectivity compared with conventional solvents. The addition of 5 mol% Sc(OTf)3, however, results in a large increase in both reaction rate and selectivity, and permits the isolation of high yields
of product via a simple workup procedure. The ionic liquid/Sc(OTf)3 mixture may also easily be recycled with good maintenance of yield and stereoselectivity.
Nitroarenes can be reduced in high yields to the corresponding
anilines using zinc metal and NH4Cl in water without any organic
solvent at 80 °C with a simple procedure at low cost. The procedure is
powerful enough to reduce sterically hindered 2,6-dimethylnitrobenzene and
is chemoselective for nitro groups; ester, amide and halide substituents on
aromatic rings are unaffected.
It has been demonstrated that ionic liquids based upon substituted imidazolium cations may be used as alternative solvent media for the selective oxidation of alcohols to aldehydes and ketones. The ruthenium catalyst tetrapropylammonium perruthenate has been used in conjunction with either N-methylmorpholine-N′-oxide or molecular oxygen as oxidants in two different catalytic systems. Benzylic alcohols are oxidized in good to excellent yields whereas aliphatic alcohols require far greater reaction times and give poor yields. The reaction products can be easily removed from the reaction mixture by extraction with diethyl ether.
Diels–Alder reactions in neutral ionic liquids (such as 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, and 1-butyl-3-methyl-imidazolium lactate) are reported. Rate enhancements and selectivities similar to those of reactions performed in lithium perchlorate–diethyl ether mixtures have been observed. As the ionic liquids used have no measurable vapour pressure, are thermally robust, will tolerate impurities such as water, and are recyclable, it is envisaged that these systems could be used on an industrial scale.
The ionic salt [bmim][BF4] is an attractive solvent
for Wittig reactions, allowing both easier separation of alkenes from
Ph3PO together with efficient reuse of the solvent.
The air and moisture stable system [bmim][BF4]–[Ru4(η6-C6H6)4][BF4] {[bmim]+ = 1-butyl-3-methylimidazolium cation} presents a novel medium for conducting hydrogenations of arenes; the environmental problems associated with related aqueous–organic biphasic regimes are eliminated.
Azo compounds, both symmetric and unsymmetric, are cleaved to amine(s) by using commercial zinc dust and ammonium formate or formic acid in methanol, tetrahydrofuran or dioxane at room temperature. The reductive cleavage occurs without hydrogenolysis or hydrogenation of reducible moieties, such as -OH, -CH3, -OCH3, -COOH, -COCH3, halogen, etc. The cleavage is very fast, clean, cost effective and high-yielding if compared with earlier methods, such as those using cyclohexene/5% Pd on asbestos, cyclohexene/10% PdC or hydrazine/10% PdC or Raney nickel.
The Diels-Alder cycloaddition reaction between methyl acrylate and cyclopentadiene has been investigated in a number of air and moisture stable ionic liquids. The endo/exo ratio of the reaction has been used as an initial probe of the nature of the solvents.
Hydrated zirconia has been found to be an efficient and reusable catalyst for the regiospecific acylations for of arenes and selective reductions of azobenzenes to produce benzo-phenones and hydrazobenzenes respectively.
Various azobenzenes and azoxybenzenes were reduced almost quantitatively to the corresponding hydrazobenzenes by sodium dithionite under mild conditions without the formation of aniline derivatives, using dioctyl viologen as an electron-transfer catalyst in acetonitrile-water.
The ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate (bmim PF6) (6) has been studied as catalyst medium for biphasic homogeneous hydrogenations of sorbic acid (1). As catalyst we used the Cp*-ruthenium-complex [Cp*Ru(η4-CH3—CHCH—CHCH—COOH) (CF3SO3)] which efficiently enables the stereoselective hydrogenation of sorbic acid leading to the formation of cis-3-hexenoic acid (3) in selectivities of up to 90% with turnover frequencies of up to 1100 h—1. Compared to other biphasic systems the hydrogenation in bmim PF6 proceeds with enhanced activity. The kinetics can be described with a Michaelis Menten-equation, and the activation energy for the whole process was determined to be EA = 78 ± 5 kJ/mol.
In, Sn and Zn metals mediate the allylation of carbonyl compounds in [bmim][BF4] or [emim][BF4] to give the corresponding homoallylic alcohols in good to excellent yields. Tin was found to be the metal of choice among the metals examined.
Tributyltin hydride when reacted with a series of substituted azoarenes afforded hydrazo compounds with high chemoselectivity and good to high yields. With ortho-substituted azoarenes, mixtures of hydrazo derivatives and N-heterocycles or cyclic products only were obtained. The kinetic law of the process was determined in the presence and in the absence of AIBN; with the radical initiator the reaction proceeds via a radical chain mechanism, whereas without AIBN the presence of stannyl free radicals could be discarded. The mechanism of the noninitiated reaction is discussed. EPR characterization of spin adducts obtained by reacting group IVB organometallic radicals with azo compounds is reported.
The products of rearrangement of 2,2′-hvdrazonaphthalene (I) in ethanol, aqueous ethanol, acetone and tetrahydrofuran have been quantitatively isolated. The two products, 2,2′-diamino-1,1′-binaphthyl (II) and 3.4:5,6-dibenzocarbazole (III) are formed in approximately the same proportions in these solvents; that is 80-85% of II and 15-20% of III. The rates of rearrangement of I have been measured in these solvents and in others at several temperatures. At 80° the rates in anhydrous ethanol are faster than those in acetone, dioxane, tetrahydrofuran and pyridine, the rates in the last four solvents being close to each other. The rate of rearrangement in aqueous ethanol increases with water concentration and a plot of log rate constant against Grunwald-Winstein "Y" values is linear. From rates of rearrangement at 80°, 90°, 98° and 105° in ethanol, dioxane and pyridine, the activation energies and entropies of activation were found to be 23.2, 29.5 and 30.9 kcal./mole and -13.4, -4.0 and -1.0 cal./deg./mole. Attempts to obtain similar data for acetone and tetrahydrofuran solutions were not successful. It is believed that these experiments show that the rearrangement of I in hydroxylic solvents involves a transition state that is polar. It is believed that the rate is enhanced in solutions of alcohols by hydrogen-bonding from hydroxyl hydrogen to the hydrazo nitrogens. The transformation of I to II and III via the polar transition state thus formed is enhanced as the solvent becomes more ionizing; that is, more aqueous. The rates of rearrangement in the nonethanolic solutions are believed to suffer some retardation by hydrogen-bonding from hydrazo hydrogen to solvent, but for the most part to be independent of the solvent.
1. The rearrangements of three 3,3′,5,5′-tetrasubstituted hydrazobenzenes, in which the substituents are methyl, bromine and chlorine, respectively, are reported. In each case, rearrangements to a benzidine, a diphenyline, and a 2,2′-diaminobiphenyl occur in 2:1 sulfuric acid medium; and disproportionation in considerable amount ac-companies the rearrangements. A semidine may have been formed in one case. 2. Certain assessments of the polar and steric effects of the substituants and of medium effects upon the rates of rearrangements, the product ratios and degree of disproportionation are made. 3. The ultraviolet absorption spectra of the rearrangement products are reported and compared.
The reaction of 1-n-butyl-3-methylimidazolium chloride (BMIC) with sodium tetrafluoroborate or sodium hexafluorophosphate produced the room temperature-, air- and water-stable molten salts (BMI+)(BF4−) (1) and (BMI+)(PF6−) (2), respectively, in almost quantitative yield. The rhodium complexes RhCl(PPh3)3 and [Rh(cod)2][BF4] are completely soluble in these ionic liquids and they are able to catalyse the hydrogenation of cyclohexene at 10 atm and 25°C in a typical two-phase catalysis with turnovers up to 6000.
Although the use of CO as a reductant had been in the past confined to few reactions, its use in organic synthesis, especially in the reductive carbonylation of nitro aromatics and the oxidative carbonylation of aromatic amines, has increased dramatically. Since the discovery of CO-induced reduction of nitro groups, there has been a wide spread increase of interest in the application and mechanistic understanding of this reaction. In a major review published in 1988 it was noted, that in practice no studies of the mechanism of N-carbonylation of aromatic nitro compounds with alcohols leading to carbamates have been carried out. This review clearly shows a major change since that publication. Indeed, metal-catalyzed reductive carbonylation of nitro aromatics using CO as reducing agent has been in the past 10 years the subject of intense investigation both in academia and in the chemical industry. Several articles and reviews have covered the subject up to the late 1980s. The authors will concentrate on more recent literature, but sometimes older data will be used to establish an understanding of these reactions. 127 refs.
[reaction: see text]. A simple and mild TEMPO-CuCl catalyzed aerobic oxidation of primary and secondary alcohols to the corresponding aldehydes and ketones in ionic liquid [bmim][PF6] with no trace of overoxidation to carboxylic acids has been developed. The product can be isolated by a simple extraction with organic solvent, and the ionic liquid can be recycled or reused.
Treatment of nitrobenzene and other various nitroarenes with 6 equiv of samarium(II) under strictly anhydrous conditions allows for the isolation of aniline or the corresponding arylamine. Reducing the number of samarium(II) equivalents allows for the isolation of intermediate species, e.g., azoarenes or hydrazines. Use of Sm[N(SiMe(3))(2)](2), in place of the typically used SmI(2), has allowed for the detailed examination of the aqueous and nonaqueous species formed in this reduction and has been instrumental in delineation of the stepwise reaction mechanism. This is the first time that the reaction intermediates of an organic reaction mediated by samarium(II) have been isolated and analyzed by (1)H NMR and X-ray crystallography.
The ionic liquid [bmim][PF6] was found to provide
extra stability to the air-sensitive chiral catalyst Rh–MeDuPHOS in
asymmetric hydrogenation of enamides.
The chemical industry is under considerable pressure to replace many of the volatile organic compounds (VOCs) that are currently used as solvents in organic synthesis. The toxic and/or hazardous properties of many solvents, notably chlorinated hydrocarbons, combined with serious environmental issues, such as atmospheric emissions and contamination of aqueous effluents is making their use prohibitive. This is an important driving force in the quest for novel reaction media. Curzons and coworkers, for example, recently noted that rigorous management of solvent use is likely to result in the greatest improvement towards greener processes for the manufacture of pharmaceutical intermediates. The current emphasis on novel reaction media is also motivated by the need for efficient methods for recycling homogeneous catalysts. The key to waste minimisation in chemicals manufacture is the widespread substitution of classical 'stoichiometric' syntheses by atom efficient, catalytic alternatives. In the context of homogeneous catalysis, efficient recycling of the catalyst is a conditio sine qua non for economically and environmentally attractive processes. Motivated by one or both of the above issues much attention has been devoted to homogeneous catalysis in aqueous biphasic and fluorous biphasic systems as well as in supercritical carbon dioxide. Similarly, the use of ionic liquids as novel reaction media may offer a convenient solution to both the solvent emission and the catalyst recycling problem.
- A Sudalai
- V H Deshpande
Sudalai, A.; Deshpande, V. H. Tetrahedron Lett. 1997,
38, 2137–2140 and references cited therein.
- D Nanni
- G F Pedulli
- A Tundo
- G Zanardi
- K K Park
Nanni, D.; Pedulli, G. F.; Tundo, A.; Zanardi, G. J. Org.
Chem. 1992, 57, 607–613; (b) Park, K. K.; Han, S. Y.
- For
- P Wasserscheid
- W Keim
- A Alberti
- R Leardini
For recent reviews, see: (a) Welton, T. Chem. Rev. 1999,
99, 2071–2083; (b) Wasserscheid, P.; Keim, W. Angew.
16. (a) Alberti, A.; Bedogni, N.; Benaglia, M.; Leardini, R.;
- M L Patil
- G K Jnaneshwara
- D Sabde
Tetrahedron Lett. 1996, 37, 6721–6724; (c) Patil, M. L.;
Jnaneshwara, G. K.; Sabde, D. P.; Dongare, M. K.;
- R B Carlin
- W O Forshey
- Jr
- H J Shine
- J C Trisler
(a) Carlin, R. B.; Forshey, W. O., Jr. J. Am. Chem. Soc.
1950, 72, 793–801; (b) Shine, H. J.; Trisler, J. C. J. Am.
Chem. Soc. 1960, 82, 4054–4058.
- T Welton
- P Wasserscheid
- W Keim
- Angew
For recent reviews, see: (a) Welton, T. Chem. Rev. 1999,
99, 2071-2083; (b) Wasserscheid, P.; Keim, W. Angew.
The results are listed under Table 3. Similarly, the ionic
liquid [bmim][BF 4 ] was recycled and used for three runs
(Table 3).
- A Alberti
- N Bedogni
- M Benaglia
- R Leardini
- D Nanni
- G F Pedulli
- A Tundo
- G Zanardi
- K K Park
- S Y Han
- M L Patil
- G K Jnaneshwara
- D P Sabde
- M K Dongare
- A Sudalai
- V H Deshpande
Alberti, A.; Bedogni, N.; Benaglia, M.; Leardini, R.;
Nanni, D.; Pedulli, G. F.; Tundo, A.; Zanardi, G. J. Org.
Chem. 1992, 57, 607-613; (b) Park, K. K.; Han, S. Y.
Tetrahedron Lett. 1996, 37, 6721-6724; (c) Patil, M. L.;
Jnaneshwara, G. K.; Sabde, D. P.; Dongare, M. K.;
Sudalai, A.; Deshpande, V. H. Tetrahedron Lett. 1997,
38, 2137-2140 and references cited therein.
- R B Carlin
- W O Forshey
- Jr
- H J Shine
- J C Trisler
Carlin, R. B.; Forshey, W. O., Jr. J. Am. Chem. Soc.
1950, 72, 793-801; (b) Shine, H. J.; Trisler, J. C. J. Am.
Chem. Soc. 1960, 82, 4054-4058.
- J Dupont
- R F De-Souza
- P A Z Suarez
For recent reviews, see: (a) Welton, T
- Steines
- Yu
- Ley
-butyl-3-methylimidazolium tetrafluoroborate
- S Guernik
- A Wolfson
- M Herskowitz
- N Greenspoon
- S Geresh
- P A Z Suarez
- J E L Dullius
- S Einloft
- R F De-Souza
- J Dupont
- Polyhedron