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Chemoselective Reduction of Aromatic Nitro and Azo Compounds in Ionic Liquids Using Zinc and Ammonium Salts.

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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.

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... 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. ...
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... 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. ...
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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. ...
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... 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. ...
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... 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. ...
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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. ...
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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. ...
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... 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. ...
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... 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]. ...
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... 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). ...
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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. ...
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... 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. ...
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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).
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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.
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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
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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.
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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.
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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.
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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—CHCH—CHCH—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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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% PdC or hydrazine/10% PdC or Raney nickel.
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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.
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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.
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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.
Article
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.
Article
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.
Article
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.
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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.
Article
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.
Article
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.
Article
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.
Article
[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.
Article
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.
Article
The ionic liquid [bmim][PF6] was found to provide extra stability to the air-sensitive chiral catalyst Rh–MeDuPHOS in asymmetric hydrogenation of enamides.
Article
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