Liquid-Phase Hydrogenation of Aromatic Mononitro Compounds on Supported Porous Catalysts at Partial Hydrogen Pressures Lower than 0.1 MPa

The influence of the hydrogen partial pressure varied in the interval (4.3–100) × 10³ Pa on the kinetics of liquid-phase catalytic hydrogenation of aromatic mononitro compounds in the presence of platinum and iridium supported on activated carbon in various percent ratios (Pt/C-2.5% and Ir/C-5%) was studied for 3,4-dichloronitrobenzene as example. A decrease in the hydrogen partial pressure leads to a significant decrease in the rate of the nitro compound consumption and in the yield of the intermediate arylhydroxylamine. A kinetic mechanism of hydrogenation of the nitro compound, satisfactorily describing the experimental data, was suggested.     

Selective Hydrogenation of Aromatic Aminoketones by Pd/C Catalysis

We report an alternative hydrogenation of aromatic aminoketones by heterogeneous catalyst of palladium on carbon (Pd/C) in which nitro, in particular carbonyl groups in the ketones, could be selectively transformed to corresponding amino ketone, secondary alcohol, or methylene compound.     

Disproportionation of N-arylhydroxylamines in the presence of hydrogenation catalysts and sulfur compound additives

Conclusions The yield of N-arylhydroxylamines increases in the liquid-phase catalytic hydrogenation of aromatic nitro compounds due to a reduction in the rate of the secondary transformations of these products upon the introduction of thiophene, sulfolane, and other sulfur compound additives.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 489–490, February, 1985.     

A convenient and general ruthenium-catalyzed transfer hydrogenation of nitro- and azobenzenes

An easily accessible in situ catalyst composed of [{RuCl(2)(p-cymene)}(2)] and terpyridine has been developed for the selective transfer hydrogenation of aromatic nitro and azo compounds. The procedure is general and the selectivity of the catalyst has been demonstrated by applying a series of structurally diverse nitro and azo compounds (see scheme).     

One pot synthesis of N-ethylaniline from nitrobenzene and ethanol

A novel method for the one pot synthesis of N-alkyl arylamines from nitro aromatic compounds and alcohols is proposed through the combination of the aqueous-phase reforming of alcohol for hydrogen production, the reduction of nitro aromatic compounds for the synthesis of aromatic amine and the N-alkylation of aromatic amine for the production of N-alkyl arylamine over an identical catalyst under the same conditions of temperature and pressure in a single reactor. In this process, hydrogen generated from the aqueous-phase reforming of alcohols was used in-situ for the hydrogenation of nitro aromatic compounds for aromatic amine synthesis, followed by N-alkylation of aromatic amine with alcohols to form the corresponding N-alkyl arylamines at a low partial pressure of hydrogen. For the system composed of nitrobenzene and ethanol, under the conditions of 413 K and PN2 = 1 MPa, the conversion degrees of nitrobenzene and aniline were 100%, the selectivity to N-ethylaniline and N, N-diethylaniline were 85.9% and 0%-4%, respectivity, after reaction for 8 h at the volumetric ratio of nitrobenzene:ethanol:water = 10:60:0. The selectivity for N, N-diethylaniline production is much lower than that through the traditional method. In this process, hydrogen and aromatic amines generated from the aqueous-phase reforming of alcohols and hydrogenation of nitro aromatic compounds, respectively, could be promptly removed from the surface of the catalyst due to the occurrence of in-situ hydrogenation and N-alkylation reactions. Thus, this may be a potential approach to increase the selectivity to N-alkyl arylamine.     

Selective hydrogenation of aromatic compounds using modified iridium nanoparticles

Till now, Ionic liquid‐stabilized metal nanoparticles were investigated as catalytic materials, mostly in the hydrogenation of simple substrates like olefins or arenes. The adjustable hydrogenation products of aromatic compounds, including quinoline and relevant compounds, aromatic nitro compounds, aromatic ketones as well as aromatic aldehydes, are always of special interest, since they provide more choices for additional derivatization. Iridium nanoparticles (Ir NPs) were synthesized by the H₂ reduction in imidazolium ionic liquid. TEM indicated that the Ir NPs is worm‐like shape with the diameter around 12.2 nm and IR confirmed the modification of phosphine‐functionalized ionic liquids (PFILs) to the Ir NPs. With the variation of the modifier, solvent and reaction temperature, substrate like quinoline and relevant compounds, aromatic nitro compounds, aromatic ketones as well as aromatic aldehydes could be hydrogenated by Ir NPs with interesting adjustable catalytic activity and chemoselectivity. Ir NPs modified by PFILs are simple and efficient catalysts in challenging chemoselective hydrogenation of quinoline and relevant compounds, aromatic nitro compounds, aromatic ketones as well as aromatic aldehydes. The activity and chemoselectivity of the Ir NPs could be obviously impacted or adjusted by altering the modifier, solvent and reaction temperature.     

Reaction kinetics of nitrobenzene hydrogenation on a palladium catalyst supported on nanodiamonds

The kinetics of nitrobenzene hydrogenation on a palladium triphenylphosphine catalyst supported on nanodiamonds was studied. It was found that the reaction is of first order with respect to the catalyst and hydrogen and of zero order with respect to nitrobenzene. The apparent constant and activation energy of the reaction were calculated. A probable reaction mechanism was proposed. The effects of the triphenylphosphine-to-palladium ratio and the nature of the solvent and an aromatic nitro compound on the activity of the test catalyst were demonstrated.     

Catalytic hydrogenation of aromatic nitro compounds by non-noble metal complexes of chitosan

Silica-supported mono-metal (such as Ni, Cu) complexes and mixed metal (such as Cu/Zn, Cu/Cr) complexes of chitosan have been prepared. It is found that these non-noble metal complexes could be used as efficient catalysts for the hydrogenation of aromatic nitro compounds. The effects of type of metal, reaction temperature and pressure, solvent, nitrogen/metal molar ratio in the complex catalysts on the yields from nitrobenzene to aniline have been examined. It was also found that catalysts are active for the catalytic hydrogenation of other aromatic nitro compounds such as 2-nitroanisole, 2-nitroaniline, 2-nitrotoluene and 1-chloro-4-nitrobenzene.     

Enantioselective Sequential‐Flow Synthesis of Baclofen Precursor via Asymmetric 1,4‐Addition and Chemoselective Hydrogenation on Platinum/Carbon/Calcium Phosphate Composites

Continuous‐flow synthesis of baclofen precursor ( 2 ) was achieved using achiral and chiral heterogeneous catalysts in high yield with high enantioselectivity. The key steps are chiral calcium‐catalyzed asymmetric 1,4‐addition of a malonate to a nitroalkene and chemoselective reduction of a nitro compound to the corresponding amino compound by using molecular hydrogen. A dimethylpolysilane (DMPS)‐modified platinum catalyst supported on activated carbon (AC) and calcium phosphate (CP) has been developed that has remarkable activity for the selective hydrogenation of nitro compounds.     

Pd/C(en) catalyzed chemoselective hydrogenation in the presence of aryl nitriles

Aromatic nitriles are not only important components of natural products, pharmaceuticals, herbicides and agrochemicals but also a synthetic equivalent of various functionalities. The development of synthetic methods of aromatic nitriles have been increasing in terms of its usefulness. Since aromatic nitriles are susceptible to the hydrogenation, it has been desired for the development of chemoselective hydrogenation method with retention of nitrile groups. Pd/C is one of the most popular catalysts for hydrogenation and many of reducible functional groups such as multiple bonds, benzyl ethers, N-Cbzs, nitro groups and so on could be easily reduced under the conditions. Therefore, it is very difficult to achieve the chemoselective hydrogenation of substrates containing two or more reducible functional groups. We have found that a Pd/C catalyst formed an isolable complex with ethylenediamine (en) employed as catalytic poison, and the complex [Pd/C(en)] catalyzed chemoselective hydrogenation of a variety of reducible functionalities distinguishing O-benzyl, N-Cbz and O-TBDMS protective groups, benzyl alcohols and epoxides. In the course of these investigations, we found the aryl nitriles could survive under the Pd/C(en)-catalyzed hydrogenation conditions in THF whose choice is important for the effective suppression. This methodology could be applied to the selective hydrogenation of alkene and alkyne functionalities in the presence of aromatic nitrile.     

Efficient synthesis of N-alkyl-2,7-dihalocarbazoles by simultaneous carbazole ring closure and N-alkylation

The N-alkyl-2,7-dihalocarbazole as the main product was formed by the reaction of 4,4′-dihalo-2-nitrobiphenyl with aromatic nitro compound and trialkyl phosphite. The presence and crucial role of aromatic nitro compound causes simultaneous carbazole ring closure and N-alkylation unlike the Cadogan ring closure where non-alkylated carbazole is formed as a main product. In addition, the mixture of aromatic nitro compound and trialkyl phosphite was found to be a possible N-alkylating agent for heterocycles, such as carbazole or indole.     

Liquid-phase catalytic hydrogenation of 3,4-dichloronitrobenzene over Pt/C catalyst under gradient-free flow conditions in the presence of pyridine

Experimental data on nitro compound uptake, the intermediate product accumulation, and the corresponding amine compound generation were obtained on hydrogenating 3,4-dichloronitrobenzene over Pt/C catalyst in the gradient-free flow regime in the presence and absence of pyridine. In addition, a side reaction of dehalogenation was investigated. The role of pyridine admixture on every step of the process was analyzed and the rate of hydrogenation of the nitro compound was determined both in the presence and in the absence of inhibitor.

     

Catalytic Liquid-Phase Reduction of Aromatic Nitro Compounds Containing Highly Reactive Functional Groups

Improved procedures have been proposed for fast and selective hydrogenation of aromatic nitro compounds with the goal of obtaining practically important amines.     

钯催化甲酸为氢源的芳硝基化合物直接加氢和一锅法酰胺化

Pd/C催化剂实现了甲酸为氢源的芳硝基化合物的直接加氢及甲酸为氢源和羰基源的一锅法芳硝基化合物的酰胺化.在芳硝基化合物的直接加氢过程中,该体系体现了很好的催化活性,实现了对同时带有其它可还原官能团的芳硝基化合物的选择性加氢,得到较高收率的胺类化合物.同时,通过提高反应温度和增加甲酸的量,实现了芳硝基化合物的加氢和甲酰化的串联反应,该体系体现了较高的催化活性.     

Selective N-alkylation of amines using nitriles under hydrogenation conditions: facile synthesis of secondary and tertiary amines

Nitriles were found to be highly effective alkylating reagents for the selective N-alkylation of amines under catalytic hydrogenation conditions. For the aromatic primary amines, the corresponding secondary amines were selectively obtained under Pd/C-catalyzed hydrogenation conditions. Although the use of electron poor aromatic amines or bulky nitriles showed a lower reactivity toward the reductive alkylation, the addition of NH(4)OAc enhanced the reactivity to give secondary aromatic amines in good to excellent yields. Under the same reaction conditions, aromatic nitro compounds instead of the aromatic primary amines could be directly transformed into secondary amines via a domino reaction involving the one-pot hydrogenation of the nitro group and the reductive alkylation of the amines. While aliphatic amines were effectively converted to the corresponding tertiary amines under Pd/C-catalyzed conditions, Rh/C was a highly effective catalyst for the N-monoalkylation of aliphatic primary amines without over-alkylation to the tertiary amines. Furthermore, the combination of the Rh/C-catalyzed N-monoalkylation of the aliphatic primary amines and additional Pd/C-catalyzed alkylation of the resulting secondary aliphatic amines could selectively prepare aliphatic tertiary amines possessing three different alkyl groups. According to the mechanistic studies, it seems reasonable to conclude that nitriles were reduced to aldimines before the nucleophilic attack of the amine during the first step of the reaction.     

Conversion of N-arylhydroxylamines in the presence of metal complexes and heterogeneous catalysts

Conclusions The nature of the component distribution and the transformations in the catalytic hydrogenation of aromatic nitro compounds are analogous for the use of metal complex, colloidal, and heterogeneous catalysts. The hydrogenation features the formation of amino compounds due to disproportionation of intermediate N-arylhydroxylamines.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2846–2848, December, 1988.The author thanks A. V. Bulatov for providing samples of the metal complex catalyst.     

Transforming nonselective into chemoselective metal catalysts for the hydrogenation of substituted nitroaromatics

It is generally accepted that good hydrogenation noble and nonnoble metal catalysts such as Pt, Ru, or Ni are not chemoselective for hydrogenation of nitro groups in substituted aromatic molecules. We have found that it is possible to transform nonchemoselective into highly chemoselective metal catalysts by controlling the coordination of metal surface atoms while introducing a cooperative effect between the metal and a properly selected support. Thus, highly chemoselective and general hydrogenation Pt, Ru, and Ni catalysts can be prepared by generating nanosized crystals of the metals on the surface of a TiO 2 support and decorating the exposed (111) and (100) crystal faces by means of a simple catalyst activation procedure. By doing this, it has been possible to change the relative rate for hydrogenating competitive groups present in the molecule by almost 2 orders of magnitude, increasing the chemoselectivity from less than 1% to more than 95%.     

One pot synthesis of <Emphasis Type="Italic">N</Emphasis>-ethylaniline from nitrobenzene and ethanol

A novel method for the one pot synthesis of N-alkyl arylamines from nitro aromatic compounds and alcohols is proposed through the combination of the aqueous-phase reforming of alcohol for hydrogen production, the reduction of nitro aromatic compounds for the synthesis of aromatic amine and the N-alkylation of aromatic amine for the production of N-alkyl arylamine over an identical catalyst under the same conditions of temperature and pressure in a single reactor. In this process, hydrogen generated from the aqueous-phase reforming of alcohols was used in-situ for the hydrogenation of nitro aromatic compounds for aromatic amine synthesis, followed by N-alkylation of aromatic amine with alcohols to form the corresponding N-alkyl arylamines at a low partial pressure of hydrogen. For the system composed of nitrobenzene and ethanol, under the conditions of 413 K and P _N2 = 1 MPa, the conversion degrees of nitrobenzene and aniline were 100%, the selectivity to N-ethylaniline and N, N-diethylaniline were 85.9% and 0%–4%, respectivity, after reaction for 8 h at the volumetric ratio of nitrobenzene:ethanol:water = 10:60:0. The selectivity for N, N-diethylaniline production is much lower than that through the traditional method. In this process, hydrogen and aromatic amines generated from the aqueous-phase reforming of alcohols and hydrogenation of nitro aromatic compounds, respectively, could be promptly removed from the surface of the catalyst due to the occurrence of in-situ hydrogenation and N-alkylation reactions. Thus, this may be a potential approach to increase the selectivity to N-alkyl arylamine. Supported by the Program for New Century Excellent Talents in University (Grant No. NCET-04-0557), and the Specialized Research Fund for the Doctoral Program of High Education (Grant No. SRFDP-20060337001)     

Pd/C催化下汉斯酯1,4-二氢吡啶还原芳香叠氮化合物、芳香硝基 化合物以及碳碳双键的反应研究

汉斯酯1,4-二氢吡啶(HEH)在Pd/C催化下可以将取代的芳香叠氮化合物还原为相应的取代苯胺, 反应具有很好的选择性. 该方法也可以用于芳香硝基化合物的还原. 对于Pd/C催化下汉斯酯1,4-二氢吡啶还原碳碳双键的可行性, 论文中也进行了初步的探讨.