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.     

Selective ortho methylation of nitroheteroaryls by vicarious nucleophilic substitution

An efficient and scalable three-step one-pot approach to 6-methyl-5-nitroisoquinoline (1) from inexpensive 5-nitroisoquinoline, utilizing the vicarious nucleophilic substitution (VNS) as a key step, is described. The optimized reaction conditions can be applied to a limited number of other aromatic and heteroaromatic nitro compounds. Attempts to understand the observed selectivity in the VNS step led to the discovery of two new reaction pathways under VNS conditions, one leading to an isoxazole and the other resulting in the formal cyclopropanation of an aromatic nitro compound.     

Supported Tetramethylamonium Nitrate/Silicasulfuric Acid as a Useful Reagent for Nitration Aromatic Compounds Under Solvent‐Free Conditions

A variety of aromatic compounds are nitrated to the parent nitro aromatic compounds under solvent‐free conditions using supported tetramethylammonium nitrate/silicasulfuric acid as a useful reagent. This methodology is useful for nitration of activated and deactivated aromatic rings.     

Reduction of Sulphur-containing Aromatic Nitro Compounds with Hydrazine Hydrate over Iron(III) Oxide-MgO Catalyst

Sulphur-containing aromatic amines were prepared efficiently in good to excellent yields by reduction of the corresponding sulphur-containing aromatic nitro compounds with hydrazine hydrate in the presence of iron(III) oxide-MgO catalyst. The catalyst exhibited high activity and stability for the reduction of sulphur-containing aromatic nitro compounds. The yields of sulphur-containing aromatic amines were up to 91-99 % at 355 K after reduction for 1-4 h over this catalyst.     

First and Efficient Method for Reduction of Aliphatic and Aromatic Nitro Compounds with Zinc Borohydride as Pyridine Zinc Tetrahydroborato Complex: A New Stable Ligand‐Metal Borohydride

Pyridine zinc tetrahydroborate, [(Py)Zn(BH₄)₂], as a new stable ligand‐metal borohydride, is prepared quantitatively by complexation of 1:1 zinc borohydride and pyridine at room temperature. This reagent efficiently reduces different aromatic and aliphatic nitro compounds to their primary amines in refluxing THF. In addition, the reduction shows chemoselectivity for aliphatic nitro compounds over the aromatic nitro compounds.     

Reductive Molybdenum‐Catalyzed Direct Amination of Boronic Acids with Nitro Compounds

The synthesis of aromatic amines is of utmost importance in a wide range of chemical contexts. We report a direct amination of boronic acids with nitro compounds to yield (hetero)aryl amines. The novel combination of a dioxomolybdenum(VI) catalyst and triphenylphosphine as inexpensive reductant has revealed to be decisive to achieve this new C?N coupling. Our methodology has proven to be scalable, air and moisture tolerant, highly chemoselective and engages both aliphatic and aromatic nitro compounds. Moreover, this general and step‐economical synthesis of aromatic secondary amines showcases orthogonality to other aromatic amine syntheses as it tolerates aryl halides and carbonyl compounds.     

Synthesis of Oxidized Nitro-Polycyclic Aromatic Hydrocarbons

A series of phenolic and cis-dihydrodiol derivatives of 6-nitrobenzo[a] pyrene and 7-nitrobenz[a]anthracene were synthesized. The common structural feature of these compounds is that their nitro groups are perpendicular or near perpendicular to the aromatic moieties. From the synthesis of these compounds, it was found that an acetoxy group does not affect the regioselectivity of electrophilic nitration to a polycyclic aromatic hydrocarbon (PAH) and that a nitro substituent can substantially reduce the concerted electrophilic 1,2-addition of osmium tetroxide to the most olefinic aromatic double bond of a PAH.     

Catalyst‐Free Reductive Coupling of Aromatic and Aliphatic Nitro Compounds with Organohalides

A rare reductive coupling of nitro compounds with organohalides has been realized. The reaction is initiated by a partial reduction of the nitro group to a nitrenoid intermediate. Therefore, not only aromatic but also aliphatic nitro compounds are efficiently transformed into monoalkylated amines, with organohalides as the alkylating agent. Given the innate reactivity of the nitrenoid, a catalyst is not required, resulting in a high tolerance for aryl halide substituents in both starting materials.     

A constructive synthetic approach for reduction of nitro heterocyclics- characterization and degradation studies

A novel synthetic approach was proposed for a metal free reduction of nitro aromatic compounds to the resultant amines by sodium dithionite. A series of nitro compounds containing various reducible functional groups were chemoselectively reduced in good to excellent yield. Instantaneously some of the products are chemically degraded and all are characterized by spectral methods.     

Negative ions in organic mass spectrometry. II—Negative ion mass spectra of simple thio and dithio esters.

The 70 eV negative ion mass spectra of some simple aromatic and aliphatic thio and dithio esters are discussed. A characteristic fragmentation process, a rearrangement analogous to the nitro-nitrite conversion of aromatic nitro compounds, is observed for aromatic thio esters.     

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.     

Kinetics of the liquid-phase catalytic hydrogenation of chlorine-containing aromatic nitro compounds in the presence of pyridine

We have analyzed experimental kinetic data for nitro compound consumption, for the formation of the corresponding amino product, and for the accumulation of intermediate products and by-products in the hydrogenation of chlorine-containing aromatic nitro compounds. The reaction has been carried out under static conditions over a platinum catalyst on a porous support in the presence of pyridine. The effect of the admixture on different hydrogenation steps of a chlorine-containing aromatic nitro compound has been quantitatively interpreted.     

Vinylpyrylation of aromatic compounds

The reaction of β-ethoxyvinylpyrylium salts with aromatic compounds gives styrylpyrylium salts, which are also formed from methylpyrylium salts, ethyl orthoformate, and aromatic compounds. The previously unknown phenomenon of attack by a carbonium cation on the meta position of a benzene ring passivated by a nitro group (nitrobenzene) was detected.     

Contemplation on Detonation Pressures of Nitramines and ­Nitro Aromatics

A physical model and a mathematical theory for the detonation pressures of explosives materials were developed. The pressure values are expressed as function of the detonation velocity (D) and the average mass (m) of the gaseous products, and are applied for various nitramines and aromatic nitro compounds including nitro pyrimidines and nitro triazines. Some regression equations were obtained and discussed. The pressure values show poor linear dependence on the average mass of the products but good dependence on the detonation velocities alone or Dm. Moreover, for the same Dm value nitramines should produce more pressure than aromatic nitro compounds. This work deals with pressure developed by explosion products and interrelates it with detonation pressure within the constraints of certain assumptions and pays attention to so far unnoticed relationships at least under certain circumstances.     

Nitric acid in the presence of P2O5 supported on silica gel—a useful reagent for nitration of aromatic compounds under solvent-free conditions

A variety of aromatic compounds are nitrated to parent nitro aromatic compounds under solvent-free conditions using 65% nitric acid in the presence of P₂O₅ supported on silica gel is described. This methodology is useful for nitration of activated and deactivated aromatic rings.     

Contribution of the pyrylium structure to the electrochemical properties of nitroflavones

The polarographic behavior of 3- and 4-nitroflavones on a dropping mercury electrode in Britton-Robinson buffer solutions was investigated. It Is shown that, depending on its position, the nitro group displays properties that are typical only for aromatic nitro compounds or a combination of properties of aromatic and aliphatic -unsaturated nitro compounds. The deciding factor is the realization of pyrylium and pyrone structures, depending on the pH of the medium. The kinetic parameters of the chemical transformation of the nitro form to the aci form of 3-nitroflavone in an alkaline medium are presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 312–316, March, 1982.     

Reactions of Aromatic Nitro Compounds with Bases

Aromatic nitro compounds can react in many ways with bases. The reaction path followed depends mainly on the degree of nitration (with a sharp jump from mononitro to di- and trinitro compounds) and the base used. Redox reactions or nucleophilic aromatic substitutions predominate with mononitro compounds, whereas Meisenheimer additions together with nucleophilic aromatic substitutions are preferred by dinitro and trinitro compounds; deprotonations are less common. The bromine in nitrobromobenzenes can be replaced by metal at low temperatures. Very weak bases generally give electron donor-acceptor complexes.     

Simple relationship for predicting onset temperatures of nitro compounds in thermal explosions

Nitro compounds are capable of rapid chemical decompositions with a large amount of energy releases and hence pose significant thermal explosion hazards. Molecular simulation has been well established and demonstrated as an effective tool to predict physical and/or chemical properties of energetic materials, such as onset temperature, heat of reaction, and shock sensitivity. In this work, a simple relationship for predicting the onset temperature of nitro aromatic compounds containing other functional groups is developed based on their molecular structures. The results have shown that the thermal onset temperature of a specific nitro aromatic compound is strongly related to its excitation energy (a singlet state to triplet state). The predicted onset temperatures show very good agreement with respect to the measured onset temperatures by differential scanning calorimetry. Deviations compared to the experimental values are very small. These correlations can be used to computationally screen new nitro compounds for their thermal explosion hazards. These correlations can also be applied as a preliminary thermal analysis method and expedite the evaluation process of new energetic materials.     

NMR study of adducts of aromatic nitro compounds with the alizarin complex of manganese(II) — A structural analog of hydration catalysts

Conclusions Using the PMR method we have shown that aromatic nitro compounds form outer-sphere do-nor-acceptor adducts with the alizarin complex of Mn(II), which is the structural analog of metal complex catalysts for hydration of aromatic nitro compounds.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2715–2719, December, 1987.