Design of Ionic Liquid 3-Methyl-1-sulfonic Acid Imidazolium Nitrate as Reagent for the Nitration of Aromatic Compounds by in Situ Generation of NO2 in Acidic Media

Synthesis of Nitrones and Nitroalkanes via Chiral Cyclic Imines

A series of structurally chiral cyclic imines efficiently yields chiral nitrones and nitroalkanes. This is the first report of the synthesis of nitro groups by C═N bond cleavage of imines through a nitrone intermediate.

Trifluoromethanesulfonic Acid Promoted Controllable Electrophilic Aromatic Nitration

In this work, we developed a facile and controllable electrophilic aromatic nitration method with commercially available 68% HNO₃ as the nitrating reagent and trifluoromethanesulfonic acid (HOTf) as the catalyst in hexafluoroisopropanol or under solvent-free conditions. The electrophilic nitration products of different arenes can be obtained in almost quantitative yields by tuning the loading of HOTf. The strong acidity and water absorbing property of HOTf allowed this transformation to reach completion in a short time at room temperature.

Improved Regioselective Mononitration of Naphthalene over Modified BEA Zeolite Catalysts

HBEA zeolite modified with highly electronegative cations is a highly efficient and reusable catalyst for the nitration of naphthalene with nitric acid, which has been successfully prepared in this work. Catalytic selective mononitration of naphthalene was investigated. The ratio of 1-nitronaphthalene isomer to 2-nitronaphthalene could reach 19.2, with a moderate yield of 68.2%, when the reaction was carried out in 1,2-dichloroethane, with 1.0 mmol naphthalene, 0.22 mL nitric acid (95%), and 0.10 g HBEA-25 at −15 °C. The effects of reaction temperature and the quantity of zeolites on 1-nitronaphthalene were also studied. The catalyst is readily recyclable, and we believe this to be a major step forward in the area of clean technology for aromatic nitration.

Organic Nitrating Reagents

Nitro compounds are vital raw chemicals that are widely used in academic laboratories and industries for the preparation of various drugs, agrochemicals, and materials. Thus, nitrating reactions are of great importance for chemists and are even taught in schools as one of the fundamental transformations in organic synthesis. Since the discovery of the first nitrating reactions in the 19th century, progress in this field has been constant. Yet, for many years the classical electrophilic nitration approach using a mixture of strong mineral acids dominated the field. However, in recent decades, the attention of researchers has focused on new reactivity and new reagents that can provide access to nitro compounds in a practical and straightforward way under mild reaction conditions. Organic nitrating reagents have played a special role in this field since they have enhanced reactivity. They also allow nitration to be carried out in an ecofriendly and sustainable manner. This review examines the development and application of organic nitrating reagents.

1 Introduction

2 Organic Nitrating Reagents

2.1 Alkyl Nitrites

2.2 Nitroalkanes

2.3 Alkyl Nitrates

2.4 N-Nitroamides

2.5 N-Nitropyrazole

2.6 N-Nitropyridinium Salts

3 Organic Nitrating Reagents Generated In Situ

3.1 Acyl Nitrates

3.2 Trimethylsilyl Nitrate

3.3 Nitro Onium Salts

4 Organic Nitronium Salts

5 Organic Nitrates and Nitrites

5.1 Ammonium Nitrates

5.2 Heteroarylium Nitrates

5.3 Other Organic Nitrates

5.4 Organic Nitrites

6 Conclusion and Outlook

Application of novel metal-organic framework [Zr-UiO-66-PDC-SO3H]FeCl4 in the synthesis of dihydrobenzo[g]pyrimido[4,5-b]quinoline derivatives

In the current paper, we produce a new metal-organic framework (MOF) based on Zr metal, [Zr-UiO-66-PDC-SO₃H]FeCl₄, via an anion exchange method, which is fully characterized by FT-IR, SEM with elemental mapping and EDX, FE-SEM and TEM. Furthermore, the use of [Zr-UiO-66-PDC-SO₃H]FeCl₄ as a porous catalyst was examined for the one-pot synthesis of novel dihydrobenzo[g]pyrimido[4,5-b]quinoline derivatives by reaction of 6-amino-1,3-dimethylpyrimidine-2,4(1H,3H)-dione, 2-hydroxynaphthalene-1,4-dione and various aldehydes at 100 °C with good to excellent yields.

[Msim]CuCl3: as an efficient catalyst for the preparation of 5-amino-1H-pyrazole-4-carbonitriles by anomeric based oxidation

3-Methyl-1-sulfonic acid imidazolium trichlorido copper (II) {[Msim]CuCl3} was prepared and used as a new catalyst for the preparation of 5-amino-1H-pyrazole-4-carbonitriles. In this reaction, the pyrazole ring was formed by an anomeric and vinylogous anomeric effect in the structure of the product.

Site-selective and metal-free C-H nitration of biologically relevant N-heterocycles

The site-selective and metal-free C-H nitration reaction of quinoxalinones and pyrazinones as biologically important N-heterocycles with t-butyl nitrite is described. A wide range of quinoxalinones were efficiently applied in this transformation, providing C7-nitrated quinoxalinones without undergoing C3-nitration. From the view of mechanistic point, the radical addition reaction exclusively occurred at the electron-rich aromatic region beyond electron-deficient N-heterocycle ring. This is a first report on the C7-H functionalization of quinoxalinones under metal-free conditions. In contrast, the nitration reaction readily takes place at the C3-position of pyrazinones. This transformation is characterized by the scale-up compatibility, mild reaction conditions, and excellent functional group tolerance. The applicability of the developed method is showcased by the selective reduction of NO₂ functionality on the C7-nitrated quinoxalinone product, providing aniline derivatives. Combined mechanistic investigations aided the elucidation of a plausible reaction mechanism.

Recent Advances in the Nitration of Olefins

Nitroolefins are important synthetic intermediates in the field of organic synthesis as well as in medicinal chemistry. The high reactivity of nitroalkenes due to the polarized double bond which enables them to act as Michael acceptor in conjugate addition reactions, or as a dienophile in cycloaddition makes it an essential synthetic handle for accessing complex molecules. The classical method to prepare nitroolefins is indeed the Henry nitroaldol reaction, where a carbonyl compound and nitroalkane are condensed in presence of base. Direct nitration of olefin, on the other hand, serves as a useful alternative as olefins are abundant, have broad commercial availability and easy to manipulate. In this context, numerous methods have been developed over the last few decades, focusing on direct nitration of styrene and aliphatic olefins. Furthermore, thorough literature search revealed that implementation of this class of reactions are gaining momentum as a preferred pathway to access nitroolefins, despite the presence of a powerful technique such as Henry reaction. In this review, we aim to cover recent advances in direct olefin nitration and their importance in accessing biorelevant molecules, total synthesis targets and future outlook in this specific research area.

Organocatalyzed Heterocyclic Transformations In Green Media: A Review

Background:

Since the discovery of metal-free catalysts or organocatalysts about twenty years ago, a number of small molecules with different structures have been used to accelerate organic transformations. With the development of environmental awareness, to obtain highly efficient scaffolds, scientists have directed their studies towards synthetic methodologies that minimize or preferably eliminate the formation of waste, avoid toxic solvents and reagents and use renewable starting materials as far as possible.

Methods:

In this connection, the organocatalytic reactions providing efficiency and selectivity for most of the transformations have become an endless topic in organic chemistry since several advantages from both practical and environmental standpoints. Organocatalysts contributing to the transformation of reactants into products with the least possible waste production, have been serving the concept of green chemistry.

Results and Conclusion:

Organocatalysts have been classified based on their binding capacity to the substrate with covalent or noncovalent interactions involving hydrogen bonding and electrostatic interaction. Diverse types of small organic compounds including proline and its derivatives, phase-transfer catalysts, (thio)urease, phosphoric acids, sulfones, N-oxides, guanidines, cinchona derivatives, aminoindanol, and amino acids have been utilized as hydrogen bonding organocatalysts in different chemical transformations.

Application of [PVI-SO3H]NO3 as a novel polymeric nitrating agent with ionic tags in preparation of high-energetic materials

In this paper, poly(vinyl imidazole) sulfonic acid nitrate [PVI-SO3H]NO3 was synthesized and fully characterized. Then, [PVI-SO3H]NO3 was applied for the preparation of energetic materials such as 1,1-diamino-2,2-dinitroethene (FOX-7), pentaerythritol tetranitrate (PETN), 1,3,5-trinitro-1,3,5-triazinane (RDX) and trinitrotoluene (TNT). The major advantages of the presented methodology are mild, facile workup, high yields and short reaction times. [PVI-SO3H]NO3 is a suitable nitrating agent for in situ generation of NO2 and without using any co-catalysts of the described nitrating reagent.

Bifunctional acidic ionic liquid-catalyzed decarboxylative cascade synthesis of quinoxalines in water under ambient conditions

An acid-functionalized ionic liquid (IL)-catalyzed cascade decarboxylative cyclization of 2-arylanilines with α-oxocarboxylic acids was developed.

Insights into the catalytic mechanism of 5-hydroxymethfurfural to phthalic anhydride with MoO3/Cu(NO3)2 in one-pot

A synthetic approach to obtain renewable phthalic anhydride (PA) from 5-hydroxymethfurfural (HMF) with a yield of 63.2% using MoO₃/Cu(NO₃)₂ as a catalyst in one pot.

Recent advances in nitro-involved radical reactions

Significant progress in the chemistry of nitro radicals has been witnessed in the past decades, providing efficient and rapid access to nitro-containing compounds. This review describes recent advances in nitro-involved radical reactions, and summarizes various transformations.

N,N,N′,N′-Tetramethylethylene-diaminium-N,N′-disulfonic acid trifluoroacetate and pyridinium-N-sulfonic acid hydrogen sulfate as highly effective dual-functional catalysts for the preparation of N,N′-alkylidene bisamides

In this research, Brønsted-acidic ionic liquids N,N,N′,N′-tetramethylethylene-diaminium-N,N′-disulfonic acid trifluoroacetate ([TMEDSA][TFA]2) and pyridinium-N-sulfonic acid hydrogen sulfate ([Py-SO3H][HSO4]) have been introduced as dual-functional catalysts for the green, simple and effective preparation of N,N′-alkylidene bisamides by the reaction of primary amides (2 eq.) with arylaldehydes (1 eq.) under solvent-free conditions. The reaction results and conditions of the catalysts have been compared with the previously reported ones. [TMEDSA][TFA]2 and [Py-SO3H][HSO4] were superior to the previously reported catalysts in terms of two or more of these factors: reaction times (10–45 min), yields (86–98%), temperature and the reaction conditions. Additionally, a plausible and attractive mechanism based on dual functionality of the catalysts has been proposed.

IL-oxidizer/IL-fuel combinations as greener hypergols

Two ionic liquids were ignited spontaneously upon contact, suggesting an effective route to develop greener hypergolic IL–IL bipropellants.

Highly effectual synthesis of 4,6-diarylpyrimidin-2(1H)-ones using N,N,N′,N′-tetramethylethylenediaminium-N,N′-disulfonic acid hydrogen sulfate as a dual-functional catalyst

The highly effectual synthesis of 4,6-diarylpyrimidin-2(1H)-ones via the one-pot multicomponent reaction of acetophenones with arylaldehydes and urea in the presence of trimethylsilyl chloride and a catalytic amount of the ionic liquid N,N,N′,N′-tetramethylethylenediaminium-N,N′-disulfonic acid hydrogen sulfate ([TMEDSA][HSO4]2) under solvent-free conditions has been described. The reaction results and conditions of the catalytic system have been compared with previously reported catalysts. [TMEDSA][HSO4]2 afforded better results in comparison with the reported catalysts in terms of one or more of these factors: yield, temperature, the reaction media, time, and generality. Moreover, a plausible reaction mechanism based on dual functionality of the catalyst has been proposed.

A highly effective and mild protocol for the production of 1-thioamidoalkyl-2-naphthols using 1,3-disulfonic acid imidazolium trifluoroacetate as a dual-functional catalyst

A solvent-free protocol for the production of 1-thioamidoalkyl-2-naphthols via a one-pot multi-component reaction of arylaldehydes with 2-naphthol and thioacetamide using the ionic liquid 1,3-disulfonic acid imidazolium trifluoroacetate ([Dsim][TFA]) is described. Furthermore, a plausible and attractive mechanism based on the dual functionality of the catalyst is proposed. Because of the dual functionality of [Dsim][TFA] (possessing acidic and basic sites), it is found to be generally highly effective, affording the products in high yields and short reaction times under mild conditions. We claim that this is one of the best protocols for the synthesis of 1-thioamidoalkyl-2-naphthols (in terms of yield, temperature, conditions, and/or the reaction time).

Efficient pseudo five-component synthesis of 4,4′-(arylmethylene)-bis(3-methyl-1-phenyl-1H-pyrazol-5-ol) derivatives promoted by a novel ionic liquid catalyst

In this research, initial production and characterization of a novel Brønsted-acidic ionic liquid, namely, N,N,N′,N′-tetramethylethylenediaminium-N,N′-disulfonic acid hydrogen sulfate ([TMEDSA][HSO4]2), has been described (characterization was achieved using Fourier-transform infrared spectroscopy, 1H nuclear magnetic resonance (NMR), 13C NMR, and mass and thermal gravimetric spectra). Thereafter, utilization of [TMEDSA][HSO4]2 as a highly effectual catalyst for the synthesis of 4,4′-(arylmethylene)-bis(3-methyl-1-phenyl-1H-pyrazol-5-ol) derivatives through the one-pot pseudo five-component reaction of phenylhydrazine (2 eq.) with ethyl acetoacetate (2 eq.) and arylaldehydes (1 eq.) in relatively mild conditions, has been reported.

Evidence of single electron transfer from the enolate anion of an N,N'-dialkyldiketopiperazine additive in BHAS coupling reactions

A designed N,N'-dialkyldiketopiperazine (DKP) provides evidence for the role of DKP additives as initiators that act by electron transfer in base-induced homolytic aromatic substitution reactions, involving coupling of haloarenes to arenes.

Nitrogen Oxides and Nitric Acid Enable the Sustainable Hydroxylation and Nitrohydroxylation of Benzenes under Visible Light Irradiation

A new type of waste recycling strategy is described in which nitrogen oxides or nitric acid are directly employed in photocatalyzed hydroxylations and nitrohydroxylations of benzenes. Through these transformations, otherwise costly denitrification can be combined with the synthesis of valuable compounds for various applications.

Prospective Symbiosis of Green Chemistry and Energetic Materials

A global increase in environmental pollution demands the development of new "cleaner" chemical processes. Among urgent improvements, the replacement of traditional hydrocarbon-derived toxic organic solvents with neoteric solvents less harmful for the environment is one of the most vital issues. As a result of the favorable combination of their unique properties, ionic liquids (ILs), dense gases, and supercritical fluids (SCFs) have gained considerable attention as suitable green chemistry media for the preparation and modification of important chemical compounds and materials. In particular, they have a significant potential in a specific and very important area of research associated with the manufacture and processing of high-energy materials (HEMs). These large-scale manufacturing processes, in which hazardous chemicals and extreme conditions are used, produce a huge amount of hard-to-dispose-of waste. Furthermore, they are risky to staff, and any improvements that would reduce the fire and explosion risks of the corresponding processes are highly desirable. In this Review, useful applications of almost nonflammable ILs, dense gases, and SCFs (first of all, CO₂ ) for nitration and other reactions used for manufacturing HEMs are considered. Recent advances in the field of energetic (oxygen-balanced and hypergolic) ILs are summarized. Significant attention is paid to the SCF-based micronization techniques, which improve the energetic performance of HEMs through an efficient control of the morphology and particle size distribution of the HEM fine particles, and to useful applications of SCFs in HEM processing that makes them less hazardous.

Engineered P450 biocatalysts show improved activity and regio-promiscuity in aromatic nitration

Nitroaromatics are among the most important and commonly used chemicals but their production often suffers from multiple unsolved challenges. We have previously described the development of biocatalytic nitration processes driven by an engineered P450 TxtE fusion construct. Herein we report the creation of improved nitration biocatalysts through constructing and characterizing fusion proteins of TxtE with the reductase domain of CYP102A1 (P450BM3, BM3R). The majority of constructs contained variable linker length while one was rationally designed for optimizing protein-protein interactions. Detailed biochemical characterization identified multiple active chimeras that showed improved nitration activity, increased coupling efficiency and higher total turnover numbers compared with TxtE. Substrate promiscuity of the most active chimera was further assessed with a substrate library. Finally, a biocatalytic nitration process was developed to nitrate 4-Me-dl-Trp. The production of both 4-Me-5-NO₂-l-Trp and 4-Me-7-NO₂-l-Trp uncovered remarkable regio-promiscuity of nitration biocatalysts.

Synthesis of spiropyran derivatives over 1-(carboxymethyl) pyridinium iodide as nanostructured pyridinium salt under aqueous media

In this work, acetic acid functionalized pyridinium salt, namely 1-(carboxymethyl)pyridinium iodide {[cmpy]I}, has been applied as reusable nanostructured catalyst for green, simple and efficient preparation of spiropyrans by the one-pot domino Knoevenagel–Michael–cyclization reaction of isatin derivatives or acenaphthenquinone, with malononitrile, and 1,3-dicarbonyl compounds under aqueous media. Moreover, 1H and 13C NMR, mass, CHN analysis, Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), thermal gravimetric analysis (TGA), differential thermal gravimetric (DTG), X-ray diffraction analysis (XRD), and calculation of crystallite size and interplaner distance of the catalyst have been studied.