Photocatalytic reduction of nitro aromatic compounds to amines using a nanosized highly active CdS photocatalyst under sunlight and blue LED irradiation

A variety of aromatic nitro compounds were chemoselectively reduced to the corresponding anilines using conveniently prepared nanosized CdS as a photocatalyst under the sunlight and blue LED irradiation. The results demonstrated that synthesized CdS nanostructures have the potential to provide a promising visible light driven photocatalyst for chemoselective reduction of nitro aromatics in the presence of nitrile and carbonyl groups to the corresponding amines under both sunlight and blue LED irradiation. Photoreduction of nitro aromatics by the prepared nanosized CdS with high surface area was faster than when using the commercially available CdS under both sunlight and LED irradiation. Nanosized CdS photocatalyst was prepared by a simple method without any capping agent. X-ray diffraction (XRD), energy dispersive spectrometry (EDAX), transmission electron microscopy (TEM), scanning electron microscopy (SEM), N₂ absorption—desorption, diffuse reflectance spectroscopy (DRS), and flat band potential methods were employed for the characterization, which revealed that the prepared CdS nanoparticles have a well-resolved cubic structure with the size of around 10–30 nm and a band gap of 2.37 eV.     

Synthesis of a Metal–Organic Framework Material,Iron Terephthalate,by Ultrasound,Microwave, and Conventional Electric Heating: A Kinetic Study

A metal–organic framework material named MIL‐53(Fe), iron terephthalate, has been synthesized sovothermally at a relatively low temperature by not only conventional electric (CE) heating, but also by irradiation under ultrasound (US) and microwave (MW) conditions to gain an understanding of the accelerated syntheses induced by US and MW. The kinetics for nucleation and crystal growth were analyzed by measuring the crystallinity of MIL‐53(Fe) under various conditions. The nucleation and crystal growth rates were estimated from crystallization curves of the change in crystallinity with reaction time. The activation energies and pre‐exponential factors were calculated from Arrhenius plots. It was confirmed that the rate of crystallization (both nucleation and crystal growth) decreases in the order US>MW?CE, and that the accelerated syntheses under US and MW conditions are due to increased pre‐exponential factors rather than decreased activation energies. It is suggested that physical effects such as hot spots are more important than chemical effects in the accelerated syntheses induced by US and MW irradiation. The syntheses were also conducted in two steps to understand quantitatively the acceleration induced by MW and it was found that the acceleration in crystal growth is more important than the acceleration in nucleation, even though both processes are accelerated by MW irradiation.     

Rapid assessment of the impact of microwave heating coupled with UV-C radiation on the degradation of PAHs from contaminated soil using FTIR and multivariate analysis

The presence and fate of polyaromatic hydrocarbons (PAHs) in the environment are receiving a great concern. In this study, three oil-contaminated soils (industrial area, Dukhan city, and artificial soils) were utilized to examine the effect of microwave (MW) heating and UV-C irradiation on the PAHs degradation. A rapid assessment of the impact was evaluated using Fourier transform infrared (FTIR) and multivariate analysis. The total organic matter values for the maximum PAHs reduction were evaluated based on the FTIR spectra of the contaminated soils followed with the principal component analysis (PCA). The results showed that the highest total organic carbon reduction was achieved for the industrial soil sample that required a high MW power and long MW exposure time. On the other hand, the Dukhan city soil sample, which has the lowest total organic carbon, required a high MW power and short MW exposure time followed by UV-C treatment for 20 min to reach the maximal FTIR transmittance reduction. The cluster analysis was also used to evaluate the impact of MW heating, and MW heating followed by UV-C irradiation on the degradation of PAHs. The PCA results of the industrial city sample showed that neither MW treatment (100% MW, 15 min exposure time) followed by UV-C treatment for 20 min nor 10 min is significantly different from the MW treatment (100% MW, 15 min exposure time). However, for the Dukhan sample, the UV-C treatment at 10 min after high MW power and long exposure time (100% MW, 15 min exposure time) was the most efficient treatment.     

Influence of microwave irradiation on enzyme kinetics

The in vitro effect of 2.45 GHz microwave irradiation on porcine pepsin activity under controlled temperature and absorbed microwave power via kinetic parameters was evaluated. Kinetic study with respect of time of irradiation demonstrated the existence of an inactivation effect of microwaves at pH 2 on pepsin molecule. Bovine serum albumin (BSA)-bromphenol blue (BPB) complex was used as substrate for the assay of pepsin by kinetic method. Depending on absorbed microwave dose, the degree of caused inactivation varies from 39.11 to 45.91% for 5 and 20 min of pepsin MW irradiation, respectively. The V _maxapp and K _mapp were calculated for low (5 min of MW irradiation) and higher specific absorbed dose (20 min of MW irradiation), as well as for untreated enzyme, from double reciprocal Lineweaver-Burk plot. The effect of microwaves on substrate (BSA-BPB complex) was also investigated. For reaction performed with MW irradiated substrate for 5 min the reaction rate was decreased for 15.15%, while for 20 min of substrate irradiation reaction rate was decreased for 25.52% compared to the control reaction. The article is published in the original.     

Rapid microwave-assisted liquid-phase combinatorial synthesis of 2-(arylamino)benzimidazoles

An efficient, facile, and practical liquid-phase combinatorial synthesis of benzimidazoles under microwave irradiation is described. In the first step of reaction sequence, polymer-bound activated aryl fluoride was condensed with selective primary amines via an ipso-fluoro displacement reaction. Reduction of the polymer-bound nitro group followed by cyclization with isothiocyanates afforded immobilized benzimidazoles. The desired products were obtained in high yield with high purity after detaching from the soluble matrix. All reactions involved (S(N)Ar reaction, reduction, cyclization, and support cleavage) were performed completely within a few minutes under microwave irradiation. The coupling of microwave technology with liquid-phase combinatorial synthesis constitutes a novel and particularly attractive avenue for the rapid generation of structurally diverse libraries.     

The gas-phase basicity and proton affinity of 1,3,5-cycloheptatriene--energetics,structure and interconversion of dihydrotropylium ions

The hitherto unknown gas-phase basicity and proton affinity of 1,3,5-cycloheptatriene (CHT) have been determined by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Several independent techniques were used in order to exclude ambiguities due to proton-induced isomerisation of the conjugate cyclic C(7)H(9)(+) ions, [CHT + H](+). The gas-phase basicity obtained by the thermokinetic method, GB(CHT) = 799 +/- 4 kJ mol(-1), was found to be identical, within the limits of experimental error, with the values measured by the equilibrium method starting with protonated reference bases, and with the values resulting from the measurements of the individual forward and reverse rate constants, when corrections were made for the isomerised fraction of the C(7)H(9)(+) population. The experimentally determined gas-phase basicity leads to the proton affinity of cycloheptatriene, PA(CHT) = 833 +/- 4 kJ mol(-1), and the heat of formation of the cyclo-C(7)H(9)(+) ion, deltaH(f)(0)([CHT + H](+)) = 884 +/- 4 kJ mol(-1). Ab initio calculations are in agreement with these experimental values if the 1,2-dihydrotropylium tautomer, [CHT + H((1))](+), generated by protonation of CHT at C-1, is assumed to be the conjugate acid, resulting in PA(CHT) = 825 +/- 2 kJ mol(-1) and deltaH(f)(0)(300)([CHT + H((1))](+)) = 892 +/- 2 kJ mol(-1). However, the calculations indicate that protonation of cycloheptatriene at C-2 gives rise to transannular C-C bond formation, generating protonated norcaradiene [NCD + H](+), a valence tautomer being 19 kJ mol(-1) more stable than [CHT + H((1))](+). The 1,4-dihydrotropylium ion, [CHT + H((3))](+), generated by protonation of CHT at C-3, is 17 kJ mol(-1) less stable than [CHT + H((1))](+). The bicyclic isomer [NCD + H](+) is separated by relatively high barriers, 70 and 66 kJ mol(-1) from the monocyclic isomers, [CHT + H((1))](+) and [CHT + H((3))](+), respectively. Therefore, the initially formed 1,2-dihydrotropylium ion [CHT + H((1))](+) does not rearrange to the bicyclic isomer [NCD + H](+) under mild protonation conditions.     

Microwave‐assisted alkylation of diethyl ethoxycarbonylmethylphosphonate under solventless conditions

The reaction of diethyl ethoxycarbonylmethylphosphonate with a series of alkyl halides, under microwave (MW) and solventless conditions at 120°C, in the presence of Cs₂CO₃ and in the absence of a phase transfer catalyst afforded the corresponding monoalkylated products in yields of >70%. The thermal variant carried out in boiling acetonitrile was slow and led to incomplete conversions. In the MW method, the phase transfer catalyst is substituted by MW irradiation and there is no need for a solvent. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 23:241–246, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21009     

Facile Synthesis of new 3,5‐Dispiro Substituted Piperidine Analogs via Microwave‐Assisted One Pot Multicomponent Reaction

An eco‐efficient one‐pot three component reaction for the synthesis of 3,5‐dispirosubstituted piperidines is reported by condensing of 2‐thiobarbituric acid, formaldehyde, and aromatic amines in the presence of a catalytic amount of p‐toluenesulfonic acid (1.0 equivalent) in dimethyl sulfoxide. The reactions were examined by two special methods such as classical heating and microwave (MW) irradiation. In general, improvements in rates and yields were observed when reactions were carried out under MW irradiation compared to the conventional method.     

The synthesis of sterically demanding amino acid-derived cyclic phosphonamides

The preparation and utilization of C(2)-symmetric 1,4-diamines in the synthesis of amino acid-derived cyclic phosphonamides 1-3 are described. The 1,4-diamines are synthesized via three methods: (i) amino acid/fumaryl chloride coupling followed by amide reduction, (ii) amino acid/1,4-diamine coupling followed by amide reduction, and (iii) a template-supported ring-closing metathesis/hydrolysis sequence. The pseudo C(2)-symmetric cyclic phosphonamides 1-3 are prepared by condensation of the C(2)-symmetric 1,4-diamines to P(III) centers, followed by oxidation.     

Novel C 2-symmetric bis-oxazoline ligands

Two novel C ₂-symmetric bis-oxazoline ligands were synthesized and their complexes with Cu(OAc)₂ were studied as catalysts in the enantioselective Henry reaction of 4-nitrobenz-aldehyde with nitromethane giving high yield of nitro aldol with ee up to 40%.     

Synthesis of regioisomeric 2,5‐bis‐substituted‐aza‐benzothiopyranoindazoles

The synthesis of 6‐chloro‐9‐nitro‐benzothiopyranopyridin‐5‐ones 2a, 2b and 2c has been accomplished. Chemotype 2d could not be prepared since attempts to cyclize 3‐(2‐nitro‐5‐chlorophenoxy)pyridine‐2‐carboxylic acid ( 1d ) led to the decarboxylation product 3‐(2‐nitro‐5‐chlorothiophenoxy) pyridine ( 40 ). Analogues 2a, 2b or 2c on treatment with the respectively substituted hydrazine led to the 2‐(substituted)‐5‐nitro 7, 8‐ or 9‐aza substituted chemotypes 3a‐7a, 8b , and 9c‐13c . The reduction of the nitro groups of these substrates was effected by treatment with hydrogen gas (palladium catalyst) or by stannous chloride to yield the 5‐amino chemotypes 15a‐18a, 20b and 21c‐24c , respectively. The conversion of these derivatives to the 2,5‐bis (alkylamino)‐7‐, 8‐ and 9‐aza benzothiopyranoindazoles listed in Table 3 was accomplished by direct alkylations, acylations, followed by reduction of the amido group with Red‐Al or lithium aluminum hydride, or by reductive alkylations in the presence of sodium cyanoborohydride. The removal of the protective BOC‐group was effected by treatment of the appropriate substrates with anhydrous hydrogen chloride to afford the respective hydrochloride salts listed in Table 4.     

Synthesis of novel glycosyl-1,2,3-1H-triazolyl methyl quinazolin-4(3H)-ones and their effect on GLUT4 translocation

Cu(OTf)₂ catalyzed synthesis of propargylated 2,3-dihydroquinazolin-4(1H)-ones has been accomplished from 2-amino-N-propargyl benzamides and aromatic aldehydes under MW irradiation. Next, a series of novel glycosyl triazolyl methyl quinazolin-4(3H)-ones have been synthesized by CuAAC reaction of propargylated 2,3-dihydroquinazolin-4(1H)-ones with glycosyl azides followed by iodine mediated oxidation. In this series, six compounds showed promising to significant GLUT4 translocation activity comparable to rosiglitazone.     

Acylation and related reactions under microwaves. 4. Sulfonylation reactions of aromatics.

Solvent-free sulfonylation of benzene and its activated or deactivated derivatives were carried out under microwave (MW) irradiation and a catalytic amount of iron(III) chloride, which, under these conditions, is more active than other metallic salts. With more reactive and/or nonvolatile reagents (anisole, xylenes, mesitylene) expeditious conditions (short reaction time at constant MW power without control of the temperature) were used. With less reactive and/or low-boiling reagents (benzene, toluene, halobenzenes), the rise in temperature and the increase of reaction time were controlled either by sequential MW irradiation or by a temperature order. It was shown that MWs cause preferential interactions with polar species present in the reaction, especially the aryl sulfone and its FeCl3-complexed form. A MW nonthermal effect was not observed when identical temperature gradients were produced by classical heating and MW irradiation, and if reaction temperature was strictly controlled.     

Using microwave along with TiO<Subscript>2</Subscript> for degradation of 4-chloro-2-nitrophenol in aqueous environment

In this project, microwave (MW) irradiation, photolysis, and photo catalyst were used for degradation of 4-chloro-2-nitro phenol (4-C2NP) in aqueous environment. The influence of main operating parameters such as initial pH, initial concentration of 4C2NP, power dissipation and the dosage of TiO2 on the degradation efficiency has been investigated. The optimum conditions was obtained such as initial concentration of 4C2NP at 30 mg L^?1, initial pH at 6, power dissipation at 16 W for UV irradiation, and the amount of TiO₂ at 0.2 g L^?1. The removal of 4C2NP and chemical oxygen demand (COD) after 100 min of reaction in the combined method (MW/UV/TiO₂) was obtained as 80.5% and 47.3%, respectively. Almost all processes are followed from the pseudo first order kinetics and the degradation rate of 4C2NP obeyed the following order: UV/TiO₂/MW > UV/TiO₂ > MW/UV > UV>MW.     

Microwave-assisted synthesis of metallic nanostructures in solution

Microwave (MW) rapid heating has received considerable attention as a new promising method for the one-pot synthesis of metallic nanostructures in solutions. In this concept, advantageous application of this method has been demonstrated by using some typical examples for the preparation of Ag, Au, Pt, and AuPd nanostructures. Not only spherical nanoparticles, but also single crystalline polygonal plates, sheets, rods, wires, tubes, and dendrites were prepared within a few minutes under MW heating. Morphologies and sizes of nanostructures could be controlled by changing various experimental parameters, such as the concentration of metallic salt and surfactant polymer, the chain length of the surfactant polymer, the solvent, and the reaction temperature. In general, nanostructures with smaller sizes, narrower size distributions, and a higher degree of crystallization were obtained under MW heating than those in conventional oil-bath heating. The origin of these characteristic features under MW irradiation is discussed in terms of thermal and non-thermal effects under MW irradiation.     

Some Aspects of the Chemistry of Nitro Compounds

The present brief account relates our discovery of new reactions revolving around the chemistry of the NO₂ group. It covers the condensation of MeNO₂ with hindered ketones, and the synthesis of pyrroles, triazoles, and enamides. It also describes new transformations of allylic nitro compounds, such as their conversion to allylic sulfones and unsaturated lactones, their sigmatropic rearrangement into allylic nitrites and thence into allylic alcohols, as well as their use in a short synthesis of nitroestrone derivatives. This is followed by an unusual reduction method furnishing unsubstituted amines (RR′C?NH) under conditions where these hydrolytically labile species can be captured inter‐ or intramolecularly. Finally, a mechanistic study of a strange alkyne‐forming reaction, first reported by Abidi and later shown by Corey and co‐workers to proceed through allylic nitro intermediates, ultimately led to a practical and powerful synthesis of alkynes starting from β‐keto esters.     

Comparison of solid-phase and solution-phase chiral auxiliaries in the alkylation/iodolactonization sequence to gamma-butyrolactones

Five prolinol-based chiral auxilaries have been compared for the stereoselective synthesis of gamma-butyrolactones via the sequence of N-acylation, C(alpha)()-allylation, and iodolactonization under both solution-phase and solid-phase conditions. Comparisons of stereoselectivity of both the C(alpha)()-allylation and iodolactonization processes indicate that incorporation of a non-C(2)-symmetric auxiliary as a polymer cross-link gives results superior to those obtained either in solution or with other non-C(2)-symmetric auxiliaries and comparable to those observed using a polymer-supported pseudo-C(2)-symmetric auxiliary.     

Wheat straw lignin extraction with bio-based solvents using enabling technologies

Two bio-based solvents, natural deep eutectic solvents (NaDESs) and γ-valerolactone (GVL), have been used under microwave (MW), and ultrasound (US) irradiation to design an efficient and sustainable process for wheat straw delignification and have been compared with the traditional alkali procedure. Best delignification (45%) was achieved with a three-component NaDES (lactic acid/glycerol/choline chloride) under MW irradiation (at 120 °C in 30 min), with solid/liquid ratio of 1:50. A GVL/water mixture (8:2) also gave an efficient delignification (27%) under US irradiation (40 kHz, 200 W) at 50 °C for 60 min. Analytical pyrolysis (Py) coupled with GC/MS/FID, provides valuable information on the extracts’ chemical profile. DPPH and Folin–Ciocalteu tests highlighted the efficiency of MW- and US-assisted extraction as well as the extracts quality. The highest antioxidant activity for the NaDES extracts was obtained under US irradiation.     

Arylene imine macrocycles of C3h and C3 symmetry from reductive imination of nitroformylarenes

Novel C(3)-symmetric phenylene imine macrocycles have been synthesized by reductive imination of single nitroformylarenes. Pore size and geometric shape are dictated by the distance between and orientation of the nitro and aldehyde moieties in the precursor backbone. This reaction is facile, requires no purification of the products, and is environmentally friendly.     

Environmentally Friendly Methods for Syntheses of New Aromatic Bisesters

Two environmentally friendly methods, one in liquid and the other in solid phase, for preparation of phenyl bisesters (bearing alkylating groups) under microwave (MW) irradiation are presented. The MW remarkably enhanced the rate of acceleration for esterification: the reaction time decreased dramatically, the reaction conditions are milder, and the consumed energy decreased considerably. In the most cases, in the liquid phase under MW irradiation, the yields are better, in some cases substantially (almost 75%). In the solid phase under MW irradiation, the yields are moderate to good compared to the liquid phase but excellent compared to conventional heating. Both methods are fast, general, and facile, but because the solid-phase reactions are solvent-free, we consider this one to be the most suitable for synthetic chemistry. A comparative study of MW and conventional heating was done.