Reaction of nitroanilines with aldehydes. Refinement of the Doebner–Miller reaction mechanism

Due to intramolecular hydrogen bonding between the amino and nitro groups, o-nitroaniline is incapable of forming Schiff bases in the reactions with acetaldehyde and crotonaldehyde but is converted to quinoline derivative under Doebner–Miller reaction conditions via addition to the C=C double bond of the α,β-unsaturated aldehyde. Under analogous conditions, p-nitroaniline possessing a free amino group gives rise to the product of Doebner–Miller quinoline synthesis through intermediate formation of Schiff base dimer. The reaction of p-nitroaniline with benzaldehyde also yields the corresponding Schiff base, whereas o-nitroaniline is converted to N-benzyl derivative.     

Synthesis of 4- and 6-substituted nitroindoles

Enolizable ketones react with m-nitroaniline in the presence of strong base such as t-BuOK to give 4- and 6-substituted nitroindoles. The reaction proceeds via oxidative nucleophilic substitution of hydrogen in m-nitroaniline with enolate anions in positions ortho to the amino group giving anionic σ^H adducts that are additionally stabilized by intramolecular interaction between the amino and the carbonyl group. Spontaneous oxidation of the σ^H adducts followed by the Bayer type condensation of the produced ortho-aminonitrobenzyl ketones gives 4- and 6-substituted nitroindoles. The scope of this reaction and its basic mechanistic features are discussed.     

Separation and determination of nitroaniline isomers by capillary zone electrophoresis with amperometric detection

In this paper, capillary zone electrophoresis with amperometric detection (CZE-AD) was firstly applied to the simultaneous separation and determination of nitroaniline positional isomers. The three analytes could be perfectly analyzed by using the buffer of extreme pH. The effects of several important factors were investigated to find optimum conditions. A carbon-disk electrode was used as working electrode. The optimal conditions were 40 mmol/L tartaric acid-sodium tartrate (pH 1.2) as running buffer, 17 kV as separation voltage and 1.10 V (versus saturated calomel reference electrode, SCE) as detection potential. Under the optimum conditions, o-, m- and p-nitroaniline were separated successfully and good linearity, reproducibility and recovery results were obtained. The detection limit for m-nitroaniline was as low as at 9.06 × 10⁻⁹ mol/L. This proposed method demonstrated long-term stability and reproducibility with relative standard deviations of less than 1.8% for migration time and 1.1% for peak areas. The utility of this method was demonstrated by monitoring dyestuff wastewater and the assay results were satisfactory.     

Fragmentation of protonated amides through intermediate ion-neutral complexes: Neighboring group participation

It has been shown that neighboring group participation plays an important role in the fragmentation of protonated amides; the attachment of an adjacent functional group capable of accepting a proton provides alternative pathways of low energy for the formation of the inevitable N-protonated species in the fragmentation of the amide bond. Under methane chemical ionization (CI) conditions, protonated aniline (m/z 94) is only 1. 6% of the base peak MH⁺ ion for acetanilide; the abundance of the m/z 94 ion is increased to 15% for acetoacetanilide and protonated o-methoxyaniline reaches a relative intensity of 49% for N-acetyl-o-methoxyaniline. A more striking difference in ease of the formation of protonated anilines is found for acetanilides bearing a nitro group at different positions. Protonated nitroaniline (m/z 139) is the base peak in the methane CI spectrum of N-acetyl-o-nitroaniline; the m/z 139 ion drops to only 0.7% for the para isomer, and this ion is increased to 31.5% in the spectrum of N-acetoaceto-p-nitroaniline. By employing low energy collision-induced dissociation, it has been found that the fragmentation of protonated amides proceeds by way of ion-neutral complexes. In the case of acetanilide, for example, the cleavage of the amide bond gives rise to an acetylium ion and neutral aniline, which are bound together as a complex. An α-hydrogen of the acetylium ion, which is activated by the positive charge, is captured by aniline due to its higher proton affinity as compared with ketene. For those compounds having mobile protons other than the amidic hydrogen, it is indicated that such proton has the priority to be transferred in the reaction. Thus, the proton on the free carboxyl group of N-phenyl succinic and maleic monoamides is transferred in the fragmentation, leading to anhydrides as the neutral species in the formation of protonated aniline.     

Chemical oxidative polymerization of m-phenylenediamine and its derivatives using aluminium triflate as a co-catalyst

Aromatic diamine monomers, including m-phenylenediamine (mPD), 2-methyl-m-phenylenediamine (2Me-mPD), 4-methyl-m-phenylenediamine (4Me-mPD) and trimethyl-m-phenylenediamine (tMe-mPD), were polymerized by chemical oxidation using ammonium persulfate as an oxidant. Aluminium triflate (Al(OTf)₃) was also used for the first time as a co-catalyst under various polymerization conditions. The polymerization yield was improved when Al(OTf)₃ was introduced to the polymerization reaction for most polymers. The poly(2-methyl-m-phenylenediamine) (P(2Me-mPD)), poly(4-methyl-m-phenylenediamine) (P(4Me-mPD)) and poly(trimethyl-m-phenylenediamine) (P(tMe-mPD)) polymers exhibited better solubility than poly(m-phenylenediamine) (P(mPD)) polymers in most common solvents. The homopolymers obtained were characterized by FT-IR, ¹H and ¹³C NMR, WAXD and TGA. The results showed that the yield, solubility and structure of the polymers are significantly dependent on the polymerization conditions. TGA measurements indicated that the polymers have good thermal stability and decompose above 400 °C in nitrogen.     

Heat-gradient analytical technique for the simultaneous determination of some aromatic amines

A new sensitive analytical technique has been developed for the simultaneous determination of aromatic amines (aniline, p-nitroaniline, m-nitroaniline, o-nitroaniline, 1,3-phenylenediamine, and 1,4-phenylenediamine). It is based on the differential migration of colored derivatives formed by the reaction of diazotized amines with 8-hydroxy quinoline 5-sulphonic acid (FERRON) on a silica gel plate. Quantitative evaluation of amines is made by visual comparison of the intensities of color by spectrophotometry. The Beer’s law, molar absorptivity, and Sandell’s sensitivity have been determined. The effect of the analytical parameters on the migration and analysis have been evaluated. The method is highly reproducible and has been applied to the determination of amines in environmental samples. The text was submitted by the authors in English.     

A Molecular Probe with Both Chromogenic and Fluorescent Units for Detecting Serine Proteases

A molecular probe with l-phenylalanine p-nitroanilide and l-lysin 4-methylcoumaryl-7-amide, in which these amino acid derivatives are connected through a succinic-acid spacer, was prepared. Trypsin and papain were detected by blue-fluorescence emission of generated 7-amino-4-methylcoumarin (AMC). α-Chymotrypsin and nattokinase were detected from both the blue-fluorescence emission of AMC and the UV absorbance of p-nitroaniline. In addition, different time courses of p-nitroaniline and AMC were observed between the reaction of P1 with α-chymotrypsin and that with nattokinase. In the case of nattokinase, both the fluorescence emission and UV absorbance slowly increased. In contrast, the increasing UV absorbance was saturated at the early stage of the reaction of the present probe with chymotrypsin, whereas the fluorescence emission continuously increased in the following stages.     

Synthesis of organic-inorganic polymer structures via the interaction of orthoboric acid with m-phenylene-bismaleimide

The structure and properties of products arising from the reaction of orthoboric acid with m-phenylene-bismaleimide in melt at 200°C have been studied by spectral and physicochemical methods. The data of IR spectroscopy and thermomechanical analysis suggest that, under the chosen conditions, chemical interaction between the reagents occurs. The conversion increases with the time of reaction and the content of m-phenylene-bismaleimide. High-temperature plasticizers, such as diphenyl and triphenylphosphate, unexpectedly favor formation of more rigid polymer structures, whereas a “temporary plasticizer” (decamethylene glycol) hinders interaction between orthoboric acid and m-phenylene-bismaleimide. The temperature corresponding to a 20% weight loss of the polymer synthesized during heating in air at orthoboric acid: m-phenylene-bismaleimide = 80: 20 is 440–445°C, and the carbon-containing fragments are present in the pyrolysate up to 800°C. The polymer samples retain their shape in air for long time and in water vapor for several days. The hydrolytic stability of the products increases with the content of m-phenylene-bismaleimide.     

Spectrophotometric determination of nitrite with p-nitroaniline and 2-methyl-8-quinolinol in hexadecyl-trimethylammonium bromide solution

Nitrite ion at low concentrations is determined spectrophotometrically by diazotization of p-nitroaniline and coupling of the diazonium salt with 2-methyl-8-quinolinol. The resulting dye is solubilized in hexadecyltrimethylammonium bromide micelles. The molar absorptivity is 4.72 × 10⁴ l mol^-1 cm^-1, and the Sandell sensitivity is 9.7 × 10^-4 μg cm^-2. Some interferences are reported, and preconcentration by evaporation is evaluated. The solubility of hexadecyltrimethylammonium bromide in water was determined as a function of temperature; the Krafft point is 19.6°C. Salting-in of the surfactant by potassium nitrate is described.     

Crystal structures and phase transitions of Sr2CrSbO6

Sr₂CrSbO₆ was synthesized by the conventional solid-state reaction process. X-ray powder diffraction (XRPD) and neutron powder diffraction (NPD) has been used to reinvestigate the structure at room temperature and to study the phase transitions at high- and low-temperature. Rietveld analysis revealed that Sr₂CrSbO₆ crystallizes at room temperature in a monoclinic system having a space group I2/m, with a=5.5574(1) Å; b=5.5782(1) Å; c=7.8506(2) Å and β=90.06(2), no P2₁/n space group as was previously reported. The high-temperature study (300-870 K) has shown that the compound presents the following temperature induced phase-transition sequence: I2/m-I4/m-Fm-3m. The low-temperature study (100-300 K) demonstrated that the room-temperature I2/m monoclinic symmetry seems to be stable down to 100 K.     

One-pot to fused pyrazoles by a double cyclization of o-alkynylaldehydes with ketones and hydrazine under metal-free condition

An efficient one-pot synthesis of fused pyrazoles has been developed. The procedure involved three components reaction of o-alkynylaldehydes 1a–s with ketones 2a–m and hydrazine under mild, metal-free reaction conditions. The desired products were obtained in one-step up to 85% yield. The molecular structure was confirmed by the X-ray crystallographic analysis.     

Reactions of O with CO van der Waals molecules and clusters

The reaction of O(³ P) with COR _m clusters to produce electronically excited CO₂ was studied under molecular beam conditions. It was found that the spectrum of the chemiluminescence produced extended from the blue all the way to the near infrared. The dependence of the total emission intensity on stagnation pressure was investigated for (CO) _m as well as for COR _m , R=He, Ne, Ar, N₂, CO₂ and SO₂. The low pressure data indicate that small (CO) _m polymers are more efficient than clusters of CO with other species in inducing the chemiluminescent reaction. The larger CO-rare gas clusters, however, exhibited larger reaction cross-sections than those of the CO polymers. Rare gas clusters ofm≧5, on the other hand have successively smaller cross sections for reaction. The reactivity of the CO₂ and SO₂ clusters seems to peak at aboutm=1 and then decreases for larger species. An equilibrium model for cluster formation was proposed and it was found capable of explaining and simulating the experimental observations. Contrary to what was reported from afterglow experiments, no barrier for the reaction was detected.     

In vitro release of incorporated model compounds in poly(sebacic anhydride-co-ethylene glycol)

Poly(sebacic anhydride-co-ethylene glycol) was synthesized by using sebacic anhydride prepolymer and poly(ethylene glycol) for encapsulation of p-nitroaniline and brilliant blue G as modeling drugs to investigate the behavior of hydrophobic and hydrophilic drug release, respectively. Since p-nitroaniline is likely located in the sebacic anhydride-rich phase and brilliant blue G in the PEG-rich phase, respectively, their incorporation would affect the phase behavior of the host polymer. Different pore structure of eroded polymer matrix and drug release behavior were identified for hydrophobic and hydrophilic compounds. With a certain amount of PEG in the copolymer matrix, low drug release rate was accomplished for hydrophobic drug incorporation.     

Three-component synthesis of novel trifluoromethyl-containing tetrahydropyran derivatives

l-Proline-catalyzed reaction of ethyl 4,4,4-trifluoroacetoacetate, cinnamaldehyde and anilines provide a novel method for preparation of ethyl-6-(arylamino)-2-hydroxy-4-phenyl-2-(trifluoromethyl)tetrahydro-2H-pyran-3-carboxylate derivatives in good yields. The reaction was conducted by initial Michael addition, followed by intra-molecular cyclization under mild conditions. The structure of a typical ethyl-2-hydroxy-4-phenyl-6-(m-tolylamino)-2-(trifluoromethyl)tetrahydro-2H-pyran-3-carboxylate (4h) was confirmed by XRD analysis. A plausible mechanism is presented.     

New Grafted Copolymers Carrying Betaine Units Based on Gellan and N-Vinylimidazole as Precursors for Design of Drug Delivery Systems

New grafted copolymers possessing structural units of 1-vinyl-3-(1-carboxymethyl) imidazolium betaine were obtained by graft copolymerization of N-vinylimidazole onto gellan gum followed by the polymer-analogous reactions on grafted polymer with the highest grafting percentage using sodium chloroacetate as the betainization agent. The grafted copolymers were prepared using ammonium persulfate/N,N,N′,N′ tetramethylethylenediamine in a nitrogen atmosphere. The grafting reaction conditions were optimized by changing one of the following reaction parameters: initiator concentration, monomer concentration, polymer concentration, reaction time or temperature, while the other parameters remained constant. The highest grafting yield was obtained under the following reaction conditions: c_i = 0.08 mol/L, c_m = 0.8 mol/L, c_p = 8 g/L, t_r = 4 h and T = 50 °C. The kinetics of the graft copolymerization of N-vinylimidazole onto gellan was discussed and a suitable reaction mechanism was proposed. The evidence of the grafting reaction was confirmed through FTIR spectroscopy, X-ray diffraction, ¹H-NMR spectroscopy and scanning electron microscopy. The grafted copolymer with betaine structure was obtained by a nucleophilic substitution reaction where the betainization agent was sodium chloroacetate. Preliminary results prove the ability of the grafted copolymers to bind amphoteric drugs (cefotaxime) and, therefore, the possibility of developing the new sustained drug release systems.     

Deoxyfluorination of alcohols using N,N-diethyl-α,α-difluoro-(m-methylbenzyl)amine

Deoxyfluorination of alcohols was carried out using N,N-diethyl-α,α-difluoro-(m-methylbenzyl)amine (DFMBA). Primary alcohols were effectively converted to fluorides under microwave irradiation or conventional heating. Deoxyfluorination of an anomeric hydroxy group in sugars by DFMBA proceeded at below room temperature and glycosyl fluorides could be obtained in good yields. The deoxyfluorination reaction chemoselectively proceeded and various protecting groups on the sugar can survive under the reaction conditions.     

Fabrication and Performance of a Low Operating Pressure Nanofiltration Poly（vinyl chloride） Hollow Fiber Membrane

A low operating pressure nanofiltration membrane is prepared by interfacial polymerization between m-phenylenediamine(MPDA) and trimesoyl chloride(TMC) using PVC hollow fiber membrane as supporting.A series of PVC nanofiltration membranes with different molecular weight cutoff(MWCO) can be obtained by controlling preparation conditions.Chemical and morphological characterization of the membrane surface was carried out by FTIR-ATR and SEM.MWCO was characterized by filtration experiments.The preparation conditions were investigated in detail.At the optimized conditions(40 min air-dried time,aqueous phase containing 0.5% MPDA,0.05% SDS and 0.6% acid absorbent,oil phase containing 0.3% TMC,and 1 min reaction time),under 0.3 MPa,water flux of the gained nanofiltration membrane reaches 17.8 L/m2·h,and the rejection rates of methyl orange and MgSO4 are more than 90% and 60%,respectively.     

Binary electrolyte small-signal frequency response

The frequency response is considered of a two-electrode linearized system containing a single positively charged species and a single negatively charged species. These species may have arbitrary valences and mobilities and may individually react at the electrodes. The results follow from a detailed solution of the equations of charge motion given earlier. Normalized response is exhibited for this unsupported, intrinsic-conduction situation for a wide range of mobility ratios, valence number ratios, and reaction rate ratios. Results are given in the form of specific formulas, impedance-plane plots, and the dependences on normalized frequency of series and parallel resistive and capacitative components of the normalized total impedance of the system.Impedance-plane plots exhibit from one to three connected arcs, depending on the specific situation. Approximate Warburg frequency response appears for the “interface” impedance over a certain frequency region when normalized reaction rate parameters differ, but it only shows up strongly in the total impedance when the mobility ratio departs appreciably from unity as well. Under such conditions, a plateau region, where the total parallel capacitance remains essentially independent of frequency over a wide frequency range, may appear at frequencies just above the Warburg region. The plateau capacitance is close to but not identical to the conventional double-layer capacitance present when both species of charge are completely blocked. In incomplete blocking cases, however, this double-layer capacitance only makes a significant appearance in the approximate equivalent circuit under slow reaction conditions; it is thus not present when one of the reaction rate constants is infinite.In general, the system can show ω^?m frequency response for the parallel capacitance over a wide frequency range with 0?m?2, and with the experimentally common regions where m≌0, 0.5, 1.5, and 2 especially likely. Particular attention is given to deviations from ideal Warburg behavior which led to a combined charge-transfer and heterogeneous chemical reaction resistance. Results are compared to those from conventional supported treatments and show both important similarities and differences. Finally, several new equivalent circuits are presented which are pertinent in various frequency ranges for the unsupported situation.     

Experimental and theoretical study of the structure of N,N-dimethyl-4-nitroaniline derivatives as model compounds for non-linear optical organic materials

Molecular and crystal structure of a series of derivatives of N,N-dimethyl-4-nitroaniline has been studied by both X-ray diffraction method and high-level ab initio calculations. According to these data, the dimethylamino groups were found to have a trigonal-pyramidal configuration and are considerably turned with respect to the ring plane in all molecules having a substituent in the ortho-position; on the contrary, this group is planar in the meta-substituted molecules. Topological analysis of the electron density function for all molecules studied within the framework of Bader's ‘atoms in molecules’ (AIM) theory revealed that introduction of a substituent into the ortho- or meta-position of the ring results in increasing of the contribution of the resonance forms different from the quinoid one. Contribution of the latter form is predominant for the structure of N,N-dimethyl-4-nitroaniline (1). Topological analysis of the electron density distribution was used to explain a decreasing of the molecular hyperpolarisabilites of the ortho- and meta-substituted compounds as compared with those for 1.     

Preparation and Application of a Hydrochar-Based Palladium Nanocatalyst for the Reduction of Nitroarenes

In the present study, a novel heterogeneous catalyst was successfully fabricated through the decoration of palladium nanoparticles on the surface of designed Fe₃O₄-coffee waste composite (Pd-Fe₃O₄-CWH) for the catalytic reduction of nitroarenes. Various characterization techniques such as XRD, FE-SEM and EDS were used to establish its nano-sized chemical structure. It was determined that Pd-Fe₃O₄-CWH is a useful nanocatalyst, which can efficiently reduce various nitroarenes, including 4-nitrobenzoic acid (4-NBA), 4-nitroaniline (4-NA), 4-nitro-o-phenylenediamine (4-NPD), 2-nitroaniline (2-NA) and 3-nitroanisole (3-NAS), using NaBH₄ in aqueous media and ambient conditions. Catalytic reactions were monitored with the help of high-performance liquid chromatography. Additionally, Pd-Fe₃O₄-CWH was proved to be a reusable catalyst by maintaining its catalytic activity through six successive runs. Moreover, the nanocatalyst displayed a superior catalytic performance compared to other catalysts by providing a shorter reaction time to complete the reduction in nitroarenes.