Metal-free visible-induced C(sp2)-C(sp2) coupling of quinoxalin-2(H)-ones via oxidative cleavage of the C-N bond.

A C(sp2)-C(sp2) reaction between aromatic hydrazines and quinoxalines has been developed through a photocatalytic system. The protocol is established for C(sp2)-N bond cleavage and direct C(sp2)-H functionalization for the coupling of C(sp2)-C(sp2) via photocatalysis under mild and ideal air conditions without the presence of a strong base and metal. The mechanistic studies reveal that the generation of a benzene radical via the oxidative cleavage of aromatic hydrazines for the cross-coupling of C(sp2)-C(sp2) with the assistance of a photocatalyst is essential. The process exhibits excellent compatibility with functional groups and provides convenient access to various 3-arylquinoxalin-2(1H)-ones in good to excellent yields.

DIPEA-induced activation of OH- for the synthesis of amides via photocatalysis.

The development of green protocols for photocatalysis where water acts as a nucleophile, induced by a weak organic base, is difficult to achieve in organic chemistry. Herein, an efficient light-mediated strategy for the synthesis of amides in which a weak organic base acts as a reductant to induce the formation of OH- from water under metal-free conditions is reported. A mechanistic study reveals that the generation of an N,N-diisopropylethylamine (DIPEA) radical via single electron transfer (SET), with the assistance of photocatalyst, that increases the nucleophilicity of the water molecules with respect to the cyanides is essential. Moreover, the removal rate of nitrile in wastewater can be as high as 83%, indicating that this strategy has excellent potential for nitrile degradation.

Electrochemically induced synthesis of quinazolinones via cathode hydration of o-aminobenzonitriles in aqueous solutions.

An efficient and practical electrochemically catalyzed transition metal-free process for the synthesis of substituted quinazolinones from simple and readily available o-aminobenzonitriles and aldehydes in water has been accomplished. I2/base and water play an unprecedented and vital role in the reaction. By electrochemically catalysed hydrolysis of o-aminobenzonitriles, the synthesis of quinazolinones with benzaldehyde was first proposed. The synthetic utility of this method was demonstrated by gram-scale operation, as well as the preparation of bioactive N-(2,5-dichlorophenyl)-6-(2,2,2-trifluoroethoxy) pteridin-4-amine, which enables straightforward, practical and environmentally benign quinazolinone formation.

Electro-oxidative cyclization: access to quinazolinones via K2S2O8 without transition metal catalyst and base.

A K2S2O8-promoted oxidative tandem cyclization of primary alcohols with 2-aminobenzamides to synthesize quinazolinones was successfully achieved under undivided electrolytic conditions without a transition metal and base. The key feature of this protocol is the utilization of K2S2O8 as an inexpensive and easy-to-handle radical surrogate that can effectively promote the reaction via a simple procedure, leading to the formation of nitrogen heterocycles via direct oxidative cyclization at room temperature in a one-pot procedure under constant current. Owing to the use of continuous-flow electrochemical setups, this green, mild and practical electrosynthesis features high efficiency and excellent functional group tolerance and is easy to scale up.

[Synthesis and application of a surface molecularly imprinted adsorbent for di(2-ethylhexyl)phthalate base on graphite oxide].

A molecularly imprinted polymer (MIP) base on the surface of graphite oxide (GO) has been developed for the selective recognition of di(2-ethylhexyl)phthalate (DEHP), and applied for the extraction of DEHP in a milk bag sample, with detection by high-performance liquid chromatography. The surface-molecularly imprinted material was prepared by precipitation polymerization in N,N-dimethylformamide (DMF) solvent, using GO as the supporting material, DEHP as the template molecule, and methacrylic acid (MAA) as the functional monomer; the synthesis conditions were also optimized. The obtained GO-MAA-MIP was characterized by Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM). The adsorption properties of the product were evaluated by adsorption experiments, including adsorption isotherms, kinetics, selectivity, saturated adsorption capacity, adsorption equilibrium time, and reusability. Under optimized conditions, DEHP was effectively extracted in the real sample (milk bag) and detected by HPLC. Linearity was obtained with a correlation coefficient (R2) of 0.9979 in a linear range of 0.5-50 mg/L. The limits of detection and quantitation were 0.03 mg/L and 0.1 mg/L, respectively. The average recoveries of the spiked samples at three concentration levels of DEHP ranged from 81.6% to 92.4% with relative standard deviations (RSDs) less than 7%. The results indicated that the proposed GO-MAA-MIP-SPE (solid phase extraction) protocol with HPLC-UV detection could be applied for the selective analysis of DEHP in real samples.

[Preparation of octadecyl methacrylate-based polymer stationary phase by in-situ polymerization for open tubular capillary electrochromatography].

The preparation of porous polymethacrylate-based open tubular capilary columns by in-situ copolymerization of octadecyl methacrylate (OMA), and ethylene dimethacrylate (EDMA) in N,N-dimethylformamide (DMF) solvent are proposed. The parameters of the preparation procedure of the stationary phase are discussed in detail. The surface of the cross-section of an open tubular (OT) column by scanning electron microscope (SEM) showed wrinkle configuration, which is expedient to enhance proportion of stationary phase and column capacity. Efficient separation of six alkyl benzene homologous series (namely, toluene, ethylbenzene, propylbenzene, butylbenzene, amylbenzene and hexylbenzene) were performed by CEC using the prepared column, and their elution order was in agreement with their hydrophobicity. So, the OT columns bonded with octadecyl ligands yielded reversed-phase retention behavior toward nonpolar solutes. In addition, the separation of four antiepileptics was also investigated with satisfactory effectiveness. The column efficiency range was 35 300-49 800 plates/m. The results showed that the C18-OT column of organic matrix for reversed-phase chromatography was successfully prepared via in-situ polymerization in this work. Hereby, this new column thus offers a promising new alternative in OT-CEC and will be useful in separation science.

[Preparation and evaluation of open tubular capillary electrochromatographic column modified with carboxymethyl chitosan].

Via covalent coupling of epoxy group, an open tubular column covalently modified with carboxymethyl chitosan (CMC) as stationary phase was prepared. The parameters of column pretreatment, silanization and chemically bonding of CMC were optimized. The morphology of inner wall of the open tubular column was observed by scanning electron microscope (SEM), which showed that the inner wall of the prepared column was evenly coated with a polymer film. Either positive or negative electroosmotic flow (EOF) could be achieved by varying the pH values of running buffer. Good reproducibility was obtained with the relative standard deviations (RSDs) of EOF less than 0.8% for run-to-run (n = 6), less than 3.5% for day-to-day (n = 3), less than 4.3% for column-to-column (n = 3) and less than 6.1% for batch-to-batch (n = 3). Nucleotides (AMP, GMP, CMP and UMP) were analyzed on the open tubular column modified with CMC, with high column efficiencies ranging from 36 000 to 182 000 plates/m. The results indicate that the developed method is effective, easy and stable.

Carboxymethylchitosan covalently modified capillary column for open tubular capillary electrochromatography of basic proteins and opium alkaloids.

A novel open tubular (OT) column covalently modified with hydrophilic polysaccharide, carboxymethylchitosan (CMC) as stationary phase has been developed, and employed for the separations of basic proteins and opium alkaloids by capillary electrochromatography (CEC). With the procedures including the silanization of 3-aminopropyltrimethoxysilane (APTS) and the combination of glutaraldehyde with amino-silylated silica surface and CMC, CMC was covalently bonded on the capillary inner wall and exhibited a remarkable tolerance and chemical stability against 0.1 mol/L HCl, 0.1 mol/L NaOH or some organic solvents. By varying the pH values of running buffer, a cathodic or anodic EOF could be gained in CMC modified column. With anodic EOF mode (pH<4.3), favorable separations of basic proteins (trypsin, ribonuclease A, lysozyme and cytochrome C) were successfully achieved with high column efficiencies ranging from 97,000 to 182,000 plates/m, and the undesired adsorptions of basic proteins on the inter-wall of capillary could be avoided. Good repeatability was gained with RSD of the migration time less than 1.3% for run-to-run (n=5) and less than 3.2% for day-to-day (n=3), RSD of peak area was less than 5.6% for run-to-run (n=5) and less than 8.8% for day-to-day (n=3). With cathodic EOF mode (pH>4.3), four opium alkaloids were also baseline separated in phosphate buffer (50 mmol/L, pH 6.0) with column efficiencies ranging from 92,000 to 132,000 plates/m. CMC-bonded OT capillary column might be used as an alternative medium for the further analysis of basic proteins and alkaline analytes.