Radical trifluoromethylation.

The trifluoromethyl group plays an increasingly important role in pharmaceuticals, agrochemicals and materials. This tutorial describes recent advances in trifluoromethylation of carbon-centered radical intermediates.

Copper-Catalyzed Ring-Opening 1,3-Aminotrifluoromethylation of Arylcyclopropanes.

The copper-catalyzed reaction of arylcyclopropanes, N-fluorobis(arenesulfonyl)imides, and (bpy)Zn(CF3)2 (bpy = 2,2'-bipyridine) at room temperature affords the corresponding ring-opening 1,3-aminotrifluoromethylation products in satisfactory yields. The protocol is highly regioselective, providing a convenient entry to γ-trifluoromethylated amines. A mechanism involving the trifluoromethylation of benzyl radicals is proposed.

Copper-Catalyzed Radical Aminotrifluoromethylation of Alkenes.

We report herein an unprecedented protocol for aminotrifluoromethylation of alkenes. With Cu(OTf)2 as the catalyst, the reaction of alkenes, (bpy)Zn(CF3)2, and N-fluorobis(benzenesulfonyl)imide (NFSI) at room temperature provides the corresponding aminotrifluoromethylation products in satisfactory yields with high regioselectivity opposite to those driven by CF3 radical addition. The method exhibits a broad substrate scope and wide functional group compatibility. A mechanism involving N-radical addition to alkenes followed by trifluoromethylation of alkyl radicals is proposed.

Copper-Catalyzed Ring-Opening Radical Trifluoromethylation of Cycloalkanone Oximes.

The copper-catalyzed ring-opening C-trifluoromethylation of cycloalkanone oximes with Zn(CF3)2 complexes is described. The reaction proceeds in dichloromethane under mild conditions, providing an efficient and general entry to γ- or δ-CF3-substituted nitriles via tandem N-O and C(sp2)-C(sp3) bond cleavage and C(sp3)-CF3 bond formation. The protocol exhibits a broad substrate scope and wide functional group compatibility. A radical mechanism involving the CF3 transfer from Cu(II)-CF3 complexes to alkyl radicals is proposed.

Copper-Catalyzed Remote C(sp3 )-H Trifluoromethylation of Carboxamides and Sulfonamides.

Reported herein is an unprecedented protocol for trifluoromethylation of unactivated aliphatic C(sp3 )-H bonds. With Cu(OTf)2 as the catalyst, the reaction of N-fluoro-substituted carboxamides (or sulfonamides) with Zn(CF3 )2 complexes provides the corresponding δ-trifluoromethylated carboxamides (or sulfonamides) in satisfactory yields under mild reaction conditions. A radical mechanism involving 1,5-hydrogen atom transfer of N-radicals followed by CF3 -transfer from CuII -CF3 complexes to the thus formed alkyl radicals is proposed.

Comparison of coagulation pretreatment of produced water from natural gas well by polyaluminium chloride and polyferric sulphate coagulants.

This study aimed to optimise coagulation pretreatment of the produced water (PW) collected from a natural gas field. Two coagulants, polyferric sulphate (PFS) and polyaluminium chloride (PACl), were applied separately for the organics, suspended solids (SS), and colour removal. Treatment performance at different coagulant dosages, initial pH values, stirring patterns, and the addition of cationic polyacrylamide (PAM) was investigated in jar tests. The optimal coagulation conditions were dosage of PACl 25 g/L or PFS 20 g/L with that of PAM 30 mg/L, initial pH of 11, and fast mixing of 1.5 min (for PACl) or 2 min (for PFS) at 250 rpm followed by slow mixing of 15 min at 50 rpm for both coagulants. PACl performed better than PFS to remove chemical oxygen demand (COD), total organic carbon (TOC), SS, and colour, and achieved a removal efficiency of 90.1%, 89.4%, 99.0%, and 99.9%, respectively, under the optimal condition; while PFS efficiency was 86.1%, 86.1%, 99.0%, and 98.2%, respectively. However, oil removal was higher in PFS coagulation compared to PACl and showed 98.9% and 95.3%, respectively. Biodegradability, ratio of the biological oxygen demand (five-day) (BOD5)/COD, of the PW after pretreatment increased from 0.08 to 0.32 for PFS and 0.43 for PACl. Zeta potential (Z-potential) analysis at the optimum coagulant dosage of PACl and PFS suggests that charge neutralisation was the predominant mechanism during coagulation. Better efficiency was observed at higher pH. The addition of PAM and starring pattern had a minor influence on the removal performance of both coagulants. The results suggest that PACl or PFS can be applied for the pretreatment of PW, which can provide substantial removal of carbon, oil, and colour, a necessary first step for subsequent main treatment units such as chemical oxidation or biological treatment.

Plant uptake of diclofenac in a mesocosm-scale free water surface constructed wetland by Cyperus alternifolius.

This study aimed to assess the uptake of diclofenac, a widely used nonsteroidal anti-inflammatory pharmaceutical, by a macrophyte Cyperus alternifolius in a mesocosm-scale free water surface (FWS) constructed wetland. Quantitative analysis of diclofenac concentrations in water solution and plant tissues was conducted by high performance liquid chromatography analysis after sample pre-treatment with solid-phase extraction and liquid extraction, respectively. The FWS with Cyperus alternifolius obtained a maximum 69.3% diclofenac removal efficiency, while a control system without plant only had a removal efficiency of 2.7% at the end of the experiment period of 70 days. Based on mass balance study of the experimental system, it was estimated that plant uptake and in-plant conversion of diclofenac contributed about 21.4% of the total diclofenac removal in the mesocosm while the remaining 78.6% diclofenac was eliminated through biotic and abiotic conversion of diclofenac in the water phase. Diclofenac on the root surface and in roots, stems and leaves of Cyperus alternifolius was found at the concentrations of 0.15-2.59 µg/g, 0.21-2.66 µg/g, 0.06-0.53 µg/g, and 0.005-0.02 µg/g of fresh weight of plant tissues, respectively. The maximum bioaccumulation factor of diclofenac was calculated in roots (21.04) followed by root surface (20.49), stems (4.19), and leaves (0.16), respectively. Diclofenac translocation potentiality from root to stem was found below 0.5, suggesting a slow and passive translocation process of diclofenac. Current study demonstrated high potential of Cyperus alternifolius for phytoremediation of diclofenac in FWS and can be applied in other engineered ecosystems.

Phytoremediation of levonorgestrel in aquatic environment by hydrophytes.

Adsorption and degradation of levonorgestrel (LNG) by two hydrophytes, Cyperus alternifolius (CA) and Eichhornia crassipes (EC), were investigated under light-shielding conditions in the water column. Variations of LNG concentrations in water, plant root epidermis, root, stem and leaf of the plants were analyzed. The results indicated that the removal efficiency of LNG by hydrophytes over the period of 50days was significantly greater than the blank control (p<0.05), with the removal rates of 79.80%±3.10% and 78.86%±2.55% for CA and EC, respectively. Compared with bio-adsorption, bio-conversion of LNG was found to be the dominant elimination pathway, evidenced by relatively high conversion rates (77.31%±2.68% for CA and 77.82%±2.95% for EC), while the adsorption rates were lower (1.77%±0.90% for CA and 1.05%±0.40% for EC). The bio-adsorption and conversion of LNG showed no significant differences between the two hydrophytes. Additionally, the mineralization on root epidermis played an important role in the reduction of LNG in water.

Retention and distribution of Cu, Pb, Cr, and Zn in a full-scale hybrid constructed wetland receiving municipal sewage.

This study was conducted to investigate the retention and distribution of Cu, Pb, Cr, and Zn in a hybrid constructed wetland (CW) that consists of both vertical baffled flow wetlands (VBFWs) and horizontal subsurface flow wetlands (HSSFs) with unique flow regimes and oxygen distribution. The heavy metal concentrations in water, sediments, and plant tissues in the hybrid CW were analysed. The removal of heavy metals from the water stream in the monitoring period was not statistically significant. Metal concentrations in the sediments generally decreased along the wastewater treatment process. The reductive anaerobic condition in the VBFW may promote the sulphate reduction and form highly insoluble Cu, Pb, and Zn sulphides, resulting in the higher concentration of the bivalent cations in the VBFW sediments than the corresponding values in the HSSF; however, the aerobic and anoxic environments in the HSSF enhanced the removal of Cr with the co-precipitation of iron and manganese oxides, and their hydroxides. Metal concentrations in plant tissues were not significantly influenced by the concentrations in sediments, while roots contained statistically higher metal concentrations than stems and leaves. The sediments stored 94.01, 86.31, 95.85, and 89.51% of the total Cu, Pb, Cr, and Zn retained in the hybrid CW system, respectively, while only small fractions (<10%) were accumulated in the harvestable macrophyte tissues. It is important to clean not only the accessible sediments in free water surface tank and ponds but also the embedded sediments in vegetated beds for the sustainable removal of heavy metals.

Variation of dissolved oxygen and redox potential and their correlation with microbial population along a novel horizontal subsurface flow wetland.

AIMS: This study was conducted to evaluate the performance of a novel horizontal subsurface flow wetland (HSFW) in naturally improving the dissolved oxygen (DO) and the impact on redox condition, microbial activity and the nitrogen removal in the HSFW bed. MATERIALS AND METHODS: The HSFW, equipped with cascaded natural aeration ditches (NADs), was the second stage of a hybrid constructed wetland (CW) after vertical-baffled flow wetland beds. The performances of the HSFW for organics and nitrogen removal in a full-scale hybrid CW system treating municipal wastewater for more than three years have been analysed. The spatial distributions of the oxidation-reduction potential (ORP), DO, microbial population density and specific oxygen uptake rate were determined, and their correlations were analysed in one selected section of the HSFW bed. RESULTS: A 7-m-long shallow NAD increased the DO concentration from 0.28 mg O2 L(-1) to 3.80 mg O2 L(-1) and the ORP from +37.3 mV to +247.7 mV, creating an aerobic zone with a hydraulic retention time (HRT) of 0.5 h and an anoxic zone of another 0.5 h in series in the subsequent wetland bed. For the whole HSFW with three NADs, the macro aerobic and anoxic environment with a total HRT of 3 h can be created. CONCLUSIONS: The unique DO distribution in HSFW may contribute to an optimum environment for partial nitrification and anammox, and obtain a high performance for nitrogen removal. Correlation analysis showed that the microbial activity in the HSFW relied obviously on the redox condition.

Development and application of a water pollution emergency response system for the Three Gorges Reservoir in the Yangtze River, China.

There are many watercraft and production accidents in the Three Gorges Reservoir Area (TGRA) of the Yangtze River in China every year. Accidents threaten the water quality of the 1085 km2 surface area of the TGRA and millions of local people if oil and chemical leakage were to occur. A water pollution management system for emergency response (WPMS_ER) was therefore designed for the management of pollution in this area. An integrated geographic information system (GIS)-based water pollution management information system for the TGRA, called WPMS_ER_TGRA, was developed in this study. ArcGIS engine was used as the system development platform, and Visual Basic as the programming language. The models for hydraulic and water quality simulation and the generation of body-fitted coordinates were developed and programmed as a dynamically linked library file using Visual Basic, and they can be launched by other computer programs. Subsequently, the GIS-based information system was applied to the emergency water pollution management of a shipwreck releasing 10 tons of phenol into the Yangtze River during two hours. The results showed that WPMS_ER_TGRA can assist with emergency water pollution management and simulate the transfer and diffusion of accidental pollutants in the river. Furthermore, it can quickly identify the affected area and how it will change over time within a few minutes of an accident occurring.

[Effect of DO distribution on contaminated urban stream water treatment performance in constructed wetland].

We evaluated the effect of dissolved oxygen (DO) on the performance of two pilot-scale constructed wetlands in treating contaminated water from an urban stream. The aim of this study was to investigate a more effective DO distribution in contaminated stream water treatment wetland that may aid future constructed wetland design effort. The results show poor natural aeration condition and inadequate DO in wetland directly result in the deterioration of effluent water quality. Natural waterfall is an effective aeration way and can improve DO concentration in wetland. The aeration capability of waterfall can be evaluated by oxygen deficit ratio (the ratio of difference between concentration of saturated DO and DO measured before and after waterfall). The distributions of DO obviously correlated with the quantity distribution of micrdorganism and removal rate of organic contaminants in wetland, however there was no obvious relationship between DO and TP removal rate. Results of the study also indicate setting multi-waterfall in plug-flow wetland can balance the distribution of DO and improve the nitrification.