17 research outputs found
Iron-Catalyzed Ī±āArylation of Deoxybenzoins with Arenes through an Oxidative Dehydrogenative Approach
A novel
Ī±-arylation of deoxybenzoins with non-prefunctionalized
arenes is developed through an iron-catalyzed oxidative dehydrogenative
approach. The reaction shows broad substrate scope and functional
group tolerance and thus provides efficient access to synthetically
useful 1,2,2-triarylethanones. A reasonable mechanism is also proposed
Iron-Catalyzed Ī±āArylation of Deoxybenzoins with Arenes through an Oxidative Dehydrogenative Approach
A novel
Ī±-arylation of deoxybenzoins with non-prefunctionalized
arenes is developed through an iron-catalyzed oxidative dehydrogenative
approach. The reaction shows broad substrate scope and functional
group tolerance and thus provides efficient access to synthetically
useful 1,2,2-triarylethanones. A reasonable mechanism is also proposed
Iron-Catalyzed Ī±āArylation of Deoxybenzoins with Arenes through an Oxidative Dehydrogenative Approach
A novel
Ī±-arylation of deoxybenzoins with non-prefunctionalized
arenes is developed through an iron-catalyzed oxidative dehydrogenative
approach. The reaction shows broad substrate scope and functional
group tolerance and thus provides efficient access to synthetically
useful 1,2,2-triarylethanones. A reasonable mechanism is also proposed
Concentrations of DDTs and Enantiomeric Fractions of Chiral DDTs in Agricultural Soils from Zhejiang Province, China, and Correlations with Total Organic Carbon and pH
Dichlorodiphenyltrichloroethanes (DDTs) are persistent
organic
pollutants that were widely used in China, especially eastern China,
as insecticides. This work investigated the concentration, dissipation,
and volatilization of DDTs and enantiomeric fractions (EFs) of <i>o</i>,<i>p</i>ā²-DDD and <i>o</i>,<i>p</i>ā²-DDT in agricultural soils collected in 2006 from
58 sites in Zhejiang province. Correlations between DDT residues and
soil properties were assessed to determine the effect of soil properties
on the environmental attenuation of DDTs. High concentrations and
detection frequencies were found for DDTs in agricultural soils in
the region even though large-scale use of DDTs was banned over 20
years ago. The amount of DDTs was about 485 tons in the upper 20 cm
of the soil column of cropland in the province in 2010, with a dissipation
half-life of ā¼9 years. The mass flux of DDTs was 43 ng m<sup>ā2</sup> h<sup>ā1</sup>, which corresponds to emissions
of 7.6 tons with an emission factor of 1.6% in 2006. The low <i>p</i>,<i>p</i>ā²-DDT/<i>p</i>,<i>p</i>ā²-DDE ratios and high <i>o</i>,<i>p</i>ā²-DDT/<i>p</i>,<i>p</i>ā²-DDT
ratios suggest that there were no recent inputs of DDTs but fresh
application of dicofol, which contains DDT (<i>o</i>,<i>p</i>ā²-DDT in particular) impurities. The significant
positive correlation between concentrations of DDTs and total organic
carbon content (TOC) indicates the distribution of DDTs fit a typical
āsecondary distributionā pattern. DEVrac of <i>o</i>,<i>p</i>ā²-DDD, which is defined as the
absolute value of EFs subtracted from 0.5, was significantly related
with most of the physicochemical and microbial soil properties. The
most significant correlation is that between DEVrac of <i>o</i>,<i>p</i>ā²-DDD and soil pH (<i>p</i> <
0.001), indicating that the soil pH plays a key role in enantioselective
residues of DDTs
NH<sub>4</sub>HF<sub>2</sub> as a Selective TBS-Removal Reagent for the Synthesis of Highly Functionalized Spiroketal via Tandem Deprotection/Spiroketalization Procedure
NH<sub>4</sub>HF<sub>2</sub> has been used for the first time to
selectively remove the TBS protecting groups from diol ketone precursors
in the synthesis of highly functionalized spiroketals. This method
allows the synthesis of [5,6], [6,6], and [6,7] spiroketal skeletons,
as well as benzannulated spiroketal with retention of acid-sensitive
groups. In this way, spiroketals can be synthesized with diverse substituent
groups in the skeleton or on side chains. To demonstrate the utility
of this methodology, the diverse transformations of highly functionalized
spiroketal <b>3f</b> were also investigated
Assessing and Forecasting Atmospheric Outflow of Ī±-HCH from China on Intra-, Inter-, and Decadal Time Scales
Atmospheric outflow of Ī±-HCH from China from 1952
to 2009
was investigated using Chinese Gridded Pesticide Emission and Residue
Model (ChnGPERM). The model results show that the outflows via the
northeast boundary (NEB, longitude 115ā135 Ā°E along 55
Ā°N and latitude 37ā55 Ā°N along 135 Ā°E) and the
mid-south boundary (MSB, longitude 100ā120 Ā°E along 17
Ā°N) of China account for 47% and 35% of the total outflow, respectively.
Two climate indices based on the statistical association between the
time series of modeled Ī±-HCH outflow and atmospheric sea-level
pressure were developed to predict the outflow on different time scales.
The first index explains 70/83% and 10/46% of the intra-annual variability
of the outflow via the NEB and MSB during the periods of 1952ā1984
and 1985ā2009, respectively. The second index explains 16%
and 19% of the interannual and longer time scale variability in the
outflow through the NEB during JuneāAugust and via the MSB
during OctoberāDecember for 1991ā2009, respectively.
Results also revealed that climate warming may potentially result
in stronger outflow via the NEB than the MSB. The linkage between
the outflow with large scale atmospheric circulation patterns and
climate warming trend over China was also discussed
Decabrominated Diphenyl Ethers (BDE-209) in Chinese and Global Air: Levels, Gas/Particle Partitioning, and Long-Range Transport: Is Long-Range Transport of BDE-209 Really Governed by the Movement of Particles?
In
this paper, we report air concentrations of BDE-209 in both gas- and
particle-phases across China. The annual mean concentrations of BDE-209
were from below detection limit (BDL) to 77.0 pgĀ·m<sup>ā3</sup> in the gas-phase and 1.06ā728 pgĀ·m<sup>ā3</sup> in the particle-phase. Among the nine PBDEs measured, BDE-209 is
the dominant congener in Chinese atmosphere in both gas and particle
phases. We predicted the partitioning behavior of BDE-209 in air using
our newly developed steady state equation, and the results matched
the monitoring data worldwide very well. It was found that the logarithm
of the partition quotient of BDE-209 is a constant, and equal to ā1.53
under the global ambient temperature range (from ā50 to +50
Ā°C). The gaseous fractions of BDE-209 in air depends on the concentration
of total suspended particle (TSP). The most important conclusion derived
from this study is that, BDE-209, like other semivolatile organic
compounds (SVOCs), cannot be sorbed entirely to atmospheric particles;
and there is a significant amount of gaseous BDE-209 in global atmosphere,
which is subject to long-range atmospheric transport (LRAT). Therefore,
it is not surprising that BDE-209 can enter the Arctic through LRAT
mainly by air transport rather than by particle movement. This is
a significant advancement in understanding the global transport process
and the pathways entering the Arctic for chemicals with low volatility
and high octanolāair partition coefficients, such as BDE-209
Residues of Currently and Never Used Organochlorine Pesticides in Agricultural Soils from Zhejiang Province, China
Studies on residues of currently and never used organochlorine
pesticides (OCPs) facilitate the assessment of the contamination level,
distribution, sources, transportation, and trend of these selected
OCPs in China. In this work we investigated the concentration levels
of endosulfans and chlordane, which are currently used, and the never
used aldrin and dieldrin in the province of Zhejiang, a rainy, and
hilly tea-growing province in eastern China. The average/mean residue
levels of OCPs was in the order āendosulfan > āchlordane
> aldrin > dieldrin. The residue level was in good agreement
with
the usage of OCPs in Zhejiang. The spatial distribution showed that
the residues of OCPs in soils from the mountain area were always higher
than those in soils from the plains. The distribution characteristics
were related to usage for current-use OCPs and temperature for never
used OCPs. The isomeric ratios and enantiomeric fractions are useful
tools to identify the degradation preference of contaminants. The
wide range of ratios between <i>trans</i>-chlordane (TC)
and <i>cis</i>-chlordane (CC) indicated that the degradation
of the two isomers of chlordane was different at different sites.
Nonracemic residues of TC and CC were observed in most soils; this
is significant since the enantiomers have different toxicities
In Situ Cross-Linked Polymerization toward Poly(ether sulfone)/Poly(sodium acrylate) Hybrid Particles for the Removal of Environmental Toxins
In
this study, polyĀ(ether sulfone) (PES)/polyĀ(sodium acrylate)
(PSA) hybrid particles for the removal of environmental toxins were
prepared via in situ cross-linked polymerization coupled with a liquidāliquid
phase separation technique. The particles were characterized by Fourier
transform infrared spectroscopy (FTIR), thermogravimetric analysis
(TGA) and scanning electron microscopy (SEM). Batch experiments were
performed to verify the adsorption capability of the particles, and
the initial concentrations and pH values of the solutions significantly
affected the adsorption process. In addition, both adsorption kinetic
and adsorption isotherm models were used to analyze the adsorption
process of Cu<sup>2+</sup>. The modified PES particles showed high
adsorption capability for Cu<sup>2+</sup> and methylene blue (MB),
and a particle column was used to further study the removal ability
of environmental toxins. The results indicated that the hybrid particles
had great potential to remove heavy metal ions and cationic dyes for
wastewater treatment on an industrial scale
Comparative Assessment of the Global Fate of Ī±- and Ī²-Hexachlorocyclohexane before and after Phase-Out
Technical hexachlorocyclohexane (HCH) was one of the
most widely
used pesticides during the 20th century. Although production and use
were phased-out during the 1990s, two of its major components, Ī±-
and Ī²-HCH, are still ubiquitous in the environment. Here, we
have collected and analyzed data on concentrations of Ī±- and
Ī²-HCH in the atmosphere and oceans, including spatial and temporal
trends and seasonalities. We apply a global fate and transport model
to both isomers over the period 1950 to 2050 to rationalize current
levels and trends at remote locations with estimated emissions and
to forecast into the near future. Our model results indicate that
secondary emissions from soils and oceans are currently controlling
the observed rates of decline in the atmosphere. Ī²-HCH is declining
more slowly than Ī±-HCH due to its higher persistence, and we
hypothesize that it will eventually become the predominant isomer
of HCH in the environment. The model reproduces over 70% of measured
concentrations of Ī±-HCH in air and ocean water within factors
of 3 and 5, respectively, and over 70% of measured concentrations
of Ī²-HCH within factors of 8 and 20, respectively. The model
results are only weakly sensitive to climate change-induced trends
in Arctic sea-ice cover and temperature