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Noteworthy Chemistry

March 2, 2015


Hanford's PCB problems linger. Just the mention of Hanford, WA, evokes a multitude of reactions, including “Will it ever end?” Almost 75 years after the opening of the Hanford nuclear production site along the Columbia River (see locator map), the legacy of the facility’s radioactive and chemical pollution persists in the soil, the river, and the aquatic biota.

Location of Hanford site

As part of a risk assessment to support the Hanford cleanup, L. A. Rodenburg at Rutgers University (New Brunswick, NJ), D. Delistraty* at the Washington State Department of Ecology (Spokane), and Q. Meng at Rutgers University (Piscataway, NJ) studied the patterns of polychlorinated biphenyl (PCB) congener patterns in six fish species in four specific areas, up- and down-river from Hanford, as well as within site boundaries.

Monsanto manufactured PCB mixtures under the trade name Aroclor. At Hanford and elsewhere, the primary use of Aroclors was in electrical substations, transformers, and capacitors. Aroclors also were used in roofing, paints, and sealants.

PCBs can be altered by bacteria in soil and sediments; absorption, distribution, metabolism, and excretion (ADME) processes alter the congener patterns in fish. Tissue concentrations of PCBs depend on the ADME process.

By using EPA Method 1668a for analysis, the authors identified 209 PCB congeners in tissues of the six species. They then used positive matrix factorization to identify PCB congener patterns within the species and linked them to each area of origin. They identified six factors on the basis of a weight-of-evidence approach. Most (≈76%) of the PCB mass in the data set fell within three factors: No. 2, “similar to Aroclor 1254”; No. 3, “weathered Aroclor 1254”; and No. 6, “weathered Aroclor 1260”.

Aroclors 1248, 1254, and 1260 were used at Hanford; and all three are reflected in the fish tissue data. The average concentration of PCBs in all of the species was significantly higher in two Hanford areas. A distinct PCB signature in the sturgeon and whitefish collected in the Hanford study areas implicates Hanford as a unique source of PCBs. Research such as this study reveals more about the extent of the Hanford situation and helps scientists as they continue the decontamination process. Sci. Technol. DOI: 10.1021/es504961a; Beth Ashby Mitchell)

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Dead-end pores can pump out trapped particles. Natural structures often contain “dead-end” pores, through which fluids cannot flow when conventional pressure-driven mechanisms are used. Pumping water into reservoirs, however, helps recover oil in dead-end geological channels; and biomolecules diffuse through muscle tissue in part through transport in dead-end pores.

A. Sen, D. Vegelol, and co-workers at Pennsylvania State University (University Park) show that particles and solutions can flow into and out of dead-end pores with the use of chemically driven convective flow and a phenomenon they call "transient diffusio-osmosis" (see schematic). The flow velocity depends on a transient electrolyte gradient, generated in situ, and the intrinsic charge on the pore wall.

Schematic of diffusio-osmotic flow in a dead-end pore

The authors used glass capillary tubes to model dead-end pores. They prepared sodium chloride solutions with concentration gradients that varied with time; the gradients arose from the diffusion and convection of ionic species. To help visualize the flow patterns, they used two types of polystyrene latex beads: red 4-μm sulfate-functionalized beads and green 2-μm amine-functionalized beads.

The saline gradient in the solution generated an electric field, producing an electro-osmotic fluid flow near the pore wall. At the same time, the tracer beads migrated electrophoretically, independent of the electro-osmotic flow. The net observed transport rate was a combination of the two effects.

Video microscopy showed that the beads moved faster, and convective flow dominated over diffusion, near the mouth of the dead-end capillary. The amine-functionalized beads moved mostly by electro-osmosis; and their electrophoretic migration was slower than that of the sulfate-functionalized beads. The sulfate-functionalized beads moved toward the dead end, and the amine-functionalized beads moved toward the center of the capillary.

Carbonate solutions produced effects similar to the NaCl solutions. Beads in a potassium chloride gradient showed very little lateral motion, in contrast to the NaCl gradient, because potassium and chloride ions have almost identical diffusion coefficients and produce almost no electrical field. (ACS Nano DOI: 10.1021/nn506216b; Nancy McGuire)

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Ireland promotes academic involvement in process R&D. A. R. Maguire and coauthors at University College Cork (UCC, Ireland) and Eli Lilly (Kinsale, Ireland, and Indianapolis) describe the outcome of a fruitful collaboration between the two institutions for developing and optimizing reactions on the kilogram scale and beyond. In three of the four case studies, UCC researchers developed and/or optimized the chemistry; in the fourth (aminopyridoimidazole and aminobenzimidazole synthesis via cyclization of aminoureas), UCC explored the generality of the reaction.

In the first three examples (an aromatic hydroxymethylation, a decarboxylative cross coupling, and an ortho-lithiation), the oxidation sequences all involved typical process development work such as telescoped procedures and improved process mass intensity metrics. The academic chemists who performed the studies worked with the Lilly process R&D group and manufacturing personnel. (Org. Process Res. Dev. DOI: 10.1021/op5003825; Will Watson)

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Thin-film sensors use the Fujiwara reaction to detect chloroform. Chloroform (CHCl3) is a common chlorinated hydrocarbon that is widely used in a variety of industries. But CHCl3 is hazardous and may accumulate and circulate in the environment, which makes monitoring it a necessity. Current CHCl3 detection relies on complicated, expensive techniques (e.g., gas chromatography–mass spectrometry and infrared spectroscopy) that are inconvenient to use in real-time field tests.

To overcome this problem, Z.-L. Xue and coauthors at the University of Tennessee (Knoxville) and InnoSense LLC (Torrance, CA) developed CHCl3 optical sensors that use a modified Fujiwara reaction in thin films. Carbenes generated from CHCl3 in the presence of a base react with pyridyl compounds in the film to form colored products.

The authors chose tetra-n-butyl ammonium hydroxide (TBAH) as the base and 2,2’-dipyridyl as the coupling agent (see figure). They incorporated these nonvolatile Fujiwara reagents into thin films that consist of an ethyl cellulose (EC) polymer supported on silica gel mounted on glass substrates. The EC sensors change color when they react with CHCl3 in organic solutions by forming products with absorption maxima at 450 nm, which allow the naked eye to detect CHCl3 down to 5 ppm.

Reaction sequence for visual detection of CHCl3

Quantitative spectroscopic measurements of EC thin films indicated a detection limit of 0.83 ppm and a quantification limit of 2.77 ppm for CHCl3 in organic solution. The visible detection limit for CHCl3 in aqueous solution is 500 ppm.

The reaction-based optical sensors for CHCl3 are simple and inexpensive. The authors believe that by tuning the compositions of the Fujiwara reagents, it may be possible to develop CHCl3 sensors with enhanced sensitivity, compatibility, and detection ranges, as well as sensors for other chlorinated hydrocarbon analytes. (Anal. Chem. DOI: 10.1021/ac503920c; Xin Su)

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Two studies produce green routes to sulfonamides. Sulfonamides are an important class of compounds in medicinal chemistry. The major route to sulfonamides is based on the reaction between sulfonyl chlorides and amines. Two research groups independently report easy access to sulfonamides (2) by using sodium sulfinates (1) and iodine (see figure).

General method for producing sulfonamides from sulfinates

G. Yuan and co-workers at the South China University of Technology (Guangzhou) used the reaction of sodium p-toluenesulfinate and N-benzylamine as a model and discovered that in aqueous solution at room temperature, the sulfonamide is produced in 98% yield in 3 h. The authors propose a mechanism that is based on radical reactions. (Green Chem. DOI: 10.1039/C4GC02115K)

Q. Song and co-workers at Huaqiao University (Fujian, China) used aniline and sodium benzenesulfinate as their model and found that the best conditions were ethanol solvent, room temperature, and a 20-min reaction time. They obtained the sulfonamide in 76% yield. In contrast to the first study, the authors show that the mechanism is not radical. They present two possible mechanistic sequences but do not go into detail about them. (Green Chem. DOI: 10.1039/C4GC02236J)

Other than the divergent assumptions about mechanism, both protocols are practical, green routes to sulfonamides. In both cases, the methods are applicable to other substrates and are readily scalable. (José C. Barros)

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