Thomas Junk

Hydrogen isotope exchange reactions involving C–H (D, T) bonds

Exchange reactions involving the displacement of hydrogen bonded to carbon by its heavier isotopes are of interest for both mechanistic and product-orientated research. This review surveys practical strategies for the preparation of isotopically labelled compounds, discusses recent progress made in developing mild and regioselective exchange protocols, and summarizes the mechanistic aspects of C–H bond activation under homogeneous and heterogeneous exchange conditions.

Sonochemical degradation of aromatic organic pollutants.

This work examines the use of ultrasound to mineralize 4-chlorophenol, 2,4-dichlorophenol, [aryl-2H3]2,4-dichlorophenol, 4-chloro-3,5-dimethylphenol, 4-fluorophenol, 2,4,6-trinitrotoluene, 2-amino-4,6-dinitrotoluene and 4-amino-2,6-dinitrotoluene in dilute aqueous solution. Mineralization rates were determined as a function of substrate structure and concentration, bulk phase temperature, pH and the presence of co-solutes such as detergents and humic acids. All substrates were found to degrade sonochemically, as evidenced by the release of Cl- and NO3- respectively. Product analyses by GC-MS, HPLC, and micellar electrokinetic capillary chromatography (MECC) indicated mineralization with little formation of organic byproducts, a significant advantage over other remediation methods. Chloride release from chlorophenols was approximately proportional to substrate total chlorine content, irrespective of structural differences, and reached 80% of the theoretical limit. Fluoride release from 4-fluorophenol was ca. 10-fold lower than that of chloride from 4-chlorophenol. Changes in the bulk phase temperature from 9.5 to 34 degrees C, and 12.5 to 30 degrees C, respectively, were of little consequence to observed mineralization rates for nitroaromatics and chlorophenols. A significant mineralization rate increase resulted from sonication of 4-chlorophenol in acidified media. Additions of amphiphilic co-solutes resulted in modest, but statistically significant, sonolysis enhancements.

Synthesis of polydeuterated benzothiazoles via supercritical deuteration of anilines

2-[ 2 H]Benzothiazole, readily available according to the literature, was observed to undergo slow isotope exchange in water. This necessitated development of practical syntheses for benzothiazoles carrying deuterium labels in positions other than 2. [4,5,6,7- 2 H 4 ]Benzothiazole and 4-[ 2 H 3 ]methyl[5,6,7- 2 H 3 ]benzothiazole were prepared in good yields from [ 2 H 7 ]aniline and 2-[ 2 H 9 ]toluidine, which were obtained by novel rapid isotope exchange in supercritical deuterium oxide.

Facile access to aryltellurium compounds from arylboronic acids

Abstract Arylboronic acids were treated with tellurium tetrachloride to generate substituted aryltellurium trichlorides, which were reduced to the corresponding diaryl ditellurides in good to excellent overall yields. Representative products include diphenyl ditelluride, bis(2-nitrophenyl) ditelluride, bis(3-nitrophenyl) ditelluride, bis(4-methylphenyl) ditelluride and bis(2-chlorphenyl) ditelluride. 3,5-Dimethylphenyl 2′-nitrophenyl telluride and 3,5-dimethylphenyl 3′-nitrophenyl telluride were prepared in analogous fashion, in modest yields, from 3,5-dimethylphenyltellurium tribromide and the corresponding nitrophenylboronic acids.

Environmental transformation products of 2,4,6-trinitrotoluene

AbstractThe availability of environmental transformation products of 2,4,6-trinitrotoluene (TNT) as high purity standards is important for the conduct of work related to the assessment and remediation of contaminated sites, and the speciation of transformation products found at these sites. Considerable discrepancies exist in the literature regarding the structural assignments and properties of the materials addressed in this study. Six prominent TNT transformation products were prepared and characterized, three of which (4,4’,6,6’-tetranitro-2,2’-azotoluene, 2,2’,6,6’-tetranitro-4,4’-azotoluene and 2-hydroxylamino-4,6-dinitrotoluene) previously had been poorly accessible.

Tri­bromo(3,5-di­methyl-2-nitro­phenyl-κ2C1,O)­tellurium(IV), bromo(3,5-di­methyl-2-nitro­phenyl-κ2C1,O)­tellurium(II) and bromo(3,5-di­methyl-2-nitro­so­phenyl-κ2C1,O)­tellurium(II)

All three title compounds, prepared from bis(3,5-dimethyl-2-nitrophenyl)ditellurium, exhibit high degrees of intramolecular Te-O coordination. Their Te-O distances increase in the order C(8)H(8)BrNOTe < C(8)H(8)BrNO(2)Te < C(8)H(8)Br(3)NO(2)Te, with distances of 2.165 (3), 2.306 (1) and 2.423 (6) A, respectively, indicating that C(8)H(8)BrNOTe may be more aptly described as 1-bromo-4,6-dimethyl-2,1,3-benzoxatellurazole.

Effects of Static vs. Tidal Hydraulic Conditions on Biogeochemical Processes in Mesocosms: Degradation of Aromatic Hydrocarbons (AHs)

This study addressed the feasibility and practical considerations related to the possible use of contaminated sediments in coastal wetland restoration and creation efforts. Dredge and other sediments are frequently contaminated with chemical pollutants, and large volumes of this potentially recoverable resource are disposed of in dumpsites rather than utilized. This work addresses the possible deployment of sediments contaminated with aromatic hydrocarbons (AHs) in salt marsh creation efforts. The experimental system was a hydrodynamic mesocosm developed to study well-drained, permanently saturated-flooded and alternately flooded-drained (tidal) hydraulic effects on biogeochemical and plant processes. The target AHs for this work were naphthalene, phenanthrene, 1-methylnaphthalene, 1,3-dimethylnaphthalene, 3-methylphenanthrene, and 3,6-dimethylphenanthrene. The results of this work confirmed that different hydraulic conditions and the resultant biogeochemical properties of salt marshes influence the rate, transformation-time profile, and completeness of transformation of AHs in sediments. In general, the relative transformation rates for the AHs in the different systems examined here were drained/oxidized Eh ≥ tidal/oscillating Eh ≫ flood/reduced Eh, as observed previously with other classes of organic chemicals. The generation of hydroxylated AHs coincided with observed compound transformation profiles: decreases in target compounds on sediments were correlated with increases in hydroxylated AHs in the water. While well-drained aerobic conditions seem to be optimal for the transformation/depuration of AHs in salt marsh sediments, in natural settings this kind of system would not be a “wetland” either geohydrologically or with respect to vegetation. So, when evaluating the use of contaminated sediments in “wetland” construction or expansion, the relevant zones are streamside and marsh interior. This work indicates that AH contaminated sediments can be used, alone or mixed with clean sediments or other industrial materials (e.g., phosphogypsum and bauxite “red mud”), for wetland creation or enhancement. It would seem that either or both marsh locations (interior vs. streamside) are appropriate, at least with respect to rapid degradation and elimination of these AHs from the sediments. The tradeoff involves time and potential offsite risks: at streamside, the removal rates were twice as fast as and somewhat more complete than in the interior, but the action of the tides could mobilize contaminants to the estuary and beyond. The interior sediments will allow for less exchange of the pollutants with the estuarine water, but will take longer to depurate, particularly if the sediments become compacted.

1H and 13C NMR study of perdeuterated pyrazoles

The 1H and 13C chemical shifts as well as the 1H–2H and 2H–13C coupling constants of perdeuterated 3,5-dimethylpyrazole and 3,5-diphenylpyrazole have been measured and the values compared with those of the unlabelled compounds.