Rearrangements of the Radical Cations of 3-Aryl-5-fluoroisoxazoles: Further Evidence for Existence of Benzocyclopropenyl Cation.

The fragmentation reaction of the radical cations of 3-aryl-5-fluoroisoxazoles formed via EI-MS is described. A new rearrangement accompanied by fluorine atom migration is discovered. A mechanistic rationale for the rearrangement supporting the existence of a fluorinated benzocyclopropenyl cation was proposed based on the experimental data and quantum chemical calculations.

R4NHal/NOHSO4: A Usable System for Halogenation of Isoxazoles, Pyrazoles, and Beyond.

A new convenient and versatile halogenating system (R4NHal/NOHSO4), giving straightforward and general access to halogenated 3,5-diaryl- and alkylarylisoxazoles, pyrazoles and electron-rich benzenes from the corresponding scaffolds, is suggested. The method provides excellent regioselectivity, scalability to the gram scale, and a broad scope for both aromatics and halogens. A three-step, one-pot reaction protocol was developed, and a series of 3,5-diaryl-4-haloisoxazoles has been efficiently synthesized from 1,2-diarylcyclopropanes under suggested nitrosating-halogenating conditions.

Dynamics of PCB removal and detoxification in historically contaminated soils amended with activated carbon.

Activated carbon (AC) can help overcome toxicity of pollutants to microbes and facilitate soil bioremediation. We used this approach to treat a Histosol and an Alluvial soil historically contaminated with PCB (4190 and 1585 mg kg(-1), respectively; primarily tri-, tetra- and pentachlorinated congeners). Results confirmed PCB persistence; reductions in PCB extractable from control and AC-amended soils were mostly due to a decrease in tri- and to some extent tetrachlorinated congeners as well as formation of a bound fraction. Mechanisms of PCB binding by soil and AC were different. In addition to microbial degradation of less chlorinated congeners, we postulate AC catalyzed dechlorination of higher chlorinated congeners. A large decrease in bioavailable PCB in AC-amended soils was demonstrated by greater clover germination and biomass. Phytotoxicity was low in treated soils but remained high in untreated soils for the duration of a 39-month experiment. These observations indicate the utility of AC for remediation of soils historically contaminated with PCB.