Many investigations of gas-phase atmospheric PCB show a strong relationship between concentration and air temperature, especially near PCB sources. Comparative gas-phase atmospheric PCB trends during an annual temperature regime at two sites near a former PCB manufacturing plant and nearby PCB landfills in Anniston, AL, indicate a departure from this trend. The Mars Hill sampling site, located closest to the plant and landfills, shows an annual average sigmaPCB concentration of 27 ng m(-3) (ranging from 8.7 to 82 ng m(-3)) three times the average at Carter, 1.5 km away (9 ng m(-3), ranging from 1.1 to 39). However, total PCB and congener concentrations vary more with air temperature at Carter where PCB are evaporating from surfaces during warmer weather. The slopes of the Clausius-Clapeyron plots of 18 of the most concentrated congeners representing dichloro- through heptachlorobiphenyl homologues are significantly higher at the Carter site. While some of the atmospheric PCB at Mars Hill is derived from ground surface evaporation, the source of much of it apparently is the material buried in the landfills, which has different thermal properties than surface materials and is not in equilibrium with air temperature.
Tetrahydrocarbazoles have been prepared in one‐flask syntheses from indoles, ketones or aldehydes, and maleimides, with acid catalysis. The reactions involve a condensation of the indole with the ketone or aldehyde, followed by an in situ trapping of the vinylindole in a Diels‐Alder addition with a maleimide. Isomerization of the double bond into the indole nucleus gave the tetrahydrocarbazoles which were isolated (6, 9, and 10). Variation of the indole, carbonyl compound, and maleimide has been explored. The predominant stereochemistry of the tetrahydro ring in the products is all‐cis, although a second stereoisomer has been isolated. Two regioisomers were generated from all unsymmetrical 2‐alkanones, except 2‐butanone, which gave the single isomer 9a. Aromatization of tetrahydrocarbazoles 6 to carbazoles 7 was accomplished with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone.
In situ Vinylindole Synthesis. Diels-Alder Reactions with Maleimides to Give Tetrahydrocarbazoles.-Acid-catalyzed condensation of the indoles (I) with ketones or aldehydes leads to vinylindole intermediates, which are in situ trapped by maleimides to give the carbazoles (IV) or (VII) of all-cis configuration. In some cases a trans isomer such as (VIII) is isolated as well. Similar reaction of asym. 2-alkanones (X) gives the 2 regioisomers (XI) and (XII) with the exception of 2-butanone (Xa), which only reacts to a single isomer (XIa). -(NOLAND, W. E.; WALHSTROM, M. J.; KONKEL, M. J.; BRIGHAM, M. E.; TROWBRIDGE, A. G.; KONKEL, L. M. C.; GOURNEAU, R. P.; SCHOLTEN, C. A.; LEE, N. H.; CONDOLUCI, J. J.; GAC, T. S.; POUR, M. M.; RADFORD, P. M.; J. Heterocycl. Chem. 30 (1993) 1, 81-91; Dep. Chem., Univ. Minn., Minneapolis, MN 55455, USA; EN)
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