Hexachlorofulvene. I. Synthesis and reactions under Diels-Alder conditions

McBee, E. T.; Wesseler, E. P.; Crain, D. L.; Hurnaus, Rudolf; Hodgins, T.

doi:10.1021/jo00970a001

Cited by 22 publications

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“…These assignments are based on the retention times of products during trichloroethylene decomposition studies of Earl and Titus, 64 where unambiguous structural assignments were made from IR spectroscopic evidence. Further, peaks identified with those of 1,1,2,5,6,6-hexachloro-1,5-hexadien-3-yne are also observed in the IR spectrum of our deposits (see Figure 5), 84 but none associated with perchlorofulvene 85 were detectable. At higher temperatures, the yield of the nonaromatic isomers is reduced; in fact, during pyrolyses with an 8.4 mm diameter aperture (therefore, relatively high temperatures), we find ratios of chromatographic peaks (which we equate to product ratios) of 13:3.5:83 for 1,1,2,5,6,6-hexachloro-1,5-hexadien-3-yne:perchlorofulvene:hexachlorobenzene (compare with Figure 4, where aromatic formation is only 4 times that of the linear species, and, indeed, the near-equimolar yields of linear to aromatic species in the TCE/C 4 Cl 6 copyrolyses depicted in Figure 9 performed with 6 and 5.3 mm aperture diameters, i.e.…”

Section: ■ Experimental Resultssupporting

confidence: 64%

Molecular Mechanisms in the Pyrolysis of Unsaturated Chlorinated Hydrocarbons: Formation of Benzene Rings. 2. Experimental and Kinetic Modeling Studies

McIntosh

Russell

2013

J. Phys. Chem. A

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The mechanism of formation of benzene rings during the pyrolysis of dichloro- and trichloroethylenes has been investigated by the method of laser powered homogeneous pyrolysis coupled with product analysis by gas chromatography. Additionally, selected (co)pyrolyses between the chlorinated ethylenes, CH2Cl2, C4Cl4, C4Cl6, and C2H2 have been performed to explicitly probe the roles of 2C3 and C4/C2 reaction pairs in aromatic growth. The presence of odd-carbon products in neat C4Cl6 pyrolyses indicates that 2C3 processes are operative in these systems; however, comparison with product yields from C2HCl3 suggests that C4/C2 processes dominate most other systems. This is further evidenced by an absence of C3 and other odd-carbon species in (co)pyrolyses with dichloromethane which should seed C3-based growth. The reactions of perchlorinated C4 species C4Cl5, C4Cl3, and C4Cl4 with C2Cl2 were subsequently explored through extensive kinetic simulations of the possible reaction pathways based on previous kinetic models and the exhaustive quantum chemical investigations of our preceding work. The experimental and theoretical results strongly suggest that, at moderate temperatures, aromatic ring formation from chlorinated ethylenes normally follows a Diels-Alder coupling of C4 and C2 molecular units followed by internal shifts; the one exception is the C4Cl4 + C2Cl2 system, where steric factors lead to the formation of nonaromatic products. There is little evidence for radical-based routes in these systems.

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Section: ■ Experimental Resultssupporting

confidence: 64%