NEIGHBORING OLEFINIC DOUBLE-BOND PARTICIPATION IN GAS-PHASE PYROLYSIS OF SOME ALKENYL CHLORIDES

4‐Chloro‐1‐butene, 5‐chloro‐1‐pentene, and 6‐chloro‐1‐hexene have been shown to decompose, in a static system, mainly to hydrogen chloride and the corresponding alkadienes. In packed and unpacked clean Pyrex vessels the reactions were significantly heterogeneous. However, in a vessel seasoned with allyl bromide these reactions were homogeneous, unimolecular, and follow a first‐order law. The working temperature range was 389.6–480.0°C and with a pressure range of 53–221 Torr. The rate constants for the homogeneous reactions were expressed by the following Arrhenius equations: 4‐chloro‐1‐butene: logk(sec−1) = (13.79 ± 0.17) – (223.8 ± 2.1)kJ/mole/2.303RT; 5‐chloro‐1‐pentene: logk(sec−1) = (14.25 ± 1.20) – (238.4 ± 12.7)kJ/mole/2.303RT; and 6‐chloro‐1‐hexene: logk(sec−1) = (12.38 ± 0.22) – (209.6 ± 2.9)kJ/mole/2.303RT. The olefinic double bond has been found to participate in the rate of dehydrohalogenation of 4‐chloro‐1‐butene. The insulation of the CH2CH in chlorobutene by one or two methylene chains to the reaction center does not indicate neighboring group participation. The three‐membered conformation is the most favored structure for anchimeric assistance of the double bond in gas phase pyrolysis of alkenyl chlorides. The heterolytic nature of these eliminations is also supported by the present work. Copyright © 1979 John Wiley & Sons, Inc.