Gas Phase Reaction between Thietane and Hydrogen Atom

The reaction of thietane with hydrogen atom was investigated at 300 K and 2130 Pa using a conventional discharge flow apparatus. In the wide range of conversion of thietane, propylene was mainly produced, and small amounts of ethylene, cyclopropane, propane and ethane were also obtained (Table 1). In the reaction of 3, 3-dimethylthietane with hydrogen atom, isobutene and 1,1-dimethylcyelopropane were mainly produced (Table 2). These results are different from those of thietane-carbon atom systems, where cyclopropane was selectively produced. When deuterium atom was used instead of hydrogen atom, propylene produced was found to be composed of C8H5D, which attained 85% of total propylene (Table 3 and Fig. 1). Since H-D exchange for thietane was not observed at all, deuterium atom of C₃H₅D was considered to be taken in either during or after propylene was formed. In order to make this point clearer, the reaction of propylene with deuterium atom was undertaken. It was found that H-D exchange for propylene did not proceed so rapidly and was accompanied with considerable deuteration and deuterolysis (Table 4). Since the ratio CsH5D/propane in propylene-D system was found to be much smaller than that in thietane-D system, it was concluded that deuterium atom of C₃H₅D was taken in during propylene was formed. The reaction mechanism analogized from the similar, systems (thietane-C, thiirane-H, thio-lane-H) was found not to be able to explain the above results. The following mechanism including allyl radical was proposed tentatively. The first step producing allyl radical is estimated to be exothermic (Table 5) and the second step [formula omitted] is considered to produce a definite ratio of propylene and ethylene via chemically activated propylene (Table 6). The characteristic feature of thietane-H (or-D) system was able to be explained qualitatively by assuming the inclusion of allyl radical. Based on the above reaction mechanism, the reaction of 3,3-dimethylthietane with hydrogen atom is considered to go on a different reaction path because of the presence of two methyls. The reaction mechanism analogous to thiirane-H system seems to explain the main product isobutene.