Continuous‐wave CO₂ laser‐induced SF₆‐sensitized decomposition of chloroalkanes

Abstract

It has recently been suggested [ll that when l,l,l-trichloroethane is irradiated with a continuous-wave COP laser in the presence of SF6 sensitizer, the decomposition occurs in a molecular manner, viz.rather than by a radical-chain mechanismas has been proposed as the main component of the thermally induced decomposition [21. The evidence for this is largely based on the following observations:(1) No induction period was observed in the laser-induced SF6-sensitized decomposition of l,l,l-trichloroethane although induction periods are a feature of the thermal decomposition of this and certain other alkyl chlorides. (2) Upon addition of propene, the laser-induced SF,-sensitized reactions of l,l,l-trichloroethane and 1-chloropropane were retarded in a similar way although the latter is unaffected by propene when undergoing thermal decomposition. (3) When ethyl chloride and l,l,l-trichloroethane were irradiated together with SF6 no ethane, methane, or chloroform was detected. We have considered these arguments and carried out some similar experiments with two molecules (chloroethane and 1,l-dichloroethane) whose thermal decomposition is known to proceed molecularly [3,41 and two molecules (1,2-dichloroethane and l,l,l-trichloroethane) known to decompose thermally via a radical chain mechanism [2,51.

Kinetics of the CCl3 + CH3 Radical−Radical Reaction

“…Thermal decomposition of CH 3 CCl 3 is known to occur via both HCl elimination and Cl elimination, − although evaluations of the relative importance of these two channels differ. The Cl elimination pathway can be expected to have a relatively “loose” transition state compared to a “tighter” one for the HCl elimination.…”