The Reactions of Oxygen Atoms and Monofluoromethylene Radicals with Fluorinated Ethylenes in the Gas Phase

Abstract

Oxygen atoms generated in a mercury photosensitized decomposition
of nitrous oxide were reacted with 1,2-difluoroethylene and trifluoroethylene
and observed to form mainly monofluoromethylene (CHF) radicals
and carbonyl fluoride. The CHF radicals then added to fluoroethylene
to form "hot" fluorocyclopropanes which could be stabilized by collision
(or isomerize or fragment). The mechanism of these reactions have
been studied in detail.

The main products of the reaction of CHF radical with trans-
1,2-difluoroethylene were found to be . rare 1,2,3-trifluorocyclo-
‘propane, cis- and trans- 1,2,3-trifluoropropylene whereas the reaction
with cis- 1,2-difluoroethylene gave both cis- and trans- 1,2,3-trifluorocyclopropane,
cis- and trans- 1,2,3-trifluoropropylene. The
electronic state of CHF radical was believed to be singlet according
to the stereospecific addition reaction and the lack of change in the
products yield in the presence of small amount of molecular oxygen.
The exothermicity of the addition reaction was estimated as 286 kJ mol‾1

<FORMULA>

The reaction products of the reaction of CHF radical with trifluoroethylene
were cis- and trans- 1,2,3,3-tetrafluorocyclopropane,
cis- and trans- 1,2,3,3-tetrafluoropropylene, 1,1,2,3-
tetrafluoropropylene, cis- and trans- 1,2-difluoroethylene, tetrafluoroethylene
and pentafluorocyclopropane. Some CF2 elimination
from “hot" cyclopropane occurred even at atmospheric pressure. The,
_pentafluorocyclopropanes were formed by addition of CF, to the trifluoroethylene.
Principal features of the mechanism are shown in
the following scheme:
<FORMULA>

Following the detailed studies of the reaction, the systems
were used to determine relative reactivities of CHF radicals with
all the fluorinated ethylenes. Relative rate constants for the
reaction with propylene and fluoroethylenes were measured by a
competitive method. at 23 + 2°c. The results are summarized below
<TABLE>

Date of Award	Sept 1973
Original language	English
Awarding Institution	Aston University