THE WORK described in this thesis has been carried out over the
last ten years at the Chemistry Department of the University of
Edinburgh. The work is in the field of gas phase reaction
kinetics. Two main aspects of the subject have been studied -
gas phase halogenation and gas phase oxidation. These are
connected experimentally by the extensive use of gas chromatography
as the analytical tool. The author's early studies in both
fields were amongst the first in which gas chromatography was
applied to reaction kinetics.
The work on competitive halogenation reactions (that is the
halogenation of mixtures) has resulted in the accurate determination
for the first time of forty rate constants and Arrhenius parameters
of reactions of the general type:
X + RH = XH + R (X = F, CI, Br)
and an attempt has been made to give a theoretical interpretation
of the A factors of these reactions using a simple model. The
results should be of particular value as a check on any more
sophisticated theoretical calculations which may be made in the
future. They may also form the basis of a valuable method for
the accurate determination of bond strengths in hydrocarbons.
The work on oxidation developed from a study of the cool flame
oxidation of propane carried out for a Ph.D. degree. By the use
of gas chromatography for the analysis of the products from the
earliest stages of the oxidation of propane between 318 and 475°C
and of ethane between 320 and 386°C it has been established that at
least 80$ of the alkane initially removed appears in the products as
an olefin with the same number of carbon atoms. The most probable
reactions are (with propane for example).
X + C₃H₈ = XH + C₃H₇
C₃H₇ + O₂ = O₃H₆ +HO₂
X may be H0₂ but there are thermochemical arguments against this
view and the nature of X is still a matter for speculation.
Below 400°C the minor products are apparently formed by decomposition
of the RO₂ radical but above 400°c pyrolysis reactions of the
alkyl radicals become important.
By oxidising mixtures of alkanes it has been established that
the radical, or radical mixture, X has a reactivity between that of
Cl and CH₃O and is therefore unlikely to be HO₂ which is expected
to be much more selective than CH₃0 or Cl.
Kinetic studies of the oxidation of propane and ethane at
about 320°C have shown that surface reactions are kinetically
important during the induction period and that the autocatalysis of
the oxidations is assisted by the formation of olefins which
probably yield branching intermediates more readily than the parent
The overall mechanism of alkane and olefin oxidation, taking
account of the above observations, is discussed in the most recent
papers of the series on the oxidation of ethane and ethylene.
The thesis concludes with a brief section on the author's
work on various aspects of gas chromatography.