njit-etd2003-111 - New Jersey Institute of Technology

CHAPTER 3
THERMOCHEMICAL AND KINETIC ANALYSIS OF
THE ACETYL RADICAL + 02 REACTION SYSTEM
3.1 Background
Several studies have illustrated that the reactions of ethy14955 and isopropyl56 radicals
at pressures from 1 to 6000 Torr and temperatures from 300 to 900 K, exhibit
significant negative temperature dependence (NTD) and complex falloff with
pressure. Acetyl radical reaction with 02 is expected to have similar complexities.
The ethyl radical + 02 reaction is the system best characterized in the
literature, and it is a useful model with which to compare CH3C.0 + 02 reaction
paths and kinetics. Analysis of the C2H5 + 02 reaction system 57_59 invokes formation
of a chemically activated adduct (C2H S00•*), which can be stabilized, dissociate
back to C2H5 + 02, undergo concerted elimination to C2114 + H02 , or undergo
intramolecular hydrogen transfer to hydroperoxide alkyl radical (C.112CH200H*).
The C0112CH20OH* isomer can be stabilized, react to an epoxide YCOC + OH
(Y=cyclic), or undergo elimination to ethylene + H02. The stabilized adduct
(C211 500.) can undergo the same reactions as C2HS00.*, but at a lower rate because
of its lower energy (5cheme 3.1).
The rate of ethyl radical loss decreases significantly with temperature 5, but
increases with pressure; this is explained by invoking reversible formation of a
weakly bound adduct. The C2H500• adduct is readily stabilized at low temperatures
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