a Reaction conditions: 10 mL cumene, 25 mL
min-1 O2, 353 K, 8 h.
b Oxidation products cannot be detected.
The analysis of
oxidation mechanism of cumene oxidation
For decades, autoxidation
chemistry has explained the oxidation of hydrocarbons in the absence of
a catalyst.[30-33] Now, it has been proposed to
explain the oxidation mechanism of cumene with CNTs as catalysts, as
shown in Figure 1. The reactions
(1-5) that in network are the major reaction of
cumene.[32, 34] The initial reaction (1) can be a
unimolecular reaction or catalytic reaction. If it is the former, not
only is this unimolecular dissociation very slow, but also the
radical-pair (cumenyl radical (R·), H·) quickly recombines because of
the effect of solvent cage.[35] It has been
reported that CNTs can activate O2, resulting in ROS
catalyzing the reaction (1). Then the R· radical combines with
O2 to produce the
cumyl peroxy radicals (ROO·)
(reaction 2). ROO· is a reactive radical can abstract a H atom from
cumene to produce CHP and R· (reaction 3). Once CHP is produced, the CHP
adsorbed on CNTs tends to decompose into
cumenyl oxygen radical
(RO·) (reaction 4), which can
abstract a H atom from cumene to produce R·. The formed R· will go on
enter the reaction (2). Combined with the above, there are three ways to
the generation of crucial R· in reactions (1, 3, 5) involving cumene. In
these three reactions, the reactive species (ROO·, RO·, ROS) induce
abstraction of H atom. It is possible that Zn2+inhibits the reactivity of those species, thus completely inhibits the
oxidation of cumene. To prove the point, the interaction of
Zn2+ and those reactive substrates (ROO·, RO·, ROS)
are calculated by DFT.