Reaction of criegee intermediates with H2O
By the decomposition, the criegee intermediates I2a, I2b, I2c, and I2d
are leads to produce CH2Cl, CH2OO
radical, and chlorine containing hydrocarbons. The stabilized criegee
intermediates CH2OO, and two I6 intermediates are formed
such as I6c and I6d, derived from chloroalkenylperoxy radical
intermediates I2c and I2d respectively. Under the humid condition,
CH2OO reacts with H2O leads to the
formation of hydroxymethyl hydroperoxide (HMHP) intermediate I7a along
with the activation energy values of 7.612 kcal/mol and it is shown in
the relative energy profile Figure 10) . This reaction is
energetically more favorable and it is compared with previously
available literature reported with the activation energy value of 8.1
kcal/mol [45]. The reaction between
CH2OO and H2O starts with the formation
of hydrogen-bond (COO⋯H2O) and it is shown inFigure 9 . The existence of hydrogen bond has been recently
pointed out by Aplincourt et al and Ramon Crehuet et al[45,46]. During the addition of
H2O, the bond length of (O4—O5) and (C1—O4) atoms
are found to be 1.3Å and 1.2Å respectively and these found bond lengths
are agreed well with the previously reported value of 1.3 and 1.2Å with
other methods [47]. While in the formation of
hydroxymethyl hydroperoxide (HMHP) intermediates I7a, the bond lengths
increased around 0.05Å and 0.17Å respectively. Before the formation of
HMHP, the reaction of CH2OO with H2O
goes on through the TS7 and it is confirmed by the IRC calculation. As
shown in (Table 5) the thermodynamic calculation for the
formation of intermediate HMHP is found to be exothermic and exoergic
with the enthalpy (ΔH) value of -41.501 kcal/mol and Gibbs free energy
value of -0.063 kcal/mol respectively. From the thermodynamic
parameters, negative values indicate that the reaction is feasible and
more spontaneous. Thermodynamically obtained enthalpy and Gibbs free
energy values are compared with the previously reported values of -40.7
kcal/mol and -41.3 kcal/mol respectively [45].
Finally, HMHP undergoes unimolecular decomposition to produce
H2CO+H2O2 with the
activation energy value of 55.17 kcal/mol and it is compared with the
previously available literature 48.1 kcal/mol[45]. As shown in Figure 9, the bond
length of (O5—O4) and (C1—O7) atoms are found to be 1.417Å and
1.396Å respectively in HMHP and the bond length between (O5—O4) atoms
elongated around 0.006Å due to the addition of hydrogen atom.
Thermodynamic parameters for the formation of
H2CO+H2O2 are found to
be endoergic and endothermic with the enthalpy (ΔH) value of 13.63
kcal/mol and the Gibbs free energy value of 10.63 kcal/mol respectively.
The positive values of the formation of
H2CO+H2O2 reveal that
the reaction is less feasible and nonspontaneous. These results agree
with the experimental observation [48] that
indicates only the formation of formic acid in the decomposition of
HMHP. The obtained final by product in the present work is in good
agreement with the previous experimental work[48].
On the other hand in the presence of H2O the formed
intermediates I6b and I6c from chloroalkenylperoxy radical intermediates
(I2c&I2d) lead to the formation of hydroxy hydroperoxide intermediates
I7b and I7c with the activation energy values of 9.840 and -26.469
kcal/mol respectively. The reaction between intermediates (I7b & I7c)
and H2O starts with the formation of a hydrogen bond
(COO⋯H2O) and it is shown in Figure. 9. During
the addition of H2O with intermediate I6b, the bond
length of (C2—C1), (C3—C1), (C1—O11), and (O11—O12) atoms are
found to be 1.475Å, 1.457Å, 1.261Å, and 1.377Å respectively, whereas, in
the formation of intermediate I7b, the bond length become elongated
around 0.04Å, 0.05Å, 0.16Å, and 0.04Å respectively. In the formation of
I7b, the bond angle decreased around 13.8°, 10.50°, 8.49°, and 8.64°
respectively. Further, the intermediate I7b decomposed to yield the
product P6 (MVK) as a SOAs and H2O2 as
shown in Figure 9 . As shown in Figure 11 , the product
P6 is formed with the activation energy value of 47.877 kcal/mol. The
product P6 is obtained through the transition state TS8b with a single
imaginary frequency value of -1799.744 cm-1 and it is
confirmed by IRC calculation. J.Fan et al [49] and
D. Huang et al [50] also indicated the yield of
MVK experimentally through decomposition and this result is in good
agreement with the present work. During the formation of product P6, the
calculated enthalpy (ΔH) and Gibbs free (ΔG) energy values are 6.219 and
2.369 kcal/mol which shows that the reaction is endothermic and
endoergic. Based on thermodynamic parameters, the formation of MVK
through the addition of H2O is found to be less feasible
and non-spontaneous compare to the formation of MVK in product P3.
During the addition of H2O with intermediate I6c, the
bond length of (C4—C1), (C3—C1), (C2—C1), and (O11—O12) atoms
are found to be 1.3Å, 1.4Å, 1.5Å, and 1.3Å respectively whereas, during
the formation of I7c, the bond length become elongated around 0.1Å,
0.06Å, 0.004Å, and 0.03Å respectively. Beyond this, the formed
intermediate I7c decomposed to produce product P7 (MACR) as a SOAs and
H2O2. As shown in Figure 11,the product P7 is formed with the activation energy value of 48.427
kcal/mol and it is formed through the transition state TS8c with the
single imaginary frequency value of -1805.916 cm-1which is verified by the IRC calculation. As given in (Table
5), the formation of MACR is found to be endothermic with the enthalpy
(ΔH) value of 7.794 kcal/mol and endoergic with the Gibbs free energy
(ΔG) value of 3.615 kcal/mol. The calculated thermodynamic values
revealed that the formation of end product P7 via intermediate I7c is
less feasible and non-spontaneous when compared with the formation of
end product P4 through Cl addition in the present work. Hence, the
non-spontaneity of this reaction reveals that the water molecule could
affect the properties of potential end products P6 (MVK) and P7 (MACR).