1P21
Application of kinetic isotope effect for the investigation of the reaction of
nitrate radical with phenol
(Tokyo Gakugei University) Masaya Sasaoka, Yukio Nakano
For the reaction of nitrate radical (NO3) with phenol in the gas phase, two reaction pathways
have been reported.1,2 One of those is the reaction pathway proceeding via the abstraction of the
hydrogen atom from the hydroxyl group of phenol (reaction pathway A). Another is the reaction
pathway proceeding via the abstraction of the hydrogen atom from the benzene ring of phenol
(reaction pathway B). The reaction of NO3 with phenol is reported to proceed via both pathways
simultaneously, but the ratio of two reaction pathways has not been reported.3 In this study, the ratio
of the two reaction pathways was determined by comparing the rate constants of the reactions of NO3
with phenol isotopes such as C6H5OH, C6D5OH, C6H5OD and C6D5OD.
(A)
(B)
We applied a Fourier transform infrared (FTIR) spectrometer equipped with a long path length
gas cell for the measurements of the rate constants. C6D5OD or C6H5OH was added into the gas cell
and then the mixed systems of C6D5OH/C6D5OD or C6H5OH/C6H5OD were achieved by H/D
exchange reactions. In these measurements, the rate constants were determined by using the relative
rate method. In relative rate method, the reaction of NO3 with CH3SCH3 was used as the reference
reaction.
Figure shows the loss of C6H5OH versus that of CH3SCH3 in the presence of NO3 in 100 Torr of
Air. The solid line in Figure is a result of the linear least squares fit. Linear least squares analysis
of the data in figure gives the rate constant of the reaction of NO3 with C6H5OH (kNO3 + C6D5OD) by
using reported value of the reaction of NO3 with CH3SCH3. The rate constants of NO3 with the other
phenol isotopes were also determined and summarized in Table. By comparing and analyzing the
rate constants of these four kinds of phenol isotopes, the ratio of the reaction pathways A and B were
optimized that the reaction pathways A and B proceed in the ratio of 3:7. Moreover, the kinetic
isotope effects (KIE) on the abstraction of hydrogen from the hydroxyl group and the benzene ring
were analyzed and obtained. Consequently, the KIE value in O-H bond was determined to be
kOH/kOD = 3.27 and the KIE value in C-H bond was determined to be kCH/kCD = 1.56.
Table Rate constants of the reactions of
NO3 with C6H5OH, C6D5OH, C6H5OD
and C6D5OD
Figure The loss of C6H5OH versus that of CH3SCH3
in presence of NO3 radicals in 100 Torr of Air
References:
phenol isotopes
kNO3 + phenol / 10-12 cm3
molecule-1 s-1
C6H5OH
(4.5 ± 0.3)
C6D5OH
(3.2 ± 0.4)
C6H5OD
(3.4 ± 0.5)
C6D5OD
(2.4 ± 0.3)
1) R. Atkinson et al., Environ. Sci. Technol., 26, 1397-1403 (1992) 2) E. Bolzacchini et al., Environ. Sci. Technol., 35,
1791-1797 (2001) 3) Y. Nakano et al., Reac. Kinet. Mech. Cat, 118, 349-363 (2016)