Gas-phase degradation of 2-butanethiol initiated by OH radicals and Cl atoms: Kinetics, product yields and mechanism at 298 K and atmospheric pressure

Article abstract of DOI:10.1039/c9ra04051j

Relative rate coefficients and product distribution of the reaction of 2-butanethiol (2butSH) with OH radicals and Cl atoms were obtained at atmospheric pressure and 298 K. The experiments were performed in a 480 L borosilicate glass photoreactor in synthetic air coupled to a long path "in situ" FTIR spectrometer. The rate coefficients obtained by averaging the values from different experiments were: k_OH = (2.58 ± 0.21) × 10^-11 cm³ per molecule per s and k_Cl = (2.49 ± 0.19) × 10^-10 cm³ per molecule per s. The kinetic values were compared with related alkyl thiols and homologous alkyl alcohols, where it was found that thiols react faster with both oxidants, OH radicals and Cl atoms. SO₂ and 2-butanone were the major products identified for the reactions of 2-butanethiol with OH radicals and Cl atoms. The product yield of the reaction of 2-butanethiol and OH radicals were (81 ± 2)percent, and (42 ± 1)percent for SO₂ and 2-butanone, respectively. For the reactions of 2-butanethiol with Cl atom, yields of SO₂ and 2-butanone were (59 ± 2)percent and (39 ± 2)percent, respectively. A degradation mechanism was proposed for the pathways that leads to formation of identified products. The product distribution observed indicated that the H-atom of the S-H group abstraction channel is the main pathway for the reaction of OH radicals and Cl atoms with 2-butanethiol.

Full text of DOI:10.1039/c9ra04051j

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Gas-phase degradation of 2-butanethiol initiated
by OH radicals and Cl atoms: kinetics, product
yields and mechanism at 298 K and atmospheric
pressure†
Cite this: RSC Adv., 2019, 9, 22618
a
b
a
b
Alejandro L. Cardona,
Rodrigo G. Gibilisco, Marıa B. Blanco, Peter Wiesen
´
and Mariano Teruel *a
Relative rate coefficients and product distribution of the reaction of 2-butanethiol (2butSH) with OH radicals
and Cl atoms were obtained at atmospheric pressure and 298 K. The experiments were performed in
a 480 L borosilicate glass photoreactor in synthetic air coupled to a long path “in situ” FTIR
spectrometer. The rate coefficients obtained by averaging the values from different experiments were:
ꢂ11
3
ꢂ10
3
k
OH ¼ (2.58 ꢀ 0.21) ꢁ 10
cm per molecule per s and kCl ¼ (2.49 ꢀ 0.19) ꢁ 10
cm per molecule
per s. The kinetic values were compared with related alkyl thiols and homologous alkyl alcohols, where it
was found that thiols react faster with both oxidants, OH radicals and Cl atoms. SO
were the major products identified for the reactions of 2-butanethiol with OH radicals and Cl atoms. The
product yield of the reaction of 2-butanethiol and OH radicals were (81 ꢀ 2)%, and (42 ꢀ 1)% for SO
and 2-butanone, respectively. For the reactions of 2-butanethiol with Cl atom, yields of SO and 2-
2
and 2-butanone
2
2
Received 29th May 2019
Accepted 14th July 2019
butanone were (59 ꢀ 2)% and (39 ꢀ 2)%, respectively. A degradation mechanism was proposed for the
pathways that leads to formation of identified products. The product distribution observed indicated that
the H-atom of the S–H group abstraction channel is the main pathway for the reaction of OH radicals
and Cl atoms with 2-butanethiol.
DOI: 10.1039/c9ra04051j
rsc.li/rsc-advances
have aroused great interest, especially because of the experi-
mental evidence about their presence in various environmental
1
Introduction
3,4,14
In the atmosphere, sulfur is central to many environmental systems.
2-Butanethiol was detected in samples of air from
issues including acid rain and climate change. Volatile Organic sewerage treatment tanks of chemical petroleum, geothermal
Sulfur Compounds (VOSCs) can exist at high concentrations areas, muddy beach water and wastewater treatment
2
,15–18
and they are released into the environment from natural plants.
1–5
emissions and anthropogenic sources.
Human activity is
There are several experimental and theoretical studies of the
closely related to the increase of pollution in different envi- reactions of alkyl thiols with Cl atoms and OH radicals.
19–27
In
ronmental settings, VOSCs could contribute 35–40% of VOCs all cases the rates coefficients for Cl-atoms were an order of
emitted during the aerobic composting processes of food magnitude faster than the corresponding reaction with OH
1
wastes due to high contents of organic matter and moisture. radical. Hence, tropospheric concentrations of Cl need to be
Other anthropogenic sources of VOSCs include landll facili- atmospherically important to their reactions compete with OH
3
5,6
ties heavy polluted rivers and creeks. All these sources radicals. Cl-atoms concentrations could be signicant at the
28
contribute to the rising concentrations of VOCS in the air of marine boundary layer and even in the mid-continental areas
cities with high population density.
7
2
due to the presence of ClNO precursor at signicant levels, as
The main and most studied VOSCs are H S, CS and reported in eld measurement observations on regions remote
2
2
8
–13
29
dimethyl sulde (DMS). However, in recent years, alkyl thiols from the coastline.
The dominant fate of VOSCs in the atmosphere is the
chemical transformations to produce sulfur dioxide and
carbonyl compounds, where these gas species can contribute to
acid rain as well as aerosol and cloud formation, affecting the
a
LUQCA-Instituto de Investigaciones en Fisicoqu ´ı mica de C ´o rdoba, Facultad de
Ciencias Qu ´ı micas, Universidad Nacional de C ´o rdoba, Ciudad Universitaria, 5000
´
ordoba, Argentina. E-mail: mteruel@fcq.unc.edu.ar
C
b
3,30,31
Institute for Atmospheric and Environmental Research, Bergische Universit a¨ t climate and the radiation balance.
Some authors discussed
Wuppertal, 42097 Wuppertal, Germany
the role of the VOSC in atmospheric chemistry as primary irri-
tant and ubiquitous offensive odor pollutants with very low
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c9ra04051j
1
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3,4,6
32
sensory thresholds.
Friedman et al. proposed that even (Air Liquide, 99.999%), 2-butanethiol (Merk 99%), isobutene
a small anthropogenic perturbation of SO2 concentrations (Messer Griesheim, 99%), E-2-butene (Messer Griesheim, 99%),
could impact the oxidation chemistry of biogenic VOCS, and Cl (Messer Griesheim, >99.8%).
2
increasing the aerosol acidity and ammonium sulphate aerosol
Methyl nitrite was prepared by the drop-wise addition of 50%
formation. Additionally, exposure to high levels of sulfur sulphuric acid to a saturated solution of sodium nitrite in water
dioxide in the air can cause breathing difficulties, obstructing and methanol. The reactions products were carried through
33
airways, bronchitis and other respiratory illness. A knowledge a concentrated solution of sodium hydroxide and over anhy-
of kinetics and mechanisms of the oxidation of these sulphur drous calcium chloride into a trap cooled at dry-ice tempera-
35
containing compounds is relevant to understand their chem- ture. Methyl nitrite was collected and stored at 193 K purity
istry and impact in the atmosphere.
was conrmed by IR spectroscopy.
In this work, we investigate the kinetics, mechanism and
products yields of the reactions of 2-butanethiol with Cl atoms
and OH radicals. There are two previous studies of the kinetics
of the reaction of 2-butanethiol with Cl atoms at low pressure
2
.2 Kinetic and product distribution analyses
OH radicals were generated by the photolysis of CH ONO/air
mixtures with the uorescent lamps,
3
26,27
(0.75 Torr) and at atmospheric pressure.
This work repre-
sents the rst study of identication and quantication of
reaction products. As far as we know there is not previous work
for reaction of 2-butanethiol with Cl atoms at atmospheric
conditions of pressure and temperature. Atmospheric implica-
tions of the reactions studied are discussed.
CH
CH O + O / CH O + HO
2
3
ONO + hn / CH
3
O + NO
(1)
(2)
(3)
in
3
2
2
HO + NO / OH + NO
2
2
and chlorine atoms were generated by the photolysis of Cl
air, also with the uorescent lamps:
2
2
Materials and methods
2.1 Experimental procedures
Cl
2
+ hn / 2Cl
(4)
Both kinetic determinations and products distributions exper-
iments were performed at atmospheric pressure of synthetic air
and 298 ꢀ 2 K in an atmospheric simulation chamber. Detailed
Once formed the oxidant species X (OH radicals or Cl atoms),
it reacts with both the 2-butanethiol (2butSH) and reference
compounds (R) in the following way:
3
4
description of the reactor used can be found elsewhere. A brief
description of the system is given here. The chamber is
composed of a cylindrical borosilicate glass vessel (3 m in
length and 45 cm inner diameter) closed at both ends by
aluminium end anges with a total volume of 480 L. The reactor
contains 32 uorescent lamps (Philips TLA 40 W, 300 # l #
X + 2butSH / products
X + R / products
(5)
(6)
4
50 nm, lmax ¼ 360 nm) spaced evenly around the outside of the
The relative rate technique was used to obtain the rate
reactor. To ensure homogeneous mixing of the reactants, coefficients of the title reactions. In steady-state concentrations
a magnetically coupled Teon mixing fan was placed inside the conditions of the oxidants species, the relative rate technique is
chamber. The system is evacuated by a pumping system con- based in the assumption that both 2butSH and reference
sisting of a turbo-molecular pump backed by a double stage compound are consumed only by reactions (5) and (6) and the
ꢂ3
rotary fore pump to 10 Torr. The detection system is a FTIR reactions are competitive with each other. A graphical rela-
spectrometer Nicolet Magna 520 equipped with a liquid tionship between the rst order decays of reactants and the rate
nitrogen cooled mercury-cadmium-telluride (MCT). The beam coefficients of reactions (5) and (6) can be obtained in the
is reected into the chamber and a White-type mirror system following way:
mounted internally in the chamber enables in situ monitoring
of the reactants in the infrared range 4000–700 cm . The White
ꢀ½
ꢁ
ꢀ
ꢁ
2butSHꢃ
k
k
5
6
½Rꢃ
ꢂ1
0
0
ln
¼
ln
(7)
½
2butSHꢃ
½Rꢃ
t
t
mirror system was operated with the total optical absorption
path length set to 48.11 m and infrared spectra were recorded
ꢂ1
with a spectral resolution of 1 cm . Typically, 64 interfero-
Plots of ln([2butSH] /[2butSH] ) versus ln([R] /[R] ) should
0 t 0 t
grams were co-added per spectrum over a period of approxi- yield straight lines with slope k
mately 1 minute and 15 spectra were recorded per experiment. [2butSH] and [R] are the concentrations of 2butSH and refer-
The initial concentration employed of reactants in ppmV (1 ence compounds before irradiation and at time t, respectively,
5 6 0 0
/k , where [2butSH] , [R] ,
t
t
1
3
3
ppmV ¼ 2.46 ꢁ 10 molecule per cm at 298 K) were: (9.0–9.5) and k
5 6
and k are the rate coefficients of reactions (5) and (6)
ppmV for 2butSH; (9.0–9.5) ppmV for 2-methyl-propene; (8.0– respectively.
9
2
.0) ppmV for propene; (9.0–9.5) ppmV for E-2-butene; (20.0–
0.5) ppmV for methyl nitrite and (10.0–10.5) ppmV for tests were performed: (i) mixtures of reactants with synthetic air
in absence of radical precursor species, were irradiated for 30
In order to test the presence of secondary reactions various
chlorine.
The following chemicals, with purities as stated by the minutes using the uorescent lamps checking possible
supplier, were used without further purication: synthetic air photolysis of the reactants. (ii) Mixtures of reactants with
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synthetic air in absence of radical precursor species were
prepared in order to test deposition or wall losses of reactants
and (iii) mixtures of reactants with chlorine or methyl nitrite
were prepared and allowed in the dark for 30 minutes to test for
reaction of the reactants with the radical precursor before
irradiation. Photolysis, wall losses and dark reactions of reac-
tants with oxidant precursor were negligible over the typical
periods of time employed in this study.
For reaction products studies, mixtures of 2butSH and
chlorine or methyl nitrite in synthetic air were irradiated using

uorescent lamps. 5 spectra was taken before irradiation to test
initial conditions. Then, 10 more spectra were taken with the
lamps on to generate reaction products. The reference spectrum
of reactants were subtracted to each reaction spectrum. Then,
residual spectrum was compared with calibrated reference
spectra stored in the IR spectral database at the University of
Wuppertal.
Fig. 1 Plots of kinetic data of reaction of 2butSH with OH radicals at
298 K and atmospheric pressure of synthetic air using 2-methyl-
propene and E-2-butene as reference compounds.
3
Results and discussion
3
.1 Relative rate coefficients with OH radicals and Cl atoms
We can notice that the value of kCl is almost an order of
magnitude larger than the value for kOH. This may mean, that
the atmospheric degradation with chlorine atoms could be
important, if Cl atoms concentrations are signicant. The re-
ported values for kOH are bigger than the obtained in this study
The rate coefficients for the reactions of 2butSH with OH radi-
cals and Cl atoms were experimentally obtained at (298 ꢀ 2) K
and atmospheric pressure of synthetic air. The rate coefficients
for the title reactions were obtained relative to the rate coeffi-
cients of 2-methyl-propene and E-2-butene for the OH radicals,
and 2-methyl-propene and propene for Cl atoms according with
the following reactions:
ꢂ11
3
26,27
(
ꢄ3.8 ꢁ 10
cm per molecule per s).
We think that this
could be related with the differences in the experimental
27
conditions. The absolute value of Wine et al. was obtained at
low pressure conditions (75 Torr). While, the relative value of
Barnes et al. was obtained at higher concentrations of reac-
tants that those used in this study (Table 1).
On the other hand, the value kCl determined in this study is
the rst reported rate coefficient for the reaction of Cl atoms
with 2butSH, and therefore no direct comparison with literature
(
CH
CH CH]CHCH
CH C]CH
CH CH]CH + Cl / products
3
)
2
C]CH
2
+ OH / products
+ OH / products
+ Cl / products
(8)
(9)
26
3
3
(
3
)
2
2
(10)
(11) can be made. However, a comparison of the rate coefficients
3
2
ꢂ11 36
ꢂ11 37
where k
8
(5.14 ꢀ 1.03) ꢁ 10
,
k
9
(6.39 ꢀ 1.28) ꢁ 10
,
k
10
ꢂ10
ꢂ11
(3.40 ꢀ 0.28) ꢁ 10
(ref. 38) and k11 (2.64 ꢀ 0.21) ꢁ 10
(ref.
3
3
8). All values are expressed in cm per molecule per s.
The data were tted to a straight line by linear least-squares
procedure and the rate coefficients was obtained from eqn (7).
Plots of kinetic data for the reactions of OH and Cl with 2butSH
with different references are shown in Fig. 1 and 2. A minimum
of three experiments were made with each reference, however,
only one example is show for clarity. A good agreement was
obtained between the results of experiments with different
references (Table 1). The rate coefficients, obtained by averaging
the values from different experiments, are the following:
kOH ¼ (2.58 ꢀ 0.55) ꢁ 10ꢂ11 cm per molecule per s
3
Cl ¼ (2.49 ꢀ 0.70) ꢁ 10ꢂ10 cm per molecule per s
3
k
The uncertainties are a combination of the 2 s statistical
errors from the linear regression analysis and a contribution to
Fig. 2 Plots of kinetic data of reaction of 2butSH with Cl atoms at 298
K and atmospheric pressure of synthetic air using 2-methyl-propene
cover errors in the rate coefficients of the reference compounds. and propene as reference compounds.
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Table 1 Slopes k2butSH/kreference and rate coefficients obtained for the reactions of 2butSH with OH radicals and Cl atoms at (298 ꢀ 2) K and
atmospheric pressure of synthetic air
a
Reaction
Reference
k2butSH/kreference
k
2butSH
ꢂ11
ꢂ11
ꢂ11
ꢂ11
ꢂ11
ꢂ11
ꢂ11
ꢂ11
ꢂ10
ꢂ10
ꢂ10
ꢂ10
ꢂ10
ꢂ10
ꢂ10
CH
3
CH
2
CH(SH)CH
3
(CH
(CH
3
3
3
)
)
)
2
2
2
C]CH
C]CH
C]CH
2
2
2
0.540 ꢀ 0.001
0.537 ꢀ 0.003
0.563 ꢀ 0.003
0.341 ꢀ 0.005
0.396 ꢀ 0.006
0.402 ꢀ 0.013
0.369 ꢀ 0.011
(2.78 ꢀ 0.28) ꢁ 10
(2.76 ꢀ 0.29) ꢁ 10
(2.89 ꢀ 0.30) ꢁ 10
(2.19 ꢀ 0.08) ꢁ 10
(2.53 ꢀ 0.10) ꢁ 10
(2.57 ꢀ 0.14) ꢁ 10
(2.36 ꢀ 0.12) ꢁ 10
(2.58 ꢀ 0.55) ꢁ 10
(2.14 ꢀ 0.18) ꢁ 10
(2.58 ꢀ 0.22) ꢁ 10
(2.32 ꢀ 0.20) ꢁ 10
(2.84 ꢀ 0.24) ꢁ 10
(2.61 ꢀ 0.21) ꢁ 10
(2.44 ꢀ 0.20) ꢁ 10
(2.49 ꢀ 0.70) ꢁ 10
+
OH
(
CH
CH
CH
CH
CH
3
3
3
3
CH]CHCH
CH]CHCH
CH]CHCH
CH]CHCH
3
3
3
3
Average
CH
3
CH
2
CH(SH)CH
3
(CH
(CH
3
3
3
)
)
)
2
2
2
C]CH
C]CH
C]CH
2
2
2
0.634 ꢀ 0.002
0.764 ꢀ 0.002
0.686 ꢀ 0.001
1.075 ꢀ 0.002
0.990 ꢀ 0.002
0.924 ꢀ 0.001
+
Cl
(
CH
CH
CH
CH
3
3
3
CH]CH
CH]CH
CH]CH
2
2
2
Average
a
3
cm per molecule per s.
determined in this study with the literature values of another reports that indicate the lack of selective nature of Cl atoms
alkyl thiols and homologous alcohols is shown in (Table 2). In reactions, it seems that the reactivity of chlorine atoms against
almost all cases the reactions of OH radicals and Cl atoms with the VOCS is less affected with any long range effect or interac-
39,41
alkyl thiols are faster than with the homologous alcohols. A tion in gas phase reactions.
possible reason for this behaviour could be that the H-
abstraction in the reactions with OH radicals and the corre-
sponding reactions with Cl atoms with alkyl alcohols appears to
3
.2 Reaction products study
Further experiments were made to investigate the mechanism
and the product distribution of OH radicals and Cl atoms
initiated oxidation of 2-butanethiol under similar conditions of
the kinetic experiments.
.2.1 2-Butanethiol + OH oxidation. Fig. 3 shows the usual
IR spectra obtained during the reaction. Trace A shows the IR
spectrum for a mixture of 2butSH and methyl nitrate (CH ONO)
in air acquired before irradiation and trace B shows the spec-
trum aer irradiation and subtraction of the 2butSH and
CH ONO absorptions. Traces C, D, E, F and G show the refer-
ence spectra for SO , 2-butanone, formaldehyde (HCHO), for-
39
occur exclusively from the C–H bonds. Meanwhile, the very
stable prereactive complex formed during the reaction with
alkyl thiols, where in both cases the sulfur seems to be bound to
the reactive species (OH or Cl) favour the H-abstraction on the
3
24,40
S–H group which is more favoured thermodynamically.
these sense, the value reported for CH CH CH CH SH, lower
than its homologous alcohol, was obtained at reduced pres-
In
3
2
2
2
3
24
sure, which could avoid the formation of the prereactive
complex, affecting the value of the rate coefficient.
3
We cannot conclude that there is a relationship between the
rate coefficient with the length of the carbon chain, despite
observing a slight increase in the value of the rate coefficient by
increasing the number of alkyl groups in reactions with the OH
radicals. In the reaction with Cl atoms, the values are very close
to the collision limit, as to propose a relationship with the
length of the alkyl chain. This fact is in agreement with previous
2
mic acid (HC(O)OH) and peroxyacetyl nitrate (PAN),
respectively, which have been identied as reaction products of
2
-butSH with OH radicals. Finally, the trace H shows the
residual spectrum aer to subtract the spectra of the identied
products. SO , 2-butanone and HCHO are the main primary
products identied. PAN and HC(O)OH are formed from
2
Table 2 Rate coefficients of alkyl thiols and alkyl alcohols with OH radicals and Cl atoms at 298 K of temperature
ꢂ11 a
ꢂ10 a
k
OH (ꢁ10
)
k
cl (ꢁ10
)
Alkyl group
R ¼ OH
R ¼ SH
R ¼ OH
R ¼ SH
b
d
d
d
d
d
k
e
g
h
i
CH
CH
CH
3
3
3
R
CH
CH
0.10 ꢀ 0.02
0.35 ꢀ 0.05
0.55 ꢀ 0.04
0.58 ꢀ 0.08
0.86 ꢀ 0.07
0.88 ꢀ 0.15
3.60 ꢀ 0.40
4.50 ꢀ 0.50
5.30 ꢀ 0.60
3.90 ꢀ 0.40
5.60 ꢀ 0.40
2.58 ꢀ 0.55
0.56 ꢀ 0.06
1.01 ꢀ 0.06
1.49 ꢀ 0.07
0.84 ꢀ 0.04
2.04 ꢀ 0.14
1.32 ꢀ 0.14
2.0 ꢀ 0.34
1.9 ꢀ 0.20
2.37 ꢀ 0.66
2.70 ꢀ 0.60
1.58 ꢀ 0.40
2.49 ꢀ 0.70
b
b
b
b
c
b
b
b
b
f
2
R
CH
2
2
R
h
j
3 2 2
(CH ) CH R
CH
CH
3
CH
CH
2
CH
CH(R)CH
3
2
2
CH R
k
3
2
a
3
b
c
d
e
f
g
h
i
j
k
cm per molecule per s. Ref. 39. Ref. 43. Ref. 26. Ref. 53. Ref. 54. Ref. 55. Ref. 20. Ref. 56. Ref. 54. This work.
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ꢂ1
ꢂ1
following bands (2972 cm ) for 2butSH, (1361 cm ) for SO
2
ꢂ1
and (2992 cm ) for 2-butanone. Plots of the arising concen-
trations of reaction products versus the loss of 2butSH are
shown in Fig. 4. The plots results in a straight line, from the
least square analysis of the slopes of plots yields (81 ꢀ 2)%, and
(
42 ꢀ 1)% have been obtained for SO
2
and 2-butanone,
respectively. We do not calculate yields PAN because is
a secondary product and for formaldehyde and HC(O)OH due
that the formaldehyde (HCHO) is also formed as a secondary
product from the CH ONO photolysis via reaction (2) and our
3
experimental conditions do not allow us to discriminate the
reaction of source. To best of our knowledge there are no
previous product studies of the reaction OH-initiated oxidation
of alkyl thiols. Hence, this is the rst reported product distri-
bution study of the reaction of OH radicals with 2-butanethiol.
3
.2.2 2-Butanethiol + Cl oxidation. Fig. 5 shows the typical
spectrum taken during the product identication experiments
Fig. 3 Trace A shows the IR spectrum for a mixture of 2butSH and of the reactions of 2butSH and Cl atoms. Trace A shows an IR
methyl nitrate (CH ONO) in air acquired before irradiation and the spectrum of 2butSH and Cl in air before irradiation. Trace B
trace B shows the residual spectrum after irradiation and subtraction of
the 2butSH, CH ONO, CO, CO and H O abortions. Traces C show the
reference spectrum for SO , traces D show the reference spectrum of
-butanone, traces E show the reference spectrum of (HCHO), traces
3
2
shows the IR spectra obtained at the end of reaction and aer to
subtract the absorption due 2butSH that remained unreacted.
3
2
2
2
2
Traces C, D and E are the reference spectra for SO , 2-butanone
2
F show the reference spectrum of formic acid (HC(O)OH), traces G and HCl, respectively. The residual spectrum aer subtraction
show the reference spectrum of peroxyacetyl nitrate (PAN) and H of the spectra of the identied products is show in trace F. Apart
traces show the residual spectrum after to subtract the spectra of the
identified compounds. For comparison proposes all spectra were
dehyde or acetaldehyde were identied. As in the OH oxidation
normalized.
from these primary products, no other products like formal-
the unidentied bands could be consequence of absorptions of
minor products of secondary reactions or sulfur containing
compounds formed from the H-abstraction on the C–H groups
in the alkyl chain of the thiol. The reference spectra and the IR
secondary reactions. PAN is a product generated from the
reaction of the peroxyacetyl radicals and the NO formed in the
2
cross sections calculations were made in the following bands
reaction (3) during the irradiation of CH ONO to produce OH
3
ꢂ1
ꢂ1
ꢂ1
(
2972 cm ) for 2butSH, (1361 cm ) for SO
2
and (1745 cm
)
radicals. The formation of HC(O)OH is attributed to the reac-
for 2-butanone. The concentration–time proles of SO
2
and 2-
42
tion of formaldehyde and HO radicals. The concentration–
2
butanone show that both are primary (see Fig. S2 of the ESI†).
The yields obtained, from the least square analysis of the slopes
time proles of the products (Fig. S1 in ESI†) shows that all
products observed are primary whereas the delayed formation
in the prole of PAN and HC(O)OH show that its formations are
secondary in nature. The identied products and the high yield
2
for SO observed in these reactions supports is that H-
abstraction of S–H group mechanism is the main reaction
step. We could not identied products coming from alkyl thio
alkoxy radicals (R(Oc)SR) which would be formed if the reaction
proceed via H-abstraction from the C–H group of the alkyl chain
of the thiol. The unidentied absorptions in the residual spec-
trum are due to products from the H-abstraction on the alkyl
chain of the thiol like thio-acetic acid (CH
3
COSH) or thio-
2
ONO )
propanoic acid (CH CH COSH) or methyl nitrate (CH
3
2
3
formed by the reaction of residual methyl nitrite (CH ONO) with
3
a alkyl peroxy radical (ROOc). The absorptions bands also could
be generated by peroxy nitrate compounds formed through
secondary reaction of the main products. Unfortunately, no
reference spectra of these compounds are available to compare
with our experimental results. However, simulated spectra was
used to check if the unidentied bands in the residual spectrum
belong to these compounds (see ESI†).
2
Fig. 4 Plot of the products concentrations of SO and 2-butanone as
function of reacted 2butSH with OH radicals at atmospheric pressure
of synthetic air and 298 K.
Once identied the reactions products, these were quanti-

ed using the reference spectra and the IR cross sections of the
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Table 3 Products yields observed in reaction of Cl atoms with 2butSH
and comparison for the yield of SO
2
with others VOSC's at atmo-
spheric pressure of synthetic air and 298 K
VOSC's
Product
HCl
Yield (%)
CH
CH
3
CH
2
CH(SH)
97 ꢀ 2
39 ꢀ 2
59 ꢀ 2
39
a
3
3 2 3
CH CH C(O)CH
SO
SO
SO
SO
2
b
CH
CH
CH
3
3
3
SCH
SCH
CH
3
2
c
2
CH
3
2
2
55 ꢀ 3
c
2
SCH
2
CH
3
52 ꢀ 5
a
b
c
This work. Ref. 9. Ref. 57.
most important degradation channel in agreement with
19,21,23,24,43
previous kinetic studies for alkyl thiols.
3.3 Mechanistic analyses
Fig. 5 Trace A shows the IR spectrum for a mixture of 2butSH and Cl
2
A proposed H-abstraction of S–H group reaction mechanism
based in the products distribution is shown in Fig. 7. The rst
, traces D step is the H-abstraction by OH radical or Cl atoms form the
in air acquired before irradiation and the trace B shows the residual
spectrum after irradiation and subtraction of the 2butSH, CO and CO
absorptions. Traces C show the reference spectrum for SO
2
2
show the reference spectrum of 2-butanone, traces E show the
reference spectrum of HCl and F traces show the residual spectrum
after to subtract the spectrum of the identified compounds. For
comparison proposes all spectra were normalized.
alkyl thiyl radical (RSc). Products of H-abstraction from the C–H
groups of the alkyl chain or addition on the S atom could not be
identied in our experimental setup. The alkyl thiyl radical
reacts further exclusively with molecular oxygen to form the
RSOO radicals, which mainly decomposes to SO and an alkyl
2
radical (Rc). No evidence of dimerization of the corresponding
dialkyl disulde was observed. Under atmospheric conditions
the alkyl radical reacts rapidly with oxygen to form alkyl peroxy
radicals, which react with another ROO radical to form alkoxy
of the plots of arising concentration of the products versus
2
2
butSH consumed, were: (59 ꢀ 2)% and (39 ꢀ 2)% for SO and
2
-butanone, respectively (Fig. 6). This is the rst product yield
quantication of the reaction of 2-butSH with Cl atoms. The
yields for SO and HCl are in good agreement with previous
3
radicals (ROc) or can react with NO (formed in the CH ONO
2
44
photo-dissociation process).
values reported for the reactions of Cl with alkyl suldes like
dimethyl sulde, ethyl methyl sulde and diethyl sulphide (see
Table 3). The product yields suggest that, like in the reaction
with OH radicals, the H-abstractions of the S–H group is the
In particular, in the 2butSH + Cl system, the reaction of the
RO radicals with O results exclusively in the 2-butanone and
2
HO radicals pathway. Meanwhile, in the 2butSH + OH system
2
we could identify products of the decomposition of the RO
radical pathway. We assume that the formation of peroxy acetyl
2
nitrate, PAN is consequence of the reaction of NO and the
peroxyacetyl radical formed. According with above, we suggest
that formaldehyde is not only generated in the reaction (2). Our
results are in agreement with previous studies focused in the
45–48
RO radicals fate
that proposed that the OH-initiated oxida-
tion in presence of NO occur via the formation of a chemically
X
activated oxy radical which decomposes promptly to yield
shorter carbon chain aldehydes. In contrast, the Cl-initiated
oxidation does not lead to C–C bond scission, even in the
45–48
presence of NO
(see Fig. S3 of ESI†).
3.4 Atmospheric implications
The values of rate coefficients for the reactions of 2butSH with
OH radicals and Cl atoms obtained in this work, have been used
to calculate the lifetimes in the atmosphere regarding these
oxidants. The expression s ¼ 1/kSH[X] was used to calculate the
X
lifetime of 2butSH in the atmosphere by OH or Cl degradation
reactions, where kSH is the rate coefficient and [X] is the OH or
Cl average concentration in the troposphere. The average
2
Fig. 6 Plot of the products concentrations of SO , 2-butanone as
function of reacted 2butSH with Cl atoms at atmospheric pressure of
synthetic air and 298 K.
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Fig. 7 Proposed mechanism for the OH radical and Cl atoms oxidation of 2butSH at 298 K and atmospheric pressure of synthetic air. We show
the more important possible H-abstraction pathways to form the identified products. X ¼ OH or Cl. The molecules enclosed in the dashed black
line rectangle were identified in the reaction with OH radicals and the enclosed in black line rectangles are the identified in the reaction with Cl
atoms.
6
3
concentrations used were 2 ꢁ 10 radicals per cm (ref. 28) and contribute to secondary aerosol formation, and act as precursor
4
3
1
ꢁ 10 atoms per cm (ref. 49) for OH radicals and Cl atoms of peroxyacyl nitrates. Even in this work, peroxyacetyl nitrate
respectively. Once the 2butSH is emitted into the atmosphere (PAN) was feasible identied, that is known by its toxicity, plant
51,52
mainly through organic matter decomposition it will be injury and as an important NO reservoir.
X
removed in the troposphere by gas phase reactions by OH
radicals during daytime conditions in about 5.4 hours and by Cl
atoms in about 4.6 days. Degradation initiated by Cl atoms will 4 Conclusions
only be important in places where the concentrations is high
enough to compete with OH radical degradation, as in the
marine boundary layer or high industrialized Mediterranean
The rate coefficients for the gas phase reaction of 2butSH with
OH radicals and Cl atoms have been determined under atmo-
spheric conditions of pressure and temperature. These kinetic
data are in good agreement with the reported values for similar
alkyl thiols. The rate coefficient values obtained were compared
with the values for the homologous alcohols (OH instead of SH
group) and it was observed that the rate coefficients for the alkyl
thiols in most of cases are bigger. However, the reactions with
Cl radicals present similar values in agreement with the less
selective nature of Cl atoms. The reactions products of the
reactions of 2butSH with both OH radicals and Cl atoms were
identied and quantied when possible. In both reactions, the
areas. Is that the Cl atoms. The 2butSH will lead mainly to SO
2
in both OH radicals and Cl atoms initiated oxidation. The
remaining alkyl radical will react again with molecular oxygen
to produce the corresponding carbonyl product. For the Cl
atoms degradation, only 2-butanone was identied as
a carbonyl product, meanwhile in the OH radicals degradation
formaldehyde and peroxyacetyl nitrate were also identied. SO
2
is well known to be further oxidized in the atmosphere to
ꢂ2
H
2
SO4(g) and SO
4
and others sulfur acids compounds which
can be incorporated into particles to produces cloud conden-
sation nuclei affecting the radiation budget and climate, as well
as contributing to episodes of acid rain or increasing the level of
most important reactions product was SO
abstraction pathway of the S–H group. Further oxidation of the
RSc radical with O will lead to the C–S bond breaking (Fig. 7).
2
formed from the H-
30,50
2
particulate material in urban areas.
These carbonyl products
For the OH reactions the identied carbonyl products were 2-
butanone, formaldehyde, formic acid and peroxyacetyl nitrate.
are important in tropospheric chemistry because they may
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No reactions products were identied from C–C breaking bond 15 W. Sye and C. Yeh, Toxicol. Environ. Chem., 1998, 66, 159–
in the reactions with Cl atoms and only the 2-butanone was 170.
identied. The yields for SO and 2-butanone were obtained for 16 Y. Nishikawa and K. Kuwata, Anal. Chem., 1985, 57, 1864–
2
both reactions, and the yield for HCl formations for the reaction
with Cl atoms are in good agreement with previous work and 17 J. Liu, S. Fang, Z. Wang, W. Yi, F. M. Tao and J. Y. Liu,
supports that the reactions proceed via H-abstraction on the Environ. Sci. Technol., 2015, 49, 13112–13120.
S–H group of the thiol. Once in the atmosphere, 2butSH will be 18 W. Sye and W. Chen, Toxicol. Environ. Chem., 2000, 77, 207–
degraded in a few hours by the OH radical or Cl atoms in places 218.
with high concentrations of this chlorine species as marine 19 D. J. Nesbitt and S. R. Leone, J. Chem. Phys., 1980, 72, 1722–
1868.
regions or industrialized continental areas.
1732.
2
2
2
0 D. Rodr ´ı guez, A. Aranda, Y. D ´ı az de Mera, B. Ballesteros and
E. Mart ´ı nez, Phys. Chem. Chem. Phys., 2003, 5, 514–519.
1 C. Wilson and D. M. Hirst, Prog. React. Kinet., 1996, 2, 69–
Conflicts of interest
1
32.
2 S. S. Cheng, Y. J. Wu and Y. P. Lee, J. Chem. Phys., 2004, 120,
792–1800.
There are no conicts to declare.
1
Acknowledgements
23 A. Garz ´o n, A. Notario, J. Albaladejo, T. Pe n˜ a-Ruiz and
M. Fern ´a ndez-G ´o mez, Chem. Phys. Lett., 2007, 438, 184–189.
The authors wish to acknowledge to FONCyT-PICT 2016-0220
Argentina, CONICET-GI 2010-2012-cod: 11220090100623
Argentina, SECyT-UNC Res. 213/14 y 103/15 Argentina, MINCYT
Argentina and the German Research Foundation DFG/16/03
Germany for nancial support of this research. M. B. B. and
R. G. G. wish to acknowledge to the Alexander von Humboldt
Foundation (AvH) and A. L. C. wishes to acknowledge to
CONICET for a doctoral fellowship and support.
2
2
2
2
2
4 A. Garz ´o n, J. Albaladejo, A. Notario, T. Pe n˜ a-Ruiz and
M. Fern ´a ndez-G ´o mez, J. Chem. Phys., 2008, 129, 1–12.
5 A. J. Hynes, P. H. Wine and D. H. Semmes, J. Phys. Chem.,
1986, 90, 4148–4156.
6 I. Barnes, V. Bastian, K. H. Becker, E. H. Fink and W. Nelsen,
J. Atmos. Chem., 1986, 4, 445–466.
7 P. H. Wine, R. J. Thompson and D. H. Semmes, Int. J. Chem.
Kinet., 1984, 16, 1623–1636.
8 O. W. Wingenter, M. K. Kubo, N. J. Blake, T. W. Smith,
D. R. Blake and F. S. Rowland, J. Geophys. Res.: Atmos.,
References
1996, 101, 4331–4340.
1
2
3
4
5
D. P. Komilis, R. K. Ham and J. K. Park, Water Res., 2004, 38, 29 J. A. Thornton, J. P. Kercher, T. P. Riedel, N. L. Wagner,
1
707–1714.
K.-C. Li and D. Shooter, Int. J. Environ. Anal. Chem., 2004, 84,
49–760.
J. Cozic, J. S. Holloway, W. P. Dub ´e , G. M. Wolfe,
P. K. Quinn, A. M. Middlebrook and B. Alexander, Nature,
2010, 464, 271–274.
7
S. K. Pandey and K.-H. Kim, Environ. Sci. Technol., 2009, 43, 30 R. J. Charlson, J. E. Lovelock, M. O. Andreae and
020–3029.
S. G. Warren, Nature, 1987, 326, 655.
M. R. Ras, F. Borrull and R. M. Marc ´e , Talanta, 2008, 74, 562– 31 I. Faloona, Atmos. Environ., 2009, 43, 2841–2854.
3
5
69.
32 B. Friedman, P. Brophy, W. H. Brune and D. K. Farmer,
Environ. Sci. Technol., 2016, 50, 1269–1279.
33 N. Sang, Y. Yun, G. Yao, H. Li, L. Guo and G. Li, Toxicol. Sci.,
2011, 124, 400–413.
Y. Sheng, F. Chen, Y. Yu, X. Wang, G. Sheng, J. Fu and
E. Y. Zeng, Environ. Monit. Assess., 2008, 143, 121–130.
A. Muezzinoglu, Chemosphere, 2003, 51, 245–252.
6
7
A. Muezzinoglu, M. Odabasi and L. Onat, Atmos. Environ., 34 I. Barnes, K. H. Becker and N. Mihalopoulos, J. Atmos. Chem.,
001, 35, 753–760.
1994, 18, 267–289.
M. Albu, I. Barnes, K. H. Becker, I. Patroescu-Klotz, 35 W. D. Taylor, T. D. Allston, M. J. Moscato, G. B. Fazekas,
2
8
R. Mocanu and T. Benter, Phys. Chem. Chem. Phys., 2006, 8,
28–736.
R. Kozlowski and G. A. Takacs, Int. J. Chem. Kinet., 1980,
12, 231–240.
7
9
C. Arsene, I. Barnes, K. H. Becker and T. Benter, Int. J. Chem. 36 R. Atkinson and J. Arey, Chem. Rev., 2003, 103, 4605–4638.
Kinet., 2005, 37, 66–73.
0 I. Barnes, V. Bastian and K. H. Becker, Int. J. Chem. Kinet.,
988, 20, 415–431.
1 S. M. Resende, J. Pliego and S. Vandresen, Mol. Phys., 2008,
06, 841–848.
37 R. Atkinson and S. M. Aschmann, Int. J. Chem. Kinet., 1984,
16, 1175–1186.
38 M. J. Ezell, W. Wang, A. A. Ezell, G. Soskin, B. J. Finlayson-
Pitts, C. J. Keoshian, B. Buehler and A. A. Ezell, Phys.
Chem. Chem. Phys., 2002, 4, 5813–5820.
1
1
1
1
1
1
1
2 C. Wilson and D. M. Hirst, J. Chem. Soc., Faraday Trans., 39 L. Nelson, O. Rattigan, R. Neavyn, H. Sidebottom, J. Treacy
997, 93, 2831–2837.
and O. J. Nielsen, Int. J. Chem. Kinet., 1990, 22, 1111–1126.
3 C. Wilson, D. M. Hirst and S. P. Urbanski, J. Chem. Phys., 40 S. M. Resende and F. R. Ornellas, J. Phys. Chem. A, 2000, 104,
015, 108, 222–234. 11934–11939.
4 M. Charles-Bernard, K. Kraehenbuehl, A. Rytz and 41 R. E. Stickel, J. M. Nicovich, S. Wang, Z. Zhao and P. H. Wine,
D. D. Roberts, J. Agric. Food Chem., 2005, 53, 4417–4425. J. Phys. Chem., 1992, 96, 9875–9883.
1
2
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 22618–22626 | 22625

View Article Online
RSC Advances
Paper
42 F. Su, J. G. Calvert, J. H. Shaw, H. Niki, P. D. Marker, 50 R. W. Clarke, P. J. Catalano, P. Koutrakis, G. G. K. Murthy,
C. M. Savage and L. D. Breitenbach, Chem. Phys. Lett.,
979, 65, 221–225.
C. Sioutas, J. Paulauskis, B. Coull, S. Ferguson and
J. J. Godleski, Inhalation Toxicol., 1999, 11, 637–656.
1
4
3 E. Jim ´e nez, B. Lanza, A. Garz ´o n, B. Ballesteros and 51 O. C. Taylor, J. Air Pollut. Control Assoc., 1969, 19, 347–351.
J. Albaladejo, J. Phys. Chem. A, 2005, 109, 10903–10909.
4 R. Atkinson, Atmos. Environ., 2007, 41, 8468–8485.
5 J. J. Orlando, G. S. Tyndall, M. Bilde, C. Ferronato, 53 G. S. Tyndall, J. J. Orlando, C. S. Kegley-Owen,
52 H. B. Singh and P. L. Hanst, Geophys. Res. Lett., 1981, 8, 941–
4
4
944.
T. J. Wallington, L. Vereecken and J. Peeters, J. Phys. Chem.
A, 1998, 102, 8116–8123.
T. J. Wallington and M. D. Hurley, Int. J. Chem. Kinet.,
1999, 31, 776–784.
4
4
4
6 P. Cassanelli, D. Johnson and R. A. Cox, Phys. Chem. Chem. 54 B. Ballesteros, A. Garz ´o n, E. Jim ´e nez, A. Notario and
Phys., 2005, 7, 3702–3710. J. Albaladejo, Phys. Chem. Chem. Phys., 2007, 9, 1210–1218.
7 H. G. Libuda, O. Shestakov, J. Theloke and F. Zabel, Phys. 55 R. Atkinson, D. L. Baulch, R. A. Cox, R. F. Hampson Jr,
Chem. Chem. Phys., 2002, 4, 2579–2586.
J. A. Kerr, M. J. Rossi and J. Troe, J. Phys. Chem. Ref. Data,
1997, 26, 521–1011.
8 N. Meunier, J. F. Doussin, E. Chevallier, R. Durand-Jolibois,
B. Picquet-Varrault and P. Carlier, Phys. Chem. Chem. Phys., 56 A. L. Cardona, M. B. Blanco, O. N. Ventura and M. A. Teruel,
003, 5, 4834–4839. Chem. Phys. Lett., 2019, 723, 69–75.
9 R. Hein, P. J. Crutzen and M. Heimann, Global Biogeochem. 57 G. Oksdath-Mansilla, A. B. Pe n˜ ´e n˜ ory, I. Barnes, P. Wiesen
2
4
Cycles, 1997, 11, 43–76.
and M. A. Teruel, Atmos. Environ., 2013, 85, 41–47.
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