2-Butoxyethanol and benzyl alcohol reactions with the nitrate radical: Rate coefficients and gas-phase products

Article abstract of DOI:10.1002/kin.20726

The bimolecular rate coefficients k NO 3 ? + 2-butoxyethanol and k NO 3 ? + benzyl alcohol were measured using the relative rate technique at (297 ± 3) K and 1 atmosphere total pressure. Values of (2.7 ± 0.7) and (4.0 ± 1.0) × 10^-15 cm³

Full text of DOI:10.1002/kin.20726

2-Butoxyethanol and Benzyl
Alcohol Reactions with the
Nitrate Radical: Rate
Coefficients and Gas-Phase
Products
JOEL C. HARRISON, J. R. WELLS
Exposure Assessment Branch, Health Effects Laboratory Division, National Institute for Occupational Safety and Health,
Morgantown, WV 26505
Received 15 August 2011; revised 9 January 2012; accepted 2 February 2012
DOI 10.1002/kin.20726
Published online in Wiley Online Library (wileyonlinelibrary.com).
•
•
ABSTRACT: The bimolecular rate coefficients kNO +2-butoxyethanol and kNO +benzyl alcohol were
3
3
measured using the relative rate technique at (297
3) K and 1 atmosphere total pres-
sure. Values of (2.7
0.7) and (4.0
1.0) × 10−15 cm3 molecule−1 s−1 were ob-
•
•
served for kNO +2-butoxyethanol and kNO +benzyl alcohol, respectively. In addition, the prod-
ucts of 2-buto3xyethanol + NO3• and benzyl alcohol + NO•3 gas-phase reactions were
investigated. Derivatizing agents O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine and N, O-bis
(trimethylsilyl)trifluoroacetamide and gas chromatography mass spectrometry (GC/MS)
were used to identify the reaction products. For 2-butoxyethanol + NO•3 reaction:
hydroxyacetaldehyde, 3-hydroxypropanal, 4-hydroxybutanal, butoxyacetaldehyde, and 4-(2-
oxoethoxy)butan-2-yl nitrate were the derivatized products observed. For the benzyl alco-
hol + NO•3 reaction: benzaldehyde ((C6H5)C( O)H) was the only derivatized product ob-
served. Negative chemical ionization was used to identify the following nitrate products:
[(2-butoxyethoxy)(oxido)amino]oxidanide and benzyl nitrate, for 2-butoxyethanol + NO•3 and
benzyl alcohol + NO•3, respectively. The elucidation of these products was facilitated by mass
spectrometry of the derivatized reaction products coupled with a plausible 2-butoxyethanol
or benzyl alcohol + NO•3 reaction mechanisms based on previously published volatile organic
3
•
ꢀ
C
compound + NO3 gas-phase mechanisms.
2012 Wiley Periodicals, Inc.∗ Int J Chem Kinet
1–11, 2012
estimated by Sarwar et al. to be approximately 1.1
parts per trillion (ppt) (2 × 107 molecules/cm3) [1].
The indoor concentrations of volatile organic com-
pounds (VOCs) can be elevated from activities such
as cleaning, washing, and painting and as a result of
building energy-saving measures [2,3]. Therefore, in
the indoor environment, reactions between VOCs and
NO•3 are possible and based on previous VOC/NO•3 rate
INTRODUCTION
Indoor environment concentrations of the nitrate rad-
ical (NO•3), an important reactive species, have been
Correspondence to: J. Raymond Wells; e-mail: ozw0@cdc.gov.
2012 Wiley Periodicals, Inc. This article is a U.S. Government
work and, as such, is in the public domain of the United States of
America.
∗
c
ꢀ

2
HARRISON AND WELLS
coefficient measurements, the transformation of VOCs
into oxygenated organic reaction products can effec-
tively compete with building air exchange [4]. Potential
VOC oxidation products include alcohols, aldehydes,
ketones, dicarbonyls, carboxylic acids, and organic ni-
trates [5–7]. These products have the potential to cause
a number of adverse health effects including asthma,
allergy, and respiratory irritation [8,9].
(BSTFA) with GC/MS and also using negative chem-
ical ionization (NCI) mass spectrometry to detect gas-
phase nitrate species.
EXPERIMENTAL
Apparatus and Materials
Benzyl alcohol, an aromatic primary alcohol, is used
as a solvent in paint stripper and waterborne-coating
applications and as an intermediate for the synthesis of
target molecules used in pharmaceuticals, cosmetics,
preservatives, and flavoring and fragrance agents. Pro-
duction capacity worldwide of benzyl alcohol is esti-
Experiments to measure the gas-phase rate coefficient
of the NO•3 + 2-butoxyethanol and benzyl alcohol re-
actions were conducted with a previously described
apparatus [19]. A brief description is provided here.
Reactants were introduced, and samples were with-
®
drawn through a 6.4-mm Teflon Swagelok fitting at-
•
mated at 50 kT [10]. The kOH +benzyl alcohol ((28 7) ×
tached to a 65-L Teflon film chamber. Compressed
air from the National Institute for Occupational Safety
and Health (NIOSH) facility was passed through an-
hydrous CaSO4 (Drierite, Xenia, OH) and molecular
sieves (Drierite) to remove both moisture and organic
contaminants. This dry compressed air was added as
a diluent to the reaction chambers and measured with
a 0–100 L min−1 mass flow controller (MKS, An-
dover, MA). Analysis of this treated compressed air
by gas chromatography/mass spectrometry revealed
that if contaminants were present they would be be-
low the part per trillion range. The treated compressed
air was also analyzed for nitric oxide (NO) using
a Thermo Electron model 42i NO–NO2–NOx ana-
lyzer (Waltham, MA) and showed that 6 ppb (1.4 ×
1011 molecule cm−3) NO is present in the background
in NIOSH air. The filler system was equipped with a
syringe injection port, facilitating the introduction of
both liquid and gaseous reactants into the chambers
with the flowing air stream. All reactant mixtures and
calibration standards were generated by this system.
An additional port was added to the Teflon chamber
to facilitate the injection of N2O5 (synthesis described
below).
Two separate 65-L Teflon-film reaction chambers
were used in these experiments. The reaction chamber
contents were sampled for 5 min, using a solid-phase
micro-extraction (SPME) fiber (Supelco, Milwaukee,
WI), which was then inserted through a Merlin Mi-
croseal (Half Moon Bay, CA) and into the heated in-
jector of either one of two (Agilent, Wilmington, DE)
6890 gas chromatographs each with a 5975 mass selec-
tive detector (GC/MS) and Agilent ChemStation soft-
ware. The GC temperature program used was the same
for both systems: An injection port was set to 250◦C,
and the oven temperature began at 40◦C for 6 min and
was ramped 20◦C min−1 to 240◦C and held for 2 min.
All data were compiled from both systems and were
used to determine the NO3• rate coefficient for each of
the compounds
10−12 cm3 molecule−1 −1) and the kO3+benzyl alcohol,
s
(∼ 6 × 10−19 cm3 molecule−1
s
−1) and the respec-
tive reaction products have been investigated previ-
ously [11]. Liu et al. have investigated electric plugin
air freshener emissions and found the benzyl alcohol
concentration reached a maximum of about 0.05 ppm
(1.2 × 1012 molecule cm−3) after about 50 h and re-
mained relatively stable even after ozone was intro-
duced into the system [12].
2-Butoxyethanol, a butyl ether of ethylene glycol,
is used as a solvent in paints and surface coatings and
other consumer products such as inks, cleaning prod-
ucts, liquid soaps, and oil spill dispersants. Worldwide
production of 2-butoxyethanol in 1994 was estimated
•
to be 300 kT [13]. The kOH +2-butoxyethanol (18.6 ×
10−12 cm3 molecule−1 s−1) [14] and the reaction prod-
ucts have been investigated [15]. A recent assessment
of emissions from a typical consumer glass cleaner
showed concentrations of 0.04–0.17 ppm (1.0–4.2 ×
1012 molecule cm−3) of 2-butoxyethanol for about 4 h
after cleaning [16]. Other studies have suggested that
2-butoxyethanol emissions will continue over hours
or even days after using a product containing this
chemical [17,18]. Exposures may take place both dur-
ing the cleaning process and from remnants left after
cleaning.
In this study, the kinetics and reaction products
of benzyl alcohol and 2-butoxyethanol with NO3•
have been determined. This is important for assess-
ing occupant exposures since both chemicals are in
wide use, and the products formed could be poten-
tial human health hazards. The relative rate tech-
nique was used to determine the NO•3 reaction kinet-
ics of benzyl alcohol and 2-butoxyethanol using gas
chromatography/mass spectrometry (GC/MS). Prod-
ucts from the reaction of these chemicals and NO•3 were
determined using the chemical derivatization agents
O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PF-
BHA) and N, O-bis(trimethylsilyl)trifluoroacetamide
International Journal of Chemical Kinetics DOI 10.1002/kin.20726

2-BUTOXYETHANOL AND BENZYL ALCOHOL REACTIONS WITH THE NITRATE RADICAL
3
Identification of reaction products was made us-
ing PFBHA to derivatize carbonyl products, whereas
carbonyl alcohols were derivatized using BSTFA [20].
Experimental methods for reaction product identifica-
tion were similar to methods used for kinetic experi-
ments, except the reference compound was excluded
from the reaction mixture.
Derivatized reaction products were analyzed using
a Varian (Palo Alto, CA) 3800/Saturn 2000 GC/MS
system operated in both the electron ionization (EI)
and chemical ionization (CI) modes [20]. Compound
separation was achieved by a J&W Scientific (Folsom,
CA) DB-5MS (0.32 mm i.d., 30-m long, 1-μm film
thickness) column and the following GC oven param-
eters: 60◦C for 1 min then 20◦C/min to 170◦C, then
3◦C/min to 280◦C and held for 5 min.
Samples were injected in the splitless mode, and
the GC injector was returned to split mode 1 min after
sample injection, with the following injector temper-
ature parameters: 60◦C for 1 min then 180◦C/min to
250◦C and held to the end of the chromatographic run
[20]. The Saturn 2000 ion trap mass spectrometer was
tuned using perfluorotributylamine (FC-43). Full-scan
EI spectra were collected from m/z 40 to 650. Ace-
tonitrile was the CI reagent used for all CI spectra.
When possible, commercially available samples of the
identified products were derivatized and subsequently
analyzed to verify matching ion spectra and chromato-
graphic retention times.
erence, N2O5, and compound of interest are run prior
to combining all of these to ensure that the compounds
or products do not have retention times that interfere
with peaks that are used for the relative rate technique.
All compounds were used as received and had the
following purities: from Sigma-Aldrich (Milwaukee,
WI): benzaldehyde (99%), 1,3,5-trimethylbenzene
(mesitylene) (98%), 4-isopropyltoluene (p-cymene)
(99%), 2-butoxyethanol (99.5%), benzyl alcohol
(99.8%), acetonitrile (99.93%), BSTFA (99%), O-(2,
3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochlo-
ride (PFBHA) (98+%), and methanol (99%). Nitro-
gen dioxide as a 5% mixture in nitrogen and ultra-high
purity (UHP) oxygen was obtained from Butler Gases
(Morrisville, PA). Helium (UHP grade), the carrier gas,
was supplied by Amerigas (Sabraton, WV) and used
as received. Experiments were carried out at (297 3)
K and 1 atmosphere pressure.
Procedures
The experimental procedures for determining the 2-
butoxyethanol or benzyl alcohol (alcohols) + NO3•
reaction kinetics were similar to those described previ-
ously [19]. The NO•3 rate coefficient experiments for 2-
butoxyethanol employed the use of two reference com-
pounds: benzaldehyde and mesitylene. The NO•3 rate
coefficient experiments for benzyl alcohol employed
the use of two reference compounds: p-cymene and
mesitylene:
Nitrate products were analyzed using NCI on an Ag-
ilent (Wilmington, DE) 6890 gas chromatograph with
a 5975 mass selective detector (GC/MS) and Agilent
ChemStation software. The GC temperature program
used was the injection port was set to 150◦C and oven
temperature began at 30◦C for 2 min and was ramped
8◦C min−1 to 150◦C and held for 16 min and then
ramped 20◦C min−1 to 220◦C and held for 5 min. Full-
scan NCI spectra were collected from m/z 40 to 700.
Hydrogen was the CI reagent used for all NCI spectra.
Nitrate radicals were generated by the thermal de-
composition of N2O5 using a similar method as de-
scribed by Atkinson et al. [5,21]. N2O5 (solid) kept at
–85◦C was removed from cold trap and allowed warm
slightly and transferred to an evacuated 2-L collection
bottle until manifold pressure was between 0.1–0.6
Torr. The collection bottle was then pressurized with
ultra-high purity nitrogen up to 1000 Torr and con-
nected to the reaction chamber via a Teflon shutoff
valve. The valve to the collection bottle and the cham-
ber shutoff valve were opened, and the system was
allowed to equilibrate for 10 s. For kinetics and prod-
uct experiments, approximately 30 min elapsed before
any samples were collected after the introduction of
N2O5. Initial experiments with just the individual ref-
kNO
+Alcohols
3
Alcohols + NO•3 −→ Products
(1)
(2)
kRef
Reference + NO•3 −→ Products
The rate equations for reactions (2) and (3) are com-
bined and integrated, resulting in the following equa-
tion:
ꢀ
ꢁ
ꢀ
ꢁ
[Alcohols]0
[Alcohols]t
k
[Ref]0
[Ref]t
NO3+Alcohols
kRef
ln
=
ln
(3)
If a reaction with NO•3 is the only removal mecha-
nism for 2-butoxyethanol or benzyl alcohol (Alcohols)
and reference, a plot of ln([Alcohols]0/[Alcohols]t )
versus ln([Ref]0/[Ref]t ) yields a straight line with an in-
tercept of zero. Multiplying the slope of this linear plot
•
•
by kRef yields kNO +2-butoxyethanol or kNO +benzyl alcohol
(Figs. 1 and 2). Using two different ref3erence com-
pounds with different NO•3 rate coefficients improves
the accuracy of the 2-butoxyethanol/NO•3 or benzyl
alcohol/NO•3 rate coefficient measurement. The si-
multaneous plotting of two Alcohols/Ref data sets
3
International Journal of Chemical Kinetics DOI 10.1002/kin.20726

4
HARRISON AND WELLS
3.8 L min−1 through an impinger containing 4 mL of
methanol with no effort to prevent methanol evapo-
ration during sample collection. The sample was re-
moved from the impinger, and 100 μL was withdrawn
and analyzed using NCI. To the remaining sample
solution (approximately 2 mL), 250 μL of 0.02 M
PFBHA in acetonitrile was added to derivatize the car-
bonyl reaction products to oximes [20]. This solution
was allowed to react for 24–48 h in the dark. The
reacted solutions were gently blown to dryness with
UHP N2, reconstituted with 100 μL of methanol, and
then 1 μL of the reconstituted solution was injected
onto the Varian 3800/Saturn 2000 GC/MS system.
The derivatization of hydroxy groups (alcohols) was
achieved by subsequent reconstitution of the dried PF-
BHA oximes with 150 μL of commercially available
BSTFA. These PFBHA/BSTFA solutions were heated
to approximately 60◦C for 45 min to complete the sily-
lation and then 1 μL of the solution was injected into
the Varian 3800/Saturn 2000 GC/MS system [22].
Figure 1 2-Butoxyethanol relative rate plot with ben-
zaldehyde (♦) and mesitylene ( ) as reference com-
ꢀ
pounds. The NO•3 + 2-butoxyethanol rate coefficient,
•
kNO +2-butoxyethanol, was measured to be (2.7
0.7) ×
3
10−15 cm3 molecule−1 s−1
.
RESULTS
2-Butoxyethanol/NO•3 Reaction Rate
Coefficient
The NO•3 rate coefficient for 2-butoxyethanol was ob-
tained using the relative rate method described above.
The plot of a modified version of Eq. (3) is shown
in Fig. 1. The ln([Ref]0/[Ref]t ) term is divided by
the respective reference rate coefficient (benzaldehyde
(2.4 0.5) × 10−15 cm3 molecule−1 s−1 or mesity-
Figure 2 Benzyl alcohol relative rate plot with p-cymen•e
ꢁ
(ꢀ) and mesitylene ( ) as reference compounds. The NO3
•
+ benzyl alcohol rate coefficient, kNO3 +benzyl alcohol, was
measured to be (4.0 1.0) × 10−15 cm3 molecule−1 s−1
.
lene (8.8
2.2) × 10−16 cm3 molecule−1
s
−1) [23]
demonstrates that other reactions are not removing 2-
butoxyethanol or benzyl alcohol.
and multiplied by 10−15 cm3 molecule−1 −1, re-
s
sulting in a unitless number. This yields a slope
that is equal to the NO•3/2-butoxyethanol rate co-
For the 2-butoxyethanol/NO•3 and benzyl alcohol/
NO•3 kinetic experiments, the typical concentrations
of the pertinent species in the 65-L Teflon chamber
were 0.3–0.9 ppm ((0.7–2) × 1013 molecule cm−3) 2-
butoxyethanol or benzyl alcohol, 0.3–0.8 ppm ((0.7–
2.0) × 1013 molecule cm−3) reference, 3.9–23 ppm
((1–5.7) × 1014 molecule cm−3) of N2O5 (0.1–0.6
Torr, which corresponds to an NO•3 concentration of
0.3–1.5 ppm at 298 K) and 6 ppb (1.4 × 1011 molecule
cm−3) NO as background in NIOSH air. The gas-phase
mixtures were allowed to reach equilibrium before ini-
tial species concentration ([X]0) samples were col-
lected. The total ion chromatogram (TIC) peak area
from the Agilent 5973 mass selective detector was used
to determine 2-butoxyethanol/benzyl alcohol and ref-
erence concentrations.
efficient, kNO +2-butoxyethanol, divided by 10−15 cm3
•
molecule−1 s−31. This modification allows for a simul-
taneous comparison of the two reference compound/2-
butoxyethanol data sets. The slope of the line shown
in Fig. 1 yields an NO3• bimolecular rate coeffi-
cient, kNO +2-butoxyethanol, of (2.7
0.2) × 10−15
•
3
cm3 molecule−1 −1. The use of benzaldehyde and
s
mesitylene as references resulted in NO•3 + 2-
butoxyethanol bimolecular rate coefficients of (2.0
0.2) and (2.9
0.4) × 10−15 cm3 molecule−1 s−1
,
respectively (see Table I). The data points at the
origin are experimental points before NO•3 addi-
tion, t = 0, data showed no detectable loss of 2-
butoxyethanol or reference. The error in the rate co-
efficient stated above is the 95% confidence level
from the random uncertainty in the slope. Incorporat-
ing the uncertainties associated with the reference rate
Derivatization of the carbonyl reaction products was
initiated by flowing 15–25 L of chamber contents at
International Journal of Chemical Kinetics DOI 10.1002/kin.20726

2-BUTOXYETHANOL AND BENZYL ALCOHOL REACTIONS WITH THE NITRATE RADICAL
5
2-Butoxyethanol/NO•3 and Benzyl
Alcohol/NO•3 Reaction Products Using
PFBHA and NCI
Table I Rate Constants Measured from
2-Buoxyethanol/Benzyl Alcohol + NO•3 Reaction
kalc
/
kalc[cm3
Compound
Reference
kref molecule−1 s−1
]
Derivatization of nonsymmetric carbonyls using PF-
BHA or PFBHA/BSTFA typically resulted in multi-
ple chromatographic peaks due to stereoisomers of the
oximes. Identification of multiple peaks of the same
oxime compound is relatively simple since the mass
spectra for each chromatographic peak of a particu-
lar oxime are almost identical [20]. In most cases, the
m/z 181 ion relative intensity for the chromatographic
peaks due to 2-butoxyethanol + NO•3 or benzyl al-
cohol + NO•3 reaction product oximes was the base
peak in the mass spectrum and was used to gener-
ate selected ion chromatograms. The mass spectra of
compounds additionally derivatized with BSTFA could
contain m/z 73 ion from the [Si(CH3)3]+ fragments
[20]. The product data are described below.
The following chromatographic retention time
and mass spectra data were observed utilizing PF-
BHA derivatization and the Varian 3800/Saturn 2000
GC/MS system. The reaction products’ chromato-
graphic peak areas were a function of the ini-
tial 2-butoxyethanol/benzyl alcohol concentration and
were observed only after NO•3 initiation of 2-
butoxyethanol/benzyl alcohol/methanol/air mixtures.
Derivatization experiments performed in the absence
of 2-butoxyethanol or benzyl alcohol, but in the pres-
ence of all other chemicals in the reaction chamber
(NO•3/air/methanol) did not result in any of the data
reported below.
The PFBHA reaction products observed from
the 2-butoxyethanol/NO•3 via hydrogen abstrac-
tion are hydroxyacetaldehyde, 3-hydroxypropanal, 4-
hydroxybutanal, and butoxyacetaldehyde and 4-(2-
oxoethoxy)butan-2-yl nitrate. The PFBHA reaction
product observed from the benzyl alcohol/NO•3 via
hydrogen abstraction was benzaldehyde. Elucidation
of the proposed reaction products for 2-butoxyethanol
(listed in Table II) was facilitated by mass spectrometry
of the derivatized reaction product coupled with plausi-
ble 2-butoxyethanol/NO•3 reaction mechanisms based
on the previously published VOC/NO•3 gas-phase re-
action as described below [7,23–27].
The chromatographic retention time and mass spec-
tra data were observed for NCI utilizing the Agi-
lent 6890/5975 GC/MS system. TIC from the Ag-
ilent 5973 mass selective detector was used to de-
termine products for 2-butoxyethanol/NO•3 and ben-
zyl alcohol/NO•3 reactions. The reaction products’
chromatographic peak areas were a function of
the initial 2-butoxyethanol/benzyl alcohol concentra-
tion and were observed only after NO•3 initiation
2-Butoxyethanol Benzaldehdye 1.0
2.0 × 10−15
2.9 × 10−15
2.7 × 10−15
4.3 × 10−15
4.0 × 10−15
4.0 × 10−15
2-Butoxyethanol Mesitylene
2-Butoxyethanol Overall
3.1
Benzyl alcohol
Benzyl alcohol
Benzyl alcohol
p-Cymene
Mesitylene
Overall
4.0
5.0
coefficients ( 25% for benzaldehyde and mesitylene)
[23] used to derive the 2-butoxyethanol/NO•3 rate co-
•
efficient yields a final value for kNO +2-butoxyethanol
,
3
of (2.7
0.7) × 10−15 cm3 molecule−1 s−1
•
•
3
[23]. The ratios kNO +2-butoxyethanol/kNO +benzaldehyde and
3
•
•
kNO +2-butoxyethanol/kNO +mesitylene incorporating the un-
cert3ainties are 1.0
0.3 and 3.1
0.8, re-
3
spectively. The 2-butoxyethanol/NO•3 rate coeffi-
•
cient, kNO +2-butoxyethanol, has not been previously
3
reported.
Benzyl Alcohol/NO•3 Reaction Rate
Coefficient
The NO•3 rate coefficient for benzyl alcohol was also
obtained using the relative rate method, and a plot
of a modified version of Eq. (3) is shown in Fig. 2.
The ln([Ref]0/[Ref]t ) term is divided by the respec-
tive reference rate coefficient (p-cymene (1.0 0.3)
× 10−15 cm3 molecule−1 s−1 and mesitylene (8.8
2.2) × 10−16 cm3 molecule−1
s
−1) [23] and multi-
plied by 10−15 cm3 molecule−1 −1. The slope of
s
the line shown in Fig. 2 yields an NO•3 bimolecu-
•
lar rate coefficient, kNO +benzyl alcohol, of (4.1 0.3) ×
3
10−15 cm3 molecule−1
s
−1. The use of p-cymene and
mesitylene as references resulted in NO•3 + benzyl
alcohol bimolecular rate coefficients of (4.3
0.4)
and (4.0
0.4) × 10−15 cm3 molecule−1
s
−1, re-
spectively (see Table I). The error in the rate co-
efficient stated above is the 95% confidence level
from the random uncertainty in the slope. Incorpo-
rating the uncertainties associated with the reference
rate coefficients ( 25% for p-cymene and mesity-
lene) [23] used to derive the benzyl alcohol/NO•3 rate
•
coefficient yields a final value for kNO +benzyl alcohol
,
3
of (4.0
1.0)
×
10−15 cm3 molecule−1
−1. The ratios kNO +benzyl alcohol/kNO +p-cymene and
•
•
s
3
3
•
•
kNO +benzyl alcohol/kNO +mesitylene incorporating the un-
cert3ainties are 4.0 3
1.0 and 5.0
1.0, re-
spectively. The benzyl alcohol/NO•3 rate coefficient,
•
kNO +benzyl alcohol, has not been previously reported.
3
International Journal of Chemical Kinetics DOI 10.1002/kin.20726

6
HARRISON AND WELLS
Table II Products Observed from 2-Buoxyethanol + NO•3 Reaction
Retention
Molecular
CI Ions
Time (min)
Structure
Weight (amu)
Observed
10.0
10.3
60
74
256
270
10.0
10.3
10.5
10.5
13.8
88
284
312
116
16.1
177
163
326
163
Negative chemical ionization spectra
18.5
of 2-butoxyethanol/benzyl alcohol/methanol/air mix-
tures. Experiments performed in the absence of 2-
butoxyethanol or benzyl alcohol, but in the pres-
ence of all other chemicals in the reaction chamber
(NO•3/air/methanol) did not result in any of the data
reported below. The presence of a strong m/z 46 ion
relative intensity is an indicator of a nitrate product
[28,29].
Oxime at Retention Time of 10.0, 10.3, and
10.5 min
The oxime observed with a chromatographic retention
time of 10.0, 10.3, and 10.5 min had ions of m/z (rel-
ative intensity): 99 (7%), 117 (7%), 161 (6%), 181
(100%), 194 (18%), 225 (17%), and 238 (7%). In
the CI spectra, an M + 1 ion of m/z 270 was ob-
served for the PFBHA-derivatized sample. The m/z
270 ion is the result of a PFBHA derivatization, in-
dicating a reaction product with a molecular weight
of 74. A proposed reaction product assignment of 3-
hydroxypropanal (CH( O)CH2CH2OH) was based on
the observed data.
Oxime at Retention Time of 10.0 and
10.3 min
The oxime observed with a chromatographic retention
time of 10.0 and 10.3 min had ions of m/z (relative
intensity): 57 (8%), 99 (8%), 117 (8%), 161 (8%), 181
(100%), 195 (19%), 226 (6%), and 238 (5%). In the CI
spectra, an M + 1 ion of m/z 256 was observed for the
PFBHA-derivatized sample. The m/z 256 ion is the
result of a PFBHA derivatization, indicating a reaction
product with a molecular weight of 60. A proposed
reaction product assignment of hydroxyacetaldehyde
(CH( O)CH2OH) (glycolaldehyde) was based on the
observed data and previous investigations [22].
Oxime at Retention Time of 10.5 min
The oxime observed with a chromatographic retention
time of 10.5 min had ions of m/z (relative intensity): 99
(7%), 117 (7%), 161 (7%), 181 (100%), 195 (11%), and
238 (8%). In the CI spectra, an M + 1 ion of m/z 284
was observed for the PFBHA-derivatized sample. The
m/z 284 ion is the result of a PFBHA derivatization,
indicating a reaction product with a molecular weight
of 88. A proposed reaction product assignment of
International Journal of Chemical Kinetics DOI 10.1002/kin.20726

2-BUTOXYETHANOL AND BENZYL ALCOHOL REACTIONS WITH THE NITRATE RADICAL
7
4-hydroxybutanal (CH( O)CH2CH2CH2OH) was
based on the observed data.
NCI 2-Butoxyethanol Nitrate Product at
18.5 min
For 2-butoxyethanol, the ion at a chromatographic
retention time of 18.5 min had ions of m/z (rela-
tive intensity) 46 (100%), 58 (18%), 90 (22%), 115
(70%), and 117 (25%). The proposed identity of the
ion at 18.5 min was made by observance of an ion
at m/z = 117, which is due to the loss of one NO2
molecule (m/z = 46). This loss has been commonly
observed in mass spectra of alkyl and arylalkyl ni-
trates [28,29]. The m/z 117 ion observed in the NCI
spectrum indicates a reaction product with a molecular
weight of 163. A proposed reaction product assign-
ment of [(2-butoxyethoxy)(oxido) amino]oxidanide
(CH3CH2CH2CH2OCH2CH2ONO2) was based on the
observed data.
The PFBHA reaction product observed from the
benzyl alcohol/NO•3 via hydrogen abstraction is ben-
zaldehyde. The benzyl alcohol/NO•3 reaction product
observed and positively identified using the pure com-
pound for verification by derivatization was benzalde-
hyde.
Oxime at Retention Time of 13.6 min
The oxime observed with a chromatographic retention
time of 13.6 min had ions of m/z (relative intensity):
57 (16%), 99 (7%), 161 (8%), 181 (100%), 195 (8%),
207 (12%), 225 (14%), and 239 (17%). In the CI spec-
tra, an M + 1 ion of m/z 312 was observed for the
PFBHA-derivatized sample. The m/z 312 ion is the
result of a PFBHA derivatization, indicating a reac-
tion product with a molecular weight of 116. A pro-
posed reaction product assignment of butoxyacetalde-
hyde (CH3CH2CH2CH2OCH2CH( O)) was based on
the observed data.
Oxime at Retention Time of 16.1 min
The oxime observed with a chromatographic retention
time of 16.1 min had ions of m/z (relative intensity):
45 (6%), 57 (15%), 71 (17%), 99 (6%), 117 (6%), 161
(7%), 181 (100%), 195 (9%), and 255 (16%).%). In
the CI spectra, an M + 1 ion of m/z 326 was ob-
served for the PFBHA-derivatized sample. The m/z
326 ion is the result of a PFBHA derivatization, in-
dicating a reaction product with a molecular weight
of 177. The major ion observed at 16.1 min was
m/z = 131, which is probably due to the loss of one
NO2 molecule (m/z = 46). A proposed reaction prod-
uct assignment of 4-(2-oxoethoxy)butan-2-yl nitrate
(CH3CH(NO2)CH2CH2OCH2CH( O)) was based on
the observed data.
Benzaldehyde ((C6H5)C(O)H)
The oxime observed with a chromatographic reten-
tion time of 17.2 and 17.5 min had ions of m/z (rel-
ative intensity) 181 (100%), 271 (38%), 300 (27%),
301 (55%), and 302 (11%). The m/z 301 ion is the
result of a PFBHA derivatization, indicating a reac-
tion product with a molecular weight of 106. Using
acetonitrile for CI, an M + 1 ion of m/z of 302
was observed for the PFBHA-derivatized sample. The
PFBHA-benzaldehyde oxime was synthesized to con-
firm this chromatographic assignment [11].
PFBHA and BSTFA can be utilized in a two-
step derivatization method (see above) to derivatize
compounds that contain both a carbonyl and a hydroxyl
group. The oximes at retention times of 10.0, 10.3, and
10.5 min are proposed products, all of which contain
a carbonyl and hydroxyl group. PFBHA/BSTFA ex-
periments were attempted but were unsuccessful in
capturing any of the oximes with the hydroxyl group
at retention times 10.0, 10.3, and 10.5 min. The lack
of observation could be due to their low product yield
coupled with inefficient derivatization chemistry. No
evidence of any fragments was observed at m/z 73
ions, which is a characteristic ion of the OH functional
group derivatization [20]. Glycolaldehyde has been ob-
served by this group, and both the mass spectrum and
retention times are in good agreement with previous
work [22].
NCI Benzyl Alcohol Nitrate Product at
21.1 min
For benzyl alcohol, the ion at a chromatographic re-
tention time of 21.1 min had ions of m/z (relative
intensity) 46 (90%), 62 (10%), 77 (38%), 105 (100%),
and 107 (60%). The proposed identity of the ion at
21.1 min was made by observance of an ion at m/z =
107, which is due to the loss of one NO2 molecule (m/z
= 46). The m/z 107 ion observed in the NCI spectrum
indicates a reaction product with a molecular weight of
153. A proposed reaction product assignment of benzyl
nitrate ((C6H5)CH2ONO2) was based on the observed
data.
International Journal of Chemical Kinetics DOI 10.1002/kin.20726

8
HARRISON AND WELLS
DISCUSSION
A rate coefficient of (2.7
0.7) × 10−15 cm3
molecule−1 s−1 was determined for the reaction
of NO•3 and 2-butoxyethanol using benzaldehyde
and mesitylene as references (Fig. 1). Even though
the same number of data points was collected for
each 2-butoxyethanol reference pair, the kinetic plot
shows a wider distribution of data points for the
2-butoxyethanol/mesitylene pair. This wider distribu-
tion is likely due to mesitylene’s NO•3 rate coeffi-
cient being a factor of 3 slower than benzaldehyde’s
NO•3 rate coefficient. It should be noted that the in-
dividual 2-butoxyethanol/NO•3 rate coefficients deter-
Structure 2. Benzyl alcohol.
•
An overall ratio of rate coefficients kOH• /kNO can
3
be estimated by using the average alcohol rate coeffi-
•
cient values for kOH and kNO• . These average values
can be determined from publis3hed measurements from
Atkinson and Arey for all of the alcohols rate coef-
ficients that have been measured [23]. To date, the
mined using a single reference were (2.0
0.2) ×
average alcohol kOH is 9.7 × 10−12 cm3 molecule−1
•
10−15 cm3 molecule−1 s−1 and (2.9 0.4) × 10−15 cm3
molecule−1 s−1 for benzaldehyde and mesitylene, re-
spectively. It can be observed that these two rate coef-
ficients are not within the 95% confidence limit regres-
sion error of each other as has been typically observed
by this group. However, the discrepancy in the refer-
ences’ rate coefficients does not significantly impact
the determined 2-butoxyethanol NO•3 rate coefficient
from the entire data set.
s−1 and the average alcohol kNO is 1.4 × 10−15 cm3
•
3
molecule−1 s−1 (20 alcohol kOH measurements and 4
•
•
alcohol kNO measurements) [23]. Using these average
3
•
values, the ratio of rate coefficients kOH• /kNO for the
3
entire set of alcohols that have been measured to date
is 6929, which is consistent with the rate coefficient
ratio from the measurements presented here. Dividing
•
known kOH alcohol rate coefficients by 7000 may be
•
a suitable approach for approximating unknown kNO
3
alcohol rate coefficients.
Rate Coefficient Data Comparison Ratio
2-Butoxyethanol/ NO•3 PFBHA Reaction
Products
The nitrate radical (NO•3) like the hydroxyl radi-
cal (OH•) can react with VOC by H-atom abstrac-
tion and/or addition to carbon–carbon double bonds
[7,25,27,30]. (Structures 1 and 2 show the sites for
these nitrate radical reactions.) The similarity of these
reactants’ mechanisms could be used to address the
limited number of measured NO•3 rate coefficients by
comparing measured OH• rate coefficients and NO3•
For the 2-butoxyethanol + NO•3 and benzyl alcohol
+ NO•3 reactions, the experimental parameters were
set to minimize side reactions and highlight the NO3•
hydrogen abstraction and/or NO•3 addition. The pos-
sible mechanistic steps leading to product formation
are described below. The NO2 is present due to the
dissociation of N2O5 into NO•3 and NO2.
rate coefficients. Using the value determined here, the
•
measured kNO +2-butoxyethanol of (2.7
0.7) × 10−15
3
cm3 molecule−1 s−1 and the previously measured
Oximes at Retention Time of 10.0, 10.3,
and 10.5 min. The oximes proposed as 2-
hydroxyacetaldehyde (CH( O)CH2OH) (glycolalde-
hyde), 3-hydroxypropanal (CH( O)CH2CH2OH),
and 4-hydroxybutanal (CH( O)CH2CH2CH2OH)
were observed in the PFBHA derivatization ex-
periments from the 2-butoxyethanol/NO•3 reaction.
The radical CH3CH2CH2CH2OCH(•)CH2(OH) is
formed by hydrogen abstraction (position B on
Structure 1) of the molecule as seen in Fig. 3. The
radical reacts with oxygen to form the peroxyrad-
ical, CH3CH2CH2CH2OCH(OO)(•)CH2(OH). This
species then dissociates to form (•)(OO)CHCH2(OH)
and CH3CH2CH2CH2O(•). The (•)(OO)CHCH2(OH)
radical can further react with a RO molecule to form
RO2 and CH( O)CH2OH. The CH3CH2CH2CH2O(•)
kOH +2-butoxyethanol of 18.6 × 10−12 cm3 molecule−1 s−1
•
[14] can be compared to one another. The ratio of rate
coefficients (kOH• /kNO• ) is 6889 for 2-butoxyethanol.
3
Likewise for benzyl alcohol, the ratio of rate coeffi-
cients (kOH• /kNO• ) is 7000 [11]. The similarity of these
3
two ratios prompts an expanded comparison.
Structure 1. 2-Butoxyethanol.
International Journal of Chemical Kinetics DOI 10.1002/kin.20726

2-BUTOXYETHANOL AND BENZYL ALCOHOL REACTIONS WITH THE NITRATE RADICAL
9
Figure 3 Proposed reaction mechanisms for observed products with 2-butoxyethanol and NO•3.
radical isomerizes to form CH3CH(•)CH2CH2OH or
(•)CH2CH2CH2CH2OH. The CH3CH(•)CH2CH2OH
radical reacts with oxygen to form the peroxyradical,
CH3CH(OO)(•)CH2CH2OH and then loses a CH3
group. The CH(OO)(•)CH2CH2OH radical can
further react with a RO molecule to form RO2 and
CH( O)CH2CH2OH. The (•)CH2CH2CH2CH2OH
radical reacts with oxygen to form the perox-
yradical, (•)(OO)CH2CH2CH2CH2OH. This can
further react with a RO molecule to form RO2 and
CH( O)CH2CH2CH2OH.
of the molecule as seen in Fig. 3. This then reacts
with O2 to give CH3CH2CH2CH2OCH2CH( O) and
HO2. The CH3CH2CH2CH2OCH2CH( O) molecule
can react with another NO•3 to form CH3CH(•)
CH2CH2OCH2CH( O). This then reacts with NO2 to
form CH3CH(NO2)CH2CH2OCH2CH( O).
Benzyl Alcohol/ NO•3 PFBHA Reaction
Products
Oximes at Retention Time of 13.6 and 16.1 min.
The oximes proposed as butoxyacetaldehyde (CH3CH2
CH2CH2OCH2CH( O)) and 4-(2-oxoethoxy)butan-
2-yl nitrate (CH3CH(NO2)CH2CH2OCH2CH( O))
were observed in the PFBHA derivatization experi-
ments from the 2-butoxyethanol/NO•3 reaction. The
radical CH3CH2CH2CH2OCH2CH(•)(OH) is formed
by hydrogen abstraction (position A on Structure 1)
Benzaldehyde Retention Time of 17.2 and 17.5 Min.
Benzaldehyde (C6H5C( O)H) was the only product
observed in the PFBHA derivatization experiments
from the benzyl alcohol/NO•3 reaction. The radical
(C6H5)CH(•)(OH) is formed by hydrogen abstraction
of the alkyl hydrogen (position A on Structure 2) and a
subsequent reaction with O2 to give C6H5C( O)H and
HO2 (see Fig. 4).
International Journal of Chemical Kinetics DOI 10.1002/kin.20726

10
HARRISON AND WELLS
Figure 4 Proposed reaction mechanisms for observed products with benzyl alcohol and NO•3.
the 2-butoxyethanol/benzyl alcohol + NO•3 rate co-
efficients reported here, a pseudo–first-order rate co-
efficient (kꢁ) of 0.0002–0.01 h−1 and 0.0003–0.017
2-Butoxyethanol/NO•3 and Benzyl
Alcohol/NO•3 Nitrate Reaction Products
The 2-butoxyethanol/NO•3 reaction product proposed
as [(2-butoxyethoxy)(oxido) amino]oxidanide (CH3
CH2CH2CH2OCH2CH2ONO2) was detected using
NCI. The radical CH3CH2CH(•)CH2OCH2CH2OH
is formed by hydrogen abstraction (position C on
Structure 1) of the 2-butoxyethanol molecule as
seen in Fig. 3. The radical then isomerizes to form
CH3CH2CH2CH2OCH2CH2O(•) and then adds NO2
to form CH3CH2CH2CH2OCH2CH2ONO2.
h
−1, respectively, was determined. A comparison of
this value to a typical indoor air exchange rate of 0.6
h−1 [4] suggests that air exchange is the most likely
removal mechanism for 2-butoxyethanol and benzyl
alcohol in the indoor environment. However, surface
reactions may be important due to the fact that both
compounds are large volume solvents and cleaners and
can be applied to surfaces repeatedly.
An Agilent NCI GC/MS system provides the capa-
bility to analyze reaction products directly without the
use of derivatization agents. This system can detect or-
ganic nitrates, which may be important components in
indoor air. Some specific organic nitrates such peroxy-
acyl nitrates have demonstrated the potential to cause a
number of adverse health effects including asthma, res-
piratory irritation, and is possibly a carcinogen [32,33].
It is anticipated that a number of organic nitrate com-
pounds may be present in indoor air, may have harmful
health effects, and should be investigated further [34].
The benzyl alcohol/NO3• reaction product proposed
as benzyl nitrate ((C6H5)CH2ONO2) was detected us-
ing NCI. The radical (C6H5)CH(•)(OH) is formed by
hydrogen abstraction (position A on Structure 2) of
the alkyl hydrogen (see Fig. 4). This rearranges via a
hydrogen shift to (C6H5)CH2O(•), then adds NO2 to
form (C6H5)CH2ONO2.
To investigate the role NO2 plays in the formation
of benzyl nitrate, experiments were conducted using
2 ppm NO2 and 0.75 ppm of either benzyl alcohol or
benzaldehyde in a 65-L reaction chamber using very
similar procedure as described above. The NCI sys-
tem was employed to determine the possible products.
These experiments did not lead to the formation of
any detectable benzyl nitrate. Therefore, the benzyl
nitrate formation pathway is dependent on the pres-
ence of NO•3 and the formation of the alkoxy radical
((C6H5)CH2O(•)).
DISCLAIMER
The findings and conclusions in this report are those
of the author(s) and do not necessarily represent the
official position of the Centers for Disease Control
and Prevention/the Agency for Toxic Substances and
Disease Registry.
Atmospheric Implications in Indoor Air
An indoor environment nitrate radical concentra-
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