KINETICS AND PRODUCTS OF THE REACTIONS OF SELECTED DIOLS
311
Kinetic Studies
determined by introducing measured amounts of the
chemicals into the 7900-liter chamber and conducting
several replicate GC-FID analyses [12]. The experi-
mentally measured GC-FID response factors of the
four diols, the four hydroxcarbonyl products observed,
and n-octane agreed with the calculated Effective Car-
bon Numbers [13] to within Ϯ17%, indicating that the
procedures for diol and hydroxycarbonyl introduction
into the chamber and the sampling and analysis tech-
Rate constants for the OH radical reactions were de-
termined using a relative rate method in which the
relative disappearance rates of the diols and a refer-
ence compound, whose OH radical reaction rate con-
stant is reliably known, were measured in the presence
of OH radicals [9,10]. Providing that the diols and the
reference compound reacted only with OH radicals,
then [9,10]
niques were quantitative. NO and initial NO concen-
2
trations were measured using a Thermo Environmental
Instruments, Inc., Model 42 chemiluminescent NO–
[
diol]t0
ln
ͫ
ͬ
[
diol]t
NO analyzer.
x
k1
k2
[reference compound]t0
[reference compound]t
ϭ
ln
(I)
ͫ
ͬ
Product Studies
where [diol] and [reference compound] are the con-
centrations of the diol and reference compound, re-
spectively, at time t , [diol] and [reference compound]
Products were identified and quantified from the re-
actions of the OH radical with the four diols studied,
both during the kinetic experiments (see above) and
t
0
t
0
0
t
t
are the corresponding concentrations at time t, and k1
from additional irradiated CH ONO–NO–diol–air
3
and k are the rate constants for reactions (1) and (2),
respectively.
mixtures, by GC-FID and by combined gas chroma-
tography–mass spectrometry (GC-MS). The initial
2
CH ONO and NO concentrations in the irradiated
3
CH ONO–NO–diol–air mixtures and GC-FID anal-
OH ϩ diol !: products (1)
3
ysis procedures were similar to those employed in the
kinetic experiments described above, and the initial
diol concentrations were in the range (1.51–6.42) ϫ
OH ϩ reference compound !: products (2)
OH radicals were generated by the photolysis of
13
Ϫ3
1
0 molecule cm . To verify the product identities,
methyl nitrite (CH ONO) in air at wavelengths Ͼ300
3
gas samples were collected onto Tenax-TA solid ad-
sorbent for GC-MS analyses, with thermal desorption
onto a 30-m DB-1701 fused silica capillary column in
a HP 5890 GC interfaced to a HP 5971 Mass Selective
Detector operated in the scanning mode.
nm [11], and NO was added to the reactant mixtures
3
to suppress the formation of O and hence of NO3
radicals [11]. The initial reactant concentrations (in
Ϫ
3
14
molecule cm units) were: CH ONO, ϳ2.4 ϫ 10 ;
3
14
13
NO, ϳ2.4 ϫ 10 ; 1,2-butanediol, (2.64–3.01) ϫ 10 ,
,3-butanediol, (2.21–2.36) ϫ 10 , 2,3-butanediol,
2.31–4.47) ϫ 10 , or 2-methyl-2,4-pentanediol,
2.28–2.39) ϫ 10 ; and n-octane (the reference com-
pound), ϳ2.4 ϫ 10 . Irradiations were carried out for
–45 min, resulting in up to 75% consumption of the
13
1
(
(
13
Chemicals
13
The chemicals used, and their stated purities, were:
13
1
,2-butanediol (99%), 1,3-butanediol (99ϩ%), 2,3-bu-
5
tanediol (98%), 1-hydroxy-2-butanone (95%), 3-hy-
droxy-2-butanone, 4-hydroxy-4-methyl-2-pentanone
initially present diol.
The concentrations of the diols and n-octane were
measured during the experiments by gas chromatog-
raphy with flame ionization detection (GC-FID). For
(
(
99%), 2-methyl-2,4-pentanediol (99%), and n-octane
99ϩ%), Aldrich Chemical Company; 1-hydroxy-3-
butanone (95ϩ%), TCI America; and NO (Ն99.0%),
Matheson Gas Products. Methyl nitrite was prepared
and stored as described previously [11].
the analysis of the diols, hydroxycarbonyl products
3
(
see the following) and n-octane, 100-cm volume gas
samples were collected from the chamber onto Tenax-
TA solid adsorbent, with subsequent thermal desorp-
tion at ϳ225ЊC onto a 30-m DB-1701 megabore col-
umn held at 0ЊC and then temperature programmed to
RESULTS
Ϫ
1
2
00ЊC at 8ЊC min . Based on replicate analyses in the
OH Radical Reaction Rate Constants
dark, the GC-FID measurement uncertainties for the
diols were in the range 1–5%. GC-FID response fac-
tors for the diols and hydroxycarbonyl products were
A series of CH ONO–NO–diol–n-octane–air irra-
3
diations were carried out, and the data obtained are