EPA-600/3-76-012
January 1976 Ecological Research Series
A STUDY OF
PAN-TYPE COMPOUNDS AND RELATED PRECURSORS
^£D sr^^
Environmental Self ness Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ECOLOGICAL RESEARCH series. This series
describes research on the effects of pollution on humans, plant and animal
species, and materials Problems are assessed for their long- and short-term
influences. Investigations include formation, transport, and pathway studies to
determine the fate of pollutants and their effects This work provides the technical
basis for setting standards to minimize undesirable changes in living organisms
in the aquatic, terrestrial, and atmospheric environments.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/3-76-012
January 1976
THE STRUCTURE OF PAN-TYPE
COMPOUNDS AND RELATED PRECURSORS
by
Max Lustig and Irvine J. Solomon
IIT Research Institute
10 West 35th Street
Chicago, 111. 60616
Grant No. R802966-01
Project Officer
Dr. Philip L. Hanst
Atmospheric Chemistry and Physics Division
Environmental Sciences Research Laboratory
Research Triangle Park^ North Carolina 27711
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
ENVIRONMENTAL SCIENCES RESEARCH LABORATORY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
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DISCLAIMER
This report has been reviewed by the Environmental Sciences Research
Laboratory, U.S. Environmental Protection Agency, and approved for pub-
lication. Approval does not signify that the contents necessarily re-
flect the views and policies of the U.S. Environmental Protection Agency,
nor does mention of trade names or commercial products constitute
endorsement or recommendation for use.
ii
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CONTENTS
Page
List of Figures iv
List of Tables iv
I Background and Introduction 1
II Apparatus 2
III Synthesis and Purification of PAN 3
IV Decomposition of PAN 7
V Kinetic Study 8
VI Recommendations for Future Research 11
VII References 13
iii
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FIGURES
No. Page
1 Chromatogram of PAN 5
2 Thermal Decomposition of PAN at 28° 9
3 Thermal Decomposition of PAN at 28° 10
TABLES
No. Page
1 Correlation Coefficients 8
iv
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SECTION I
BACKGROUND AND INTRODUCTION
Peroxyacetyl nitrate, known by the acronym, PAN, is the
sole member of an unusual new and novel class of compounds
that have the proposed general formula RC(0)OON02 where R is
a alkyl or aryl group. PAN was first discovered as an air
pollutant1 in 1956, although at that time its chemical formula-
tion was not understood. It is the agent responsible for
eye irritation and extensive crop damage. Other hydrocarbon
members of this group were either discovered later in ambient
air2 or reported from synthetic mixtures. 3
Most of the work concerning these compounds was performed
using impure mixtures, for only in a few cases were these
compounds examined after being obtained initially in a pure
state. Even though PAN has been discovered about twenty years
ago, fundamental information about it is very scant and even
less is known about its congeners.
The research performed under the present grant indicates
that acylated compounds present in ambient air are sufficient
for the formation of PAN-type compounds. Also, the decompo-
sition of PAN is more complex than reported previously because
hydrocarbons and oxygen are formed in addition to the reported
products, methyl nitrate and carbon dioxide and varying
amounts of nitromethane.
PAN has been synthesized in high yield and in the quantities
required for characterization and testing. This compound has
been obtained in a very pure state using preparative g.l.c.
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SECTION II
APPARATUS
VACUUM AND PURIFICATION APPARATUS
A vacuum apparatus and preparative gas chromatograph (with
a GOW MAC thermistor detector) were constructed specifically
for the manipulation and purification of PAN-type compounds.
The chromatograph and vacuum system are interconnected so
that the PAN compounds can be passed from one part of the
system to the other with minimum manipulation. Vacuum stop-
cocks coated with KEL-F grease were used throughout the system.
Pressures were measured using calibrated Wallace & Tiernan
and Acco gauges. Reactors were fabricated from Pyrex.
Plexiglass shielding was placed between the apparatus and
the operators.
THE A-H6 MERCURY-ARGON SOURCE
Because of a number of factors, chief among them being
economical operation, the Illumination Industries 1000-watt
A-H6 lamp is employed as an ultraviolet source. Another
factor that prompts its use is the high ratio of ultraviolet
to total (radiant) energy.
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SECTION III
SYNTHESIS AND PURIFICATION OF PAN
SYNTHESIS
Although there are five reported synthetic methods for
PANs,l most are the more intellectual curiosities than
realistic synthetic routes to these compounds, and there
were no procedures that would conveniently produce the
quantities of pure PAN required for this research. However,
two previously reported methods were selected for scale-up.
The first was based on a report by C. S. Tuesday2 involving
the "dark" reaction between acetaldehyde and nitrogen pentoxide
in the presence of trace amounts of oxygen.
trace 02
CHsCHO + N205 > CH3C(0)OON02 (1)
The reactant concentration in this case was in the ppm range.
But on scale-up to the pph (parts per hundred) range, an
entirely different reaction took place, i.e.,
CH3CHO + N205 -»• CH3CH(ON02)2. (2)
When this g_em-dinitrate was first detected, there was some
question concerning its identity. Was it some sort of PAN-
type compound? Was this compound important in air pollution
chemistry? After an examination of the nature of this compound
as well as its trifluoromethyl congener and the conditions
required for the formation of compounds of this type, it was
concluded that compounds of this type are not likely to be
present in contaminated air. A manuscript regarding these
compounds has been accepted for publication in the Journal
or Organic Chemistry, (see Section VII).
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Upon concluding that this synthesis was not leading to PAN
compounds on increasing the reactant concentrations , the
photolysis of biacetyl in the presence of NO and oxygen was
X
then explored. This procedure was scaled-up by increasing
the reactant concentrations to the several torr pressure range.
In a typical reaction, biacetyl (1-1/2 torr) and N02 (4 torr)
were loaded into a three-liter Pyrex bulb (7 in. diameter)
and then oxygen was introduced. The partial pressure of the
latter was 600 torr. The bulb was floated on an ice bath
and cold water from the bath was flowed over the top of the
bulb so that it was completely covered with cold water.
The temperature of the bulb during photolysis never exceeded
3°C. The UV photo source was in Illumination Industries A-H6
lamp described above, and the irradiation period was 150 minutes.
The distance between the lamp and the bottom of the reaction
bulb was 14 inches. Over 5 mi of the gas (equivalent at STP)
was produced from this run. The yield was in excess of 80%.
The results suggest the reaction,
02
CH3C(0)C(0)CH3 + N02 — > CH3C(0)OON02. (3)
This process bares some similarities to that reported by
Hanst3 because the intermediate specie in both cases is probably
CH3C(0)-. On further reaction the acylperoxy radical is formed
and the terminating step involving N02 yields PAN.
PURIFICATION
The crude PAN was first purified by vacuum line fractionation.
It was passed slowly through traps set at -80 and -196°. The
PAN along with unreacted biacetyl was retained in the former,
and methyl nitrate, carbon dioxide and the excess nitrogen
dioxide were held in the latter. This procedure was followed
by a gas chromatographic purification. The column used was
a 5-ft, 1/4-in. O.D. Pyrex tube containing a Fluoropak 80
support with a KEL-F grease (10%) stationary phase. The
4
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VO
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chromatograph is shown below in Figure 1. The shape of the
curve labelled "PAN" is influenced by its presence in the
inlet system as a liquid. The cooling effect of sweeping
it out in a helium stream is probably the reason why its
topology differs from the usual curves.
PROPERTIES
The average gas density molecular weight of PAN was found to
be 128 g/GMV (calculated: 121) and its melting point is
-48.5 + 0.5°. Its vapor pressures were measured between 0.20
and 55.6°.at the higher temperature decomposition was observed.
In this temperature range, the vapor pressure of PAN obeys
the relationship log p/torr) = -1991/T + 8.161. Its extra-
polated boiling point is 103.9° and its equilibrium vapor
pressure at 24.25° is 28.7 torr. Its latent heat of
vaporization is 9.111 kcal/mole and its entropy of vaporiza-
tion is 24.2 e.u. calculated from the vapor pressure equation.
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SECTION IV
DECOMPOSITION OF PAN
PAN at ca. 10 torr pressure was allowed to decompose in
several different Pyrex containers as well as in a Pyrex
infrared cell containing sodium chloride windows. The Pyrex
containers contained either Teflon stopclocks or glass stopcocks
coated with KEL-F grease. It was found that the nature of
decomposition did depend somewhat on the container and its
prior history. However, the products (in order to decreasing
abundance) were found to be C02) CH3ON02, CH3N02, 02, CHi,, c2H6
and smaller amounts of unidentified substances. The total
carbon nitrogen and oxygen are well in balance. Interestingly,
no N02 was found. The products were identified by their
infrared and/or mass spectra. These studies are continuing
in order to more clearly elucidate the decomposition of PAN.
This data as well as the kinetic data below must be regarded
as preliminary, and therefore any conclusions drawn are tenta-
tive.
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SECTION V
KINETIC STUDY
The kinetics of decomposition were measured by the method
used by P. Hanst for the decomposition of dimethylperoxide.4
The infrared cell was charged with PAN at an initial pressure
of 10.47 torr and the cell was kept at a 28 + 0.5° temperature
and monitored periodically.
The kinetic data plotted as f(p) (the pressure of PAN) vs time
is found in Figure 2. Zero and first-order kinetics
deviate more from linearity than do second- and third-order,
The latter two are nearly linear and are about equally close
(Figure 3). The results are not surprising because the
number and kinds of products indicate the decomposition of
PAN is complex and probably involved more than one process
(see below for speculative discussion). The correlation
coefficients also corroborate that the plots for second- and
third-order relationships closely describe the kinetics of
decomposition of PAN under the conditions to which it was
subjected (see Table 1). A second-order rate constant,
k = 2.33 x ICT1* torr"1 min~l, is calculated from the least
squares straight-line parameters.
Table 1
CORRELATION COEFFICIENTS
(r)
0th
1st
2nd
3rd
order :
order :
order :
order :
r| = 0.
r| = 0.
r| = 0.
r = 0.
93943
978255
997862
997061
2 order specific rate constant = 2.33 x 10~4 torr 1 min l
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Thermal Decomposition of PAN at 28°
Zero
Order
0 100 200 300 400 500 600 700
TIME, minutes
Figure 2. Thermal decomposition of PAN at 28°.
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Thermal Decomposition of PAN at 28°
f(p)
100 200 300 400 500 600 700
Time (min.)
Figure 3
10
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SECTION VI
RECOMMENDATIONS FOR FUTURE RESEARCH
The kinetic results indicate that there is probably more
than one mode for the decomposition of PAN and that the
resultant order (3 < x < 2) is the sum of the different rate
controlling reactions. It was previously reported that the
decomposition of PAN in dilute mixtures produces only carbon
dioxide and methyl nitrate by a cyclic intermediate and variable
amounts of nitromethane.3
0
il
CH3 0
t | > CH3ON02 + C02 (4)
0 0
ii
0
Under conditions of the experiments used in the present research
the decomposition is more complicated. The above mechanism
may indeed occur, but the results can also be interpreted in
terms of another scheme which more comprehensively explains
the products.
CH3COON02 -> CH3C . +N03- (5)
CH3• + C02 -NO, + 0
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CH3. + N03- -»• CH3ON02 (6a)
CH3- + 0 + N02 -> CH3ON02 (6b)
CH3- + N02 + CH3N02 (6c)
CH3.
CH3. H > CH4 (6e)
It is likely that the 0-0 single bond is the weakest bond in
the molecule, so that the initiation step is the fission of
the peroxide band. In CH3OOCH3, this bond energy is only
^a. 35 kcal/mole. This bond energy is likely to be less in
the case of PAN. Most simple unimolecular decompositions
(A -> B + C) follow the second-order rate law, although,
acccording to the Lindemann theory, it is entirely possible
for such reactions to be first-order. This is the case for
the decomposition of CH
In order to more clearly understand the mechanism of the
decomposition of PAN, i 70 labelling studies need to be made.
NMR, infrared, Raman, EPR, and mass spectral techniques can
be used to characterize the products and, therefore, it is
likely that a determination can be made of the modes of
decomposition.
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SECTION VII
REFERENCES
1. Stephens, E.R., Adv. In Environ. Sci. 1, 110 (1969).
2. Tuesday, C.S., The Atmospheric Photo-oxidation of Trans-
butene-2 and Nitric Oxide In: Chemical Reactions in the
Lower and Upper Atmosphere, Interscience, New York, N.Y.
1961. p. 15."
3. Gay, B., Noonan, R., Bufalini, J., and Hanst, P.L.,
private communication, 1975.
4. Hanst, P. L., and Calvert, J. G., J. Phys. Chem., 63, 104
(1959).
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TECHNICAL REPORT DATA
(Please read fmtntctions on the reverse before completing)
1. REPORT NO.
EPA-600/3-76-012
2.
3. RECIPIENT'S ACCESSI ON-NO.
4. TITLE AND SUBTITLE
A STUDY OF PAN-TYPE COMPOUNDS AND RELATED PRECURSORS
5. REPORT DATE
January 1976
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
I. J. Solomon & M. Lustig
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
IIT Research Institute
10 West 35th Street
Chicago, Illinois 60616
10. PROGRAM ELEMENT NO.
1A1008
11. CONTRACT/GRANT NO.
R 802966-01
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Sciences Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final Report
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This work was undertaken to search for preparative procedures for PAN, to study its
structure and properties, and to ellucidate more clearly the nature of its formation
and decomposition. An ideal preparative procedure for PAN had been found, high
yields of PAN have been obtained, and a statisfactory preparative g.l.c. technique
has been adapted for its purification. The results of the synthetic studies tend
to confirm prior conclusions, but the decomposition of PAN does not proceed
entirely the way previously described.
The results from this research indicate that the acyl and acylperoxy radicals are
precursors to PAN in photochemical environments containing acyl derivatives, NO >
and oxygen. In contrast to prior investigations, however, several decomposition
products of PAN have been found that were not previously reported, that is, hydro-
carbons and oxygen have been found as products in the present study. Additional
characterization data has been obtained that corroborate the structure established
for PAN.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COS ATI Field/Gioup
Air pollution Photolysis*
Smog
Peroxy organic compounds*
Oxidizers
Ozone
Chemical reactions*
Photochemical reactions*
13B
04B
07C
11G
07B
07D
J1ZE_
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