Study of Photolytic Oxidation and Chlorination Reactions of Dimethyl Ether and Chlorine in Ambient Air G.J. Kallos" and J. C. Tou Analytical Laboratories, The Dow Chemical Co., Midland, Mich., 48640
Preliminary studies show that both dimethyl ether and bis(chloromethy1) ether (BCME) are unstable in the presence of chlorine and air under visible and near UV irradiation. The rates of reactions between chlorine and dimethyl ether are dependent on the relative chlorine/dimethyl ether concentrations. The evidence is consistent with a reaction mechanism dependent upon several consecutive chlorine atom sensitized photooxidations. Parts per billion levels of BCME possibly formed during the reactions a t various concentrations of chlorine and dimethyl ether up to 300 ppm are determined, and the results are discussed. Bis(chloromethy1) ether (BCME), a carcinogen ( 1 , 2 ) , is most commonly found to be an impurity in chloromethyl methyl ether, a chloromethylating agent used in the manufacture of commercial ion-exchange resins. During the past few years, BCME has been the subject of many investigations concerning methods of analysis, its stability in the environment, and reactions by which it may be formed. Due to major concern of possible industrial exposure, many analytical techniques have been developed to determine or monitor BCME in air a t the parts per billion level. These techniques are high-resolution mass spectrometry ( 3 ) ,gas chromatography-mass spectrometry ( 4 ) , dual-column gas chromatography ( 5 ) ,gas chromatography-high-resolution mass spectrometry ( 6 ) ,and derivative gas chromatography (7,8). Formaldehyde and hydrogen chloride have been reported to react to form BCME when they coexist in moist air a t concentrations much higher than the threshold limit values (9, 10).Several reactions of formaldehyde and commonly used chloride salts investigated by Tou and Kallos (8,11)did not generate BCME a t a detection limit of low parts per trillion in the gas phase. Because of the concern for possible BCME formation in the environment and its impact on occupational health, the National Institute for Occupational Safety and Health (NIOSH) conducted a preliminary investigation in many industrial environments, and in some instances it was reported that low ppb of BCME might be present (12).As a result of these findings, NIOSH awarded a contract to Bendix Corp. (13) to survey many industrial environments for BCME. Another possible source of BCME was suspected to be from the reaction of dimethyl ether (DME) and chlorine in air. Several papers in the literature (14-1 7 )describe the photolytic synthesis of BCME in mixtures of DME and chlorine in the absence of air. Because of these findings, the question arises about its potential formation from these two components coexisting a t low levels in an industrial environment. Due to this concern and the impact on our industrial environment, a study was undertaken to investigate the possible formation of BCME in diluted gas mixtures of DME and chlorine under photolysis. The reaction under various experimental conditions was followed with a mass spectrometer, and BCME, possibly being generated from the reaction, was determined a t several reaction times with the gas chromatographic derivative technique ( 7 , 8 ) . Experimental Materials. Dimethyl ether and chlorine were obtained a t the Dow Chemical Co. Mass spectrometric analysis showed
that the dimethyl ether contained no detectable impurities. Purity of the chlorine was 99.9%. Sodium hydroxide and sodium methoxide were Baker analyzed reagents and obtained from the J. T. Baker Co., Phillipsburg, N.J. 2,4,6-Trichlorophenol was synthesized at the Dow Chemical Co. and recrystallized from hexane. Bis(chloromethy1) ether was obtained from K & K Laboratories. Methanol and hexane distilled in glass were obtained from Burdick and Jackson Laboratories, Muskegon, Mich. Apparatus and Procedure. The reaction apparatus used in this study is shown in Figure 1.The reactor was a 5-L-round Pyrex glass vessel with a standard ground glass joint in the center and three 18/9 ball joints provided with rubber septa. The joint in the center was used for connecting the dry air line to condition the reactor. The rubber septa of the three small ball joints were covered on the inside of the reactor with a Teflon sheet to minimize interaction with reactants or products. The joint ports were used for injecting chlorine, dimethyl ether, or BCME gas standards, connecting the 15-head silicone fiber probe (18)to the mass spectrometer, and for connecting the impingers containing the 2,4,6-trichlorophenate derivatizing reagent ( 7 ) .The impingers were connected t o a dry ice trap so that the correct flow of air could be adjusted through the reaction mixture with a needle valve and flow meter. An active charcoal tower was installed before the pump as an additional safety device. The reaction apparatus was thoroughly flushed with dry air for 2 h with the sunlamp on before the reaction. Approximately 20 glass beads were placed inside the reactor to accelerate the gas mixing. The light source was a GE 275-W sunlamp. The emission spectrum was obtained with a IL783 spectroradiometer system (International Light, Inc., Dexter Industrial Green, Newburyport, Mass. 01950) directed toward the light source. Figure 2 shows the comparison of the emission spectra in the chlorine absorption region from the sunlamp employed with and without the Pyrex reactor and the typical summer sun. In the preliminary study of the reactions of dimethyl ether with chlorine and the stability of BCME in chlorine, the reaction vessel was monitored with the hollow fiber probe (28) connected either to a cycloidal mass spectrometer or to a Varian-MAT CH4B mass spectrometer. The cycloidal mass spectrometer provided good sensitivity only with slow scanning (m/e 15-300 in 15 min). Although this mass spectrometer yielded valuable information about the decay of dimethyl
*olio# F8ber Probe Mais Spectrometer
-0
n I1
11
Flow Meter
Figure 1. Reaction apparatus
Volume 11, Number 12, November 1977 1101
ether during reactions and the stability of BCME under the experimental conditions, the faster scanning CH4B mass spectrometer was utilized for monitoring all ions (mle 12-140 4 s) to obtain more detail information about the reactions. The reaction was continuously monitored until completion. The chlorine concentration during the reaction was followed by a modified Mast Model 74-2 microcoulomb ozone sensor (Mast Development Co., 2212 East 12th Street, Davenport, Iowa 52803). The sensing of the chlorine in the sample was accomplished by the well-known oxidation-reduction reaction of chlorine with potassium iodide. The free iodine produced by the chlorine reaction reacted with the hydrogen that was generated by the polarization current a t the cathode. The polarization current was measured from a voltage drop across a 1-kQresistor, and the resulting signal was recorded. A 1-cc gas syringe was used to inject the sample or a chlorine standard into the analyzer. A syringe needle reacted quantitatively with low parts per million humidified chlorine, but this problem was overcome by passing DC-200 (a Dow Corning Silicone fluid) through the needle and drying it. Parts per million standards of chlorine were made in a 10-L saran bag containing air of the same humidity as was used in the reactions. A fresh standard of chlorine was prepared daily a t the desired level. In a typical preliminary investigation, the 5-L flask was flushed for approximately 2 h while the light source was left on. Then 100 FL of distilled water were injected and allowed to equilibrate for about 1h to provide a 84% relative humidity calculated a t 25 "C. A desired quantity of dimethyl ether was injected and allowed to equilibrate for a few minutes before introducing the chlorine. DME and Clz were monitored using the silicone hollow fiber probe mass spectrometer (18) and ozone analyzer, respectively. The photolysis reaction was started by removing the shutter in front of the sunlamp which had been turned on at least 5 min for warmup before exposing to the reaction vessel. All components permeating through the silicone hollow fiber probe were followed continuously with the on-line spectrometer. T o determine the level of BCME formation, a reaction was carried out as above for a predetermined time. Then the lamp was turned off, and the products were pulled through two impinger solutions containing the 2,4,6-trichlorophenate reagent and analyzed by the gas chromatographic derivative techniques ( 7 , 8 ) .Dry air was drawn through the reactor into the impingers for 40 min a t a rate of 0.35 L/min, assuring a t least 90% depletion of the sample from the reactor. The final temperature in the reactor was measured to be 40 "C after 1 h of irradiation. The gas chromatographic work was carried out on a Hewlett-Packard Model 5710 gas chromatograph equipped with a 63Ni electron capture detector. The separation was accomplished on a 6 ft X '14 in. glass column packed with 120/140 mesh textured GLC-100 glass beads coated with 0.1% OV-275. In the determination of the 2,4,6-trichlorophenoxymethyl methoxymethyl ether derivative, the column temperature was isothermal a t 130 "C, and the flow rate was 40 mL/min using Ar/CHd (955). The injection and detector temperatures were 200 and 300 "C, respectively. However, the column temperature was set a t 190 "C to determine the more specific derivative bis(2,4,6-trichlorophenoxymethyl) ether (8). BCME Stability Study. T o determine the stability of BCME in the presence of chlorine in the dark or under visible and UV irradiation, a high concentration of BCME vapor standard was made with N:! in a saran bag, and the appropriate amount was injected into the reaction vessel to give the equivalent of 5-11 ppm BCME (v/v). The silicone rubber hollow fiber probe-mass spectrometric technique (18) was used to follow equilibration and depletion of BCME by monitoring the intense ion peak a t m/e 79. 1102
Environmental Science & Technology
Results and Discussion Stability of DME and BCME in Chlorine. Investigations of the photolytic gross reactions of DME and chlorine and of BCME with chlorine in air were undertaken to gain some preliminary information. Figure 3 shows the plot of the intensities of the major ions detected with the on-line mass spectrometer and of the chlorine concentration during the photolytic reaction of 100 ppm dimethyl ether and 100 ppm Clz in dry air. The intensities of the two characteristic ions at mle = 45 and 46 from dimethyl ether showed an initial increase and then a leveling off attributed to the mixing process in the reactor. The intensities of the ions a t m/e 45 and 46 remaining constant clearly demonstrated that dimethyl ether and chlorine did not react under dark conditions. However, soon after the light was turned on, rapid decreases of the concentrations of dimethyl ether and of chlorine occurred and were accompanied by increase intensities of the other major ions a t m/e 18, 31,44, and 60.
w
n
/ I
7 1
A
300
320
340
360
380
400
420
440
Wduelengih In nm
Figure 2. Emission spectra A Sunlamp without reactor B. Sunlamp with reactor C Midland sun on June 18, 1975, at 12:30-2:00p.m. EDT
B 0 5 cc C12. LighT O f f
400
12w
2wo
2803 T m e . Seconds
3600
44W
5200
Flgure 3. Photolytic reaction of dimethyl ether (100 ppm) and chlorine (100 ppm) in dry air
Because of their constant relative intensity which is comparable to that of a known standard under similar conditions, the ions a t m/e 31 and 60 were assigned to methyl formate formed initially during the reaction. The ions a t mle 18 and 44 were assigned to H20 and CO2, respectively. The ion at rnle 22, a characteristic doubly charged ion due to CO,", was also observed but not plotted, and this evidence further supports the formation of COz. Ion peaks a t mle 46 and 45 monitored a t a later time in the reaction closely matched in relative intensities the identical ions for formic acid. Although common ions were monitored for both DME and formic acid, there was minimal interference due to the fact that DME had largely disappeared before the appearance of formic acid, as shown in Figure 3. Methyl formate, water, and CO2 were thus found to form immediately when the light was turned on. Associated with this were significant decreases in the concentrations of DME and chlorine. As the irradiation time increased, the methyl formate passed through a maximum and decreased with further formation of CO2, HzO, and production of some formic acid. With further irradiation the formic acid concentration passed through a maximum and then decreased to zero with carbon dioxide, water, and hydrogen chloride identified as the final decomposition products. The intensity of hydrogen chloride ion peak a t mle 36 was not strong enough to plot on the scale of Figure 3. Sensitivity to this compound at low parts per million is not good due to adsorption on surfaces. I t is also recognized that the silicone hollow fiber probe-mass spectrometer technique does have some limitations to polar or nonvolatile compounds. A similar reaction of 100 ppm DME and 100 ppm Clz in air containing 2.7% water did not appear to follow a different pattern when monitored with the mass spectrometer. However, the intensity of the ion a t m/e 18 was off scale which prevented us from obtaining any additional information concerning the water formation. Since all the other components were found to be the same and to behave in the same fashion, it is assumed that this reaction would follow the same mechanistic path. This point is clearly demonstrated in Figure 4. The significant feature in this illustration is the fact that the reaction could be stopped by turning off the light and then immediately continued as soon as the light was turned back on. The chlorine concentration dropped with irradiation time. This experiment demonstrated that the reaction could be successfully quenched when the light was turned off and that the products could be recovered for BCME analysis without any complicating dark reactions. Any possible BCME formed can be recovered without loss since this compound is relatively .a h i L gl-1 On
Of'
400
360 320
7
280
3
$
240
Q 20c 160
=
120 80 40 0
400
12W
2000
2800 3600 Time. Second9
4400
5200
60W
Figure 4. Quenching test of photolytic reaction of dimethyl ether (100 ppm) and chlorine (100 ppm) in humid air (2.7% H20)
stable in humid air (19).All available evidence suggests that the DME and chlorine photolytic reaction a t low concentrations in air is a chlorine-atom sensitized oxidation reaction. The following mechanism is proposed based on analogy with the photooxidation of methyl chloride (20) in the presence of chlorine. The chlorine photodissociates and the CH30CH2. radical is produced via hydrogen abstraction from the dimethyl ether. Clz
+ hu
+
2C1.
+ C1- CH30CH2 - + HCl CH30CH2 + 0 2 CH30CH202
CH3OCH3
+
*
*
+
The peroxy radical, CH30CH202 -,will decompose to give the CHBOCH~O. radical 2CH30CHzO2-
+
+0 2
2CH30CH20.
Thus, the radical CH30CH20- disappearance is analogous to that suggested for CH2C10- (20): CH3OCH20.
+ CH30CH20y
+
CH3OCHO
+ CH30CHzOzH-
or CH30CH20-
+0 2
+
CH30CHO
+ HOy
Then the Hoe. radical would be expected to form the hydroperoxide radical (21)as follows: HOy
+ CH30CH202.
+
0 2
+ CH30CHzOzH.
The unstable hydroperoxide would decompose possibly on the walls (22) of the vessel to give more methyl formate and water. Since methyl formate concentrations decrease with further irradiation, it is proposed that chlorine atoms are further reacting with the methyl formate by hydrogen atom abstraction to form the methoxycarbonyl radical (23):
+
+
CH3OCOH C1. CHsOCO. HCI The methoxy carbonyl radical is favored thermodynamically ( 2 4 ) to form C02 and methyl radicals. Two of the products reported (25) from the oxidation of methyl radicals are H2O and formaldehyde. Since some polar compounds may adsorb on surfaces a t low ppm levels and show low permeation through the hollow fiber, formaldehyde may not have been detected by the mass spectrometer. In the photooxidation of formaldehyde, Carruthers and Norish (26) found a significant amount of formic acid and water with some carbon monoxide and COZ. Small amounts of carbon monoxide would be difficult to identify by our low-resolution mass spectrometer since it is interfered with by nitrogen a t rnle 28. Finally, the gasphase photolysis of formic acid and C12 has been reported (27) to produce hydrogen chloride and carbon dioxide. The reaction of dimethyl ether and chlorine in a nitrogen atmosphere with irradiation provided a number of components that were different than those found in dry air and in humid air environment. Mass spectral data of this reaction showed fragment ions a t rnle 45,49 (lCl), and 79 (1Cl) that were attributed to chloromethyl methyl ether and BCME. The presence of a high concentration of BCME in this reaction system was also determined by the derivative gas chromatography technique, and this will be discussed later. Several other fragment ions a t mle 59,60,63 ( l c l ? ) , 65 (lCl), and 93 (2C1?) were also detected, but the identifications are rather difficult. I t is expected that this reaction proceeds through direct chlorination to form the above chlorinated species. As the irradiation time increased, this reaction provided some CO2, methyl formate, and water since low ppm concentration of oxygen was still present in the system, +
Volume 11, Number 12, November 1977
1103
Since DME and chlorine reacted quite readily in light, it was desirable to check the stability of BCME in chlorine in a similar manner. In separate experiments, BCME was stable with chlorine under dark conditions, but it decomposed quite rapidly under light irradiation. This is shown in Figure 5 , where the characteristic fragment ion a t mle 79 e
ClCH20=C112, from BCME was monitored continuously with the mass spectrometer to determine the BCME stability. Kinetic studies of the stability of BCME in humid air (28) have shown it to be stable ( t l / z > 20 h). In contrast, 11.2 ppm BCME with 200 ppm Clz in dry air and under irradiation as demonstrated in Figure 5 provided a half-life time of only 63 s. Similar effects were also found in humid air and in nitrogen atmosphere toward decomposition of BCME. In the nitrogen atmosphere, it would appear that direct chlorination of BCME might be predominant, and free radical coupling products might be formed. With the above experimental evidence, it is concluded that an oxidation process was involved in the photoreaction of DME and chlorine in the dry air and humid air atmosphere. Therefore, the gross generation of BCME from the reaction is not possible. However, the survival of trace amounts of BCME during the course of the reactions is determined by the rate of the possible direct chlorination and the rate of the reaction of BCME in the oxidative conditions. This, indeed, deserves further careful investigation. Investigation of Possible Trace Amounts of BCME Formation. Several reactions were run a t different ratios of chlorine and DME. The rate of this reaction was strongly
160
cI
r
D
1
1 0 c c ' i a f 2600upm BCME lOcc'rof28WpprnBCME 1 cc chlorine Light On
A 0 C.
D
dependent on the relative C121DME concentrations. This is shown in Figure 6 where the intensity of the ion peak a t mle 46 is plotted against time for four different relative concentrations. At the start of the reaction, the ion a t mle 46 is due to DME. As the irradiation time increased, the intensity of this ion decreased and subsequently passed through another peak that is attributed to formic acid formation and decomposition. For example, in the reaction of 300 ppm DME and 100 ppm chlorine, slightly more than one-half of the DME was reacted in 1h. However, in the reaction of 50 ppm DME and 150 ppm chlorine, essentially all the DME was reacted in less than 5 min. Therefore, many reactions were carried out. Since the reaction proceeds through many steps, it was necessary to check the possibility for BCME formation a t different durations of reaction. The possibility of any BCME forming a t the parts per billion level was checked by the gas chromatographic techniques since direct monitoring with the mass spectrometer did not provide adequate sensitivity. In all reactions, the gas chromatographic method (7) was desirable for the determination of BCME. The results are shown in Table I. All the data reported in Table I were obtained by analyzing the 2,4,6-trichlorophenoxymethyl methoxymethyl ether BCME derivative formed in the reaction of BCME with the derivative solution ( 7 ) .Several attempted analyses using the more specific bis(2,4,6-trichlorophenoxymethyl) ether BCME derivative (8) proved unsuccessful due to the saturation of the detector from some unidentified interferences. An attempt was also made to analyze products for BCME in the reaction of 300 ppm Cla and 100 ppm DME by the gas chromatography-mass spectrometric technique ( 4 ) . Severe interferences were encountered contributing to low sensitivity and nonspecificity. Due to the interferences encountered by the GC-MS techhique and the more specific derivative, analyzing the 2,4,6-trichlorophenoxymethylmethoxymethyl
Table 1. Analytical Results of BCME from Photolytic Reactions of Dimethyl Ether and Chlorine in Ambient Air
70
40 30
t;i
20
I
1 : b A ,
0
200
I
400
,
I
6W
I
I , , I 800 loo0 1200 Time. Seconds ,
I
1
I 1400
16W
1800
1 2wO
Figure 5. Photolytic stability of BCME (11.2 ppm) in chlorine (200ppm) dry air atmosphere
_-300E
.
Cl*
I P P W I iupml
5
d
I
120 50 50
~
100 100 150
300
CI, /
OME 3
6 3 6
ppm
(CW (DME)
Water, voi Yo
300 300 100
100 100 50
0.33 0.33 0.5
100 100 100 100 100 120 100 25
100 100 100 100 100
1.o
2.7 2.7 2.7 2.7 2.7 2.7
100 100
300
DME, ppm
50 50 50
50 lOOd
Tlme Minuter
Figure 6. Photolysis kinetics as function of relative concentrations of C12/DME in ambient air 1104
Detection
Concentration
60
6
Environmental Science & Technology
CIZ,
100
100 50 300 150 150 300 300 lOOd
1.o 1.o 1.o 1.0 0.83 1.0
2.0
1.4
2.7 2.7 1.4
3.0 3.0 3.0 3.0 6.0 6.0
2.7 2.7 2.7 2.7 2.7 2.7 2.7
1.0d
Od
Reaction time min
10 60 60
5 10
10 10
BCME. Ppb (v/v)
N D ~ ND ND 0.8c
20 0.9c
1imit.a
ppb (v/v)
0.6 0.6
1.1 0.5 1.o 0.9
0.7
10
1.3c ND ND ND ND ND
60
0.2c
10
ND ND 1.4c
0.2 0.5 0.2 1.4 1.5
30 60 60 60
60 10 60 7.5d
1.5c 1.5 x 103
1.0 1.o 1.o 3.6 0.8
a Variations in the detection limits are due to interferences and changes of instrument sensitivity. ND = not detected. Because of the possible interferences and limited specificity of the technique, these numbers represent maximum values of BCME concentration. The reaction was carried out in a pure nitrogen atmosphere.
ether BCME derivative was the only method available to us for determining BCME concentration for the described reactions. Because of the limited specificity of the technique as reported previously (8),the values of the BCME concentration reported in Table I are the maximum values. I t is interesting to note that 1.5 ppm (v/v) BCME was found to be generated during the reaction of 100 ppm DME and 100 ppm Clz in dry nitrogen. This was in agreement with our previous observation in monitoring this reaction with the mass spectrometer. Different humid environments did not appear to change the fate of this reaction. The detection limits for BCME were established from spiked samples a t low levels and corrected for the recovery efficiency. All data indicate that BCME with concentration greater than 2 ppb (v/v) cannot be formed from the photolytic reaction of DME in ambient air and Clz even a t concentrations of Cl2 much higher than the threshold limit value (TLV = 1 PPd. Acknowledgment
The authors thank W. Dilling and J. Evans for valuable discussions and F. Leavitt, H. Gill, L. Westover, and W. Crummett for their support and encouragement to complete this project.
Literature Cited (1) VanDuuren, B. L., Goldschmidt, B. M., Katz, C., Langseth, L., Mercado, G., Sivak, A., Arch. Enuiron. Health, 16,472 (1968). (2) Drew, R. T., Laskin, S., Kuschner, M., Nelson, N., ibid., 30, 61 (1975). (3) Collier, L., Enuiron. sci. Technol., 6,930 (1972). (4) Shadoff, L. A., Kallos, G. J., Woods, J. S.,Anal. Chem., 45,2341 (1973).
(5) Wilkins, R. L., Frankel, L. S., US.Patent 3,807,217 (1974). (6) Evans, R. P., Mathias, A., Mellor, N., Silvester, R., Williams, A. E., Anal. Chem., 47,821 (1975). (7) Solomon, R. A,, Kallos, G. J., ibid., p 955. (8) Tou, J. C., Kallos, G. J., ibid., 48,958 (1976). (9) Kallos, G. J., Solomon, R. A., Am. Ind. Hyg. Assoc. J., 34, 469 (1973). 110) Frankel. L. S.. McCallum. K. S.. Collier. L.. Enciron. Sci. Technol., 8,356 (1974). (11) Tou, J . C., Kallos, G. J., Am. Ind. H y.g-. Assoc. J , 35, 419 (1974). (12) Marceleno, T., Phillip, P. E., Bierbaum, J., American Industrial Hygiene Assoc. Conf., Miami, Fla., May 12-17, 1974. (13) Bendix Launch Support Div., Special Projects, “Bis(Ch1oromethyl) Ether Formation and Detection in Selected Work Environments”. NIOSH. Contract No. 210-75-0056. (14) Friedel,’C., Compt. Rend., 84,247 (1877). (15) Evans. L. R.. Nelipan. R. E.. Ind. E m . Chern.. 52.379 (1960). (16) Summers, L., C h e k Reu., 55,301 (1555). (17) Neunhoeffer, O., Schmidt, G., Chem. Tech. Berlin, 10, 103 (1958). (18) Westover, L. B., Tou, J. C., Mark, J. H., Anal. Chern., 46,568 (1974). (19) Tou, J . C., Kallos, G. J., ibid., p 1866. (20) Sanhueza. E., Heicklen, J., J . Phvs. Chem., 79. 7 (1975). (21) Hoare, D: E., Pearson, G. S.,”Aduan. Photochern., 3, 83 (1964). (22) Heicklen, J., ibid., 7,57 (1969). (23) Yee Quee, M. J., Thynne, J.C.T., Trans. Faraday Soc., 63 (7), 1656-64 (1967). (24) Thynne, J.C.T., ibid., 58,636 (1962). (25) Barnard, J. A,, Cohen, A,, ibid., 64 ( 2 ) , 296-404 (1968). (26) Carruthers, J. E., Norrish, R.G.W., J. Chem. SOC.,1936, p 1036. (27) Jensen, R. J., Pimentel, G. C., J . Phys. Chem., 71, 1803 (1967). (28) Tou, J. C., Kallos, G. J., Anal. Chern., 46, 1866 (1974).
Received f o r reuieu February 28,1977. Accepted June 20, 1977.
Photochemical Reactions Among Formaldehyde, Chlorine, and Nitrogen Dioxide in Air Philip L. Hansf‘ and Bruce W. Gay, Jr. Environmental Sciences Research Laboratory, Environmental Protection Agency, Research Triangle Park, N.C. 277 11
Cl2 Photochemical reactions among chlorine, nitrogen dioxide, and formaldehyde were studied, using parts-per-million concentrations in 1 atm of air. The reactant mixtures were irradiated by ultraviolet fluorescent lamps and simultaneously analyzed by the Fourier transform infrared technique by use of folded light paths up to 504 m. With an excess of NO2 over Clz, the reaction products included 0 3 , CO, “ 0 3 , N205, HCl, and nitryl chloride (ClN02). When chlorine exceeded NO*, the principal product was peroxy nitric acid (HOON02).Peroxy formyl nitrate, nitrous acid, and chlorine nitrate were not seen. The nitryl chloride was stable even with the ultraviolet lights on. The peroxy nitric acid disappeared from the cell with a half-life of about 10 min. Formyl radicals (HCO), unlike acetyl radicals, did not combine with 0 2 and NO2 by addition. HCO reacted with 0 2 to yield CO and H02. The H02 will then add to NO2 to yield HOON02. If NO is present, the H02 will prefer to react with it, oxidizing it to NO2. An earlier paper described a method of producing organic peroxy acyl nitrates through the reaction of chlorine, aldehydes, and nitrogen dioxide in air (1). Molecular chlorine was photodissociated into chlorine atoms:
+ hu
-
2c1
The C1 atoms abstracted hydrogen from the aldehyde: 0
0
I1
C1 + R-C-H
+
II
R-C
+ HC1
The resultant free radical then added 0 2 and NO2 in succession to yield the peroxy acyl nitrate: 0 R-C
II
0
II
+ 0, + R-C-0-0
0
II
R-C-0-0
0 + NO,
/I
+
R-C-0-0-NO,
These reactions produced the peroxy acyl nitrate cleanly and in high yield. Apparently, any desired member of the family could be produced, starting with the appropriate parent aldehyde. This type of reaction seemed to include the production of the smallest homolog of the family, peroxy formyl nitrate, which had been sought in laboratory studies for many years ( 2 ) . A spectrum attributed to peroxy formyl nitrate was published in our earlier paper. A puzzling aspect of that Volume 11, Number 12, November 1977
1105
