J. Phys. Chem. 1986,90, 4637-4640 surface capacity factor (total number of catalyst sites divided by the number of gas-phase molecules in reactor) period of external forcing volume correction term
20
7
9
Subscripts
F rs
feed relaxed steady state
species 1 species 2 species 3 species 4 species v
4637
CO
oxygen (molecular if gas phase, atomic if surface) C3H6 C02
vacant
Registry No. CO, 630-08-0; C3H6, 115-07-1; Pt, 7440-06-4.
Hg-Sensitized Photolysis of Diethylamine in the Absence and Presence of 0, or N,Ot George DeStefano and Julian Heicklen* Department of Chemistry and Center for Air Environment Studies, The Pennsylvania State University, University Park, Pennsylvania 16802 (Received: September 6, 1985)
The Hg-sensitized photolysis of diethylamine (DEA) was studied in the absence and presence of O2or N 2 0 at rwm temperature. In the absence of foreign gases, the products were H2. CH3CH=NCzH5, and N,N’-diethylbutane-2,3-diamine(111), with respective quantum yields of 1.0, 1.0, and -0.02. Thus CH3CHNHC2H5radicals are produced exclusively and they are removed by self reaction: 2CH3CHNHC2H5 DEA + CH3CH=NC2H5 (4a) and 2CH3CHNHC2H5 diamine 111 (4b), with k4a/k4b= 47.0 5.6. In the presence of O2 the radicals are scavenged exclusively by abstraction of the H atom on the nitrogen to give the imine CH3CH=NC2H5 as the exclusive product: CH3cHNHC2H5+ O2 CH3CH=NC2H5 + H 0 2 (5). The Hg-sensitized photolysis of N 2 0 gives O(’P) atoms, which in the presence of DEA react to give the imine and (C2H5)2NOH(DEHA) as products in concerted parallel steps: O(3P) (C2H5)zNH CH3CH=NCzH5 HzO (9a) and O(3P) (C2H5)zNH (C2H5),NOH (9b), with k9a/k9b 9.5 i 1.7.
-
*
+
-
Introduction In general, amines do not have a very high ambient air concentration. However, Pitts and his co-worker~l-~ have shown that the formation of alkyl-substituted nitrosamines and nitramines from the corresponding alkyl-substituted amino radicals is a fairly efficient process under simulated atmospheric conditions. Where the amine concentrations are small, nitrosamines and nitramines will be unimportant. However, carcinogenic N-nitrosamines have been detected in air at or near several industrial plant^.^ The health hazards of nitrosamines and nitramines cannot be underestimated. Diethylnitrosamine, (C2H5),NN0, is a potent c a r c i n ~ g e n . ~ - Dimethylnitramine, ’~ (CH3)2NN02,shows carcinogenic activity in animals.I3 The carcinogenicity of diethylnitramine, (CzH5),NN02, is unknown at the present time. There has been some previous work done on the photooxidation of diethylamine in the presence of NO, and H20.1-3914The main carbon-containing products were C H 3 C H 0 and (C2HS)2NN02. (CzH5)2NN0was formed in the dark, but it was destroyed by photolysis. Due to the observance of both C H 3 C H 0 and (CzH & N N 0 2 as products, the abstraction of H atoms from nitrogen and from the secondary carbon must occur. It has been previously suggested that H-atom abstraction by HO from the N-H bond is competitive with H-atom abstraction from the secondary C-H bond in secondary amines.15 Our study was undertaken in order to examine the oxidation of (C2H&NH, DEA, in the absence of oxides of nitrogen. We hoped to be able to determine the fate of the radicals formed upon H-atom abstraction from either the nitrogen or the secondary carbon. Allan and SwanI6 found that the ultraviolet photolysis of diethylamine vapor in a quartz reaction vessel gave as initial products mainly N-but-2-enylideneethylamine(I) with smaller amounts of 1,3-diethyl-2,4,5-trimethylimidazolidine(II), N,N’-diethylbutane-2,3-diamine (III), and tetraethylhydrazine (IV). Product I was believed to have come from the dimer of CH3CH=NC2HS, which would have been an unstable precursor in their system. Products 111 and IV would be primary and could come from the dimerization of CH3CHNHC2H5and (C2H5)2Nradicals, re‘CAES Report No. 753-85.
-
-
+
I
-
-
+
r,:
CH3CH-N CH3CH- N CHCH3
I
I1 C%-CH-NHC2Hs
I
Cb-CH-NHC2Hs
I11 (C2H6 )2NN(C2&)2
IV spectively. Product I1 was thought to be secondary and arise from the reaction of CH3CH=NCzH5 with 111. The reaction of O(3P) atoms with several amines (though not diethylamine) was studied by Atkinson and Pitts” who suggested that the reaction could proceed by addition to form an amine oxide (1) Pitts, J. N., Jr.; Grosjean, D.; van Cauwenberghe, K.; Schmid, J. P.; Fitz, D. R. Environ. Sci. Technol. 1978, 12, 946. (2) Tuazon, E. C.; Winer, A. M.; Graham, R. A.; Schmid, J. P.; Pitts, J.
N., Jr. Environ. Sci. Technol. 1978, 12, 954. (3) Pitts, J. N., Jr. Philos. Trans. R . SOC.London, A 1979, 290, 551. (4) Herrold, K. McD. Cancer 1964, 17, 114. (5) Hoffman, F.; Graffi, A. Arch. Geschwulsrforsch. 1964, 23, 274. (6) Mohr, U.; Althoff, J.; Anthaler, A. Cancer Res. 1966, 26, 2349. (7) Druckrey, D.; Preussmann, R.; Ivankovic, S.; Schmahl, D.; Afkham, J.; Blum, G.; Mennel, H. D.; Muller, M.; Petropoulos, P.; Schneider, H. Krebsforschung 1967, 69, 103. (8) Montesano, R.; Saffiotti, U. Cancer Res. 1968, 28, 2197. (9) Greenblatt, M.; Rijhsinghani, K. J . Nut. Cancer, Inst. 1969, 42, 421. (10) Mohr, U.; Althoff, J.; Emminger, A.; Bresch, H.; Spielhoff, R. Z. Krebsforsch. 1972, 78, 13. (1 1) Feron, V. J.; Emmelot, P.; Vossenaar, T. Eur. J . Cancer 1972,8,445. (12) Graw, J. J.; Berg, H.; Schmahl, D. J . Natl. Cancer Inst. 1974.53, 589. (13) Goodall, C. M.; Kennedy, T. H.Cancer Lett. 1976, I , 295. (14) Hanst, P. L.; Spence, J. W.; Miller, S. M. Enuiron. Sci. Technol. 1977, 1I , 403. (15) Atkinson, R.; Perry, R. A,; Pitts, J. N., Jr. J . Chem. Phys. 1978, 68, 1850. (16) Allan, L. T.; Swan, G. A. J . Chem. Soc. 1965, 4822. (17) Atkinson, R.; Pitts, J. N., Jr. J . Chem. Phys. 1978, 68, 911.
0022-3654/86/2090-4637$01.50/00 1986 American Chemical Society
4638
The Journal of Physical Chemistry, Vol. 90, No. 19, 1986
DeStefano and Heicklen
TABLE 111: Effect of Diethylamine Pressure on the Hg-Photosensitized Decomposition of Diethylamine"
+
[ ( C Z H A N H I , Torr 20 50 70 100
0.74' 0.91 0.90 0.95
@{imine)
@(diamine)
@{imine) @{diamine)
0.95 1.04 1.18
0.023 0.018 0.019 0.024
0.97 1.06 1.20 I .20
1.18
@{imine)/ @{diamine) 41.3 57.7 47.4 41.7 av = 47.0 f 5.6
QIrradiation time = 20.0 min; I, = 16.6 mTorr/min. bAverage of values in Table I
followed either by decomposition or by rearrangement to the hydroxylamine. More experimental evidence was provided for this by Slagle et a1.18 who studied the reactions of 0 atoms with a number of amines including DEA. Their data indicated that the initially formed excited amine oxide could rearrange to excited diethylhydroxylamine which decomposes to imine H 2 0 or R2N OH.
+
TABLE IV: Effect of O2 Pressure on the Hg-Photosensitized Decomposition of Diethylamineo [O,], Torr @(imine) [O,], Torr @{imine1 2.0 8.2
+
Experimental Section The Hg-sensitized photolyses were performed at room temperature in a 3.08-L spherical quartz reaction cell which contained 3 or 4 drops of triply distilled mercury (Bethlehem Instrument Apparatus Co., Inc.). The cell was attached to a conventional vacuum line and kept grease-free by the use of Teflon stopcocks with FETFE or Viton "0"rings. Irradiation was from a low-pressure Conrad-Hanovia Hg lamp, Model No. 21400-013, which emitted 1847- and 2537-A radiation. The 1849-A line was removed by the air between the lamp and reaction cell. After irradiation, the gases noncondensable at -196 "C (N, and/or H2) were measured with a McLeod gauge. The condensable products were altered by freezing. Thus to measure them it was necessary to take a 6-mL aliquot portion of the reaction mixture for direct gas chromatographic analysis on a HewlettPackard 401 B programmable gas chromatograph using flame in. glass column was packed ionization detection. The 6 ft X with 25% SE-30 (polydimethylsiloxane) on 80/100 mesh Supelcoport (Supelco Co.). The column temperature was increased 4 OC/min from 35 to 185 OC. The carrier gas flow rate was 25 mL/min. Identification of the products CH3CH=NC2H5, (C2H&NOH (DEHA), and the diamine (111) was made by gas chromatography-mass spectrometry for identical gas-chromatographic conditions described above for the Hewlett-Packard system. Actinometry was performed by the Hg-sensitized photolysis of 20-500 Torr of N 2 0 in the presence of -2 Torr of C3Hs to scavenge the O(3P) atoms produced. For this system the quantum yield of N 2 was l.O.I9 Diethylamine (DEA) was obtained from Fluka Chemical Corp. a t a reported purity of 99.8%. This was confirmed by gas chromatography-mass spectrometry, where the only impurity found was triethylamine. The DEA was used as received, without further purification. N-Ethylideneethanamine (CH3CH=NHC2H5) was prepared as described by TiollaiszOby the dropwise addition at 0 OC of 99% acetaldehyde (Aldrich Chemical Co.) to ethylamine (Fluka) which previously had been vacuum distilled from -63 to -94 OC. The CH,CH=NHC,H5 was purified by fractionation with the middle fraction being collected. It was then analyzed by gas chromatography and quadruople mass spectrometry to measure the purity of sample, which was found to be -85% pure with the major contaminant being ethylamine. N,N'-Diethylbutane-2,3-diamine (111) and the tetraethylhydrazine IV were prepared by the methods described by Smith and Swan.*' After distillation, purity was determined by gas (18) Slagle, I. R.; Dudich, J. F.; Gutman, D. J . Phys. Chem. 1979, 83, 3065. (19) Cventanovic, R. J.; Falconer, W. G.; Jennings, K. R. J . Chem. Phys. 1961, 35, 1225. (20) Tiollais, R . BuN. SOC.Chim. 1947, 14, 708. (21) Smith, G.; Swan, G. A. J . Chem. SOC.1962, 886.
1.10 0.97
15.3 20.2
0.67 0.32
a [(C,H&NH] = 20.4 f 0.2 Torr; irradiation time = 20.0 min; I , = 16.3 mTorr/min.
TABLE VI: Effect of N20Pressure on the Hg-Photosensitized Decomposition of N 2 0 in the Presence of Diethylamine" "1, 19 216 229 400
@{imine1+
+
@"
Torr
@{imine)/
@{HJ @{imine/ @.IDEHAJ @(DEHAI @{DEHA] 0.82 0.92 0.00 0.92 0.94 0.98 0.92
1.02 1.03 1.10
0.09 0.08 0.1 1
1.11 1.11 1.21
13.3 12.9 10.0
a [(C,H,),NH] = 20.4 f 0.6 Torr; irradiation time = 20.0 min; I, = 16.5 mTorr/min.
chromatography and quadrupole mass spectrometry. No extraneous peaks were observed. The N 2 0 and 0,were supplied by Matheson Gas Products. Before use the N,O was degassed at -196 "C. The O2was used without further purification. Authentic samples of anhydrous DEHA and 99% C H 3 C H 0 were obtained, respectively, from the Pennwalt Corp. and the Aldrich Chemical Co. They were used to obtain gas-chromatographic retention times and sensitivities.
Results and Discussion Identification of Products. The products of the reaction, except H2, which was assumed to be the gas noncondensable at -196 OC in the Hg-sensitized photolysis of DEA, were identified by gaschromatographic retention times and mass spectrometry. The mass spectra of authentic samples of the imine CH3CH=NC2HS, the diamine 111, and (C2H5)zNOH(DEHA) are given in Table I along with mass spectra of the products of the reaction (see paragraph at end of text regarding supplementary material). Good mass spectral matches were found for all three compounds, and their gas-chromatographic retention times agreed exactly with those of authentic samples. Hg-Sensitized Photolysis of DEA. The Hg-sensitized photolysis of DEA produced H,, the imine CH3CH=NC2H5, and the diamine 111. There was no evidence for tetraethylhydrazine IV, its quantum yield being less than 0.01. The quantum yields were independent of irradiation time, indicating that all three products are primary. This is shown in Table I1 (supplementary material). As shown in Table 111, the quantum yields are also independent of pressure, within the scatter of the data, except for @(H2)which is lower at 20 Torr of DEA than at higher pressures. Since the only compound found with higher molecular weight than DEA was the diamine 111, all abstractions of H atoms must occur from the a-carbon position in DEA. Thus the mechanism is Hg + hv Hg* (1) Hg*
--
+ (C2H5),NH
Hg
+
+ H + CH3CHNHCzH,
H + (C2H5)2NH H2 + CH3CHNHC2H5 2CH,CHNHC2H5 (C,H,)*NH + CH,CH=NC2H5 diamine 111
(2) (3)
(4a) (4b)
The Journal of Physical Chemistry, Vol. 90, No. 19, 1986 4639
Hg-Sensitized Photolysis of Diethylamine
TABLE VII: Effect of Total Pressure on the Hg-Phootsensitized Decomposition of N20 in the Presence of Diethylamine" total press., W21, [(CZHS)ZNHI, [NzOI/ @"I + @.(imine) + @{DEHA) @.(DEHA} Torr Torr @{Hz] @.(imine} Torr [(CZH,),NH] 93 200 295 495
91 210 310 519
23 20 20 22
4 10 15 23
1.oo 1.03 0.98 1.11
0.92 0.95 0.91 0.92
0.088 0.10 0.09 0.10
@.(imine)/ @{DEHA} 11.4 10.3 10.4 11.1
1.09 1.13 1.07 1.21
"Irradiation time = 20.0 min; I, = 16.5 mTorr/min
TABLE VIII: Effect of Diethylamine Pressure on the Hg-Photosensitized Decomposition of N20in the Presence of Diethylamine"
a
I(C,H&NHl, Torr
@IN21+ @IHzl
1.08 2.10 5.00
1.oo 1.10 1.09
[N,O] = 509
@.(imine)+
+{DEHA}
@{imine] 0.64 0.83 0.95
@.(imine)/
@{DEHA}
@.(DEHA}
0.73 0.95 1.04
0.09 0.12 0.10
7.1 6.9 9.5
* 3 Torr; irradiation time = 20.0 min; I, = 20.2 mTorr/min.
where Hg* represents the excited 3P,state of Hg. This mechanism predicts that
@(H2)= 1.0 @(imine}+ @{diamine}= 1.0
(b)
= k4J k4b @{imine)/@{diamine}
(c)
(a)
From 50 to 100 Torr of DEA pressure, @{H2} = 0.90-0.95, which, within the experimental uncertainty, is equal to 1.0. However, at 20 Torr of DEA, a'(H2]= 0.74 = 0.03 for irradiation times from 20 to 60 min, and even lower at 10-min irradiation. The reason for this is not clear. Possibly under these conditions, some of the H atoms are scavenged on the reaction vessel wall. The sum of @{imine)and @(diamine]is 1.0 to within the experimental uncertainty as required by eq b. The disproportionationambination ratio k,/ k4bis determined from eq c and it is 47.0 = 5.6. Hg-Photosensitized Oxidation of DEA. The effect of O2 additions on the Hg-sensitized photolysis of DEA is seen in Table IV. At low [02]/[DEA], @{imine]is the only product found condensable at -196 OC. Its quantum yield is 1.0. In particular tetraethylhydrazine IV, the diamine 111, DEHA, and C H 3 C H 0 are absent, their respective quantum yields being XO.01, XO.01,
