J . Phys. Chem. 1985,89, 33-38
33
ARTICLES Chemiluminescent Reactlons of Ozone with Dimethyl Sulfoxide and Dlmethyl Disulfide. Formatlon of Electronically Excited Sulfur Dioxide Robert J. Chskit and David A. Dixon* Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455 (Received: May 16, 1984; In Final Form: August 13, 1984) The spectra from the chemiluminescent reactions of ozone with dimethyl sulfoxide and dimethyl disulfide ((CH3S),) have been studied at low pressure in a beam-gas apparatus. The chemiluminescence emission for each reaction was monitored as a function of the ozone and fuel pressures over a total pressure range from 0.05 to 50 mtorr. In the reaction of ozone with dimethyl sulfoxide weak, unstructured emission was observed in the region from 280 to 500 nm. This emission was found to be congruent to that observed in the reactions of ozone with H2S, CH3SH, and CH3SCH3under similar conditions and was attributed to fluorescence from electronicallyexcited SO2. The reaction of ozone with (CH3S), also yielded broad-band fluorescence from SO2 as well as a vibrationally resolved SOzphosphorescence feature. Chemiluminescence from the HSO radical was observed to the red of 530 nm in the reaction of ozone with (CH3S)2. Mechanisms have been proposed for each reaction based on the character of the luminescence and the dependence of the emission on reactant pressure. Results are contrasted with previous work on other simple sulfides.
Introduction Ozone has been found to yield visible chemiluminescence (CL) upon reaction with a variety of gas-phase organic and inorganic compounds, such as olefins,' metal carbonyl^,^ silane: and sulfur c o m p o ~ n d s . ~There .~ has also been interest in the use of C L as a detection scheme for reduced sulfur compound^.^^^ Recently we presented vibrationally resolved chemiluminescence spectra from the reaction of ozone with methyl mercaptan at low pressure (lo0 mtorr) the reaction of ozone with H2S, CH3SH, and SO yield identical spectra in the same wavelength region.s The sum of these data indicates that electronically excited SO2is the C L producing species and that SO2* is formed in the reaction SO
+ O3
-
SO2 + O2
+ 106 kcal mol-'
(1)
a t moderate reactant pressures. In a subsequent study, we presented strong evidence suggesting that the reaction
H2S (CH3SH) + O3
-
SO2* + H 2 0 ( C H 3 0 H )
(2)
made a significant contribution to the production of CL from SO2 at very low pressures (x0.i mtorr1.9 A C L feature corresponding to emission from the HSO radical has also been identified in the reaction of ozone with H2Sl0and CH3SH." Chemiluminescence from HSO* is thought to arise from the reaction
HS
+ O3
-
HSO
+ O2 + 56 kcal mol-'
(3)
We report, here, the results of our experiments on the reactions of ozone (0,)with dimethyl sulfoxide ((CH3),SO) and dimethyl sulfide ((CH3S)2). Spectra are reported for each reaction which identify the emitters following previous studies. The dependences of the CL on added reactant pressure are reported as aids in the Present address: Cooperative Institute for Research in Environmental Sciences, Campus Box 449, University of Colorado/NOAA, Boulder, CO 80309. *Present address: Central Research and Development Dept., E.I. Dupont DeNemours and Company, Experimental Station, Bldg. E-328, Willmington, DE 19898. Camille and Henry Dreyfus Teacher-Scholar, 1978-1983.
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determination of the mechanism leading to formation of the emitter
Experimental Section As described previously,6 an effusive beam of ozone was injected into a pumped, large-volume chamber filled with a low pressure of the fuel. Pumping was accomplished by either a mechanical pump for pressures above 1 mtorr or an oil diffusion pump for pressures below 1 mtorr. Pressures (P)were measured with a Granville-Phillips Convectron gauge (PI 0.1 mtorr) or an ion gauge ( P I 1 mtorr). The Convectron gauge was calibrated against an MKS Baratron capacitance manometer for ozone pressures of 1 to 100 mtorr and was found to have a linear response that was within 25% of the Baratron reading. The ion gauge was calibrated against the Convectron gauge in the region between 0.1 and 1.O mtorr and was found to have a linear response within about 40% of the true (Baratron) pressure. The gas inlet lines were stainless steel. The flow rates were controlled by fine-control needle valves. Chemiluminescence generated in the chamber was viewed through a quartz window which was parallel to the effusive beam. A lens of radius 25 mm and focal length 30 cm was set one focal length from the entrance slit of a 0.75-m scanning monochromator. Two gratings with blaze angles of 300 and 500 nm were available (1) Bailey, P. S. "Ozonolysis in Organic Chemistry"; Academic Press: New York, 1982; Vol. 1. (2) Borders, R. A.; Birks, J. W. J . Phys. Chem., 1982, 86, 3295-3302. (3) Buntin, S.;Mitchell, A.; Dixon, D. to be submitted. (4) Glinski. R. J.: Dixon. D. A.: Mitchell. A.: Buntin. S.: Gole. J. L.. to be submitted ( 5 ) (a) Akimoto, H.; Finlayson, B. J.; Pitts, J. N., Jr. Chem. Phys. Lett. 1971, 12, 199-202. (b) Pitts, J. N., Jr.; Kummer, W. A.; Steer, R. P.; Finlayson, B. J. Adv. Chem. Ser. 1972, No. 113, 246-254. (c) Becker, K. H.; Inocencio, M. A,; Schurath, U. Znt. J . Chem. Kinet. 1975, Symp. I , 205-220. (d) Halstead, J. C.; Thrush, B. J. Proc. R.SOC.London, Ser. A 1966, 295, 380-398. (6) Glinski, R. J.; Sedarski, J. A,; Dixon, D. A. J. Phys. Chem. 1981,85, 2440-2443. (7) Kelly, T. J.; Gaffney, J. S.; Phillips, M. F.; Tanner, R. L. Anal. Chem. 1983,55, 135-138. (8) Nelson, J. K.; Getty, R. H.; Birks, J. W. Anal. Chem. 1983, 55, 1767-1770. (9) Glinski, R. J.; Sedarski, J. A.; Dixon, D. A. J. A m . Chem. SOC.1982, 104, 1126-1128. (10) Schurath, U.; Weber, M.;Becker, K. H. J . Chem. Phys. 1977, 67, 110-119. (11) Glinski, R. J. Ph.D. Thesis, University of Minnesota, 1983.
0 1985 American Chemical Society
Glinski and Dixon
The Journal of Physical Chemistry, Vol. 89, No. 1, 1985
34
I
I
I
I
I
I
I
0
0
c
1
i
I
I
1 I
I
MTORR
-
+
0
Y)
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0
c
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0
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I
(a 1
0 . 0
-
0
51
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mom
0
mo
0
-
0
.
(a)
0
m.m*'
1
I
500
450
I
400 NM
I
I
350
300
250
U 0
0.1
I I 0.4 0.5 P (DMSO) MTORR
0.2
0.3
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I
1
I
I 210
I
I
I 0.6
I
0.7
I
i
t 260
I 250
I
240
NM Figure 1. (a) Digital chemiluminescent spectrum taken with low resolution (- 10 nm) produced in the reaction of 6.0 mtorr of ozone and 0.3 mtorr of (CH@O. (b) Digital chemiluminescent spectrum near the blue origin (266 f 4 nm) produced in the reaction of 8.0 mtorr of ozone and 0.3 mtorr of (CH3)$30. Error bars are f one standard deviation in the number of counts.
when better blue or red efficiency was desired. Photons were detected with an EM1 9558QB. photomultiplier (PMT) cooled to 3 mtorr of ozone, is roughly linear. This approximate first-order dependence occurs when the higher ozone density allows CH3S to collide reactively with an ozone molecule before encounterin a wall, Le., k12[03]> k13[M’]. Hence, eq 14 reduces to describing first-order kinetics in ozone in the transition region. We now return to examine the low-pressure region of Figure 7a. The observation of CL intensity below 0.1 mtorr of ozone is significant and implies that a less complex channel forming SO2* may exist. This is because the mean free path is greater than 50 cm at pressures less than 0.1 mtorr which corresponds to a distance greater than the diameter of the reaction chamber. Therefore, any radical intermediate in a chain leading to SO2*will probably contact a wall before making another collision with a reactant molecule. Hence a less complex pathway forming SOz* than the set of reactions above is suggested to account for the emission below 0.1 mtorr in Figure 7a. A one- or two-step formation of SO radical, which can be expected to survive numerous collisions with the wall from previous work on the H2S-03 system,ll is suggested to account for the efficiency of production of luminescence at low pressure in Figure 7a by reaction l.25 (23) Martinez, R. I.; Herron, J. T. Int. J. Chem. Kinet. 1978,10,433-452. (24) Baulch, D. L.; Cox, R. A,; Crutzen, P. J.; Hampson, R. F. Jr.; Kerr, J. A.; Troe, J.; Watson, R. T. J . Phys. Chem. Ref. Data 1982, 1 1 , 321-496. Estimate based on k = 6.7 X for OH 0,. (25) The possibility of a single-collision mechanism producing SO2* also exists at very low pressures. The predominantly nonlinear ozone pressure dependence, however, shows that this will not be a dominant factor. The proposed single-collision reaction is
+
(CH&
-
+ 0,
SO2 + SO + C2H6+ 118 kcal mo1-l
where the disulfide linkage is abstracted by the 03.This complex reaction is unlikely because of the many bond rearrangements but does have the required exoergicity to account for the production of SO2*. We also note that SO is produced in the reaction and this could be a source for SO required for the short chain production of SO2*.
J . Phys. Chem. 1985, 89, 38-41
38
The HSO luminescence from the reaction of (CH& and O3 is now discussed. The emission from HSO is undoubtedly due to reaction 3, since the HSO* spectrum of Figure 5 is virtually identical with that of Schurath et al.,1° who have shown that HSO* is most likely formed by reaction 3. Our observation of HSO* in this reaction system implies rather interesting kinetics for formation of the HS radical. Involvement of the HS radical is also suggested by the ozone dependence of Figure 8b. The greater than first-order dependence of Figure 8b implies that a radical, highly reactive with the walls, is involved in competitive consecutive reactions leading to the emitter. The approximately first-order dependence on (CH3S)2pressure, shown in Figure 8a, implies that (CH3S), is not involved in a reaction with a highly reactive radical species to form the HS radical. Although the source of HS in the reaction of (CH,S), with ozone may not be clearly elucidated by these data, certain possibilities are implied. The observation of HSO emission at relatively low pressure, -10 mtorr total, suggests that HS is not formed through an involved chain of reactions of highly reactive intermediates. We suggest that HS is formed by a hydrogen transfer during the rearrangement of an energy-rich production of the highly exoergic reaction
-
CH3S + O3
CH3S0
+ O2 +
=56 kcal mol-’
(17)
The C H 3 S 0 product can be formed with as much as 56 kcal mol-’ and could undergo subsequent rearrangement as follows CH3SO* CHzO HS (18) +
+
Although there is no direct evidence, the forms of the pressure dependences support this assertion. The pronounced decline in intensity beyond the maxima of the pressure dependences observed in Figure 8, a and b, demonstrates that some intermediate is efficiently quenched by both reactants. Participation of the CH3S radical in the chain leading to HSO’ is also suggested by the greater than first-order behavior of the ozone pressure dependence, since CH3Swas also proposed as an intermediate leading to SO2* and was responsible for the second-order dependence on ozone as discussed above.
Summary In extending our work on the low-pressure ozonolysis of simple sulfides, we have observed chemiluminescence from electronically excited SOzin the reaction of ozone with dimethyl sulfoxide and dimethyl disulfide. We have proposed mechanisms for the formation of the emitter based on the spectra, pressure dependences, and results of previous work. We have also obtained a chemiluminescence spectrum of the HSO radical in the reaction of ozone with dimethyl disulfide, suggesting interesting kinetics for formation of this species. Acknowledgment. We acknowledge the Graduate School of the University of Minnesota for partial support of this research and the Cooperative Institute for Research in Environmental Sciences for the facilities used in preparing this manuscript. Registry NO.03,10028-15-6; (CHJ,SO, 67-68-5; (CHjS)2,624-92-0; S02, 7446-09-5; HSO, 62470-71-7.
Very Low Pressure Pyrolyds of Furan, 2-Methytfuran, and 2,5-Dimethylfuran. The Stability of the Furan Ring M. A. Grela, V. T. Amorebieta, and A. J. Colussi* Department of Chemistry, University of Mar Del Plata, 7600 Mar Del Plata, Argentina (Received: June 8, 1984)
Furan (F), 2-methylfuran (MF), and 2,5-dimethylfuran (DMF) decompose between 1050 and 1270 K by ring breakdown unimolecular reactions. Loss of carbon monoxide is either the exclusive process or a major one in the case of F and MF or DMF decompositions, respectively. A common mechanism involving skeletal isomerization of the furans via cyclopropenylcarbonyl intermediates competing with decomposition through stabilized biradicals is proposed. The analysis of kinetic data leads to similar overall activation parameters for the three furans.
Introduction Reliable information on the high-temperature behavior of heterocyclic compounds is sparsel-“ and almost nonexistent for the important class of fivemembered heteroaromatic ringss This fact contrasts with the widespread natural Occurrence of these species and the growing recognition of their role in several fields such as air pollution,6 petroleum refining, and coal liquefaction and gasification processes.’ Thus, in addition to the general interest in the possible decomposition modes of furan and its derivatives, basic data on the stabiity of the furan units present in coal structure may help to understand the phenomenon of increased coal reactivity after thermal treatment.* (1) Braslavsky, S.;Heicklen, J. Chem. Rev. 1977, 77, 473.
(2).Frey, H. M.;Walsh, R. ‘Gas Kinetics and Energy Transfer”; The Chemical Society: London, 1978; Vol. 3, p 1. (3) Robinson, P. J. “Reaction Kinetics”; The Chemical Society: London, 1975; VOI. 1, pp 146-9. (4) Robinson, P. J.; Holbrook, K. A. “Unimolecular Reactions”; Wiley: New York, 1972; p 214. ( 5 ) Klute, C. H.; Walters, W. P. J . Am. Chem. Sac. 1946, 68, 506. (6) Lee, J. H.; Tang, I. N. J . Chem. Phys. 1982, 77,4459. (7) Sickles, J. E.; Ripperton, L. A.; Eaton, W. C.; Wright, R. S.Environmental Protection Agency Publication: Washington, DC; EPA-600/778-029.
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In this paper we report a kinetic study of the thermal unimolecular decompositions of furan, 2-methylfuran, and 2,S-dimethylfuran under very low pressure conditions, reactions 1 and 2, which have not been hitherto inve~tigated.~
F. R=H MF. R=CH, Q ,R
-
CO
+
CH ,,
H$
+
C6H6
(2)
DMF, R=CH3
All species seem to open their rings to produce stabilized biradicals. Such biradicals, whose thermochemistry is at least compatible with estimates based on simple additivity rules,l0 finally convert into the observed products after undergoing plausible intramolecular H-atom transfers. The fact that D M F also gives carbon monoxide reveals concomitant rearrangement reactions proceeding at competitive rates through valence isomers of the ( 8 ) Haggin, J. Chem. Eng. News 1982, 60 (jlZ), 17.
0 1985 American Chemical Society
