chemical physics of discharges - Argonne National Laboratory
chemical physics of discharges - Argonne National Laboratory chemical physics of discharges - Argonne National Laboratory
~ tation 272 It is reasonable to expect that the same path is followed also in 1 the present case of discharge excitation. Since the rate of formation cf adduct 11 is independent of the concentration of maleic anhydride (experiments 2 and 4) it is concluded that the formation of the intermediate monoadduct is the rate-determining step. The same conclusion has been reached in the photochemical fcrmation of adduct I1 (3,4). Adduct I1 is not, however, the only product formed in the reaction; a considerably larger amount oi resinous material (tabulated as adduct "TyDe I") is also formed in all cases. This material arlses from a free radical reaction similar to the one giving. rise to adduct I in peroxide- ' initiated reactions. The chain length of these reactions is about 20 to ; 100, as mentioned earlier. On the other hand it has been shown that the quantum yield of adduct TI formed in photochemical reaction is about 0.1 (4). Since in the present experiments adduct IT is formed in amounts 4 about one quarter of the RInoUnt of "type I" adduct although about ten excited molecules, or charge-transfer complexes, are necessary to produce one molecule of TI, while one free radical will produce 20 to 100 ! molecules of T, it must be concluded that the great majority of active species in the liquid phase in contact with the discharge are excited molecules and not free radicals. Tn fact it can be estimated that 98% to 99% of the active species are excited molecules. The absence of free radicals as important reaction intermediates has also been deduced by product analysis in the microwave glow discharge of aromatics in helium, (11) In the photochemical reaction benzene forms an adduct I1 at a higher rate than the alkylbenzenes, which in turn react in relative rates indi- cative of steric hindrance. No such effect was observed in the present 1 work, as shorn by the power yields in the table. These yields are also 4 measures of the rate of formation of adduct I1 since roughly equal power levels of discharge were maintained in all cases. Comparison of runs 1 and 2 shows that formation of adduct I1 is fevored at fhe lower frequency with a correspondingly higher potential difference applied across the electrodes. Although the electric field strength between the dielectric surfaces is not necessarily proportional 4 to the externally measured potential difference (12), it appears that electrons of higher average energy favor the production of adduct 11, as evidenced by the fact that the rate of formation of I1 is higher in a helium than in a nitrogen atmosphere (runs 4 and 5). It is known that the average electron energy for equal field strength is quite larger in the former gas (13). Of cource the presence of organic vapors modifies the electron eneru distribution but it is reasonable to expect that 4 some difference still exists. "he mechanism of energy transfer cannot be deduced with certiihty f'rom the present data. ComDarison of yields at two temperatures (runs 2 and 3) shows higher yield at the higher temperature, a fact which may' be interpreted as meaning that benzene vapors in the dircharqe are excited by collision with electrons: at the higher temperature the conced tration of benzene in the gas phare is higher. While this conclusion may be correct it is not unambiguous because of mechanical difficultie~ at the lower temperature, arising from the fact that adduct 11 was sparingly soluble in benzene at this temperature and quickly coated the dielectric surfaces where it was partly decomposed. Another way of excf< would involve bombardment of the liquid phase with electrons generated in the discharge. This method of excitation has been shown to ' prevail in the discharge-Induced oxidation of acidified water and ferrou) 4 d I '
273 ion (1L.). Zxcitei-ion by collision with excited nitrcpr. or helium cannot be an inportant 3rocess, cmsi+eri~~ tiiet the first excited state of 'neliixn contoins 19.81 EV of enert7y (15). Tollision with siich a species ~0~~1.' result in cxicnsivf f'rapentation of pn or,-anic rnoleclrlo, vrhereas the preseyt results point to the fact that free radical initiation is ;.cry li lite6 it: this sgsten. Table I. Cordcnseticn of maleic anhydride with ben;-ene nnd slkylben7enes under tne influence of silent t lectric discharie. Clar e, Trequ. Potent.Tgmn.Adduct, rms Yie d of I1 g.p. .briber fas Kc/s* c KV C. Type 1 mmo:e/kw-hr C. 1 250 TII benz. l?.O 26.5; a) 15.6 i2 .s: MA, N2 3.6 17.0 74 14.5 2.77 26.2 5 380 ml benz. 17 F TU, I!€ 3.6 13.0 75 15.1 11.16 33.3 355-57 6 390 ml tolu. 13 g XA, ?e 3.6 13.0 '32 30.0 11.79 30.4 245-60 7 168 ml -tbz. 29 . w, N;2 3.6 13.0 121 25.1 7.35 36.0 260-61 3 LlC ml cme. 7- 29 g X', 12 3 .6 13.0 1?7 23.0 5.18 29.8 255-57 T ~ product F was brown. i.bbreviations: HA, benz, tolu, etbz, cume denote correspondingly maleic R~I hy c? r i de , b en zene , t olu en e, ethyl h en z ene and cumsne. References. 1. b4.G. Bickford, ".S. Fisher, Y.:!. Dcllear an? C-.E. Swift, J.Am.011 . Chern.Soc. w, 251 2. 3.Y. Beavers to Rohm and. IIaas Coy 1J.S. Patent 2,692,270 (1954) 3. T). Pryce-Smith and, b.. Gilbert, J.Chem.Soc. 1965, 918 4. G.S. 3amond and l,'.:!. !lardham, ?roc.Shexn.Son963, 63 5. D. Bryce-Snith 2nd J.Y. Lod.ye, J.Chcm.Soc. xm67.5 6. ' 2. Grovehstein, Jr, q.V. Rao and J.W. Taylor, J.Am.Chem.Soc. a, 1705 (196.1) 7. O.n. Schenck and R. Steinmetz, Tetr.Letters,.lo 21, 1 (1960) 8. H.J.F. Ants and 9. Bryce-smith, J.Chem.Soc. 4791 9. D. ?ryce-Smith, 1. 'lilbert- an?< €3. Vickery, Chznd - 1962, 2060; British Patent 986,348 (1965) 10. Z. Raciszevski, Chem.In?. s, 418 11. A. Streitwieser, Jr, an& H.R. ':ard, J.Am.Chem.Soc. 539 (1963) 12. il. Rartnikas and J.Y.E. Levi, Rev.Sci.Instr. 2, 12%*(1966) 13. L.E. Loeb, "3asic 9rocesses of "rase.ous Electronics", University of California Press (1961) 1L. .I. Yokohatp an? S. Tsuda, Sull.Chem'.Scc.Japan, 3, 46, 1640 (1966) 15. L.B. Loeb, "Xectric:,l Coronas", Tlniversity of California Press (1965)
- Page 221 and 222: 7 h \ F 221 600°C and 1 atmosphere
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- Page 225 and 226: R L ' -1 9mm O.D. 5mm I.D. 45mm 0.D
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- Page 241 and 242: 241 Discussion The systematic varia
- Page 243 and 244: I \ 1 243 FORMATION OF HYDROCARBONS
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- Page 275 and 276: Apparatus and Procedure 275 EXPERIM
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- Page 289 and 290: DISCUSSION 289 The salient features
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- Page 301 and 302: - ;i Y . 15. Pressure lOmm 5 > 10-
- Page 303 and 304: 302 the best and in many practical
- Page 305 and 306: GENERATION AND MEASUREMENT OF AUDIO
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- Page 318 and 319: 317 i Cuencb svsten w.nnar;itus use
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273<br />
ion (1L.). Zxcitei-ion by collision with excited nitrcpr. or helium cannot<br />
be an inportant 3rocess, cmsi+eri~~ tiiet the first excited state <strong>of</strong><br />
'neliixn contoins 19.81 EV <strong>of</strong> enert7y (15). Tollision with siich a species<br />
~0~~1.' result in cxicnsivf f'rapentation <strong>of</strong> pn or,-anic rnoleclrlo, vrhereas<br />
the preseyt results point to the fact that free radical initiation is<br />
;.cry li lite6 it: this sgsten.<br />
Table I. Cordcnseticn <strong>of</strong> maleic anhydride with ben;-ene nnd slkylben7enes<br />
under tne influence <strong>of</strong> silent t lectric discharie.<br />
Clar e, Trequ. Potent.Tgmn.Adduct, rms Yie d <strong>of</strong> I1 g.p.<br />
.briber fas Kc/s* c KV C. Type 1 mmo:e/kw-hr C.<br />
1 250 TII benz.<br />
l?.O<br />
26.5;<br />
a) 15.6<br />
i2 .s: MA, N2 3.6 17.0 74 14.5 2.77 26.2<br />
5 380 ml benz.<br />
17 F TU, I!€ 3.6 13.0 75 15.1 11.16 33.3 355-57<br />
6 390 ml tolu.<br />
13 g XA, ?e 3.6 13.0 '32 30.0 11.79 30.4 245-60<br />
7 168 ml -tbz.<br />
29 . w, N;2 3.6 13.0 121 25.1 7.35 36.0 260-61<br />
3 LlC ml cme.<br />
7-<br />
29 g X', 12 3 .6 13.0 1?7 23.0 5.18 29.8 255-57<br />
T ~ product F was brown.<br />
i.bbreviations: HA, benz, tolu, etbz, cume denote correspondingly maleic<br />
R~I hy c? r i de , b en zene , t olu en e, ethyl h en z ene and cumsne.<br />
References.<br />
1. b4.G. Bickford, ".S. Fisher, Y.:!. Dcllear an? C-.E. Swift, J.Am.011<br />
. Chern.Soc. w, 251<br />
2. 3.Y. Beavers to Rohm and. IIaas Coy 1J.S. Patent 2,692,270 (1954)<br />
3. T). Pryce-Smith and, b.. Gilbert, J.Chem.Soc. 1965, 918<br />
4. G.S. 3amond and l,'.:!. !lardham, ?roc.Shexn.Son963, 63<br />
5. D. Bryce-Snith 2nd J.Y. Lod.ye, J.Chcm.Soc. xm67.5<br />
6. ' 2. Grovehstein, Jr, q.V. Rao and J.W. Taylor, J.Am.Chem.Soc. a,<br />
1705 (196.1)<br />
7. O.n. Schenck and R. Steinmetz, Tetr.Letters,.lo 21, 1 (1960)<br />
8. H.J.F. Ants and 9. Bryce-smith, J.Chem.Soc. 4791<br />
9. D. ?ryce-Smith, 1. 'lilbert- an?< €3. Vickery, Chznd - 1962, 2060;<br />
British Patent 986,348 (1965)<br />
10. Z. Raciszevski, Chem.In?. s, 418<br />
11. A. Streitwieser, Jr, an& H.R. ':ard, J.Am.Chem.Soc. 539 (1963)<br />
12. il. Rartnikas and J.Y.E. Levi, Rev.Sci.Instr. 2, 12%*(1966)<br />
13. L.E. Loeb, "3asic 9rocesses <strong>of</strong> "rase.ous Electronics", University<br />
<strong>of</strong> California Press (1961)<br />
1L. .I. Yokohatp an? S. Tsuda, Sull.Chem'.Scc.Japan, 3, 46, 1640 (1966)<br />
15. L.B. Loeb, "Xectric:,l Coronas", Tlniversity <strong>of</strong> California Press<br />
(1965)
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