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The photolysis of NH3 in the presence of substituted acetylenes: A possible source of oligomers and HCN on Jupiter
ICARUS95, 54-59 (1992)
The Photolysis of NH 3 in the Presence of Substituted Acetylenes: A Possible Source of Oligomers and HCN on Jupiter JAMES P. FERR1S, RICHARD R. JACOBSON, AND JEAN CLAUDE GUILLEMIN Department of Chemistry, Rensselaer Polytechnic Institute, Troy, New York 12180-3590
Received May 29, 1990; revised May 23, 1991
H C N is formed and that acetonitrile (1) and acetaldazine (acetaldehyde ethylidenehydrazone) (2) are reaction intermediates. A yellow-brown solid, with a v a p o r p r e s s u r e less than 0.01 T o r r at 300 K and which differed f r o m the one p r o d u c e d by the direct photolysis of acetylene was also formed. It was p r o p o s e d that this material m a y be one of the c h r o m o p h o r e s o b s e r v e d on Jupiter. An a b b r e v i a t e d reaction scheme for H C N f o r m a t i o n is given in Eqs. (I)-(3). A complete reaction s c h e m e is given in Ferris and Ishikawa (1988).
Photolysis of NH 3 in the presence of propyne yields dimethylketazine (4) as the main product along with dimethylketimine, isopropylamine, and propioazine (7). Dimethylketazine and isopropylamine are the principal reaction products when the photolysis is performed at 198 K. The conversion to dimethylketazine is about 35 times greater at 198 K because it is not volatile and condenses on the wall of the photolysis cell out of the UV flux. Photolysis of dimethylketazine at 185 nm yields acetonitrile and small amounts of N-methyldimethylketimine (8). Photolysis of 8 gives acetonitrile. Photolysis of NH 3 in the presence of 2-butyne gives the cis and trans isomers of 2-butene as the principal products along with the corresponding azine (9). Photolysis of azine 9 yields acetonitrile and propionitrile. Photolysis of hydrazine in the presence of propyne yields acetonitrile and isopropylamine but no azines were detected as reaction products. Quantum yields and percentage conversion to products are reported. These studies show that acetyienic hydrocarbons formed by the photolysis of methane in the stratosphere of Jupiter may react with radicals formed by N H 3 photolysis to give nonvolatile yellow-brown polymers, diaikylazines, alkylnitriles, and eventually HCN. This scenario accounts for the observation of both HCN and chromophores on Jupiter. ~ 1992 Academic Press, Inc.
N H 3 h ~ H" + "NH 2 N H 2- + H" + C2H 2 CH3CN + C H 3 C H ~ N N ~ C H C H 1 2 (CH3CH~N)2
h~ CH3CN
HL) H C N
3 (2)
(3)
Since it is k n o w n that p r o p y n e (3) and possibly higher acetylenes are present in the a t m o s p h e r e of Jupiter (Kim et al. 1985; A t r e y a 1986), we u n d e r t o o k an investigation of the scope of this reaction to see if these acetylene derivatives m a y also contribute to the formation of H C N and c h r o m o p h o r e s .
INTRODUCTION The detection of H C N on Jupiter (Tokunaga e t al. 1981) p r o m p t e d speculation on the p a t h w a y s by which it is f o r m e d f r o m m e t h a n e and a m m o n i a . Lighting (Bar-Nun and Podolak 1984) thermal synthesis (Lewis and Fegley 1984), and photochemical routes (Ferris and Morimoto 1981) were postulated. The synthesis of H C N by the photolysis of N H 3 in the presence of C H 4 is inhibited by h y d r o g e n and other inert gases, a finding that suggests it is not a major source of H C N on Jupiter (Raulin et al. 1979, Ferris and M o r i m o t o 1981). A proposal for the f o r m a t i o n of H C N by the photolysis of N H 3 in the p r e s e n c e of acetylene ( K a y e and Strobel 1983) p r o m p t e d our experimental study of this s y s t e m (Ferris and I s h i k a w a 1987, 1988). It was o b s e r v e d that 0019-1035/92 $3.00 Copyright © 1992by AcademicPress, Inc. All rights of reproduction in any form reserved.
(1)
EXPERIMENTAL G e n e r a l p r o c e d u r e s . N M R spectra were determined in CDCl3 on a Varian XL-200 s p e c t r o m e t e r . Gas chromatography was carried out on a H e w l e t t - P a c k a r d 5890A gas c h r o m a t o g r a p h using a 30-m HP5 (5% phenyl methyl silicone) capillary column. The p r e s e n c e of m e t h a n e and ethane was established by F T - I R using a P e r k i n - E l m e r 1800. Materials. Ammonia (Linde, electronic grade, 99.999%) was degassed by three f r e e z e - p u m p - t h a w cycles and stored on a v a c u u m line. H y d r a z i n e was distilled under argon (bp l 13°C), degassed by three
54
OLIGOMERS AND HCN ON JUPITER
freeze-pump-thaw cycles, and stored on a vacuum line. Propyne (Pfaltz and Bauer, technical grade) and butyne (Pfaltz and Bauer, 98%) were degassed by three freeze-pump-thaw cycles and used directly. Isopropylamine, acetonitrile, and propionitrile were obtained from Aldrich.
Photochemistry. Most photolyses were performed using a low pressure mercury lamp with principal emissions at 184.9 and 253.7 nm. The flux at 184.9 nm was 3.58 × 10~5 quanta sec -~ (Keane 1990). Photolyses at 310 nm were carried out in a Rayonet Photochemical Reactor using 300-nm lamps and a Pyrex filter. Gas mixtures were prepared on a mercury-free vacuum line equipped with a MKS 270B signal conditioner and a 370HA sensor for pressure measurements. Photolyses were performed in 10 × 2.8-cm cylindrical quartz cells with a volume of about 50 cm 3. At the end of the photolyses a weighed sample of CDCI3 was added to the cell to dissolve the soluble reaction products and this was transferred to a 5mm NMR tube. The amount of CHC13 in the CDC13 used was measured by comparison of the area of the CHC13 peak with that of a known amount of CHECI2. The yields of the reaction products were determined relative to the area of the CHC13 signal. The identity of the reaction products was established by comparison of the ~H NMR spectra with those of authentic samples. Dimethylketazine. A modification of the procedure of Curtius and Zinkeisen (1898) was used. To a solution of 20 g (0.62 mol) of anhydrous hydrazine in 100 ml ofCH2C1z was slowly added 88 g (1.3 mol) of acetone and 40 g of 4-,A molecular sieves. The reaction mixture was stirred overnight, filtered, and the CHzCI2 was removed using a rotary evaporator. The product was distilled at reduced pressure to give 42 g (56%) of a colorless oil; ~H NMR (CDCI 3) 8 1.842 (s, 6H), 2.015 (s, 6H); UV ~m~x278 nm, e 2.65 cm- 1 atm- J. Methylethylketazine. To a solution of 5.0 g (0.16 mol) of anhydrous hydrazine in 50 ml of CHC13 was added 28 g (0.39 mol) of 2-butanone and 40 g of 4-,A molecular sieves. The reaction mixture was refluxed for 2 h, then stirred overnight at room temperature. The product was filtered and the CHCI 3 removed by rotary evaporation. Distillation at reduced pressure gave 13.4 g (61%) of a colorless oil; IH NMR (CDC1)3 (a mixture of three isomers) 8 0.95-1.18 (overlapping triplets, 6H); 1.78-2.00 (singlets, 6H); 2.22-2.36 (overlapping quartets, 4H). N-Methyldimethylketimine. This was prepared by a procedure in a patent (American Home Products, 1954). To 37 g (1.2 mol) of methylamine cooled to -80°C in a 250-ml round bottom flask was added 31 g (0.53 mol) of cooled acetone and 50 g of anhydrous K2CO3. The flask was stoppered, warmed slowly to room temperature, and allowed to stand for 5 days. The product was purified by
55
trap-to-trap distillation on a vacuum line until a fraction was obtained which was free of acetone and methylamine as evidenced by its NMR spectrum; JH NMR (CDCI3) 8 1.829 (q, 3H), 2.007 (q, 3H), 3.067 (br s, 3H); UV )~max239 nm, e = 3.88 cm- 1 atm- i.
Dimethylketimine, This was prepared from 2-cyano-2aminopropane by the procedure of Guillemin and Denis (1985); 1H NMR (CDCI 3) 8 2.026 (s, 6H), - 9 (br s, 1H). Reaction of N-methyldimethylketimine with N H 3 . A 50.8-ml quartz photolysis cell was filled with l0 Torr N-methyldimethylketimine and 400 Torr of ammonia. H NMR analysis showed a 25% conversion to dimethylketimine. Photolysis of the mixture for 42 min yielded a small amount of isopropylamine. Photolysis did not result in a significant increase in the amount of dimethylketimine formed. RESULTS AND DISCUSSION
The photolysis of ammonia (510 Torr) in the presence of propyne (5 Torr) was performed with 185-nm light. The reaction is initiated by ammonia photolysis since it is estimated from the extinction coefficients of propyne (60 cm-1 atm-~ at T = 273 K) (Nakayama and Watanabe 1964) and ammonia (87 cm-1 atm-~ at T = 298 K) (Ferris and Ishikawa 1988) that 99.3% of the 185-nm light is absorbed by NH3. Yellow-brown polymeric material and dimethylketazine (4), dimethylketimine (5), and isopropylamine (6) were observed as reaction products (Eqs. (4)-(10)). The polymeric material observed is formed by the same mechanism as the polymer formed by photolysis of acetylene and NH3 (Ferris and Ishikawa 1988) and it should have a similar structure but with pendant CH3 groups. The proposed pathway for the formation of these products is given in Eqs. (4)-(10). The first step is the addition of a hydrogen atom, formed in Eq. (1), to propyne with the formation of C H 3 C ~ C H 2 as the major and CH3CH--CH. as the minor adduct (Eq. (4)). Hydrogen atom addition to acetylene is the first step in the formation of 2 from acetylene (Fen-is and Ishikawa 1988). Addition of .NH 2 (Eq. (1)) to C H 3 C ~ C H 2 yields the vinylamine (Eq. (5)) which can isomerize photochemically or thermally to dimethylketimine (5) (Eq. (6)). Hydrogen atom abstraction from ketimine 5 (eq. (7)) yields a radical which rapidly dimerizes to dimethylketazine (4) (Eq. (8)) (Roberts and Winter 1979). Reduction of dimethylketimine (5) (Eq. (9)) or the corresponding vinylamine (Eq. (10)) yields isopropylamine (6) (Eq. (10)). H- + CH3C:zz---CH~ CH3C--CH 2 + CH3CH--CH3 CH3(~-~-CH2 + "NH2 ~ CH3C(NHz)--~--CH2
(4) (5)
56
FERRIS, JACOBSON, AND GUILLEM1N
CH3C(NH2)~CH 2 , h~, (CH3)2C~NH
(6)
(CH3)2C~NH + H" ~ (CH3)2C~---N' + H~
(7)
2(CH3)2C~N" ~ (CH3)~IC~NN~C(CH3) ~
(8)
(CH3)2C~---NH + 2H" ~ (CH3)2CHNH 2
(9)
CH3C(NH2)~CH 2 + 2H" ~ (CH3)2CHNH 2
(10)
Trace amounts of propioazine (7) were also detected. It is formed from CH3CH~---CH., the minor adduct of H. with CH3~---CH (Eq. (4)) by a route that is analogous to the formation of dimethylketazine (4) from CH3C~CH 2. The pathway is outlined in Eqs. (11)-(14). C H 3 C H ~ C H • + "NH2--~ C H 3 C H ~ C H N H 2 (11) CH3CH~__CHNH 2 h~~ CH3CH2CH~N H
(12)
CH3CH2CH~-NH + H" ~ CH3CH2CH~---N" + H~ (13) 2CH3CH2CH~N. CH3CH2CH~NN~CHCH2CH 3 (14) 7 The photolysis of ammonia in the presence of propyne was also performed at 198 K to assess the effect of temperature on the reaction. Dimethylketazine (4j and isopropylamine (6) were the principal products. No evidence was obtained for the presence of acetonitrile or HCN. The absence of acetonitrile suggests that azine 4 is the initial photoproduct. Since 4 condenses on the cell wall at 198 K, it is not photochemically converted to acetonitrile at this temperature, but photolysis to acetonitrile does occur at room temperature since the azine is present in the gas phase. The isopropylamine observed in these photolyses may be formed by a number of routes. It may result from hydrogen atom reduction of the enamine CH2~---CNH2
I
CH3 or the corresponding dimethylketimine (5) formed by addition of H. and "NH2 to propyne (Ferris and Ishikawa 1988). As shown in the present study ketimine 5 is also formed by the reaction of ketimine 8 with NH3. It is not clear why isopropylamine forms at 198 K while 5 is observed at 298 K. The percentage conversion and quantum yield for the formation of azine 4 is markedly higher at 198 than at 298 K (Table I). This observation suggests that 4 is formed efficiently from propyne and NH 3 as demonstrated by a quantum yield of 0.05 at 198 K. It condenses from the gas phase at this temperature and is shielded from further photolysis. Compound 4 remains in the gas phase at 298
K and is photolyzed to acetonitrile and other products. The quantum yield measured for the formation of 4 is for a series of photochemical and thermal reactions. The photolyses were performed in the presence of excess NH3 to simulate reaction conditions at the top of the NH3 clouds on Jupiter. Consequently, the bulk of the photons effect the photolysis of NH 3 to hydrazine, N2, and H2 and only a small portion of the radical intermediates combine with propyne to form 4, The quantum yields for the formation of methylamine and for isopropylamine or dimethylketimine are of the same orders of magnitude at 198 and 298 K. The UV absorption of dimethylketazine (4) extends from above 300 nm to below 200 nm so it would be expected to undergo further photolysis in Jupiter's atmosphere (Brinton and Chang 1968). It has been reported to undergo photolysis to acetonitrile and N-methyldimethylketimine (8) (Brinton and Chang 1968, Horne and Norrish 1970). The photochemistry of 4 was investigated in detail to determine if it was a source of the acetonitrile when NH3 was photolyzed in the presence of propyne. Irradiation of 7.8 Tort with a low pressure mercury lamp resulted in the formation of acetonitrile, ethane, and methane. There is a linear increase in acetonitrile with time of irradiation (Fig. 1). An 86% yield of acetonitrile is calculated after 30 min based on the unreacted 4 and the conversion of 1 eq. 4 to 2 eq. acetonitrile. The yield is corrected for the CH3NH 2 observed. It is assumed that the small amounts of 8 not converted to acetonitrile are hydrolyzed to CH3NH 2 by traces of water present in the CDC13 solvent used for IH NMR analysis. Photolysis of 7.8 Torr of 4 at about 310 nm resulted in the formation of acetonitrile and N-methyldimethylketimine (8) in a 1.3:1 ratio, respectively (Brinton and Chang 1968) (Fig. 2). A 79% conversion to 8 is calculated based on unreacted starting material and the assumption that the acetone observed is due to the hydrolysis of 4 by traces of moisture in the CDCI 3used for ~H NMR analysis. Ketimine 8 is photochemically stable when irradiated at 310 nm as expected from its lack of UV absorption at that wavelength (Brinton and Chang 1968). When compound 8 (7.0 Torr) is irradiated for 20 rain with a low pressure mercury lamp acetonitrile is formed in 80% yield (Fig. 3) (Eqs. (17) and (18)). The yield is based on unreacted starting material and the assumption that the CH3NH 2 present is due to the hydrolysis of unreacted 8 with moisture in the CDC13. From these data it is concluded that dimethylketazine is a source of acetonitrile when NH 3 is photolyzed in the presence of propyne. The mechanism of the conversion of dimethylketazine (4) to acetonitrile is given in Eqs. (15)-(18). It is known that two imino radicals are formed by the photolysis of azines (Horne and Norrish 1970) (Eq. (15)). Dispropor-
57
OLIGOMERS AND HCN ON JUPITER TABLE I Percentage Conversion(%) and Quantum Yield(~) of Formation
(CH3)2C~NN--C(CH3)2 c CH3CN d CH3NH2 e (CH3)2CHNH2 e (CH3)2C~NH e
CH3~----~CH (20 Torr) N H 3 (400 Torr) ~ 298°C
C H 3 ~ - - ' C H 2 (5 Torr) N H 3 (50 Tort) a 198°C
CH3C--==CH (4 Torr) N2H4 (7 Tort) b 298°C
%
qb
%
%
0.4 Trace 0.5 -0.1
0.005 -0.006 -0.002
qb
15 0 0.8 2.2 --
0.05 0 0.003 0.007 --
qb
1.7 1.2 1.5
0.02 0.006 0.008
T w o h o u r s irradiation. b O n e h o u r irradiation. c A s s u m e s two C H 3 C H ~ C H 2 and two p h o t o n s gives one ( C H 3 ) E C H ~ N N ~ C H ( C H 3 ) 2 . d A s s u m e s one C H 3 C H - - C H 2 and two photons gives the product. c A s s u m e s one C H 3 C H - - C H 2 and one photon gives the product.
tionation of these radicals yields acetonitrile and 8 (Eq. (16)). If the photolysis is carded out at wavelengths where 8 absorbs light it is converted to acetonitrile (Eqs. (17) and (18)).
(CHa)2C~NN~C(CH3)2
hu ) (CH3)2C~___N. (15)
2(CHa)2C~N" ~ C H 3 C ~ N + (CH3)2C~NCH 3 (CH3)2C~NCH3
hv C H 3 C ~ N C H 3 + CH3.
(16) (17)
8
C H 3 C ~ N C H 3 --* C H 3 C ~ N
+
CH 3"
(18)
The photolysis of 510 Torr N H 3 in the presence of 5 Torr 2-butyne was investigated to see if ketazines and
acetonitdle were formed from disubstituted acetylenes. Polymeric material and the cis and trans isomers of 2butene were the major reaction products. In addition, IH NMR signals consistent with the presence ofmethylethylketazine (9) in the reaction mixture were detected. The photolysis of methylethylketazine (9) was investigated since there exists the possibility of forming either CHaCN or CH3CH2CN or a mixture of both nitriles as reaction products. The azine radicals formed in Eq. (19) can eliminate an ethyl radical to give acetonitrile (Eq. (20)) or a methyl radical to give propionitrile (Eq. (21)). Irradiation of 1.2 Torr 9 with a low pressure mercury lamp for 10-15 min resulted in a 70% conversion to CHaCN and a 22% conversion to CH3CHECN (based on unreacted starting material). No other photoproducts were detected
1.2
1.4 1.2"
== o
1.0o
o
ILl
0.8"
o a
0.6-
ta
0.4-
uJ
0.8'
w o ¢3
0.6
LU
0.4
0no.
=J
..I
X
1.0'
-
"
'
0=E
"
, •
N-Methyldimethylketimine
0.2
0.2"
0.0
0.0 0
1'0
2'0
3'0
40
P H O T O L Y S I S T I M E (mln)
FIG. 1. T h e p h o t o c h e m i c a l c o n v e r s i o n of 7.8 Ton" dimethylketazine (4) to acetonitrile and N - m e t h y l d i m e t h y l k e t i m i n e (8) using a low p r e s s u r e m e r c u r y lamp.
0
10
20
30
40
50
P H O T O L Y S I S TIME (h)
FIG. 2. The photochemical c o n v e r s i o n o f 7.8 Torr dimethylketazine (4) to acetonitrile and N - m e t h y l d i m e t h y l k e t i m i n e (8) using 310-nm light.
58
FERR1S, J A C O B S O N , A N D G U I L L E M I N
by ~H NMR analysis. From the CH3CN : CH3CH2CN ratio it is determined that the ethyl radical is formed about three times as fast as the methyl radical. This observation is consistent with the report that the quantum yield for photochemical cleavage of the ethyl group from methylethylketone is 2.4 times greater than cleavage of the methyl group (Calvert and Pitts 1966).
Condensed Phase (150 K)
\
/ C~NN-~-C
/ CH3
9
\
CH3
CH2CH 3
C~N'
(19) (CH3CH=N)2 -
CH 3
<147 nm
CH3C=-CH +NH 3
\
/
CH 4
Diffusion to NH3 Clouds
CH3CH 2 hv~ 2
Photolysis Wavelength
CH3C=-CH
Polymers
CH3CH2
Gas Phase
Polymers?
J
-
1
[(CH3)2C=N]2 1
CH3CH2 C~---N"
~ CH3C~N + CH3CH 2"
(20)
CH3CN
CH3CN
HCN
HCN
CH3 CH3CH2
\
C~N"
/
nm
215-310
nm
O= 1.05 a Yield_-- 80%
\ /
147-215 • N 0.05
~ CH3CH2C~N + CH 3"
(21)
CH3 Hydrazine, a photoproduct of NH3 (Noyes and Leighton 1966), may be present in trace amounts in the gas phase and in much greater amounts in the condensed phase on Jupiter. Photolysis of hydrazine (6.9 Torr) in the presence of propyne (4 Torr) gives a yellow-brown polymer along with acetonitrile, isopropylamine, and smaller amounts of hydrocarbons including ethane and possibly propane. The quantum efficiency of a CH3CN formation from propyne and hydrazine is within a factor of 3 of quantum yield for dimethylketazine (4) formation from propyne and ammonia (Table I). Since 4 is converted to CH3CN with a quantum yield of 1 (Brinton and Chang
1.4
1-21 ~- 1.0-
x
ua 0.8 o a 0 iT" 0 . 6 o~ Ill 0.40
=E 0.2"
0,0 0
'o
2'o
3'o
.o
PHOTOLYSIS TIME (mln)
FIG. 3. T h e photochemical c o n v e r s i o n of 7.0 T o r t N - m e t h y l d i m e t h ylketimine (8) to acetonitrile using a low pressure m e r c u r y lamp.
l"
NH 3 Photolysis, 150-215 nm, O=0.1 Yield ---100%
FIG. 4. Proposed p a t h w a y for the formation of H C N from CH3~H and N H 3 on Jupiter. Brinton and Chang, 1968, Q u a n t u m yield for CH3CN formation measured at 254 nm.
1968) then the quantum efficiency of CH3CN formation will be approximately the same by either route. Neither dimethylketazine (4) Nor N-methyldimethylketimine (8) was detected as a reaction product. Photolysis of 8 Torr hydrazine in the presence of 5 Torr of 2-butyne gave acetonitrile and propionitrile as reaction products. The mechanism of the propyne-hydrazine reaction must differ markedly from that of the propyne-NH 3 system since dimethylketazine was not observed. These data suggest the possibility of additional routes to acetonitrile and therefore HCN from acetylenic compounds on Jupiter (Fig. 4). Acetylenes are formed by photolysis of CH4 in the stratosphere. Convective mixing of the acetylenes with the radicals formed by photolysis of ammonia results in the formation of azines and yellowbrown polymers. Photolysis of the azines yields alkylnitriles which, in turn, are converted to HCN by reaction with hydrogen atoms. Propyne is the only substituted acetylene currently observed on Jupiter (Atreya 1986); however, higher molecular weight acetylenes may be present in small amounts. Hydrazine may be substituted for NH3 as a source of the nitrogen in the conversion of acetylenes to CH3CN. Photolysis of NH 3 gives hydrazine (Noyes and Leighton 1966) so it will be formed in the atmosphere of Jupiter. The vapor pressure of hydrazine is estimated to be i0 8 Torr (Atreya et al. 1977) at 150 K so that it will be condensed on the NH 3 ice. It remains to be determined whether CH3CN formation can be initiated by photolysis of solid hydrazine in the presence of propyne.
OLIGOMERS AND HCN ON JUPITER ACKNOWLEDGMENTS This research was funded by NASA Grant NAGW-476. J. C. Guillemin received a stipend from C.N.R.S. of France. REFERENCES American Home Products Corp., British Patent 702,985 1954. Chem. Abstr. 49, 5515. ATREYA, S. K. 1986. Atmospheres and Ionospheres o f the Outer Planets and Their Satellites, p. 9. Springer-Vedag, Berlin. ATREYA, S. K., A. M. DONAHUE, AND W. R. KUHN 1977. The distribution of ammonia and its photochemical products on Jupiter. Icarus 31, 348-355. BAR-NUN, A., AND M. PODOLAK 1984. The contribution of thunderstorms to the abundances of CO, C2H2, and HCN on Jupiter. Icarus 64, 112-124. BRINTON, R, K., AND S. CHANG 1968. The photolyses of dimethylketazine vapor, Ber. Bunsen-Ges. Phys. Chem. 72, 217-221. CALVERT, J. G., AND PITTS, J. N., JR. 1966. Photochemistry, Wiley, New York. CURTIUS, T., AND E. ZINKEISEN 1898. Die umlagerung von ketazinen und aldazinen der fettreihe in pyrazolinderivate. J. Prakt. Chem. 58, 325-332. FERRIS, J. P., AND Y. ISHIKAWA 1987. HCN and chromophore formation on Jupiter. Nature 326, 777-778. FERRIS, J. P., AND Y. ISHIKAWA 1988. Formation of HCN and acetylene oligomers by photolysis of ammonia in the presence of acetylene: Applications to the atmospheric chemistry of Jupiter. J. Am. Chem. Soc. 110, 4306-4312. FERRIS, J. P., AND J. MORIMOTO 1981. Irradiation ofNH3-CH 4 mixtures
59
as a model of photochemical processes in the Jovian planets and Titan. Icarus 48, 118-126. GUILLEMIN, J. C., AND J. M. DENIS 1985. Flash vacuum thermolysis of ~-aminonitrile and subsequent HCN removal on solid base, a "one line" multistep sequence to reactive N-methyleneamines. J. Chem. Soc. Chem. Commun., 951-952. HORNE, D, G., AND R. G. W. NORRISH 1970. The photolyses of acyclic azines and the electronic spectra of the R1R2CN. radicals. Proc. R. Soc. London A315. 301-322. KAYE, J. A., AND D. E. STROBEL 1983. HCN formation on Jupiter. The coupled photochemistry of ammonia and acetylene. Icarus 54, 417-433. KEANE, T. 1990. Unpublished results from this laboratory. KIM, S. J., J. CALDWELL, A. R. RIVOLO, R. WAGENER, AND G. S. ORTON 1985. Infrared polar brightness of Jupiter 3. Spectrometry from the Voyager 1 IRIS experiment. Icarus 64, 233-249. LEWIS, J. S., M. B. FEGLEY, JR 1984. Vertical distribution of disequilibrium species in Jupiter's atmosphere. Space Sci. Rev. 39, 163-192. NAKAYAMA, T., AND WATANABE, K. 1964. Adsorption and photoionization coefficients of acetylene, propyne, and 1-butyne. J. Chem. Phys. 40, 558-561. NOYES, W. A., AND P. A. LEIGHTON 1966. The Photochemistry o f Gases, pp. 379-382. Dover, New York. RAULIN, F,, A. BOSSARD, AND G. TOUPANCE 1979. Abundance of organic compounds photochemically produced in the atmospheres of the outer planets. Icarus 38, 358-366. ROBERTS, B. P., AND J. N. WINTER 1979. Electron spin resonance studies of radicals derived from organic azides. J. Chem. Soc. Perkin H, 1353-1361. TOKUNAGA, A. T., S. C. BECK, T. R. GEBALLE, J. H. LACEY, AND E. SERABYN 1981. The detection of HCN on Jupiter. Icarus 48, 283-289.
The Photolysis of NH 3 in the Presence of Substituted Acetylenes: A Possible Source of Oligomers and HCN on Jupiter JAMES P. FERR1S, RICHARD R. JACOBSON, AND JEAN CLAUDE GUILLEMIN Department of Chemistry, Rensselaer Polytechnic Institute, Troy, New York 12180-3590
Received May 29, 1990; revised May 23, 1991
H C N is formed and that acetonitrile (1) and acetaldazine (acetaldehyde ethylidenehydrazone) (2) are reaction intermediates. A yellow-brown solid, with a v a p o r p r e s s u r e less than 0.01 T o r r at 300 K and which differed f r o m the one p r o d u c e d by the direct photolysis of acetylene was also formed. It was p r o p o s e d that this material m a y be one of the c h r o m o p h o r e s o b s e r v e d on Jupiter. An a b b r e v i a t e d reaction scheme for H C N f o r m a t i o n is given in Eqs. (I)-(3). A complete reaction s c h e m e is given in Ferris and Ishikawa (1988).
Photolysis of NH 3 in the presence of propyne yields dimethylketazine (4) as the main product along with dimethylketimine, isopropylamine, and propioazine (7). Dimethylketazine and isopropylamine are the principal reaction products when the photolysis is performed at 198 K. The conversion to dimethylketazine is about 35 times greater at 198 K because it is not volatile and condenses on the wall of the photolysis cell out of the UV flux. Photolysis of dimethylketazine at 185 nm yields acetonitrile and small amounts of N-methyldimethylketimine (8). Photolysis of 8 gives acetonitrile. Photolysis of NH 3 in the presence of 2-butyne gives the cis and trans isomers of 2-butene as the principal products along with the corresponding azine (9). Photolysis of azine 9 yields acetonitrile and propionitrile. Photolysis of hydrazine in the presence of propyne yields acetonitrile and isopropylamine but no azines were detected as reaction products. Quantum yields and percentage conversion to products are reported. These studies show that acetyienic hydrocarbons formed by the photolysis of methane in the stratosphere of Jupiter may react with radicals formed by N H 3 photolysis to give nonvolatile yellow-brown polymers, diaikylazines, alkylnitriles, and eventually HCN. This scenario accounts for the observation of both HCN and chromophores on Jupiter. ~ 1992 Academic Press, Inc.
N H 3 h ~ H" + "NH 2 N H 2- + H" + C2H 2 CH3CN + C H 3 C H ~ N N ~ C H C H 1 2 (CH3CH~N)2
h~ CH3CN
HL) H C N
3 (2)
(3)
Since it is k n o w n that p r o p y n e (3) and possibly higher acetylenes are present in the a t m o s p h e r e of Jupiter (Kim et al. 1985; A t r e y a 1986), we u n d e r t o o k an investigation of the scope of this reaction to see if these acetylene derivatives m a y also contribute to the formation of H C N and c h r o m o p h o r e s .
INTRODUCTION The detection of H C N on Jupiter (Tokunaga e t al. 1981) p r o m p t e d speculation on the p a t h w a y s by which it is f o r m e d f r o m m e t h a n e and a m m o n i a . Lighting (Bar-Nun and Podolak 1984) thermal synthesis (Lewis and Fegley 1984), and photochemical routes (Ferris and Morimoto 1981) were postulated. The synthesis of H C N by the photolysis of N H 3 in the presence of C H 4 is inhibited by h y d r o g e n and other inert gases, a finding that suggests it is not a major source of H C N on Jupiter (Raulin et al. 1979, Ferris and M o r i m o t o 1981). A proposal for the f o r m a t i o n of H C N by the photolysis of N H 3 in the p r e s e n c e of acetylene ( K a y e and Strobel 1983) p r o m p t e d our experimental study of this s y s t e m (Ferris and I s h i k a w a 1987, 1988). It was o b s e r v e d that 0019-1035/92 $3.00 Copyright © 1992by AcademicPress, Inc. All rights of reproduction in any form reserved.
(1)
EXPERIMENTAL G e n e r a l p r o c e d u r e s . N M R spectra were determined in CDCl3 on a Varian XL-200 s p e c t r o m e t e r . Gas chromatography was carried out on a H e w l e t t - P a c k a r d 5890A gas c h r o m a t o g r a p h using a 30-m HP5 (5% phenyl methyl silicone) capillary column. The p r e s e n c e of m e t h a n e and ethane was established by F T - I R using a P e r k i n - E l m e r 1800. Materials. Ammonia (Linde, electronic grade, 99.999%) was degassed by three f r e e z e - p u m p - t h a w cycles and stored on a v a c u u m line. H y d r a z i n e was distilled under argon (bp l 13°C), degassed by three
54
OLIGOMERS AND HCN ON JUPITER
freeze-pump-thaw cycles, and stored on a vacuum line. Propyne (Pfaltz and Bauer, technical grade) and butyne (Pfaltz and Bauer, 98%) were degassed by three freeze-pump-thaw cycles and used directly. Isopropylamine, acetonitrile, and propionitrile were obtained from Aldrich.
Photochemistry. Most photolyses were performed using a low pressure mercury lamp with principal emissions at 184.9 and 253.7 nm. The flux at 184.9 nm was 3.58 × 10~5 quanta sec -~ (Keane 1990). Photolyses at 310 nm were carried out in a Rayonet Photochemical Reactor using 300-nm lamps and a Pyrex filter. Gas mixtures were prepared on a mercury-free vacuum line equipped with a MKS 270B signal conditioner and a 370HA sensor for pressure measurements. Photolyses were performed in 10 × 2.8-cm cylindrical quartz cells with a volume of about 50 cm 3. At the end of the photolyses a weighed sample of CDCI3 was added to the cell to dissolve the soluble reaction products and this was transferred to a 5mm NMR tube. The amount of CHC13 in the CDC13 used was measured by comparison of the area of the CHC13 peak with that of a known amount of CHECI2. The yields of the reaction products were determined relative to the area of the CHC13 signal. The identity of the reaction products was established by comparison of the ~H NMR spectra with those of authentic samples. Dimethylketazine. A modification of the procedure of Curtius and Zinkeisen (1898) was used. To a solution of 20 g (0.62 mol) of anhydrous hydrazine in 100 ml ofCH2C1z was slowly added 88 g (1.3 mol) of acetone and 40 g of 4-,A molecular sieves. The reaction mixture was stirred overnight, filtered, and the CHzCI2 was removed using a rotary evaporator. The product was distilled at reduced pressure to give 42 g (56%) of a colorless oil; ~H NMR (CDCI 3) 8 1.842 (s, 6H), 2.015 (s, 6H); UV ~m~x278 nm, e 2.65 cm- 1 atm- J. Methylethylketazine. To a solution of 5.0 g (0.16 mol) of anhydrous hydrazine in 50 ml of CHC13 was added 28 g (0.39 mol) of 2-butanone and 40 g of 4-,A molecular sieves. The reaction mixture was refluxed for 2 h, then stirred overnight at room temperature. The product was filtered and the CHCI 3 removed by rotary evaporation. Distillation at reduced pressure gave 13.4 g (61%) of a colorless oil; IH NMR (CDC1)3 (a mixture of three isomers) 8 0.95-1.18 (overlapping triplets, 6H); 1.78-2.00 (singlets, 6H); 2.22-2.36 (overlapping quartets, 4H). N-Methyldimethylketimine. This was prepared by a procedure in a patent (American Home Products, 1954). To 37 g (1.2 mol) of methylamine cooled to -80°C in a 250-ml round bottom flask was added 31 g (0.53 mol) of cooled acetone and 50 g of anhydrous K2CO3. The flask was stoppered, warmed slowly to room temperature, and allowed to stand for 5 days. The product was purified by
55
trap-to-trap distillation on a vacuum line until a fraction was obtained which was free of acetone and methylamine as evidenced by its NMR spectrum; JH NMR (CDCI3) 8 1.829 (q, 3H), 2.007 (q, 3H), 3.067 (br s, 3H); UV )~max239 nm, e = 3.88 cm- 1 atm- i.
Dimethylketimine, This was prepared from 2-cyano-2aminopropane by the procedure of Guillemin and Denis (1985); 1H NMR (CDCI 3) 8 2.026 (s, 6H), - 9 (br s, 1H). Reaction of N-methyldimethylketimine with N H 3 . A 50.8-ml quartz photolysis cell was filled with l0 Torr N-methyldimethylketimine and 400 Torr of ammonia. H NMR analysis showed a 25% conversion to dimethylketimine. Photolysis of the mixture for 42 min yielded a small amount of isopropylamine. Photolysis did not result in a significant increase in the amount of dimethylketimine formed. RESULTS AND DISCUSSION
The photolysis of ammonia (510 Torr) in the presence of propyne (5 Torr) was performed with 185-nm light. The reaction is initiated by ammonia photolysis since it is estimated from the extinction coefficients of propyne (60 cm-1 atm-~ at T = 273 K) (Nakayama and Watanabe 1964) and ammonia (87 cm-1 atm-~ at T = 298 K) (Ferris and Ishikawa 1988) that 99.3% of the 185-nm light is absorbed by NH3. Yellow-brown polymeric material and dimethylketazine (4), dimethylketimine (5), and isopropylamine (6) were observed as reaction products (Eqs. (4)-(10)). The polymeric material observed is formed by the same mechanism as the polymer formed by photolysis of acetylene and NH3 (Ferris and Ishikawa 1988) and it should have a similar structure but with pendant CH3 groups. The proposed pathway for the formation of these products is given in Eqs. (4)-(10). The first step is the addition of a hydrogen atom, formed in Eq. (1), to propyne with the formation of C H 3 C ~ C H 2 as the major and CH3CH--CH. as the minor adduct (Eq. (4)). Hydrogen atom addition to acetylene is the first step in the formation of 2 from acetylene (Fen-is and Ishikawa 1988). Addition of .NH 2 (Eq. (1)) to C H 3 C ~ C H 2 yields the vinylamine (Eq. (5)) which can isomerize photochemically or thermally to dimethylketimine (5) (Eq. (6)). Hydrogen atom abstraction from ketimine 5 (eq. (7)) yields a radical which rapidly dimerizes to dimethylketazine (4) (Eq. (8)) (Roberts and Winter 1979). Reduction of dimethylketimine (5) (Eq. (9)) or the corresponding vinylamine (Eq. (10)) yields isopropylamine (6) (Eq. (10)). H- + CH3C:zz---CH~ CH3C--CH 2 + CH3CH--CH3 CH3(~-~-CH2 + "NH2 ~ CH3C(NHz)--~--CH2
(4) (5)
56
FERRIS, JACOBSON, AND GUILLEM1N
CH3C(NH2)~CH 2 , h~, (CH3)2C~NH
(6)
(CH3)2C~NH + H" ~ (CH3)2C~---N' + H~
(7)
2(CH3)2C~N" ~ (CH3)~IC~NN~C(CH3) ~
(8)
(CH3)2C~---NH + 2H" ~ (CH3)2CHNH 2
(9)
CH3C(NH2)~CH 2 + 2H" ~ (CH3)2CHNH 2
(10)
Trace amounts of propioazine (7) were also detected. It is formed from CH3CH~---CH., the minor adduct of H. with CH3~---CH (Eq. (4)) by a route that is analogous to the formation of dimethylketazine (4) from CH3C~CH 2. The pathway is outlined in Eqs. (11)-(14). C H 3 C H ~ C H • + "NH2--~ C H 3 C H ~ C H N H 2 (11) CH3CH~__CHNH 2 h~~ CH3CH2CH~N H
(12)
CH3CH2CH~-NH + H" ~ CH3CH2CH~---N" + H~ (13) 2CH3CH2CH~N. CH3CH2CH~NN~CHCH2CH 3 (14) 7 The photolysis of ammonia in the presence of propyne was also performed at 198 K to assess the effect of temperature on the reaction. Dimethylketazine (4j and isopropylamine (6) were the principal products. No evidence was obtained for the presence of acetonitrile or HCN. The absence of acetonitrile suggests that azine 4 is the initial photoproduct. Since 4 condenses on the cell wall at 198 K, it is not photochemically converted to acetonitrile at this temperature, but photolysis to acetonitrile does occur at room temperature since the azine is present in the gas phase. The isopropylamine observed in these photolyses may be formed by a number of routes. It may result from hydrogen atom reduction of the enamine CH2~---CNH2
I
CH3 or the corresponding dimethylketimine (5) formed by addition of H. and "NH2 to propyne (Ferris and Ishikawa 1988). As shown in the present study ketimine 5 is also formed by the reaction of ketimine 8 with NH3. It is not clear why isopropylamine forms at 198 K while 5 is observed at 298 K. The percentage conversion and quantum yield for the formation of azine 4 is markedly higher at 198 than at 298 K (Table I). This observation suggests that 4 is formed efficiently from propyne and NH 3 as demonstrated by a quantum yield of 0.05 at 198 K. It condenses from the gas phase at this temperature and is shielded from further photolysis. Compound 4 remains in the gas phase at 298
K and is photolyzed to acetonitrile and other products. The quantum yield measured for the formation of 4 is for a series of photochemical and thermal reactions. The photolyses were performed in the presence of excess NH3 to simulate reaction conditions at the top of the NH3 clouds on Jupiter. Consequently, the bulk of the photons effect the photolysis of NH 3 to hydrazine, N2, and H2 and only a small portion of the radical intermediates combine with propyne to form 4, The quantum yields for the formation of methylamine and for isopropylamine or dimethylketimine are of the same orders of magnitude at 198 and 298 K. The UV absorption of dimethylketazine (4) extends from above 300 nm to below 200 nm so it would be expected to undergo further photolysis in Jupiter's atmosphere (Brinton and Chang 1968). It has been reported to undergo photolysis to acetonitrile and N-methyldimethylketimine (8) (Brinton and Chang 1968, Horne and Norrish 1970). The photochemistry of 4 was investigated in detail to determine if it was a source of the acetonitrile when NH3 was photolyzed in the presence of propyne. Irradiation of 7.8 Tort with a low pressure mercury lamp resulted in the formation of acetonitrile, ethane, and methane. There is a linear increase in acetonitrile with time of irradiation (Fig. 1). An 86% yield of acetonitrile is calculated after 30 min based on the unreacted 4 and the conversion of 1 eq. 4 to 2 eq. acetonitrile. The yield is corrected for the CH3NH 2 observed. It is assumed that the small amounts of 8 not converted to acetonitrile are hydrolyzed to CH3NH 2 by traces of water present in the CDC13 solvent used for IH NMR analysis. Photolysis of 7.8 Torr of 4 at about 310 nm resulted in the formation of acetonitrile and N-methyldimethylketimine (8) in a 1.3:1 ratio, respectively (Brinton and Chang 1968) (Fig. 2). A 79% conversion to 8 is calculated based on unreacted starting material and the assumption that the acetone observed is due to the hydrolysis of 4 by traces of moisture in the CDCI 3used for ~H NMR analysis. Ketimine 8 is photochemically stable when irradiated at 310 nm as expected from its lack of UV absorption at that wavelength (Brinton and Chang 1968). When compound 8 (7.0 Torr) is irradiated for 20 rain with a low pressure mercury lamp acetonitrile is formed in 80% yield (Fig. 3) (Eqs. (17) and (18)). The yield is based on unreacted starting material and the assumption that the CH3NH 2 present is due to the hydrolysis of unreacted 8 with moisture in the CDC13. From these data it is concluded that dimethylketazine is a source of acetonitrile when NH 3 is photolyzed in the presence of propyne. The mechanism of the conversion of dimethylketazine (4) to acetonitrile is given in Eqs. (15)-(18). It is known that two imino radicals are formed by the photolysis of azines (Horne and Norrish 1970) (Eq. (15)). Dispropor-
57
OLIGOMERS AND HCN ON JUPITER TABLE I Percentage Conversion(%) and Quantum Yield(~) of Formation
(CH3)2C~NN--C(CH3)2 c CH3CN d CH3NH2 e (CH3)2CHNH2 e (CH3)2C~NH e
CH3~----~CH (20 Torr) N H 3 (400 Torr) ~ 298°C
C H 3 ~ - - ' C H 2 (5 Torr) N H 3 (50 Tort) a 198°C
CH3C--==CH (4 Torr) N2H4 (7 Tort) b 298°C
%
qb
%
%
0.4 Trace 0.5 -0.1
0.005 -0.006 -0.002
qb
15 0 0.8 2.2 --
0.05 0 0.003 0.007 --
qb
1.7 1.2 1.5
0.02 0.006 0.008
T w o h o u r s irradiation. b O n e h o u r irradiation. c A s s u m e s two C H 3 C H ~ C H 2 and two p h o t o n s gives one ( C H 3 ) E C H ~ N N ~ C H ( C H 3 ) 2 . d A s s u m e s one C H 3 C H - - C H 2 and two photons gives the product. c A s s u m e s one C H 3 C H - - C H 2 and one photon gives the product.
tionation of these radicals yields acetonitrile and 8 (Eq. (16)). If the photolysis is carded out at wavelengths where 8 absorbs light it is converted to acetonitrile (Eqs. (17) and (18)).
(CHa)2C~NN~C(CH3)2
hu ) (CH3)2C~___N. (15)
2(CHa)2C~N" ~ C H 3 C ~ N + (CH3)2C~NCH 3 (CH3)2C~NCH3
hv C H 3 C ~ N C H 3 + CH3.
(16) (17)
8
C H 3 C ~ N C H 3 --* C H 3 C ~ N
+
CH 3"
(18)
The photolysis of 510 Torr N H 3 in the presence of 5 Torr 2-butyne was investigated to see if ketazines and
acetonitdle were formed from disubstituted acetylenes. Polymeric material and the cis and trans isomers of 2butene were the major reaction products. In addition, IH NMR signals consistent with the presence ofmethylethylketazine (9) in the reaction mixture were detected. The photolysis of methylethylketazine (9) was investigated since there exists the possibility of forming either CHaCN or CH3CH2CN or a mixture of both nitriles as reaction products. The azine radicals formed in Eq. (19) can eliminate an ethyl radical to give acetonitrile (Eq. (20)) or a methyl radical to give propionitrile (Eq. (21)). Irradiation of 1.2 Torr 9 with a low pressure mercury lamp for 10-15 min resulted in a 70% conversion to CHaCN and a 22% conversion to CH3CHECN (based on unreacted starting material). No other photoproducts were detected
1.2
1.4 1.2"
== o
1.0o
o
ILl
0.8"
o a
0.6-
ta
0.4-
uJ
0.8'
w o ¢3
0.6
LU
0.4
0no.
=J
..I
X
1.0'
-
"
'
0=E
"
, •
N-Methyldimethylketimine
0.2
0.2"
0.0
0.0 0
1'0
2'0
3'0
40
P H O T O L Y S I S T I M E (mln)
FIG. 1. T h e p h o t o c h e m i c a l c o n v e r s i o n of 7.8 Ton" dimethylketazine (4) to acetonitrile and N - m e t h y l d i m e t h y l k e t i m i n e (8) using a low p r e s s u r e m e r c u r y lamp.
0
10
20
30
40
50
P H O T O L Y S I S TIME (h)
FIG. 2. The photochemical c o n v e r s i o n o f 7.8 Torr dimethylketazine (4) to acetonitrile and N - m e t h y l d i m e t h y l k e t i m i n e (8) using 310-nm light.
58
FERR1S, J A C O B S O N , A N D G U I L L E M I N
by ~H NMR analysis. From the CH3CN : CH3CH2CN ratio it is determined that the ethyl radical is formed about three times as fast as the methyl radical. This observation is consistent with the report that the quantum yield for photochemical cleavage of the ethyl group from methylethylketone is 2.4 times greater than cleavage of the methyl group (Calvert and Pitts 1966).
Condensed Phase (150 K)
\
/ C~NN-~-C
/ CH3
9
\
CH3
CH2CH 3
C~N'
(19) (CH3CH=N)2 -
CH 3
<147 nm
CH3C=-CH +NH 3
\
/
CH 4
Diffusion to NH3 Clouds
CH3CH 2 hv~ 2
Photolysis Wavelength
CH3C=-CH
Polymers
CH3CH2
Gas Phase
Polymers?
J
-
1
[(CH3)2C=N]2 1
CH3CH2 C~---N"
~ CH3C~N + CH3CH 2"
(20)
CH3CN
CH3CN
HCN
HCN
CH3 CH3CH2
\
C~N"
/
nm
215-310
nm
O= 1.05 a Yield_-- 80%
\ /
147-215 • N 0.05
~ CH3CH2C~N + CH 3"
(21)
CH3 Hydrazine, a photoproduct of NH3 (Noyes and Leighton 1966), may be present in trace amounts in the gas phase and in much greater amounts in the condensed phase on Jupiter. Photolysis of hydrazine (6.9 Torr) in the presence of propyne (4 Torr) gives a yellow-brown polymer along with acetonitrile, isopropylamine, and smaller amounts of hydrocarbons including ethane and possibly propane. The quantum efficiency of a CH3CN formation from propyne and hydrazine is within a factor of 3 of quantum yield for dimethylketazine (4) formation from propyne and ammonia (Table I). Since 4 is converted to CH3CN with a quantum yield of 1 (Brinton and Chang
1.4
1-21 ~- 1.0-
x
ua 0.8 o a 0 iT" 0 . 6 o~ Ill 0.40
=E 0.2"
0,0 0
'o
2'o
3'o
.o
PHOTOLYSIS TIME (mln)
FIG. 3. T h e photochemical c o n v e r s i o n of 7.0 T o r t N - m e t h y l d i m e t h ylketimine (8) to acetonitrile using a low pressure m e r c u r y lamp.
l"
NH 3 Photolysis, 150-215 nm, O=0.1 Yield ---100%
FIG. 4. Proposed p a t h w a y for the formation of H C N from CH3~H and N H 3 on Jupiter. Brinton and Chang, 1968, Q u a n t u m yield for CH3CN formation measured at 254 nm.
1968) then the quantum efficiency of CH3CN formation will be approximately the same by either route. Neither dimethylketazine (4) Nor N-methyldimethylketimine (8) was detected as a reaction product. Photolysis of 8 Torr hydrazine in the presence of 5 Torr of 2-butyne gave acetonitrile and propionitrile as reaction products. The mechanism of the propyne-hydrazine reaction must differ markedly from that of the propyne-NH 3 system since dimethylketazine was not observed. These data suggest the possibility of additional routes to acetonitrile and therefore HCN from acetylenic compounds on Jupiter (Fig. 4). Acetylenes are formed by photolysis of CH4 in the stratosphere. Convective mixing of the acetylenes with the radicals formed by photolysis of ammonia results in the formation of azines and yellowbrown polymers. Photolysis of the azines yields alkylnitriles which, in turn, are converted to HCN by reaction with hydrogen atoms. Propyne is the only substituted acetylene currently observed on Jupiter (Atreya 1986); however, higher molecular weight acetylenes may be present in small amounts. Hydrazine may be substituted for NH3 as a source of the nitrogen in the conversion of acetylenes to CH3CN. Photolysis of NH 3 gives hydrazine (Noyes and Leighton 1966) so it will be formed in the atmosphere of Jupiter. The vapor pressure of hydrazine is estimated to be i0 8 Torr (Atreya et al. 1977) at 150 K so that it will be condensed on the NH 3 ice. It remains to be determined whether CH3CN formation can be initiated by photolysis of solid hydrazine in the presence of propyne.
OLIGOMERS AND HCN ON JUPITER ACKNOWLEDGMENTS This research was funded by NASA Grant NAGW-476. J. C. Guillemin received a stipend from C.N.R.S. of France. REFERENCES American Home Products Corp., British Patent 702,985 1954. Chem. Abstr. 49, 5515. ATREYA, S. K. 1986. Atmospheres and Ionospheres o f the Outer Planets and Their Satellites, p. 9. Springer-Vedag, Berlin. ATREYA, S. K., A. M. DONAHUE, AND W. R. KUHN 1977. The distribution of ammonia and its photochemical products on Jupiter. Icarus 31, 348-355. BAR-NUN, A., AND M. PODOLAK 1984. The contribution of thunderstorms to the abundances of CO, C2H2, and HCN on Jupiter. Icarus 64, 112-124. BRINTON, R, K., AND S. CHANG 1968. The photolyses of dimethylketazine vapor, Ber. Bunsen-Ges. Phys. Chem. 72, 217-221. CALVERT, J. G., AND PITTS, J. N., JR. 1966. Photochemistry, Wiley, New York. CURTIUS, T., AND E. ZINKEISEN 1898. Die umlagerung von ketazinen und aldazinen der fettreihe in pyrazolinderivate. J. Prakt. Chem. 58, 325-332. FERRIS, J. P., AND Y. ISHIKAWA 1987. HCN and chromophore formation on Jupiter. Nature 326, 777-778. FERRIS, J. P., AND Y. ISHIKAWA 1988. Formation of HCN and acetylene oligomers by photolysis of ammonia in the presence of acetylene: Applications to the atmospheric chemistry of Jupiter. J. Am. Chem. Soc. 110, 4306-4312. FERRIS, J. P., AND J. MORIMOTO 1981. Irradiation ofNH3-CH 4 mixtures
59
as a model of photochemical processes in the Jovian planets and Titan. Icarus 48, 118-126. GUILLEMIN, J. C., AND J. M. DENIS 1985. Flash vacuum thermolysis of ~-aminonitrile and subsequent HCN removal on solid base, a "one line" multistep sequence to reactive N-methyleneamines. J. Chem. Soc. Chem. Commun., 951-952. HORNE, D, G., AND R. G. W. NORRISH 1970. The photolyses of acyclic azines and the electronic spectra of the R1R2CN. radicals. Proc. R. Soc. London A315. 301-322. KAYE, J. A., AND D. E. STROBEL 1983. HCN formation on Jupiter. The coupled photochemistry of ammonia and acetylene. Icarus 54, 417-433. KEANE, T. 1990. Unpublished results from this laboratory. KIM, S. J., J. CALDWELL, A. R. RIVOLO, R. WAGENER, AND G. S. ORTON 1985. Infrared polar brightness of Jupiter 3. Spectrometry from the Voyager 1 IRIS experiment. Icarus 64, 233-249. LEWIS, J. S., M. B. FEGLEY, JR 1984. Vertical distribution of disequilibrium species in Jupiter's atmosphere. Space Sci. Rev. 39, 163-192. NAKAYAMA, T., AND WATANABE, K. 1964. Adsorption and photoionization coefficients of acetylene, propyne, and 1-butyne. J. Chem. Phys. 40, 558-561. NOYES, W. A., AND P. A. LEIGHTON 1966. The Photochemistry o f Gases, pp. 379-382. Dover, New York. RAULIN, F,, A. BOSSARD, AND G. TOUPANCE 1979. Abundance of organic compounds photochemically produced in the atmospheres of the outer planets. Icarus 38, 358-366. ROBERTS, B. P., AND J. N. WINTER 1979. Electron spin resonance studies of radicals derived from organic azides. J. Chem. Soc. Perkin H, 1353-1361. TOKUNAGA, A. T., S. C. BECK, T. R. GEBALLE, J. H. LACEY, AND E. SERABYN 1981. The detection of HCN on Jupiter. Icarus 48, 283-289.