Kotra V. Krishnamurty of New York at Buffalo Buffalo, New York 14214
State University
II
carbon Trioxide
Of
the oxides of carbon, a molecular species with the formula COa, rightly named curban trioxide, is an unusual compound and was recently isolated and characterized by Moll, Clutter, and Thompson (1) using a matrix isolation technique. It was first postulated by Katakis and Taube (2) in 1962 as a kinetic intermediate to account for the observed rapid exchange between O and COz. The ultraviolet photolysis of COz intrigued chemists for a long time and has contributed in no small measure its share of the L'blame-the-walls" for all the experimental and theoretical difficulties. Fortunately, howChronological Survey of C08lnvestigotions Investigatws
Tagirov and Shevchuk (15.)'
Katakis and Taube (8)
Raper and DeMore (18)
Young and Ung (8). Ung and S c b 8 (9) Slanger (7)
Year Experimental Evidace fm C08 and Related I a i e Species 1957 Observed a band a t 1615 cm-' in the combustion reaction of CO in O1 and interpreted it as arising fmm COZ. Reported detection of C03+ a8 a secondary ion in a mass spectrometer. Postulated an unstable kinetic intermediate in the exchange of oxygen between CO* and O('D). Postulated metastable species in CO, photolysis a t 1600 %i. Reported detection of COa in a reaction between CO and electronimlly excited 0 atoms. Postulated reactive species in tbeophotolysis of Con at 1470 A. Postulrtted reactive species in the photolysis of COz a t 1236 Preparation and characterization a t 77°K by infrared spectroscopy and isotope labeling. Collected mass spectral evidence from electron bombardment of carbonate esters in gas phase for the corresponding triphly protonated species, C(OH)$+. Mass spectral detection of COs- ion in the plasma obtained in the r.f. discharges in COI, CO and 0 ~ .This observation could not be confirmed by Evans and Jennings (16).
H.
Moll, Clutter, and Thompson (1) Krishnamurty (16)
Dawson and Tickner (As reported in the paper by Evans and Jennings (16)).
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ever, the preparation and spectral characterization of C03 tend to alter the situation by putting the "COs Hypothesis" on a firmer basis to explain the obsewed photochemical data. A laboratory study of the photolysis of COz is not only of interest to the chemist, but its complete understanding has become important in recent times for the purpose of speculating and interpreting what little we know about the photochemistry of the atmospheres of Mars and Venus (8). The Mariner IV occultation experiment (4) demonstrated the stability of C02 against possible photodissociation in the Martian atmosphere and considerable aeronomic significance is now attached to the photochemical equilibrium involving the various species: COz, CO, Ox, and 0. So far, however, no predictions have been made concerning C03 in the Martian atmosphere although the seasonal bright patches on Mars, observers believe, might be due to solid Con. The occurrence of condensed COz on Martian surface has been discussed recently by O'Leary and Rea (5) as was the related frost phenomena on Mars by Anderson, Gafney, and Low (6). In general, experiments carried out by different workers (7-12) on the ultraviolet phptolysis of COz at wavelengths 1236, 1470, and 1600 A corresponding to krypton, xenon, and hydrogen sources respectively, indicate varying quantum yields for 0 depending upon the imposed experimental conditions although the quantum yield of CO, one of the products of photodecomposition, is known to be around unity. In 1960, Mahan (11) was the first to suggest the formation of O3 to account for the oxygen loss observed in the photolysis of COz. During the past three years, however, Warneck (10, l$), Ung and Schiff (9),and Slanger (7) directed their researches on the photolysis of COa to solve this anomaly and obtained supporting evidence for the "C08-Hypothesis." The chronological survey indicates the extent of interest in the GOs species. Preparation
Three diierent methods are reported (1) to yield spectrally detectable quantities of COXin a matrix of solid C02 a t temperatures (77'K) corresponding to liquid nitrogen and at lower temperatures, 50°K (solid nitrogen) and 4.2"K (liquid helium). Photolysis of solid carbon dioxide: Using a xenon resonance lamp, solid COz at 77'K has been photolyzed in a specially built glass cold cell which permits ultraviolet irradiation and enables infrared spectral investigation without transfer of material. Such special glass cold cells for optical studies a t low temperatures are now comnlercially available and were developed
earlier by Broida and co-workers (17)in their extensive study of transients a t extremely low temperatures a t the National Bureau of Standards, Washington, D. C. Photolysis of osolid ozae-carbon dioxide mizture: Using the 2537 A radiation from a Hg-arc lamp, the Oa+COz matrix has been irradiated a t 5&60°1< in a special glass cold cell as described above. Radiojrequeney discharge i n gaseous carbon dioxide: Using a radiofrequency generator operating a t -30 Mc/sec gaseous COz has been converted to COa and immediately collected by a sweeptrapping technique at 50-70°K. The essential reactions in the three methods descrihed are:
Although quantities sufficient for infrared detection and spectral characterization have been obtained by these methods in several experiments using normal carbon dioxide as well as the isotopically labeled species, 13C02(C-13, 56%), C1802(0-l8,99%), gas phase stahilization of COahas not been achieved so far. Also, the detection of C03+ion in the mass spectrometer has not been well established. Krishnamurty (15) in his recent study of the mass fragmentation of several diary1 and dialkyl carbonates obtained indirect evidence for the occurrence of C03+ via C(OH)3+, the corresponding triply protonated species. The relative abundances of the C(OH)*+ion corresponding to m / e 63 in a series of closely related dialkyl carbonates are shown in Figure 1. The appearance of C(OH)3+ at m / e 63 in the mass spectra suggests once COa breaks loose, instantaneous protonation seems to take place picking the methylenic hydrogens from the organic fragments. This is particularly strikmg by the absence of m / e 63 in the first member of the homologous series, dimethylcarbonate, where no methylenic hydrogens are readily available. The mobility of -CH3 group under mass spectral conditions is well known (19). Properties
Carbon trioxide made by photoproduction at low temperatures exhibits photodecomposition when exposed to visible and near ultraviolet light. Since these
are usually present in the xenon lamp along with the 1470 A radiation used for making COs, perhaps greater yields of COa might be achieved with the help of certain filters which would minimize photodecomposition. Isotopic labeling with carbon-13 and oxygen-18 give supporting evidence concerning the molecular formula of the species as to a one-carbon and three-oxygen moiety. From a study of the infrared spectral data of the normal and isotopically substituted molecular species the following possible tentative structures have been proposed by Moll, Clutter and Thompson (1).
The observed infrared absorption frequencies for normal C03 and the related isotopic species are shown in the table along with the known vibrational frequencies of the iaically, covalently, and coordinately bound carbonate. The large number of observed bands in the infrared spectrum of COa seems to indicate a certain similarity to the coordinated carbonate. This would suggest nonequivalence of one oxygen from the other two and the 0 - G O angle of the coordinated oxygens promotes certain carbonyl character to the third oxygen. The 0-C-0 bond angle could be as low as 90' (even 80') and this, by no means, suggests a conventional covalent bond between the two equivalent oxygens as shown in structure (C). No studies on the reactivity of COa are available in support of any of these structures. However, from the well-known reactivity of the photo-produced singlet oxygen atoms, O('D), it is reasonable to assume an insertion type reaction as suggested by Dainton (84). This might lead to one of the linear structures (D) or (E) if the addition takes place at the oxygen atom in O=C=O. On the other hand, if one assumes the same addition reaction taking place at the carbon atom, the non-linear structures (A) or (C) would best represent the
Figure 1. Moss spectra of diethyl, di-wpropyl, di-n-omyl and di-n-hexyl carbonates. The ordinote show the relative abundance per cent with resped to the b a m peak. The morg spectra were run in o Consolidated Electrodynomin torp. CEC 21-130 cycloidol focusing machine mt 77.5 voltr.
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Hg0(lP,)
Vibrational Frequencies of Various Related "COs" Species
+ COI'
=
HgCOa (yellow)
perhaps followed by a straight decomposition of HgC03, a heavy metal carbonate, to HgO (yellow). This evidence is not available, instead a collision complex of the following configuration has been invoked
'lC"Oa'3C'Q-
YL
"4
"I
14;(2) 680 (2) 879 1063 1376 (2) 677 (2) 851 1063 1F1103102,i 1416 (2) 674(2) 868 v , : C-0 symmetric stretching; vr: C-0 asymmetric stretchmg vn: out-of-plane deformation vr: in-plane deformation; Cmbonate: Convalent (Cm)
---Observed bands (cm-'Ib-
by the authors to account for their findings, including the formation of an oxalate by dimerization. However, this does not rule out the possibility of HgO formation via HgCOa and, therefore, occurrence of C03in the gas phase. The analytical composition of the yellow residue should be studied more thoroughly as a function of imposed experimental conditions before any further speculations. As of now, no XY3type molecule with a central atom X and containing 22 valence electrons has been studied although molecules of the same type with 24, 25, or 26 valence electrons are known to belong to either a Dlh or C3a type symmetry. Figure 2 shows an apCARBON
Carbonak: Co-ordinate (Cz.) Calculated and observed bands for bidentate carbonate (cm-I).
[CO(NI~~)&O~]CI 1593 1030 760 395 1265 673 430 834 *Frequency data. taken from Thode, Sbima, Rees, and Krish(Bl). namurty ($0). 1zCL803-fromUrey Wee Gatehouse, Livingstone and Nyholm (22). For daba on the frequen&s of several other Cobalt(II1) carbonate romplexes See Fujitit, hlartell, and Nakamoto ($3).
C03 molecule. In any case, for a possible future support of structure (C), it is interesting to note here the vigorous research that is going on in search of cyclopropanone, which is isoelectronic with CO1. Although cyclopropanone itself has not been isolated until now, Turro, Harnrnond, and Leermakers (26) have succeeded in isolating and characterizing the tetramethylcyclopropanone during 1965.
Additional indirect evidence derives from the studies made on COz-photosensitization using Hg('P1) atoms by WOE and Pertel (25). Along with CO, a photodecomposition product, an orange-yellow solid deposit was noticed on the walls of the reaction vessel in their studies. Among the possible compounds that contain Hg, 0, and C, only the oxide and the carbonate of mercury are yellow, not the oxalates. If the simple carbonate HgC03were shown to be forming in the observed yellow residue, it would be simpler to postulate a reaction of the type involving internal electron transfer from Hgo to the electron deficient C03' thus: 596
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Figure 2. Approximate correlation diagram for 24-electron C08(similar diagmms for COs- (23-electmn), CO1 (22-electron) and Cot+ (21 -electron1 are not presently knownl. [See reference (271.1
proximate molecular orbital correlation diagram for C03Z-where the 24 electrons are accommodated in the bonding and non-bonding orbitals. In addition to COa2-, two other closely related species are CO3- (23 valance electrons) and GOa+ (21 valence electrons). Conclusion
Experimental results indicate the existence of COa as a distinguishable moiety. However, only further refinements in technique are required to improve the yields and stability under different conditions. Spectral studies in the gas phase and also the esr spectrum should help elucidate its structure and electronic configuration. Acknowledgmenl
The author is grateful to the Research Foundation, State University of New York, for making part of this work possible by way of a faculty fellowship during 1966. Addendum
Since preparation of this manuscript Schaafsma, Steinherg, and de Boer (Rec. Trav. Chim., 85, 1170 (1966)) at the University of Amsterdam report the
synthesis of cyclopropanone from diazomethane and ketene at -7S°C in liquid propane as solvent in fair yield. The highly reactive cyclopropanone polymerizes on carefully warming to -40°C yielding a white solid, polycyclopropanone (mp 166169OC, mol. wt. -9000). Infrared and nmr data support the following structure:
Literature Cited (1) MOLL, Pi. G., CLUTI.ER,D. R., AND THOMPSON, W. E., J . Chem. Phys., 45,4469 (1966). (2) KATAKIS,D., A N D TAUBE,H., J . Chem. Phys., 36, 416 (1962).
21 (1966). B. T., AND REA,D. G., SciWKe, 155,317 (1967). (5) O'LEARY, D. M., CIFNEY,E. S., AND LOW,P. F., Science, (6) ANDERSON, 155, 319 (1967). T. G., J . C h m . Phys., 45,4127 (1966). (7) SLANGER, (8) YOUNG,R. A,, AND UNG,A. Y., J. Chem. Phys., 44, 3038
- --
119Trfil \ .. ,.
(9) UNG,A. Y., AND SCHIFF,H. I., Can. J. Chem., 44, 1981 (1866). P., J. Chem. Phy~.,41,3435(1964). (10) WARNECK, B. H., J. Ch.em.Phys.,33,959 (1960). (11) MAHAN, P., Disc. Faradny Soc., 37,57 (1964) (12) WARNECK,
R. B.,AND SHEVCHUK, I. P., Dokz. Akad. Nauk (13) TAG~ROV, SSSR, 116,797 (1957). Z.. J. Chim. Phus.. 57. 717 (14) C ! h I I ( K , V., AND HERMAN.
. ..
(16j EVANS,H. E.,~ N JENNINGR~, D P. P., Trans. ~ ~ k d Soe., a y 61,2153 (1965). L. E., A N D BROIDA,H. P., Rev. (17) SCHOEN,L. J., KUENTZEL, Sci. in st^., 29, 633 (1958). The glass cold cell used by Moll, Clutter, and Thompson (I) was built by Martin, H. S. & Son, Evanston, Illinois. (18) RBPER,0. F., AND DEMORE,W. B., J. C h m . Phys., 40, 1047 (1964). (19) See "Mass Spectrometry of Organic Ions," (Editw: McLAPFERTY,F. W.), Academic Press, Inc., New York 1963. Also, "Interpretation of Mass Spectra. of Organic Compounds," by ~uDz~IiIEw~cz, H., DJERASSI,C., A N D WILLIAMS, D. II., Holden-Day, Inc., 1964. M., REES,C. E., AND KRISHNAMURTY, (20) %ODE, H. G., SHIMA, K. V., Can. J. Chem., 43, 582 (1965). (21) UREY,H. C., J. C h m . Soe., 562 (1947). (22) GATEHOUSE,B. M., LIYINGGTONE, S. E., AND NYHOLM, R. S., J. Chem. Soc., 3137 (1958). A. E., A N D NAKAMOTO, K., J. Chem. (23) FUJITA,J., MARTELL, Phys., 36, 339 (1962). F. S., Disc. Famday Soc., 37,213 (1964). (24) DAINTON, (25) WOLFF,C. M., AND PERTEL,R., J . Phys. Chem., 69, 4047 IIU'I*) ,A""",. (26) Tunno, N. J., H M M ~ N D W., B., AND LEERMAK~RS, P. A,, J. Am. Chem. Soc., 87,2772 (1965). B. E., AND MCDANIEL,D. H., "Concepts and (27) DOUGLAS, Models of Inorgenic Chemistry," Blaisdell Publishing Co., New York, 1965.
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