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Spectroscopy of Hydrothermal Reactions 21. Decomposition Reactions and Kinetics of Ni(CO)4, Co(CO)4- and (η5-C5H5)Co(CO)2 in High Temperature Water Davide Miksa and Thomas B. Brill* Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716
The decomposition behavior of aqueous Ni(CO)4, NaCo(CO)4, and (η5-C5H5)Co(CO)2 was studied by infrared spectroscopy using a titanium flow reactor with sapphire windows. A pressure of 275 bar was applied to prevent gas-liquid phase separation. Ni(CO)4 was investigated in the 50-270 °C temperature range with selected partial pressures of CO in the range of 0-60 bar. Without added CO, the Arrhenius parameters were Ea ) 10.4 ( 1.3 kcal/mol and ln(A, s-l) ) 10.4 ( 1.9 in the 50-90 °C range where a first-order rate law was followed. Complete decomposition took place at 170 °C within 23 s. The addition of excess CO raised the decomposition temperature. Aqueous Ni(CO)4 could be detected for at least 5 s at 270 °C with a 60 bar partial pressure of CO. The isoelectronic ion Co(CO)4- was found to be more stable than Ni(CO)4. Its decomposition was characterized in the 200-240 °C range without added CO. A first-order rate law was followed up to 50% decomposition, yielding Ea ) 29.9 ( 3.7 kcal/mol and ln(A, s-1) ) 25.9 ( 3.8. The greater robustness of Co(CO)4 compared to Ni(CO)4 is attributable to the strength of the metal-carbon bond. (η5-C5H5)Co(CO)2 decomposed in the 220-240 °C range to Co(CO)4- and a considerable amount of insoluble residue. Decomposition reactions for the three studied metal carbonyls were formulated. Introduction In the well-known work in 1953 by Reppe,1 iron, cobalt, and nickel carbonyl compounds were shown to form when aqueous ammonia solutions of the M(II) salts were heated in a closed vessel with CO to temperatures above the normal boiling point of water. Subsequently, the behavior of organometallic compounds under hydrothermal conditions has received relatively scant attention, probably because most organometallic compounds require manipulation in nonaqueous solvents with scrupulous exclusion of water. More recently, interest in pursuing organometallic chemisty in water at high temperature motivated a study of various alkynes and (η5-C5H5)Co(CO)2 in supercritical water.2 The cyclotrimerized alkynes were isolated, and the organometallic was believed to be the catalyst. It has also been observed that Fe2(RS)2(CO)6 formed when FeS, CO, and alkanethiols (RSH) in water were heated to a high temperature under pressure, which is of interest regarding potential geochemical origins of biochemically active architectures.3 It is of concern in the practical use of hydrothermal reactors that highly toxic Ni(CO)4 formed in real time when a homogeneous CO/H2O solution was flowed in a reactor operating above 200 °C under a pressure of 275 bar.4 The CO appeared to have extracted Ni from the much cooler stainless steel feed line of the flow cell. Because of the well-known capability of Ni(CO)4, NaCo(CO)4 and (η5-C5H5)Co(CO)2 to function as catalysts in various processes, such as hydroformylation reactions,5 olefin coupling reactions,6 and the watergas shift reaction,7 we have pursued a more thorough understanding of the stability and lability of these organometallic compounds in water up to 270 °C. In this quest, real-time observation of the CO stretching region * Correspondence author. E-mail:
[email protected] in the infrared spectrum was employed with a flow reactor. The kinetics and some of the details of the decomposition pathways were determined and compared for the isoelectronic Ni(CO)4 and Co(CO)4- species. Because the metallic residue from these reactions is in an extremely finely divided state, it might be useful as a precursor to metal salts and as a catalyst. Although some aspects of the decomposition of (η5-C5H5)Co(CO)2 were spectrally elucidated, kinetic measurements were unsuccessful because an excessive amount of insoluble material formed, which affected the uniformity of the flow. To our knowledge, however, this work is the first to report reaction details of organometallic compounds under hydrothermal conditions. Experimental Section Preparation of Ni(CO)4 Solutions. Highly poisonous Ni(CO)4 was purchased from Powdermet Inc., Sun Valley, CA. Solutions were prepared by mixing an excess of Ni(CO)4 with 200 mL of water that had been treated by a MilliQ filtration system. Mixing was allowed to take place for 30 min in a glovebag that was continuously purged with argon. The gas effluent from the bag was bubbled through a HNO3 trap to destroy any Ni(CO)4. This afforded a 3.9 × l 0-4 m aqueous solution of Ni(CO)4 at 25 °C as determined by ICP-MS of Ni(II). This concentration is below the reported 1.05 × l0-3 m saturation limit at 9.8 °C.8 The solution was then transferred from the glovebag to the flow reactor by using an Autoclave Engineers autoclave as a storage vessel. The autoclave was first flushed with CO to remove the atmospheric gases. An attempt was made as well to dissolve Cr(CO)6, Mo(CO)6, and W(CO)6 in water and measure their decomposition kinetics. However, none of these substances were sufficiently soluble for an IR spectrum in
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the CO stretching region to be obtained. Very weak CO stretching absorptions for aqueous Fe(CO)5 were observed in the IR spectrum, but the signal-to-noise ratio (S/N) was too low for the kinetics with any degree of accuracy to be measured. Preparation of NaCo(CO)4 Solutions. NaCo(CO)4 was synthesized according to the procedure of Edgell and Lyford.9 CO2(CO)8 (1.66 g, Strem Chemicals) and an excess of NaOH were mixed in 50 mL of dry THF under a constant stream of nitrogen for 2 h. The solution was filtered, and the THF was removed from the light yellow filtrate on a vacuum line. The resulting light pink solid was stored in the absence of air and light until use. Solutions with concentrations of 0.0022 and 0.0055 m, as determined by ICP-MS of Co(II), were obtained by mixing NaCo(CO)4 with MilliQ water in a glovebag under a continuous purge of argon. A small amount of insoluble Co2(CO)8 left over from the synthesis was removed by filtration. Preparation of (η5-C5H5)Co(CO)2 Solutions. (η5C5H5)Co(CO)2 was purchased from Strem Chemicals. The aqueous solutions were prepared and manipulated in the same manner as the Ni(CO)4 solutions. Reactor and Flow System. In situ infrared measurements were conducted with a titanium (grade 2) or 316 stainless steel cell/reactor containing sapphire windows. The IR spectral band-pass was about 18002900 cm-1, which made the detection of the carbonyl modes and CO2 possible. The details of this cell and the flow, temperature, and pressure controls have been reported elsewhere,10,11 but a brief description of the experiment follows. The cell was composed of two flanges between which the sapphire windows and a gold foil spacer gasket were compressed. A slot was cut into the gold gasket that allowed a 20-µm-thick film of solution to flow between the windows. The cell body had five holes drilled along its length into which cartridge heaters were inserted. The temperature was monitored by two strategically placed K-type thermocouples. The 12-cm-long inlet and outlet tubes were made of the same material as the cell body and connected the cell to the flow system. The temperature was controlled by two Omega PID controllers, and the flow was controlled by an ISCO 260D pulseless syringe pump. Two pneumatic air actuators maintained a constant pressure of 275 bar. The cell was insulated by encapsulation between two Ca2SiO4 blocks. This unit was then aligned in the sample compartment of a Nicolet Magna 560 FT-IR spectrometer. Each spectrum was obtained as an average of 32 scans at 4 cm-1 resolution. The absorptions were fit to Voigt functions to obtain the integrated area. Eighteen different flow rates were used at each temperature, and averages of at least three sets of data were used. Weighted least-squares regression was used to calculate the error in the Arrhenius data, with care being taken during the conversion to logarithmic space.12 Product Collection Experiments. Ex situ analytical experiments were conducted to characterize the gaseous and solid decomposition products. The gaseous products were collected and identified by mass spectrometry. To obtain a sufficient quantity of solid product to examine further, batch reactions were carried out in a 12-cm3 titanium tube reactor that was heated in a fluidized sand bath for 20 min at 300 °C. The tube was first loaded with the organometallic compound and sufficient water so that the liquid completely filled the internal volume at the reaction temperature. The tube
was then cooled. For gas collection, the tube was connected to a T union, which was also connected to a vacuum line and to a polyethylene gas collection bag. Before the tube reactor was opened, the internal volume between the collection bag and the tube reactor was evacuated. The vacuum line was then closed, and the tube reactor was opened, allowing the gaseous products to escape into the collection bag. An in-line trap was used to collect the small amount of liquid that was ejected during degassing of the solution in the tube. The bag was immersed in a dry ice and acetone bath so that the water vapor was removed by freezing. The bag was then closed, and a sample of the collected gas was withdrawn with a gas syringe through a septum on the bag. The gas sample was then introduced into a Micromas AutoSpecQ mass spectrometer. Whereas CO and CO2 could be readily trapped and detected, H2, which must also be present because of the reduction of H2O, was not detected, probably because it escaped during the collection process. The solids from the tube reactor were removed by filtration and determined to be ferromagnetic or not by the use of a magnet. In the case of (η5-C5H5)Co(CO)2, the organic portion of the solid residue could not be cleanly characterized. X-ray Powder Diffraction. Multiple runs with the tube reactor enabled the collection of enough precipitate from the Co(CO)4- reaction rather it to be characterized by X-ray powder diffraction. Prudence prevented the same effort with Ni(CO)4 because of its extreme toxicity. X-ray powder diffraction measurements were performed on authentic samples of Co, CoO, and Co3O4. The diffraction patterns were obtained with a Phillips X′Pert diffractomater using Cu KR radiation. The data were collected in step mode at 2θ ) 4-110° with a 0.02° step angle. These powder diffraction measurements enabled an approximate percentage ratio of the Co, CoO, and Co3O4 phases to be determined. Results and Discussion Ni(CO)4. Ni(CO)4 was found to form at hydrothermal conditions during a recent study of the water-gas shift reaction in which the CO/H2O solution at 275 bar was in contact with the 316 stainless steel fittings used to connect the flow reactor to the titanium cell.4 Because of the conditions employed in that work, the formation and decomposition of Ni(CO)4 was observed to occur in the 200-240 °C. The present study was undertaken to learn more about the properties of Ni(CO)4 in water as a function of the CO pressure and the temperature. Ni(CO)4, however, is only very slightly soluble in water. A 0.0039 m solution, as determined by ICP analysis of Ni(II), was achieved by mixing Ni(CO)4 with H2O for 30 min. The solution was then transferred via a closed line to an autoclave and pumped through the flow cell at 275 bar. In separate studies, the solution was stored in an autoclave that had been pressurized with selected partial pressures of CO in the 0-60 bar range. The solution was then pumped through the flow cell to determine the effect of excess CO on the decomposition process. The asymmetric stretching mode (t2 symmetry) of CO in Ni(CO)4 dissolved in water occurs at 2043 cm-1 at 22 °C. Figure 1 shows that, as the solution was heated under 275 bar pressure, about 50% of the Ni(CO)4 decomposed by 90 °C in 23 s. The concentration of the CO product was below the limit of IR detection owing
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Figure 1. Time dependence of the IR spectrum of the CO stretching region of 0.0039 m Ni(CO)4 at 90 °C under 275 bar pressure. The Ti cell flow reactor was employed for these measurements.
Figure 2. First-order rate plot for the decomposition of aqueous Ni(CO)4 based on integration of the CO stretching mode in spectra such as shown in Figure 1.
to the low initial concentration and the low IR absorptivity of CO. CO was, however, detected by mass spectrometry. A small amount of black nonferromagnetic residue was collected when the reaction was run in the tube reactor at 240 °C. Ni metal is ferromagnetic, but NiO is not. However, the oxidation of Ni metal to NiO is more likely to occur at 240 °C than at 90 °C. Hence, the results are consistent with the occurrence of reaction 1 at lower temperature, followed by oxidation of very finely divided Ni metal by water at high temperature
Ni(CO)4 h Ni + 4CO
(1)
Figure 2 shows the first-order rate plot based on the decrease in the intensity of the t2 mode of CO in Ni(CO)4. The data apply up to 50% conversion in the 50-90 °C range. Figure 3 includes these data in the form of the Arrhenius plot for the decomposition of pure Ni(CO)4 in H2O without added CO. At higher temperatures, the rate plots exhibit more data scatter perhaps as a result of the formation of precipitate, which affects the uniformity of the flow through the short-path-length cell. In previous findings4 where a large excess of CO was present, an aqueous solution of Ni(CO)4 decomposed above 200 °C. Therefore, we investigated the effect of various partial pressures of CO on the temperature of Ni(CO)4 decomposition. When additional CO was added to the autoclave at a constant total pressure of 275 bar,
Figure 3. Arrhenius plot for the Ni(CO)4 rate data in Figure 2 and also for the same system with a 0.7 bar partial pressure of CO.
Figure 4. Plot of the partial pressure of CO versus the temperature range where no decomposition was detected in 25 s. The lowest temperature data point at each pressure is arbitrary.
the equilibrium in reaction 1 shifted to the left, as expected. This is illustrrated by the Arrhenius plot in Figure 3 with a 0.7 bar partial pressure of CO. This pressure corresponds to 6.3 × 10-4 m CO assuming a Henry’s law constant of 9.5 × 104 mol/(kg bar).13 Clearly, the rate of decomposition of Ni(CO)4 is decreased as the partial pressure of CO is raised. The stability of aqueous Ni(CO)4 was then determined for a series of CO partial pressures up to 60 bar. The equilibrium constant for reaction 1 was used. The results are displayed in Figure 4, which shows the temperature ranges in which little or no decomposition of Ni(CO)4 was detected in 25 s. As more CO was added to the system, the forward reaction of 1 was clearly suppressed, and a higher temperature was required to produce decomposition. Throughout this experiment, the t2 mode of Ni(CO)4 became broader up to 210 °C, but the shift in the frequency was less than 2 cm-1. Figure 4 is a practically useful representation of the CO pressure and temperature at which Ni(CO)4 is stable in a hydrothermal flow reactor in a given period of time. Previously, when the CO pressure was 60 bar, Ni(CO)4, which had been formed as a result of extraction of Ni from the stainless steel portion of the reactor by CO, was detected in the 200-240 °C range.4 Figure 4 reveals why this is the case and also indicates the conditions of stability of Ni(CO)4 in other CO pressure and fluid temperature ranges. It can be seen that some curvature exists at the highest pressure, which is due to decomposition of Ni(CO)4.
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Figure 5. Time dependence of the IR spectrum of the CO stretching region of 0.0039 m Ni(CO)4 at 250 °C under 275 bar pressure including a partial pressure of CO of 60 bar. The Ti cell flow reactor was used for these measurements.
Figure 6. Time dependence of the IR spectrum of the CO stretching region of 0.0022 m NaCo(CO)4 at 260 °C under 275 bar pressure.
At the higher CO pressures used in this study, the temperature was high enough to form CO2 by the wellknown water-gas shift reaction 24
CO + H2O h CO2 + H2
(2)
This is evident from Figure 5, which presents a spectral time series of the Ni(CO)4 solution at 250 °C that also contains 60 bar of CO. The t2 stretching mode of Ni(CO)4 appears at 2044 cm-1. Because of the high CO concentration, the IR absorbance of CO at 2153 cm-1 is now readily seen, along with that of the CO2 product at 2343 cm-1. The Arrhenius parameters for Ni(CO)4 without additional CO are Ea ) 10.4 kcal/mol and ln(A, s-l) ) 10.4. These values are much lower than the values of Ea ) 46.2 kcal/mol and ln(A, mol L-l s-l) ) 53.7 in the gas phase,14 indicating that H2O assists the reaction probably by solvating the Ni center as the CO ligand is displaced. The rate law for gas-phase decomposition was zeroth-order as a result of surface catalysis.14 These Arrhenius parameters are most easily compared in terms of the half-lives of Ni(CO)4 in solution and in the gas phase at 60 °C, which are 105 and 560 s, respectively. NaCo(CO)4. Figure 6 shows the CO stretching mode of t2 symmetry in the IR spectrum of a 0.0022 m solution of NaCo(CO)4. This mode absorbs at 1916 cm-1 at 22 °C but shifts to 1899 cm-1 at 230 °C under a pressure of 275 bar. Figure 7 reveals that the frequency shift is relatively constant over this temperature range, and that the absorptivity of the mode is relatively constant in the 100-150 °C range before a measurable extent of decomposition occurs. It is interesting to note that the t2 mode of Ni(CO)4 in water is not temperature-dependent whereas that of Co(CO)4 shows a significant red shift as the temperature is increased. This difference can be attributed to the greater interaction with water of the anionic species compared to the neutral species. The IR spectrum of NaCo(CO)4 is known to have a strong solvent dependence at room temperature.15
Figure 7. Plot of the temperature dependence of the band center and the absorptivity of the CO stretching mode of t2 symmetry in aqueous NaCo(CO)4. The pressure was 275 bar.
Figure 6 shows a time series of spectra of NaCo(CO)4 at 260 °C at 275 bar as a function of the residence time and reveals that the intensity of the CO stretching mode gradually decreases as a small amount of CO2 forms. No free CO was detected in the IR spectrum because the CO concentration was below the limit of detection given the low molar absorptivity of free CO. CO and CO2 were, however, detected in the gas collection experiments by mass spectrometry. Reaction 3 is therefore a plausible initial reaction of Co(CO)4
Co(CO)4- + H2O f Co + 4CO + OH- + 1/2H2
(3)
The postreaction solution was found to contain a small amount of insoluble ferromagnetic precipitate. Multiple runs using the Ti tube reactor produced enough residue for collection and examination by X-ray powder diffraction. Figure 8 shows that Co, CoO, and Co3O4 are present in the approximate relative ratio of 53:35:12 from an aqueous solution of NaCo(CO)4 that had been heated in the tube reactor at 300 °C for 20 min. Of these materials, only Co is ferromagnetic. Hence, reactions 4 and 5 are suggested
Co + H2O f CoO + H2
(4)
3CoO + H2O f Co3O4 + H2
(5)
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Figure 8. Comparison of the XPD patterns of Co, CoO, and Co3O4 with that of the solid residue collected from aqueous NaCo(CO)4 heated in a tube reactor at 300 °C for 20 min. Table 1. Rate Constant Comparison for the Formation of CO2 from NaCo(CO)4 Solution and the Water-Gas Shift Reaction (Reaction 2)
Figure 9. First-order rate plot for the decomposition of 0.0022 m NaCo(CO)4 in the Ti cell flow reactor under a pressure of 275 bar.
kCO2 × 105 (mol kg-1 s-1) T (°C)
NaCo(CO)4
WGSR
230 240
2.51 ( 0.11 10.2 ( 0.28
2.02 ( 0.58 12.0 ( 0.51
In a parallel study to confirm reactions 4 and 5, Co metal and CoO were separately heated in water in an agitated Ti tube reactor at 300 °C for 20 min. The IR spectrum revealed that Co3O4 was indeed formed by reaction 5, but that very little CoO was formed by reaction 4. The difference might be the fact that the cobalt metal formed by reaction 3 is expected to be more reactive owing to its nanodimensional state than the Co metal powder used in the control experiment. Reactions 3-5 are consistent with the fact that Co(CO)4- has been reported elsewhere to reduce water.16 The water-gas shift reaction 2 has recently been described in the hydrothermal regime at the same temperature and pressure using the same types of IR spectroscopy cells.4 It explains the formation of CO2 as CO becomes available. Reaction 2 followed a zerothorder rate law and appeared to be catalyzed by the cell surface.4 The rate constants based on CO2 formation with and without the NaCo(CO)4 present are compared in Table 1. Because the rates are essentially the same within the experimental uncertainty, it is reasonable to assume that NaCo(CO)4 is not serving as a catalyst and that reaction 2 is occurring as an independent step. For comparison purposes, the amount of CO2 produced at 230 °C in this time frame is about 6% of the total available CO from NaCo(CO)4. In contrast to the apparent behavior of Fe(CO)5 (reactions 6 and 7), in which nucleophilic attack on CO by OH- has been proposed as the initial stepl7 (OHcould originate from the ionization of water), reaction 3 was regarded to be a more reasonable choice for the degradation of Co(CO)4-.
Fe(CO)5 + OH- f Fe(CO)4CO2H-
(6)
Fe(CO)4CO2H- f Fe(CO)4H- + CO2
(7)
The reasons for this conclusion are the following: The IR and 1H NMR spectra of the partially reacted Co(CO)4 solution contained no evidence of HCO2, either uncoordinated or coordinated as Co(CO)3CO2H2-. Moreover, nucleophilic attack by OH- on the Co(CO)4- ion to form
Figure 10. Arrhenius plot of the rates of decomposition of NaCo(CO)4 in the Ti and 316 stainless steel cell flow reactors. A surface effect is apparent, suggesting that the reaction is at least partially catalyzed.
the Co(CO)3CO2H2- ion is disfavored by electrostatics. The IR spectrum showed no evidence of polynuclear cobalt species, such as Co2(CO)8, or the acid HCo(CO)4, which, if present, could possibly open other decomposition pathways. In sum, the experimental findings here are consistent with the occurrence of reactions 3-5 for the hydrothermal decomposition of the Co(CO)4- ion. Figure 9 presents the first-order rate plot for the initial stage of reaction 3 in 0.0022 m NaCo(CO)4 under a pressure of 275 bar in the 200-240 °C range. At higher concentrations of NaCo(CO)4 (e.g., 0.0055 m), the rate increased somewhat as the reaction progressed. It would be difficult to identify the reason for this behavior in part because the reaction medium becomes increasingly heterogeneous as the decomposition progresses. We found that the reaction is slower in the stainless steel cell than the titanium cell, which suggests that surface catalysis is a factor in the overall rate. Hence, a plausible explanation for the accelerating rate of decomposition of NaCo(CO)4 at higher concentrations is heterogeneous catalysis as nanosized Co metal forms in the reaction. The Arrhenius plot for the decomposition of 0.0022 m NaCo(CO)4 is shown in Figure 10. The Arrhenius parameters in the 200-240 °C range under a pressure of 275 bar were determined to be Ea ) 30.0 ( 3.7 kcal/ mol and ln(A, s-1) ) 25.9 ( 3.8 in the titanium cell and Ea ) 18.5 ( 4.5 kcal/mol and ln(A, s-1) ) 13.7 ( 4.6 in
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Conclusions The mononuclear metal carbonyl species appear to be sufficiently stable to be useful reagents for reactions, although as demonstrated in this work, they decompose well below the critical temperature of water. The use of high-temperature water adds the complication of thermal reactivity. Moreover, most organometallic compounds are unsuitable for use in aqueous solution because of their hydrolytic reactivity. On the other hand, the decomposition process can be expected to produce extremely small particle sizes of the metal. The resulting high degree of reactivity of the finely divided metal might be useful in applications such as heterogeneous catalysis or the formation of nanosize metal oxide and sulfide particles. Figure 11. Time dependence of the IR spectrum of the CO stretching region of aqueous (η5-C5H5)Co(CO)2 at 240 °C under 275 bar pressure, showing that Co(CO)4- forms in the decomposition process.
the 316 SS cell. The activation energy for the Co(CO)4ion is higher than that for Ni(CO)4 because the metal(dπ)-to-CO(π*) bonding is more extensive with Co- than with Ni, which strengthens the M-C bond. (η5-C5H5)Co(CO)2. In an earlier study, Jerome and Parsons2 hypothesized that the (η5-C5H5)Co portion of the (η5-C5H5)Co(CO)2 complex was retained in water at 374 °C and 200 bar and served as the catalyst for the cyclotrimerization of alkynes under these conditions for reactions lasting 0.5-2 h. (η5-C5H5)Co(CO)2 is indeed sufficiently soluble in water for IR spectra of the a′ and a′′ symmetry stretching modes of CO (2026 and 1963 cm-1) to be obtained, as shown in Figure 11. These spectra were recorded at 240 °C under 275 bar pressure. It can be seen from the time series of spectra under these conditions that (η5-C5H5)Co(CO)2 decomposes while Co(CO)4 forms in its place. A dark-red-colored nonferromagnetic residue also formed, which can be explained by the formation of CoO and an organic residue. Reaction 8 accounts for the main components of this reaction
2(η5-C5H5)Co(CO)2 + H2O f Co(CO)4- + CoO + H+ + 1/2H2 + “(C5H5)2” (8) The “(C5H5)2” entity in reaction 8 is not confirmed to be dicyclopentadiene, but rather appears to be an insoluble higher-molecular-weight residue, which might have been partially hydrogenated and/or hydrolyzed. Owing to the significant amount of insoluble material produced by reaction 8, the flow in the cell became nonuniform, which caused erratic variations in the intensities of the absorptions. Hence, kinetic measurements of the decomposition process were impossible to obtain. Nevertheless, the temperature and time scale used in Figure 11 are lower and much shorter that those employed by Jerome and Parsons, which casts suspicion on the likelihood that the (η5-C5H5)Co entity is the alkyne cyclotrimerization catalyst given the conditions they employed. Attempts to observe either real-time cyclotrimerization or Co coordination of the two water-soluble alkynes sodium propiolate and 1-hydroxy-3-butyne by the use of the IR flow reactor were also not successful.
Acknowledgment We are grateful to the Army Research Office for support of this work through Grant DAAG55-98-0253. We thank Maria Martinez and David Kragten for providing the X-ray powder diffraction analysis. ICPMS analyses were performed at the University of Delaware College of Agriculture. Literature Cited (1) Reppe, W. Toward the Knowledge of Metal Carbonyl and Metalcarbonyl Hydrides. Liebigs Ann. Chem. 1953, 582, 116. (2) Jerome, K. S.; Parsons, E. J. Metal-Catalyzed Alkyne Cyclotrimerizations in Supercritical Water. Organometallics 1993, 12, 2991. (3) Cody, G. D.; Boctor, N. Z.; Filley, T. R.; Hazen, R. M.; Scott, J. H.; Sharma, A.; Yoder, H. S., Jr. Primordial Carbonylated IronSulfur Compounds and the Synthesis of Pyruvate. Science 2000, 289, 1337. (4) Miksa, D.; Brill, T. B. Spectroscopy of Hydrothermal Reactions 17. Kinetics of the Surface-Catalyzed Water-Gas Shift Reaction with Inadvertent Formation of Ni(CO)4. Ind. Eng. Chem. Res. 2001, 40, 3098. (5) Orchin, M. HCo(CO)4, the Quintessential Catalyst. Acc. Chem. Res. 1981, 14, 259. (6) Vollhardt, K. P. C. Transition-Metal-Catalyzed Acetylene Cyclization in Organic Synthesis. Acc. Chem. Res. 1977, 10, 1. (7) Ford, P. C.; Rokicki, A. Nucleophilic Activation of Carbon Monoxide: Applications to Homogeneous Catalysis by Metal Carbonyls of the Water-Gas Shift and Related Reactions. Adv. Organomet. Chem. 1988, 28, 139. (8) Lide; D. R. Handbook of Chemistry and Physics, 72nd ed.; CRC Press: Boca Raton, FL, 1991; pp 4-78. (9) Edgell, W. F.; Lyford, J. The Preparation of Sodium Tetracarbonyl. Inorg. Chem. 1970, 9, 1932. (10) Kieke, M. L.; Schoppelrei, J. W.; Brill, T. B. Spectroscopy of Hydrothermal Reactions I: The CO2-H2O System and Kinetics of Urea Decomposition in an FTIR Spectroscopy Flow Reactor Cell Operable to 725 K and 335 bar. J. Phys. Chem. 1996, 100, 7455. (11) Schoppelrei, J. W.; Kieke, M. L.; Wang, X.; Klein, M. T.; Brill, T. B. Spectroscopy of Hydrothermal Reactions IV. Kinetics of Urea and Guanidinium Nitrate at 200-300 °C in a Diamond Cell, Infrared Spectroscopy Flow Reactor. J. Phys. Chem. 1996, 100, 14343. (12) Cvetanovic, R. J.; Singleton, D. L. Comment on the Evaluation of the Arrhenius Parameters by the Least Squares Method. Int. J. Chem. Kinet. 1977, 9, 481. (13) Wilhelm, E.; Battino, R.; Wilcock, R. J. Low-Pressure Solubility of Gases in Liquid Water. Chem. Rev. 1977, 77, 219.
Ind. Eng. Chem. Res., Vol. 41, No. 21, 2002 5157 (14) Day, J. P.; Pearson, R. G.; Basolo, F. The Kinetics and Mechanism of the Thermal Decomposition of Nickel Tetracarbonyl. J. Am. Chem. Soc. 1968, 90, 6927. (15) Edgell, W. F.; Yang, M. T.; Koizumi, N. The Nature of the Solution of Sodium Tetracarbonylate(-1) in Varous Solvents. J. Am. Chem. Soc. 1965, 87, 2563. (16) Funaioli, T.; Biagini, P.; Fachinetti, G. Cobalt Carbonyl Chemistry in Wet Ethereal Solutions: {Co6(CO)1s]2- and Co6(CO)16 Cluster Formation or Stepwise Water-Gas Shift Reaction. Inorg. Chem. 1990, 29, 1440.
(17) Torrent, M.; Sola, M.; Frenking, G. Theoretical Study of Gas-Phase Reactions of Fe(CO)5 with OH- and Their Relevance for the Water-Gas Shift Reaction. Organometallics 1999, 18, 2801.
Received for review March 11, 2002 Revised manuscript received June 24, 2002 Accepted July 28, 2002 IE020185D
