CA1099296A - Enhancing the promoting of a catalytic process for making polyhydric alcohols - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

This invention relates to the manufacture of polyhydric alcohols, their ether and ester derivatives, oligomers of such alcohols and monohydric alcohols and their ether and ester derivatives by reacting hydrogen and oxides of carbon in the presence of a rhodium carbonyl complex in combination with salt promoters which provide catalyst stability while maintaining high rates of product formation.

Description

~ 11,095 This in~ention relates to the production of polyhydric alcohols, their ether and ester derivatives, a~d oligomers of such alcohols. This invention also pro-duces monohydric alcohols such as methanol and their ether and es~er derivatives.
Polyhydric alcohols are presently being produced synthe~ically b~ the oxidation o~ petroleum derived material~. Owin~ to the limited availability of petxole~m sourcesj the cost o~ these petroleum derived ma~erials has been steadily increasing. Many h~.~e raised the dire pre-dic~ion o~ a significant oil shor~age in the uture. The consequence of this has been the recognition of the need for a new low cost source o chemicals which can be con~erted into such p~lyhydric alcohols.
This in~e~ion is directed to ~he process of m~king alkane diols and triol~, contain~ng 2, 3 or 4 carbon atoms~ and derivatives such as the~r esters. Key products of the process of this invention are e~ylene glycol and its es~er der~vati~es. Byproducts o this i~ention are the lesser valuable, but valua~le neverthe-less, monohydric alkanols such as methanol, ethanol and propan~ls, and their ether and ester derivatives. The p~oducts of the proc~ss of thi~ ln~ention co~tai~ earbon, hydrogen and oxygen.
There are described in U.S. Patent 3,833~634, issued Septem~er 3, 1974, and U.S. Patent 3,957,857, issued May 18, 1976~ processes for reacting hydrogen and

2~6 1~, 095 oxides of carbon in the presence of rhodium carbonyl com-plex catalysts. U.S. Patent 3,957,857 is concerned with a rhodium carbonyl cwmplex which is a rhodium carbonyl cluster exhibiting a particular infrared spec~rum. The conditions, broadly speaking, employed in those processes involve reacting a mîxture of an o~ide of carbon and hydrogen with a eatalytîc amount of rhodium in complex combination with carbon monoxide, at a tempera~ure of between about 100C to abou~ 375~C and a pressure of between abou~ 500 p.s.i.a. to about 50,000 p~s.i.a~ As described in these patents, the process ls carried ou~
in a homogeneous liquid phase mixture in the presence of one or more compounds seleeted from ~mong groups referred to in the patent, as organic oxygen ligands, org~nic nitrogen ligands and organic aza-oxa ligands. In addition to the aforementioned U.S. Patents, the follow-ing U.S. and Canadian Patents and Canadian applications amplify the development of the processes for making alkane polyols from mixtures of hydrogen and oxides of carbon:
U.S,P. 3,878,292 Patented April 15, 1975 U.S.P. 3,878,290 Patented April 15, 1975 U.S.P. 3,878,214 Patented ApriL 15, 1975 U.S.P. 3,886,364 Patented May 27, 1975 U.S.P~ 3,940,432 Patented February 24, 1976 U.S.P. 3,929,969 Patented December 30, 1975 U.S.P. 3,952,039 Patented April 20, 1976 U.S.P. 3,948,965 Patented April 6, 1976 U.S.P. 3,944~588 Patented March 16, 1976 U.S.P. 3,974~259 Patented August 10, 1976 U.S.P. 3,989,799 Patented November 2, 1976 U.S.P, 4,013,700 Patented March 22, 1977 U.SOP~ 3,968,136 Patented July 6, 1976 U~S~P~ 4~001,289 Patented January 4, 1977 Canadian Pat. 1,058,639 Patented July 179 1979 Canadian Pat. 1,064,968 Patented September 23~ 1979 Canadian Pak. 1,069,540 Patented January 3, 1980 Can. Ser. No. 262,263 Filed September 29, 1976

3 095 Can. S~r. No. 262,265 Filed September 29, 1976 Can. Ser. No. 262,266 Filed September 29, 1976 Can~ Ser. No. 287,745 Filed September 29, 1976 U.S. Patent No. 3,952,039 issued April 20, 1976 to Walker et al descrlbes the use of salts containing alkali metal cations to improve ~he yield of ~he desired alkane diols and triols of the învention. The process of the Walker et al paten~ involves providing a metal salt to the aorementioned homogeneous liquid phase reaction mix-~0 ture to promote the production of alkane polyols, ethylene glycol being the primary product in terms o its c~mmercial value. The salt promoter provided to ~he mixture is pres-ent in an amount to achieve the ~ptimum rate of forma~ion of said alkane polyol at the correlated catalyst concentra-tion, temperature and pressure of such reaction mix~ure.
A range of 0.5 - 1.5 atoms of cation per six atoms of rhodium is disclosed in the patent. ~len the amount of alkali metal cation in the reaction is greater or less than this 2mo~mt, the productivity of reaction to poly-hydric alcohol is significantly reduced. This invention~
however, provides for the selection of a salt pr~moter in terms of its basicity to minimize inhibition of alkane polyol production by the presence of anexcess of salt.
The follGwing postulate possible mechanisms which wou~d result in the above-described behavior:
a.) the inhibitor function of the salt is of higher kinetic order in salt than is the promoter function;

11,095 bo ) the promoter ~unction of the salt has a stoichiometric limit after which only the inhibitor function o~ the salt remains.
The tenm "inhibitor func~ion" means the func~ion of the salt which reæults in a decrease in alkane polyol yield as salt concentration increases.
An above postulate can be illustrated by the following reac~ion scheme:
The involvement of salt is described as follows L0 tRh symbolizes a rhodium~containing ~pecies):

Rh ~ salt (MX)~ h M ~ + M ~ 3 glycol [NOTE: In the above reaction scheme the charge o~ the rhodium carbonyl comple~ is no~ showrl; it contains a fixed or varying number o~ Cûls and H~s; the rate and equilibr~um constants implicity contain an~ appropriate CO and H2 concentration~.] The salt acts as a promoter because its anion helps to produce the active catalyst ~nd as an in-hibitor because its cation has an adverse mass law effect on the equilibrium concentration o a direct precursor of the active catalyst. The model sugge~ts the use of a salt and reaction conditions which produce a reactive anion and an impotent cation.
The model predicts that the rate will increase as a function of the stoichiometric concentration of salt promoter, and then decrease. As K increases, elther because of an intrinsic property of M+ or use of a sol~ent of high dielectric constant (for example, suli~olane) or 11,09~

high constant of complexation with M~,(for example, crown ether, and to a lesser extent tetraglyme) 3 the rate of decrease decreases. Any complexation of ~he cation by ~he solvent is incorporated implici~y into the deinition o K as a resuL~ of t~e cu~omary deinition of standard states. More generally, however, such a microseopic solvent effect is jus~ one example of the use of a co~plexing agent to in1uence the ion-pairing abili~y of M+. The simplest case, since it would not in~olve ~he introduction of an additional compound,would be complexation of M~ by X~.
This is described by the following equilibra XlM~ X- ~ M~ (2) ~ ~ ROX ~ ~.i T RO (3) RO ~ RO- + ~ (4) Thus, the process of U.S.Patent ~o. 3~952J039 recognizes that there is an optimum concentration for salt promoters ~o achieve maximum alkane polyol production ~nd that amounts in excess of that optimum concentration are undesirable. This in~ention contemplates increasing the concentration o the salt in excess of said opti~um c~ncentratlon for the purpose of enhancing catalyst stabilit~ in the reaction. Catalyst stability relates to the desirable feature of keeping the catalyst in solu-tion. The invention also recognizes the fact that allow-ing for some excess of the salt over the optimum concenr tration will reduce the criticality of having to operate the process under strict control of salt concentration, - 11,095 The process of this invention differs from the process described in U.S. Patent No. 3,952,039, in that there is provided in the aforementioned homogeneous liquid phase mixture a concentration of salt promoter in excess o~ the optimum such that the yield of alkane polyol is nct decreased from the maximum by more than 50%.
For the purposes of this invention, ~he ultimate salt promoter selected is one whose cation ion pairs least with the rhodi~ catalyst. One should employ such a promo~er in the homogeneous liquid phase reaction mix-ture in an amount which is greater than the minimum for producing the maximum amount of alkane polyols, partic-ularly ethylene glycol 9 using that pr~moter.
The efects of concentration of the salt pro moter on product formation in the homogeneous liquid phase mixture of the process o~ this invention has been found to be dependent upon the tempera~ure, thP rhodium concentra-tion, the solvent employed and, to a lesser degree, the pressure.
The precise role of the rhodium carbonyl com-plexes, such as the rhodium carbonyl clusters, in the reaction of ~ydrogen with oxides of carbon to produce polyhydric alcohols is not fully appreciated at present.
Under the reaction conditions of the present process the carbonyl complexes are believed to be anionic in their active forms.

11,095 Infrared spectra under reaction conditions of the present process have shown Rh(C0)4, Rhl3(CO)24H3 2, Rh6(C0)15~ , Rhl3(co)24H2 , ~nd [Rhl2(CO)34-36] anions~
and other rhodium clusters to be present at various con-centrations at different times of the reaction. These may represent the active rhodium carbonyl species re-sponsible or polyhydric alcohol formation or may be merely symptomatic of some further intermediate trans-itory rhodium carbonyL structure which serves to convert the carbon monoxide and hydrogen to the polyhydric alcohol.
The salt promoters contemplated by the present invention include any organic or inorganic salt which does not ~dversely affect the production of polyhydric alcohols.
Experimental wor~ suggest that ~any salts are beneficial as either a copromoter and/or in aiding in maintaining rhodium in solu~ion during the reaction. Illustrative of useful salt promoters are the ammonium salts and the salts of the metals of Group I a~d Group Il o~ the Periodic Table (Handbook of Chemistry and Physics 50th Edition) for instance the halide, hydroxide, alkoxide, phenoxide and carboxylate salts such as sodium fluoride 3 cesium fluoride~ cesium pyridinolate, cesium formate, cesium acetate, cesium benzoate~ cesium ~-me~hylsulfonyl-benzoa~e (CH3S02C6H4COO)Cs, rubidium ace~ate, magnesium acetate, strontium acetate, ~mmonium formate, ~mmonium benzoate and the like. Preerred are the cesium and ammonium salts.

~9~ 6 11,095 In addition, the anion of the above salt may be any of the rhodium carbonyl anions. Suitable rhodium carbonyl anions include ~Rh6(CO)15~2 ; [Rh6(CO)15Y~
wherein Y may be hydrogen or halogen, such as chlorine, bromine, or iodine, [Rh6(C0)15(COOR"] wherein R" is lower alkyl or aryl such as methyl, ethyl, or phenyl;
~Rh (CO)14]2 ; [Rh7(C0)16] ; [Rh12(C )30]
Rhl3(C0)24H3 ; and Rhl3(~0)24H2 ; Rhl3(C0)24H .
The capabilities of seven cesium carboxylates (RC02Cs) as inhibitors of alkane polyol formation in tetraglyme, 18-crown~6 and sulfolane are shown in Tables I and III and Figures 1 and 2. They decrease with in-creasing basicity of RC02 , a result consistent with ~onsideration of equilibria (5)-(8) Rh Cs~ Rh ~ ~s~ (5) RC4 Cs+ - ~ RC2 + Cs~ (6) R~02 + R'OH ~ - > RC02H ~ R'O- (7) R'O Cs+ ~ ~ R'O ~ Cs+ (8) within the framework of the previously discussed model:
Since inhibitor capability ~rate of fall-off o a plot of g glycol vs. n~moles salt (Figures 1 and 2), gO ~5~ gO 75 (Table I)3 depends on K5 , an increase in basicity Ks ~ [Cs~
of RC02 at fîxed stoichiometric ~Cs+~ leads to a decrease in ~Cs+3 and in its inhibitory effeGtO Note that ~his depend-ence on basicLty of RC02 ls not merely a general "basi ity effect" of added nucleophile (amine or anion) since variatlon of basicity of amine and anion affects oppositely the degree ll ~ o9s C`l~
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._ 11,095 of inhibition by the amine and salt, respectively. The effect of æmine basicity on inhlbition of alkane polyol formation is disclosed in copending application Canadian Ser. No. 262,263, $iled September 29, 1976.
Illustrative solvents which are generally suit-able in making the homogeneous mixture lnclude9 for ex-ample, e~hers such as ~etrahydrofuran, tetrahydropyran, crown ethers (see, for example, "S~ruc~ure and Bonding"
vol. 16, 1973, Published by Springer-Verlag), diethyl ether, 1,2-dimethoxybenzene, 1,2-diethoxybenzene, the mono- and dialkyl ethers of ethylene g7ycol, of propylene glycol, of butylene glycol, of diethylene glycol, of dipropylene glycol, of triethylene glycol, of tetraethylene glycol, of dibutylene glycol, of oxyethylenepropylene glycol, etc.;
alkanols such as methanol, ethanol, propanol, isobutanol, 2-ethylhexanol, etc.; ketones such as acetone, methyl ethyl ketone, cyclohexanone, cyclopentanone, etc~; esters such as methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl butyrate, methyl laurate, etc.; water gamma-butyrolactone, deltavalerolactone, substituted and unsubstituted tetrahydrothiophene-l,l-dioxides (sulfolanes) as disclosed in Canadian Patent 1,069,540, patented January 8, 1980, at pages 6 and 7 of the specification; and others. The mono dialkyl ethers of tetraethylene glycol, gamma bu~yrolactone, par-ticularly sulfolane, 3~4-bis(2-methoxyethoxy) sulfolane, and crown ethers, are the preferred solvents.
The temperature which may be employed can vary over a wide range of elevated temperatures. In general, the process can be conducted at a temperature in the range of from about 100C and upwards to approximately 375C, and higher. Temperatures outside this stated rang~ are 13.

~ 11,095 ~, not excluded from the scope of ~he invention. At the lower end of the temperature range, and lower, the rate of reaction to desired product becomes mar~edly slow. At the upper t.emperature range, and beyond, signs of some catalyst ins~ability are no~ed. Notwithstanding this factor, reaction continues ant alkane polyols and/or their derivativPs are producedO Additionally, one should take notice of the equilibrium re~on for forming ethylene glycol CO ~ 3H~ ~ HOCH2 CH OH
At relatively high tempera~ures ~he equilibrium inereasing~
ly favors the left hand side of ~he equation. To drive the reaction to the formation of increased quantities of ethylene glycol~ higher par~iat pressures of carbon monoxide and hydrogen are required. Processes based on correspondingly higher pressures, howeverg do not represent preferred embodiments of the invention in view of the high in~estment costs associated with erecting chemical plants which utilize high pressure utilities and the necessi~y of fabricating equipment capable of withstandin~ such enoLmous pressures. Suitable tempera-tures are between about 150 C to about 320C, and desirably from about 210C to about 300C.
The novel process is e~fected for a period of tLme sufficiPnt to produce the alkane po~yols and/or derivatives thereof. In general, the residence time can vary from minutes to several hours, e.g., from a few minutes to approximateLy 24 hours, and longer. It is readily appreciated that the residence period will be 11,095 ~19~Z~6 influenced to a significant extent by the reaction te~-p~rature, the concentration and choice of the catalyst, the total gas pressure and the partial pressures exerted by its components, the concentration and choice of diluent, and other factors. The synthesis of the desired product(s) by the reaction o~ hydrogen wlth an oxide of carbon is suitably conducted under operati~e conditions which give reasonable reaction rates and/or conversionsO

The relative amounts o~ oxide o carbon and hydrogen which are lnitially presen~ in ~he reaction mixture can be ~aried over a wide range.
In general, the mole ratio o CO:H2 is in the range o from about 20:1 to about 1:20, suitably from about 10:1 to about 1:10, and pre~erably from about 5:1 to abou~ 1:5.
It is to be understood, however9 that molar ratios outside the aforestatP.d broad range may be emplQyed. Substances or reaction mixtures which give rise to the formation o carbon monoxide and hydrogen under the reaction conditions may be employed ins~ead o mixtures comprising carbon monoxide and hydrogen which are used in preferr~d r embodimen~s in the practice of the inven~ion.
For instance, polyhydric alcohols are obtained by using mixtures containing carbon dioxide and hydrogen. ~ixtures o~ carbon dioxide, carbon monoxide and hydrogen c~n also be empLoyed. If desired, ~he reaction mixture an eompri~e ste~m a~d car~on monoxide, 11,095 The novel process can be executed in a batch, semi-continuous, or continuous fashion.
The reaction can b~ conducted in a single reaction æone or a plurality of reaction zones, in series o~ in parallel, or it may be conducted inter-mittently or continuously in an elongated ~ubular zon~ or series o such zones. The material of construction should be such that it is inert during ~he reaction and the fabriea~ion of the equipment should be able to withstand the reaction temperature and pressure. Ihe reaction zone can be fitted with inte~nal and/or external heat exchanger(s) to thus control undue tempera-ture fluctuatio~, or to prevent any possibl~
"run-away" reaction temperatures due to the exothermic nature of the reastlon~, II1 preferred embodiments o~ the invention, agitation means to vary the dcgre~ of mixi~g of the reaction mixture can be suitably employed. Mixing induced by ~ibration~ shaker~ stirrer, ro~atory, oscilla~ion, ultrasonic, etc., æe all lllus~ra~ive o ~he typ~s of agitatiQn means which are contemplated.
Such means are available ~nd we~l~known to the ar..
The catalyst may be initlally introduced into the ~ reaction æone batchwise~ or it may be contLnuously - or intermittently introduced in~o such zone during the course of the synthesis reaction. Means to introducs and/or ad~ust the reactants, either 11, 095 intermittently or contiIluously, into the reaction zone during the course of the reaction can be conveniently utilized ;n ~he novel process especially to maintain the desired molar ratios of and ~he partial pressures exerted by the reactants.

As intimated previously, the operative conditions can be adjusted to optimize the conversion of the desired product and/or the economics of the novel process. In a continuous process, for instance, when it is preferred ~o operate at relatively low conversions, it is generally desirable to recirculate unreacted synthesis gas with/with-out make-up carbon monoxide and hydrogen to ~he reaction.
Recovery o~ the desired product can be achieved by methods well-known in the art such as by distillation, fraction-ation, extraction, and the like. A fraction comprising rhodium catalyst~ g~nerally contained in byproduc~s and/or normally liquid organic diluen~, can be rec~cled to the reaction zone, if desiredO All or a portion of such .
fraction can be removed for recovery o~ the rhodium ~alues or regeneration to the active catalys~ and intermittently added to the recycle stream or directly to the reaction zone.
The acti~e forms of the rhodium carbonyl clusters may be prepared by various techniques. They can be preformed and then introduced into the reaction zone or they can be formed i~ situ.

11, 095 ~Ca9~`96 The equipment arrangement and procedure which provides the capability for determlning ~he existence of anionic rhodium carbonyl complexes or clusters having de-fined infrared spectntm characteristics, during ~he course of the manufac~ure of polyhydric alcohols from carbon mon-oxide and hydrogen, pursuant to this invention is disclosed and schematically depicted ln U.S. Patent application No.
3,957,8S7 3 issued May 18, 1976.
A particularly desirable infrared cell construc-tion is described in U.S. Patent No. 3,886,364, issued May 27, 1975. The preferred cell of U.S. Pa~ent No.
3,886,364 is well suited for use in the aforementioned procedure.
The "oxide of carbon" as covered by the claims and as used herein is intended to mean carbon monoxide and mixtures of carbon dioxide and carbon monoxide, elther introduced as such or formed in the reaction. Preferablyg the oxide o carbon is carbon monoxide.
Materials used in the followlng examples had the following characteristics:

11~095 ~ 6 Tetraglyme (Ansul), cesium formate (Alfa), and cesium acetate (Alfa) were used without urther purifica-tion. Sulfolane (Phillips) was puriied as described in E.N. Arnett and C.F. Douty, J.Am.Chem.Soc., 86, 409 (1964).
Cesium benzoate,[J H.S. Green, W. Kynaston~ and A.S.
Lindsey, Spec~rochim. Acta, 17, 486 (1961)], (recryst.
H20. Anal. Found: G,32.62; H,l.90. Calcd. for G7H50zCs:
C,33.10; H,1.98) and cesium pivalate ~P.H. Reichenbacher~
M.D. Morris, and P.S. Skell, J.Am.Chem.Soc.~ 90, 3432 (1968)], (washed with PhCl, recryst. H20. Anal. Found:
C,24.75; H,4.20. Calcd. for C5H902Cs: C,25.66; H,3.88) were prepared by use of literature procedures. Cesium p-methylsulfonyl benzoate (washed with ether, recryst.
H20. Anal. Found: C,28.26; H,2.05. Calcd. for C8H704SCs:
C,28.90; H,2.13), cesium triphenylacetate (recryst. H20.
Anal. Found: C,56.25; H,3.74. Calcd. for C20H1502Cs:
C,57.16; H,3.60), and cesium isobutyrate (washed with PhCl, recryst. H20. ~nal. Fou~d: C,21.01; H~3.32.
Calcd. or C4H702Cs: C,21.84; H,3.21) were prepared by reaction of CsOH and the corresponding acids. ~18] crown-6 solvent was obtained from Pari~h Chemical Company, Pxovo, Utah, and was heated under vacuum to remove possible volatile impurities and its purity was checked by vpc, nmr~ mel~ing point, and elemental analysis.
Pr3cedure employed in examples:
A 150 ml. capacity stainless steel reactor cap-able of withstanding pressures up to 7,000 atmospheres was charged with a premix of 75 cubic centimeters (cc) of llgO95 ~ g9296 solvent, rhodium dicarbonylacetylacetonate, and promoter(s).
The reactor was sealed and charged with a gaseous mixture, containin~ equal molar amounts of carbon monoxide and hydro-gen, to the desired pressure. Heat was applied to the reactor and its contents; when the temperature of ~he mixture inside the reactor reached 190C, as measured by a suitably pla~ed thermocouple, the carbon monoxide and hydrogen (H2:CO=l:l mole ratio) pressure was adjusted to maintain the desired gas pressure. During the course of the reaction additional carbon monoxide and hydrogen was added whenever the pressure inside the reactor dropped approximately 500 psi below the desired pressure. With these added repressurizations, the pressure inside the reactor was maintained within about 500 psi of the desired pressure over the en~ire reaction period.
A~ter the reaction p~riod, the vessel and its contents were cooled to room temperature, the excess gas vented and the reaction product mixture was removed.
Analysis of the reaction product mixture was made by gas chromatographic analysis using a Hewlett Packard FM TM
model 81Q Research Chromatograph.
Rhodium recovery was determined by atomîc absorp-tion analysis of the contents of the reactor after the ~enting of the unreacted gases at the end of the reaction.
The rhodium recovery values recited below are the percent rhodium based on the total rhodium charged to the reactor that is soluble or suspended in the reaction mixture after the specified reaction time.

11,095 g296 The same equipment and procedure were used in all the ea~amples in the Tables and Figures except or the reactants and conditions speciied. Table III
illustrates the use of cesium carboxylates in excess of optimum concentration in ~18~ crown-6 solvent and its at:tendant inc;ease in rhodium stability.
Figure 1 graphically depicts the inhibitory effect of the use of various carboxylate salts in excess of the optimum con~entration. The dissociation constant o the conjugate acid for each sal~ is also provided.
Figure 2 illustrates ~he inhibitory effect o PhCQ2Cs promoter in 2 solvents of diferent complexing ability. The inhibitory effect is shown to be weaker in the solvent of greater c~mplexing a~ility, i.e., [18] crown~6.

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Claims (7)

WHAT IS CLAIMED IS:

1. A process of producing alkane polyols by the reaction of oxides of carbon and hydrogen in a homogeneous liquid phase mixture containing a rhodium carbonyl complex catalyst in combination with a salt promoter; the catalyst concentration, the temperature of between about 100°C to about 375°C and the pressure of between about 800 psia to about 50,000 psia being correlated so as to produce such alkane polyol; the promoter being provided in combination with the catalyst in an amount determined from the promoter's basicity to achieve not less than 50% of the optimum rate of formation of the alkane polyol at said correlated catalyst concen-tration, temperature and pressure of said mixture, the amount of the promoter being greater than the minimum amount which is sufficient to produce such optimum rate of formation.

2. The process of claim 1 wherein the homo-geneous liquid phase mixture additionally contains an amine promoter.

3. The process of claim 1 wherein the mixture contains a solvent.

4. The process of claim 3 wherein the solvent is tetraglyme.

5. The process of claim 3 wherein the solvent is sulfolane.

6. The process of claim 3 wherein the solvent is a crown ether.

7. The process of claim 1 wherein the oxide of carbon is carbon monoxide.