real world of
edited by
W. C. FERNELIUS Kent State llnlverslty Kent, OH 44242
HAROLDWITTCOFF Koor Chemicals Ltd. Beer-Sheva, lsraei P.O.B. 60
Organic Chemicals from Carbon Monoxide Kenneth E. Kolb Bradley University Peoria. IL 61625 Doris Kolb Illinois Central College East Peoria, IL 61635 The orranic chemical industrv as we know i t todav is rela( I ~ I I I ! ; I , 3 % k t $ 1 1 , lllrt t ur 1 1 ~ r ~ h -: I~$ la c~ w u ~ d ~ ~i m ~ i c- . iI I~Ni~, 11w t i t u t 11 \\' Ilx.~rdt ~ A 11111,~ 1 1 111, 1 .I ~ d ' t l ~rt tI , ,1111111 ircmi l l i ~ t u r"~A >l. l ( 1 1 1 1 (~I I L . I I I ~ . R I , ~ , ~ I I .I: . oil and gas continue to go up in price and down in availability, more and more organic chemicals will be obtained from coal, the most abundant of the fossil fuels. The process of going from coal to useful organic chemicals will most likely he via synthesis gas (syn gas), a versatile mixture of carbon monoxide and hydrogen that offers great potential as a source for a wide variety of organic compounds. Treatment of coal with steam a t high temperatures yields a 1:l mixture of carbon monoxide and hydrogen. rivvl\. nnln:,
Additional hydrogen can be obtained through the classical "shift reaction."
In actual practice the manufacture of syn gas is usually carried out by oxidative steam treatment of coal, resulting in a mixture of carbon monoxide and hydrogen gases along with smaller amounts of carbon dioxide and methane (1).
In thinking about the future of CO chemistry, we may tend to forget that a number of commercial CO processes already exist. (See Table.) Most of these involve the reaction of a CO molecule with one or two other molecules to produce on principal product. In many cases the processes can be looked upon as CO insertion reactions or 1,1 additions to the CO molecule. This is an interesting and practical reaction type which has unfortunately been ignored in most organic textbooks. Of the commercial reactions listed in the table, only the methanol synthesis has been incorporated to any substantial degree into the textbook literature, and only about half of the standard organic textbooks include that one. From a pedagogical viewpoint most of these reactions can, a t least in a formal sense, he considered as 1,l electrophilic additions to the carbon atom of carbon monoxide. Classical resonance theory, molecular orbital treatment, and experimental evidence all indicate that in the CO molecule the polarization is such that the carbon atom is slightly negative.
Coulson (2) early on suggested that the electron pair on carbon is strongly directed away from the CO bond and is quite reactive (as shown by its reaction with boron hydride to form H3BCO). The reactions in the table can be looked upon as 1,l electrophilic additions in which initial attack on the CO molecule is by an electrophile (E+),with subsequent addition of a nucleophile (Nu-). 0
II
E' + C
-
E-C'
0
II
+ Nu-
-
0
I1
E4-Nu
Electrophilic and nucleophilic entities are identified in the table. We hasten to add that this is a formalism meant to help summarize a series of CO reactions and not to suggest any mechanistic path. 1) Phosgene. The industrial production of phosgene has risen r a ~ i d l vin recent vears alonr with isocvanates and produced phosgene. This is still the way it is made commercially. 2) Benzaldehyde. The second reaction in the table is the only one not being used commercially a t the present time. There is no large demand for aromatic aldehydes, and what benzaldehyde is needed is usually made from toluene (by dichlorination and hydrolysis). The reason for including this reaction here is that it is the only CO reaction that is even mentioned in many organic textbooks. Discovered in 1897 and known as the Gatterman-Koch reaction, it involves the treatment of an aromatic hydrocarbon with CO plus HCl in the presence of AlCls. (Toluene, e.g., gives a 55% yield of p methylbenzaldehyde.) 3) Methanol. Based on the pioneering work of Haber and Bosch, the hydrogenation of CO over a ZnO/Cra03 catalyst a t 300-40O0C and 275-3150 atm became the commercial process for making methanol during the 1920's. Today with new copper catalysts plants can be operated at250°C and 50 atm, thus effecting savings in both plant cost and operating energy. Methanol offers great potential as a source of organic chemicals and also as fuel, either alone or in gasohol ( 1 ) .A new Mobil Oil process converts methanol to high octane gasoline over a zeolite type catalyst. 4) Formic Acid and Derivatives. Carhon monoxide reacts with water a t 180°C to produce formic acid, but the equilibrium favors the reactants. Therefore, formic acid is removed as soon as it is formed. In the the presence of NaOH (180°C/15 atm) there are good yields of sodium formate; when methanol Volume 60
Number 1 January 1983
57
is added, methyl formate is produced. While in the presence of dimethylamine, the product is N,N-dimethylformamide (3). 5) 0x0 Aldehydes The basic oxo reaction as developed by Roelen in the early 1940's involved the use of a Co carhonyl catalyst to convert propene plus CO and hydrogen into a mixture containing roughly 60% n-hutanal and 40% of its isomer, 2-methylpropanal. Today, usmg a rhodium-hased catalyst with phosphine ligands (10O0C/10-20 atm), the . . straight chain product can be made in ratios as high as 16 to one over the branched isomer. 6) Acrylic Acids. By this process (part of Reppe acetylene chemistry) acetylene is hydrocarhoxylated to acrylic acid in the presence of Ni(C0I4 in an aqueous system. Since the 1960's this process using expensive acetylene has had to compete with direct oxidation of the much cheaper propene. 7 ) Propanoic Acid. Hydrocarhoxylation of ethylene, by treating ethylene with CO, Hz0, and a Ni(C0)4 catalyst, yields propanoic acid. 8) Neopentyl Acids. Alkenes of four or more carbons in the presence of an acid such as Hi304 react with CO and H 2 0 (80°C/100 atm) to yield neopentyl or Koch type acids. The acid promotes rearrangement of the alkene to the more stable tertiary carhonium ion, R3Cf, which reacts with CO and HzO to give RsCCOzH. These acids are available commerciallywith total carhon counts of CS to Cll. 9) Acetic Acid. Within recent years ethanal oxidation and butane oxidation have been joined by a third commercial process for making acetic acid. It is carhonylation of methanol with CO using an iodide-promoted rhodium catalyst at 20OoC/15 atm. The iodide ion seems to convert methanol to
methyl iodide, from whichthe methyl electrophile is generated on the Rh surface, where it is carhonylated in excellent yield and purity to acetic acid. 10) Acetic Anhydride. In 1980 Tennessee Eastman announced plans for a plant to produce acetic anhydride by carhonylation of methyl formate in the presence of a catalyst containing iodide plus a metal. Methanol is produced from syn gas and then reacted with acetic acid to yield methyl acetate, which upon carbonylation becomes acetic anhydride. The anhydride is used to acetylate cellulose, thus regenerating acetic acid which is recycled. A commercial reaction of CO not listed in the tahle (because of the small size of the operation) is a process for making hydroquinone. Reppe made hydroquinone from acetylene, CO, and Hz0 by the following reaction:
Today's commercial process uses a Ru/Rh catalyst at 20O0C/200 atm. Another commercial reaction not listed in the tahle is the Fischer-Tropsch reaction. The product in this case is not a single organic compound hut a wide mixture of hydrocarbons. In this process CO and Hz are reacted over a Co catalyst (containinp T h o ? and MrO and s u o ~ o r t e don kieseleuhri to operating with this process since 1955. A second plant was built in 1980, and a third is now under construction. Current research on chemicals from syn gas promises to create many more commerc~alCO processes. For example:
Commercial Reactions of Carbon Monoxide Reagent
Electrophole
Nucleophk
Product
C1-C41
1) Cln
phosgene
0
/I
2) HCI
H-C-CI 0
(formy1 chloride)
H-C-Ph 0.
benzaldehyde
I1
benzene
I/
3) H2 Hz
H+
H-
H-C-H HiCOH 0
(formaldehyde) methanol
4a) HOH
H+
H-
H-C-OH 0
formic aeid
b) CH30H
C)
HN(CH&
Ht
Ht
I1
OCHz-
(CH&N-
I1
H
