Other Carbonylation and Hydrocarboxylation Reactions

There are some relatively small-volume but value-added chemicals that are commercially manufactured by carbonylation or hydrocarboxylation reactions. A few examples with some details are given in Table 4.2. 

The mechanism of the Montedison reaction has been studied in some detail, and tentative mechanisms have been offered. The proposed catalytic cycle is shown in Fig. 4.11. The biphasic reaction medium consists of a layer of diphenyl ether and that of aqueous alkali. In the presence of alkali, the precatalyst Co2(CO)8 is converted into 4.7. The sodium salt of 4.7 is soluble in water but can be transported to the organic phase, that is, a diphenyl ether layer by a phase-transfer catalyst. The phase-transfer catalyst is a quaternary ammonium salt (R4N+X ). The quaternary ammonium cation forms an ion pair with [Co(CO)4]. Because of the presence of the R groups, this ion pair, [R4N]+[Co(CO)4], is soluble in the organic medium. In the nonaqueous phase benzyl chloride undergoes nucleophilic attack by 4.7 to give 4.40, which on carbonylation produces 4.41. The latter in turn is attacked by hydroxide ion transported from the aqueous phase, to the organic phase again by the phase-transfer catalyst. The product phenyl acetate and 4.7 are released in the aqueous phase as the sodium or quaternary ammonium salts. 

As mentioned in Table 4.2, the industrial Ube reaction is probably carried out on a heterogeneous catalyst. The probable mechanism is based on generation of an alkyl nitrite and oxidative addition of the alkyl nitrite onto a Pd° center. Nitric oxide is used as a co-catalyst in the Ube process. The Hoechst 

TABLE 4.2 Chemicals Manufactured by Carbonylation or Hydrocarboxylation Reactions 

Montedison Phenylacetic acid an intermediate for pesticide and perfumes Cobalt catalyst PhCH2Cl, CO, and HO- are the reactants T 55°C, P = a few bars Reaction carried out in a biphasic medium with a phase-transfer catalyst 

In the Rh-catalyzed carbonylation of -propanol, a similar hydrocarboxylation cycle involving the hydride intermediate 4.9 also operates. In other words, PrCO H and PrCO H are formed from carbonylation (Fig. 4.2) as well as from hydrocarboxylation (Fig. 4.7) reactions. 

As mentioned earlier, under the operating conditions, small amounts of propylene are formed from the dehydration of -propanol. Propylene displaces a CO ligand of 4.9 and inserts into the Rh-H bond in Markovnikov and anti-Markovnikov fashion to give 4.18 and 4.19. Subsequent CO insertions generate 4.20 and 4.21, which on hydrolysis give a mixture of PrCO H and PrCO H and complete the catalytic cycle. 

It is important to note that the hydrocarboxylation and carbonylation catalytic cycles involve common intermediates, but there are clear differences. In the hydrocarboxylation reaction, there is no oxidative addition or reductive elimination step, and all the intermediates have Rh. Other Fe-, Ru-, Co-, Rh-, Ir-, Pd-, and Pt-based hydrocarboxylation and/or hydroesterification catalysts are also known. Eastman Chemical has reported a Mo(CO)g-catalyzed ethylene hydrocarboxylation process that involves a radical mechanism. 

Four other carbonylation reactions are to be noted. These are industrial manufactures of phenyl acetic acid and ibuprofen, the versatile Pauson-IChand reaction (PKR) for the cyclopentenone ring system, and the carbonylation of epoxides to give j3-lactones. The last two reactions are important from the point of view of their potential applications in the catalytic syntheses of fine chemicals and organic intermediates. 

In the presence of alkali, the precatalyst Co2(CO)g is converted into [Co(CO)J. The sodium salt of [Co(CO)J is soluble in water but not in diphenyl ether. It can, however, be transported to the diphenyl ether layer by a phase-transfer catalyst. 

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The catalytic hydrocarbonylation and hydrocarboxylation of olefins, alkynes, and other TT-bonded compounds are reactions of important industrial potential.Various transition metal complexes, such as palladium, rhodium, ruthenium, or nickel complexes, have widely been used in combination with phosphines and other types of ligands as catalysts in most carbonylation reactions. The reactions of alkenes, alkynes, and other related substrates with carbon monoxide in the presence of group VIII metals and a source of proton affords various carboxylic acids or carboxylic acid derivatives.f f f f f While many metals have successfully been employed as catalysts in these reactions, they often lead to mixtures of products under drastic experimental conditions.f i f f f In the last twenty years, palladium complexes are the most frequently and successfully used catalysts for regio-, stereo-, and enantioselective hydrocarbonylation and hydrocarboxylation reactions.f ... 

One of the first mechanistic proposals for the hydrocarboxylation of alkenes catalyzed by nickel-carbonyl complexes came from Heck in 1963 and is shown in Scheme 24. An alternate possibility suggested by Heck was that HX could add to the alkene, producing an alkyl halide that would then undergo an oxidative addition to the metal center, analogous to the acetic acid mechanism (Scheme 19). Studies of Rh- and Ir-catalyzed hydrocarboxylation reactions have demonstrated that for these metals, the HX addition mechanism, shown in Scheme 24, dominates with ethylene or other short-chain alkene substrates. Once again, HI is the best promoter for this catalytic reaction as long as there are not any other ligands present that are susceptible to acid attack (e g. phosphines). 

Cobalt, nickel, iron, ruthenium, and rhodium carbonyls as well as palladium complexes are catalysts for hydrocarboxylation reactions and therefore reactions of olefins and acetylenes with CO and water, and also other carbonylation reactions. Analogously to hydroformylation reactions, better catalytic properties are shown by metal hydrido carbonyls having strong acidic properties. As in hydroformylation reactions, phosphine-carbonyl complexes of these metals are particularly active. Solvents for such reactions are alcohols, ketones, esters, pyridine, and acidic aqueous solutions. Stoichiometric carbonylation reaction by means of [Ni(CO)4] proceeds at atmospheric pressure at 308-353 K. In the presence of catalytic amounts of nickel carbonyl, this reaction is carried out at 390-490 K and 3 MPa. In the case of carbonylation which utilizes catalytic amounts of cobalt carbonyl, higher temperatures (up to 530 K) and higher pressures (3-90 MPa) are applied. Alkoxylcarbonylation reactions generally proceed under more drastic conditions than corresponding hydrocarboxylation reactions. 

To date, mechanistic studies into the carbonylations of secondary alcohols with the same type of rhodium/RI catalyst system have used 2-propanol as a model substrate. At least part of the reason for this has been to minimize the expected complexities of the product analyses. The carbonylation of 2-propanol gives mixtures of n- and isobutyric acids. Two studies have been (24b, 32) reported with this system. The first of these (32) concluded that the reactivity could be described in terms of the same nucleophilic mechanism as has been described above, despite the fact that the reaction rates at 200°C were approximately 140 times faster than predicted by this type of chemistry (24b). Other data also indicated that this SN2-type reactivity was probably not the sole contributor to the reaction scheme. For example, the authors were not able to adequately explain either the effect of reaction conditions on product distribution or the activation parameters. They also did not consider the possible contribution of a hydrocarboxylation pathway, which is known to be extremely efficient in analogous systems (55). For these reasons, a second study into the carbonylation of 2-propanol was initiated (24b, 57). 

The acid-catalyzed hydrocarboxylation of alkenes (the Koch reaction) can be performed in a number of ways. In one method, the alkene is treated with carbon monoxide and water at 100-350°C and 500-1000-atm pressure with a mineral acid catalyst. However, the reaction can also be performed under milder conditions. If the alkene is first treated with CO and catalyst and then water added, the reaction can be accomplished at 0-50°C and 1-100 atm. If formic acid is used as the source of both the CO and the water, the reaction can be carried out at room temperature and atmospheric pressure.The formic acid procedure is called the Koch-Haaf reaction (the Koch-Haaf reaction can also be applied to alcohols, see 10-77). Nearly all alkenes can be hydrocarboxylated by one or more of these procedures. However, conjugated dienes are polymerized instead. Hydrocarboxylation can also be accomplished under mild conditions (160°C and 50 atm) by the use of nickel carbonyl as catalyst. Acid catalysts are used along with the nickel carbonyl, but basic catalysts can also be employed. Other metallic salts and complexes can be used, sometimes with variations in the reaction procedure, including palladium, platinum, and rhodium catalysts. The Ni(CO)4-catalyzed oxidative carbonylation with CO and water as a nucleophile is often called Reppe carbonylationP The toxic nature of nickel... 

For technical purposes standard carbonylation catalysts such as Co2(CO)g and Ni(CO)4 have been used to prepare fatty-acid esters [1]. More recently, other catalysts based on Pd, Pt, Rh, and Ru found widespread use because of their better performance under milder reaction conditions [2]. As seen in eq. (1) and Table 1, hydrocarboxylation of simple olefins with palladium catalysts occurs at temperatures of 70-120 °C and 0.1-20 MPa, while cobalt catalysts needed 150-200 °C and 15-20 MPa. 

Rhodium cationic and zwitteiionic complexes proved to be superior catalysts for the hydroformylation of vinylsilanes, producing either a- or ff-silyl aldehydes depending on the reaction conditions [162], On the other hand, carbonylation of vinylsilanes in the reaction related to hydrocarboxylation and hydroesterification afforded P- and a-silyl esters in high yields (eq. (14) [163]). 

As described by H. W. Sternberg [440], hydrocarboxylation of acetylenes is possible also in alkaline medium, where (Ni3(CO)8) is believed to function as the CO-donor. Thus, Sternberg obtained 25 % of trans-a-phenyl cinnamic acid besides 67 % of tetraphenyl butadiene, starting from diphenyl acetylene. Starting with octynes J. M. J. Tetteroo reported a considerably lower yield [146]. As mentioned on page 83, different reaction products are obtained with Co- or Fe-carbonyls on the one hand and Ni(CO)4 on the other hand. Contrary to nickelcarbonyl, cobaltcarbonyls are of such activity that the initially formed unsaturated acids are hydrocarboxylated a second time at the double bond. Thus, dicarboxylic acids or their derivatives are obtained by hydrocarboxylation of acetylenes with cobaltcarbonyls as catalysts [226, 388-391, 393-397, 441] (see also table 39). 

For a long time experiments failed to produce normal carbonylation products starting from dienes. Under the usual conditions the conjugated dienes underwent a Diels-Alder reaction with subsequent hydrocarboxylation of the prior formed isolated alicyclic dienes. Thus, e. g. butadiene first reacted to give vinylcyclohexene which then yielded a mixture of dicarboxylic adds [493]. In other cases cyclic ketones were obtained from dienes and carbon monoxide (see section on ring closure reaction with carbon monoxide). 

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