Catalytic hydrocarboxylation

Table 5.1. Catalytic hydrocarboxylation of benzyl halides in aqueous systems...

Figure 8 shows kinetic data on the catalytic hydrocarboxylation of methyl linolenate. There is initial conjugation of the triene system. Monocarboxy acids formed as initial products peak after 2 hrs and disappear almost completely. The dicarboxy acids are important intermediates and carboxylate further to give tricarboxy acids. The conversion to tricarboxy acids at 140°C does not exceed 50 to 53% (Runs 9 and 11, Table I). Cyclic ketones are formed as in linoleate in small but significant amounts. 

Narayanan P, Clubley B G, Cole-Hanulton D J et al. (1991) Polycarboxylic acids via catalytic hydrocarboxylation of polybutadienes. J Chem Soc Chem Commun issue 22 1628-1629... 

Catalytic hydrocarboxylations and related esterifications as well as amidations of alkenes belong to a family of carbonylation reactions which has attracted considerable industrial interest. Minor changes in the catalyst system as well as in reaction conditions can lead to simple carboxylic acids, diacids, polyketones, or unsaturated acids as products (Scheme 1). Most importantly, these methods provide routes to monocarboxylic acids, e.g., ethylene to propanoic acid (see Section 2.1.2.2), or 1-olefins (readily available from the oligomerization of ethylene discussed in Section 2.3.1.3) to higher carboxylic acids. 

The production of polymers with carboxylated backbones is of particular interest due to potential application of such polymers in films and surface coatiug. t The polycarboxylic acids can now be easily prepared via catalytic hydrocarboxylation of... 

The distribution of the products (1 and 2) is approximately 9 1 in favor of 1 when R is phenyl or a straight-chain alkyl group 2 is favored when R is t-Bu and is the exclusive product when R is SiMej. hitemal alkynes (R, R H) also undergo catalytic hydrocarboxylation with formic acid, but the regioselectivity is not as high as for terminal alkynes. 34]... 

The dependence of the induction period and half-time values on the pressure is well demonstrated by table 35 and fig. 14, showing the catalytic hydrocarboxylation of n-octynes in the presence of Ni(CO)4. 

Zhang Y, Riduan SN (2011) Catalytic hydrocarboxylation of alkoies and alkynes with C02-Angew Chem Int Ed 50 6210-6212... 

Real J, Prat E, Gonzalez-Cabello S, Pages M, Polo A. Direct evidence of cfs-addition in the catalytic hydrocarboxylation of acenaphthylene to acenaphthene-l-carboxylic acid. Orga-nometallics 2000 19 4715 719. 

K. Tani and Y. Kataoka, begin their discussion with an overview about the synthesis and isolation of such species. Many of them contain Ru, Os, Rh, Ir, Pd, or Pt and complexes with these metals appear also to be the most active catalysts. Their stoichiometric reactions, as well as the progress made in catalytic hydrations, hydroal-coxylations, and hydrocarboxylations of triple bond systems, i.e. nitriles and alkynes, is reviewed. However, as in catalytic hydroaminations the holy grail", the addition of O-H bonds across non-activated C=C double bonds under mild conditions has not been achieved yet. 

The hydrocarboxylation of styrene (Scheme 5.12) and styrene derivatives results in the formation of arylpropionic acids. Members of the a-arylpropionic acid family are potent non-steroidal anti-inflammatory dmgs (Ibuprofen, Naproxen etc.), therefore a direct and simple route to such compounds is of considerable industrial interest. In fact, there are several patents describing the production of a-arylpropionic acids by hydroxycarbonylation [51,53] (several more listed in [52]). The carbonylation of styrene itself serves as a useful test reaction in order to learn the properties of new catalytic systems, such as activity, selectivity to acids, regioselectivity (1/b ratio) and enantioselectivity (e.e.) in the branched product. In aqueous or in aqueous/organic biphasic systems complexes of palladium were studied exclusively, and the results are summarized in Table 5.2. 

Figure 8 Proposed catalytic cycle in the Pdf tppts)j-catalysed hydrocarboxylation of olefins.

The papers in this volume concern results observed in catalytic systems. They span a broad range of catalytic reactions including hydro-formylation, hydrocarboxylation, hydrogenation, carbonylation, cyana-tion, and olefin oxidation. To some extent, the results provide a significant extension of our understanding of previously studied catalysts and catalytic reactions. However, some of the papers are concerned with newer areas of research and feature results of both scientific and potential industrial importance. 

The final step in the catalytic cycle is the cleavage of the metal-alkyl bond with acid, which must take place faster in the hydrocarboxylation of alkenes than -elimination. 

The 1,2-addition of H and CO2H, or CO2R to alkenes and alkynes is called hydrocarboxylation, or hydroesterification, and proceeds with catalytic amounts of... 

Other approaches that have been suggested include catalytic asymmetric hydroformylation of 2-methoxy-6-vinylnaphthalene (6) using a rhodium catalyst on BINAPHOS ligand followed by oxidation of the resultant aldehyde 7 to yield 5-naproxen (Scheme 6.3).22 However, the tendency of the aldehyde to racemize and the co-generation of the linear aldehyde isomer make the process less attractive. Other modifications related to this process include catalytic asymmetric hydroesterification,23 hydrocarboxylation,24 and hydrocyanation.25... 

In the previous chapters we discussed alkene-based homogeneous catalytic reactions such as hydrocarboxylation, hydroformylation, and polymerization. In this chapter we discuss a number of other homogeneous catalytic reactions where an alkene is one of the basic raw materials. The reactions that fall under this category are many. Some of the industrially important ones are isomerization, hydrogenation, di-, tri-, and oligomerization, metathesis, hydrocyana-tion, hydrosilylation, C-C coupling, and cyclopropanation. We have encountered most of the basic mechanistic steps involved in these reactions before. Insertions, carbenes, metallocycles, and p -allyl complexes are especially important for some of the reactions that we are about to discuss. 

Finally, it should be apparent that the nature of the reaction media has a profound effect on the reactivity of this system, and that, particularly for secondary alcohols, generation of olefins (and metal hydrides) occurs quite easily. Since this involves only the organic equilibria, this situation is not unique to rhodium chemistry. Unless great care has been taken to eliminate possible contributions of the hydrido/olefin pathway to the total reaction scheme, then, the hydrocarboxylation route should probably be considered to be a contributing reaction with other catalytic systems. 

The reaction of an aUcene (or aUcyne), CO, and H2O to directly produce a carboxylic acid is called Reppe carbony-lation chemistry or, more recently, hydrocarboxylation (see Reppe Reaction). An excellent review of palladium-catalyzed Reppe carbonylation systems has been published recently by Kiss, and coverage of this important material will not be repeated here. This catalytic reaction has been known for quite some time, although the stoichiometric Ni(CO)4-based carbonylation of acetylene was the first commercial carbonylation process implemented (equation 13). The extreme toxicity of Ni(CO)4, however, has limited practical applications (see Nickel Organometallic Chemistry). Co, Rh, and Pd catalysts have certainly replaced Ni(CO)4 in smaller-scale laboratory reactions, though for historical reasons a number of the fim-damental mechanisms discussed in this section are based on Ni(CO)4. 

The hydrocarboxylation reactions discussed above have been proposed to involve direct addition of water to the metal center prior to elimination of the product, analogous to the oxidative addition of hydrogen to a metal center at the end of a hydroformylation catalytic cycle. Another class of hydrocarboxylation reactions is more analogous to the haUde-promoted Monsanto acetic acid process, where one has a reductive elimination of an acyl halide species that is rapidly hydrolyzed with free water to generate the carboxylic acid and HX. 

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). 

The results indicate that the Ni-cyclam catalytic system offers the best yields of carboxylation, and up to 92% of CO2 incorporation into 4 could be achieved. However, the carboxylic acids were not issued from the expected hydrocarboxylation of the double bond. We could respectively identify the two (E) and (Z) isomers of the p,y-unsaturated acids 7 and 8 (isolated as their methyl esters, eq. 3), containing a vinyl fluorine substituent. The relative yields of products 7 and 8 were 45% (E/Z = 30/70) and 56% E/Z = 37/63), respectively. 

Many catalytic reactions described in this book depend on carbon monoxide and hydrogen as feedstock chemicals. Hydroformylation (CO + H2) and simple hydrogenation (H2) are typical examples. In many cases carbon monoxide undergoes side reactions, among which the water-gas shift reaction is well studied in terms of the mechanism. This explains why carbon monoxide in the presence of water (e. g., aqueous media) can be used to hydrogenate substrates such as olefins, nitroaromatics, and other unsaturated organic compounds. In a number of industrial processes (e. g., the hydrocarboxylation of ethylene), however, this is an unwanted side reaction. 

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