Hydrocarboxylation

Novel heterogeneous catalysts containing a palladium complex anchored on meso-porous supports for hydrocarboxylation of aryl olefins and alcohols were found to give high regioselectivity, activity, and recyclability without leaching of palladium complex from the supports. In styrene hydrocarboxylation at 115 °C and 31 bar CO pressure, 2-phenyl-propionic acid is formed with 99% selectivity at 2600 mol styrene mol palladium h turnover frequency [137]. 

High catalytic activity (TOF = 282h ) and selectivity to the branched product ( 91%) were found in the biphasic hydrocarboxylation of vinyl aromatic compounds to the isomeric atylpropanoic adds using a novel water-soluble palladium complex, ]Pd(pyridine-2-carboxylato)(TPPTS)] hrsO , as the catalyst [138]. 

The polymer-supported bimetallic catalyst system PVP-PdCl2-NiCl2/TPPTS/ PPh3 (PVP = polyvinylpyrrolidone) was found to have good activity in the hydro-xycarbonylation of styrene under aqueous-organic two-phase condition and can be reused four times with little loss of catalytic activity. The effects of temperature, CO pressure, and reaction time were studied to obtain optimum reaction conditions (Equation 7.14) [139]. 

The ruthenium(II) complex jac-[Ru(C0)2(H20)3C(=0)C2H5][CF3S03] dissolved in aqueous tetrabutylammonium hydrogen sulfate or sodium hydrogen sulfate catalyzed the hydrocarboxylation of ethylene to propionic acid under water gas shift conditions at 150 °C and 88 bar CO C2H4 = 1 1 [140]. 

The catalytic potential of transition metal sulfides for abiotic carbon fixation was assayed. It was found that at 2000 bar and 250 °C, the sulfides of iron, cobalt, nickel, and zinc promote the hydrocarboxylation reaction via carbonyl insertion at a metal sulfide bound alkyl group. The results of the study support the hypothesis that transition metal sulfides may have provided useful catalytic functionality for geochemical carbon fixation in a prebiotic world [141]. 

Another useful C—C bond-forming reaction is hydrocaiboxylation of olefins using carbon monoxide and water or alcohols (1 IS). Under the influence of Ni, Co, Pd, or Ru complexes, hydrogen and carboxyl or 

ASYMMETRIC CATAI YSIS VIA CHIRA1 META1 COMP1 EXES 

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As a unique reaction of Pd(II), the oxidative carbonylation of alkenes is possible with Pd(ll) salts. Oxidative carbonylation is mechanistically different from the hydrocarboxylation of alkenes catalyzed by Pd(0), which is treated in Chapter 4, Section 7.1. The oxidative carbonylation in alcohol can be understood in the following way. The reaction starts by the formation of the alkoxy-carbonylpalladium 218. Carbopalladation of alkene (alkene insertion) with 218 gives 219. Then elimination of /3-hydrogen of this intermediate 219 proceeds to... 

Hydrocarbons C1-C6 Hydrocarbon separation Hydrocarbon solvents Hydrocarbons Survey Hydrocarbon waxes Hydrocarbonylation Hydrocarboxylation Hydrochloric... 

It has been known since the early 1950s that butadiene reacts with CO to form aldehydes and ketones that could be treated further to give adipic acid (131). Processes for producing adipic acid from butadiene and carbon monoxide [630-08-0] have been explored since around 1970 by a number of companies, especially ARCO, Asahi, BASF, British Petroleum, Du Pont, Monsanto, and Shell. BASF has developed a process sufficiendy advanced to consider commercialization (132). There are two main variations, one a carboalkoxylation and the other a hydrocarboxylation. These differ in whether an alcohol, such as methanol [67-56-1is used to produce intermediate pentenoates (133), or water is used for the production of intermediate pentenoic acids (134). The former is a two-step process which uses high pressure, >31 MPa (306 atm), and moderate temperatures (100—150°C) (132—135). Butadiene,... 

With the exception of acetic, acryUc, and benzoic all other acids in Table 1 are primarily produced using oxo chemistry (see Oxo process). Propionic acid is made by the Hquid-phase oxidation of propionaldehyde, which in turn is made by appHcation of the oxo synthesis to ethylene. Propionic acid can also be made by oxidation of propane or by hydrocarboxylation of ethylene with CO and presence of a rhodium (2) or iridium (3) catalyst. 

C-19 dicarboxyhc acid can be made from oleic acid or derivatives and carbon monoxide by hydroformylation, hydrocarboxylation, or carbonylation. In hydroformylation, ie, the Oxo reaction or Roelen reaction, the catalyst is usually cobalt carbonyl or a rhodium complex (see Oxo process). When using a cobalt catalyst a mixture of isomeric C-19 compounds results due to isomerization of the double bond prior to carbon monoxide addition (80). 

In hydrocarboxylation, the Reppe reaction, the catalyst can be nickel or cobalt carbonyl or a palladium complex where R = H or alkyl. 

The nickel or cobalt catalyst causes isomerization of the double bond resulting in a mixture of C-19 isomers. The palladium complex catalyst produces only the 9-(10)-carboxystearic acid. The advantage of the hydrocarboxylation over the hydroformylation reaction is it produces the carboxyUc acids in a single step and obviates the oxidation of the aldehydes produced by hydroformylation. 

Carbonylation, or the Koch reaction, can be represented by the same equation as for hydrocarboxylation. The catalyst is H2SO4. A mixture of C-19 dicarboxyhc acids results due to extensive isomerization of the double bond. Methyl-branched isomers are formed by rearrangement of the intermediate carbonium ions. Reaction of oleic acid with carbon monoxide at 4.6 MPa (45 atm) using 97% sulfuric acid gives an 83% yield of the C-19 dicarboxyhc acid (82). Further optimization of the reaction has been reported along with physical data of the various C-19 dibasic acids produced. The mixture of C-19 acids was found to contain approximately 25% secondary carboxyl and 75% tertiary carboxyl groups. As expected, the tertiary carboxyl was found to be very difficult to esterify (80,83). 

The dimer acids [61788-89-4] 9- and 10-carboxystearic acids, and C-21 dicarboxylic acids are products resulting from three different reactions of C-18 unsaturated fatty acids. These reactions are, respectively, self-condensation, reaction with carbon monoxide followed by oxidation of the resulting 9- or 10-formylstearic acid (or, alternatively, by hydrocarboxylation of the unsaturated fatty acid), and Diels-Alder reaction with acryUc acid. The starting materials for these reactions have been almost exclusively tall oil fatty acids or, to a lesser degree, oleic acid, although other unsaturated fatty acid feedstocks can be used (see Carboxylic acids. Fatty acids from tall oil Tall oil). 

Most ring syntheses of this type are of modern origin. The cobalt or rhodium carbonyl catalyzed hydrocarboxylation of unsaturated alcohols, amines or amides provides access to tetrahydrofuranones, pyrrolidones or succinimides, although appreciable amounts of the corresponding six-membered heterocycle may also be formed (Scheme 55a) (73JOM(47)28l). Hydrocarboxylation of 4-pentyn-2-ol with nickel carbonyl yields 3-methylenetetrahy-drofuranone (Scheme 55b). Carbonylation of Schiff bases yields 2-arylphthalimidines (Scheme 55c). The hydroformylation of o-nitrostyrene, subsequent reduction of the nitro group and cyclization leads to the formation of skatole (Scheme 55d) (81CC82). 

The hydrocarboxylation of an olefin, catalyzed by strong mineralic acids (Koch-Haaf reaction), leads to branched carboxylic acids [57] ... 

Having greater resemblance to natural fatty acids are the products of the coordination-catalyzed hydrocarboxylation of olefins with water and carbon monoxide (Reppe reaction) [58] ... 

If cobalt carbonylpyridine catalyst systems are used, the formation of unbranched carboxylic acids is strongly favored not only by reaction of a-olefins but also by reaction of olefins with internal double bonds ( contrathermo-dynamic double-bond isomerization) [59]. The cobalt carbonylpyridine catalyst of the hydrocarboxylation reaction resembles the cobalt carbonyl-terf-phos-phine catalysts of the hydroformylation reaction. The reactivity of the cobalt-pyridine system in the hydrocarboxylation reaction is remarkable higher than the cobalt-phosphine system in the hydroformylation reaction, especially in the case of olefins with internal double bonds. This reaction had not found an industrial application until now. 

In the metal-carbonyl catalysed hydrocarboxylation of alkynes ( Reppe reaction ) nearly exclusive cia-addition of H—COOH is found (Ohashi et al., 1952). 

Addition of unsaturated boranes to methyl vinyl ketones Hydrocarboxylation of triple bonds Addition of acyl halides to triple bonds 1,4-Addition of acetals to dienes... 

Monflier et al. (1997) have suggested Pd catalysed hydrocarboxylation of higher alpha olefins in which chemically modified P-cyclodextrin (especially dimethyl P-cyclodextrin) is u.sed in water in preference to a co-solvent like methanol, acetone, acetic acid, acetonitrile, etc. Here, quantitative recycling of the aqueous phase is possible due to easy phase separation without emulsions. A similar strategy has been adopted by Monflier et al. (1998) for biphasic hydrogenations for water-in.soluble aldehydes like undecenal using a water-soluble Ru/triphenylphosphine trisulphonate complex with a. suitably modified p-cyclodextrin. 

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. 

Historically, the rhodium catalyzed carbonylation of methanol to acetic acid required large quantities of methyl iodide co-catalyst (1) and the related hydrocarboxylation of olefins required the presence of an alkyl iodide or hydrogen iodide (2). Unfortunately, the alkyl halides pose several significant difficulties since they are highly toxic, lead to iodine contamination of the final product, are highly corrosive, and are expensive to purchase and handle. Attempts to eliminate alkyl halides or their precursors have proven futile to date (1). 

Ojima, I. Eguchi, M. Tzamarioudaki, M. Transition Metal Hydrides Hydrocarboxylation, Hydroformylation, and Asymmetric Hydrogenation. In Wilkinson, G. Stone, F. B. A. Abel, E. W., Eds., Comprehensive Organometallic Chemistry 2, Vol. 12, Pergamon, Oxford, 1995, Chapter 2. 

The hydrocarboxylation of suitably substituted hydroxyalkylacetylenes and alkenes has been widely used to prepare a variety of butenolides and butyrolactones (see Scheme 63101,102 and Refs. 8 and 10a for reviews of earlier literature) a closely related reaction is shown in Scheme 64.103,104... 

A specific synthesis of 1,3-dioxohexahydroisoquinoline employing a conventional oxo hydrocarboxylation process is outlined in Scheme 149.224... 

The commercially applied biphasic processes are compiled in Table 5.3. Tests to produce economically interesting profens or other analgesics by two-phase hydrocarboxylation [40] remain industrially unsuccessful. 

The hydroformylation reaction has been the subject of excellent reviews (for example I, 6-8) therefore, the object of this particular treatise is not to provide comprehensive coverage of all aspects. The basic chemistry is presented, along with recent developments of interest as reported in the literature, although not in chronological order. Stereochemical studies (6) are included only when pertinent to another point under consideration. Carbonylations or hydrocarboxylation reactions which produce ketones, esters, acids, esters, or amides are not included (/). Also not included is the so-called Reppe" synthesis, which is represented by Eq. (1). 

The related field involving the hydrocarboxylation of alkenes is also under investigation11481, not least because of its potential importance in the synthesis of NSAI drugs. An indirect way to the latter compounds involves the hydro-vinylation of alkenes. For example catalysis of the reaction of ethylene with 2-methoxy-6-vinylnaphthalene at 70°C using (allylNiBr)2 and binaphthyl (63)... 

In this process, double bonds were found to be less reactive than triple bonds. Thus norbornene or styrene were hydrocarboxylated in low yields (10-40%) [121]. In unconjugated as well as conjugated ene-ynes, only the alkyne moiety was carboxylated with regio- and stereoselectivity similar to that observed for alkynes [122]. 

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

Until there is a sufficient excess of ethene over [PdH(TPPTS)3] their fast reaction ensures that aU palladium is found in form of tratts-[Pd C(CO)Et (TPPTS)2]. However, at low olefin concentrations (e.g. in biphasic systems with less water-soluble olefins) [PdH(TPPTS)3] can accumulate and through its equihbrium with [Pd(TPPTS)3] (eq. 5.5) can be reduced to metallic palladium. This is why the hydroxycarbonylation of olefins proceeds optimally in the presence of Brpnsted acid cocatalyts with a weekly coordinating anion. Under optimised conditions hydrocarboxylation of propene was catalyzed by PdC + TPPTS with a TOE = 2507 h and l = 57/43 (120 °C, 50 bar CO, [P]/[Pd] = 4, P-CH3C6H4SO3H) [38], In neutral or basic solutions, or in the presence of strongly coordinatmg anions the initial hydride complex cannot be formed, furthermore, the fourth coordination site in the alkyl- and acylpaUadium intermediates may be strongly occupied, therefore no catalysis takes place. 

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. 

Higher olefins have negligible solubility in water therefore their hydrocarboxylation in aqueous/organic biphasic systems needs co-solvents or phase transfer agents. With the aid of various PT catalysts 1-octene and 1-dodecene were successfully carbonylated to the corresponding carboxylic acids with good yields (< 85 %) and up to 87 % selectivity towards the formation of the linear add with a [Co2(CO)g] catalyst precursor under forcing conditions (150 °C, 200 bar CO) [57],... 

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