Acetylenes hydroformylation

The interest of alkyne and allene hydroformylation is the formation of a,) -unsamrated aldehydes, which are valuable intermediates in fine chemical and pharmacy. In contrast to alkenes, the studies on the hydroformylation of alkynes are relatively scant. The first case of acetylene hydroformylation was reported by Natta and Pino in 1951 [79]. It was found that in the presence of metallic cobalt at 120-150°C and 200-300 atm, acetylene reacted with synthesis gas yielding a mixture of high-boiling, unidentified products. During the following 40 years, hydroformylation of alkynes to a,/l-unsaturated aldehydes had little success [80-85]. The early investigations usually resulted in low selectivity and/or low yield of unsaturated aldehydes, primarily because the formation of the corresponding saturated aldehydes and non-carbonylated olefins could hardly be suppressed. 

The first systematic B3LYP DPT investigation into the hydroformylation of alkynes and allene was carried out by Huo et al. [92,93]. It was fotmd that acetylene hydroformylation has very similar catalytic mechanism as that of propene, therefore only the differences are emphasized, and no general comparison is made. Scheme 17 shows the activation and reaction free energies. 

Scheme 17 Activation (bold and italics) and reaction free energies (kJ/mol, based on HCo(CO)3, acetylene, CO, and H2, scaled at 403 K and 200 atm.) of acetylene hydroformylation...

Succinic acid diesters are also obtained by one-step hydrogenation (over Pd on charcoal) and esterification of maleic anhydride dissolved in alcohols (40) carbonylation of acrylates in the presence of alcohols and Co complex catalysts (41—43) carbonylation of ethylene in alcohol in the presence of Pd or Pd—Cu catalysts (44—50) hydroformylation of acetylene with Mo and W complexes in the presence of butanol (51) and a biochemical process from dextrose/com steep Hquor, using Jinaerobiumspirillum succiniciproducens as a bacterium (52). 

The hydroformylation of acrolein cyclic acetals has received considerable attention in the recent patent literature as a route to 1,4-butanediol (76-52). This diol is a comonomer for the production of polybutylene terephthalate, an engineering thermoplastic. The standard method for its manufacture has been from acetylene and formaldehyde, as shown in Eqs. (37) and (38) ... 

Two syntheses of Rh4(CO)i2 at ordinary pressure have been developed 81, 279 making this compound easily available, and CO scrambling in this molecule has been carefully examined 110,112,164. Strong nucleophiles including CO at high pressure destroy the Rh cluster 45, 396, but with phosphines of limited donor strength, with cyclooctatetraene, and with acetylenes up to four CO groups could be replaced with retention of the Rh4 unit 45, 247, 396. Rh4-like Rhg-clusters show catalytic activity (7 04, 364 which has been used for hydroformylation 88 and oxidation (297) reactions. 

Few studies have been conducted on the hydroformylation of alkynes. Terminal acetylenes give saturated isomeric aldehydes supposedly through the initially formed alkenes.73 Conclusive evidence was obtained that internal alkynes, in contrast, first undergo hydroformylation to yield a,p-unsaturated aldehydes, which are subsequently hydrogenated to give the saturated aldehyde end products.74... 

Photosensitized generation of hydrido-metal complexes in aqueous media provides a general route for H2-evolution, hydrogenation of unsaturated substrates (i.e. olefins, acetylenes), or hydroformylation of double bonds, see Scheme 2. Co(II) complexes, i.e. Co (II)-fn s-bipyridine, Co(bpy) +, or the macrocyclic complex Co(II)-Me4[14]tetraene N4, act as homogeneous H2-evolution catalysts in photosystems composed of Ru(bpy) + (or other polypyridine (Ru(II) complexes) as photosensitizers and triethanolamine, TEOA, or ascorbic acid, HA-, as sacrificial electron donors [156,157], Reductive ET quenching of the excited photosensitizer... 

The water-soluble Wilkinson-type catalyst chlorotris(diphenylphosphinoben-zene-m-sulfonate)rhodium(I), RhQfdpm) (19), acts as catalyst for H2-evolution [158], hydrogenation and hydroformylation [159]. In a photosystem composed of Ru(bpy)i+ as photosensitizer, ascorbic acid, HA, as electron donor and RhCl(dpm)3, hydrogen evolution proceeds with a quantum efficiency corresponding to (p = 0.033. In the presence of ethylene or acetylene, hydrogen evolution is blocked and hydrogenation of the unsaturated organic substrates predominates. Table 6 summarizes the quantum yields for H2-evolution and... 

The interaction of unsaturated molecules, for example olefins and acetylenes, with transition metals is of paramount importance for a variety of chemical processes. Included among such processes are stereospecific polymerization of olefin monomers, the production of alcohols and aldehydes in the hydroformylation reaction, hydrogenation reactions, cyclo-propanation, isomerizations, hydrocyanation, and many other reactions. 

The production of carboxylic acids via carbonylation catalysis is the second most important industrial homogeneous group of processes. Reppe developed most of the basic carbonylation chemistry in the 1930s and 1940s. The first commercial carbonylation process was the stoichiometric Ni(CO)4-based hydroxycarbonylation of acetylene to give acrylic acid (see Section 3.5 for details). This discovery has since evolved into a trae Ni-catalyzed process, used mainly by BASF. The introduction of rhodium catalysts in the 1970s revolutionized carboxylic acid production, particularly for acetic acid, much in the same way that Rh/PPhs catalysts changed the importance of hydroformylation catalysis. 

The complex- imns-RhCI(CO)(PPh3)2 has recently been show-n to act as a catalyst for the hydroformylation of olefins and acetylenes under mild conditions, and for decarbonylation of aldehydes and of acyl and aroyl halides. ... 

Asymmetric hydroformylation of acetylenes such as 2-butyne, 1-octyne or phenylacetylene can yield chiral saturated aldehydes via prior or subsequent hydrogenation22. Results of this variant, mainly investigated for mechanistic reasons22, are compiled in Table 8. 

Several important homogeneous catalytic reactions (e.g. hydroformylations) have been accomplished in water by use of water-soluble catalysts in some instances water can act as a solvent and as a reactant for hydroformylation. In addition, formation of aluminoxanes by partial hydrolysis of alkylaluminum halides results in very high activity bimetallic Al/Ti or Al/Zr metallocene catalysts for ethene polymerization which would be otherwise inactive. Polymerization of aryl diiodides and acetylene gas has recently been achieved in water with palladium catalysts. Finally, nickel-containing enzymes, such as carbon monoxide dehydrogenase (CODH) and acetyl-CoA synthase, operate in water with reaction mechanisms comparable with those of the WGSR or of the Monsanto methanol-to-acetic-acid process. ... 

Grubbs and coworkers (35) while examining Rh and Co catalysts derived from 14 reported the loss of infrared CO stretches and visual darkening of the catalysts after use for hydrogenation of olefins, aldehydes or ketones, cyclohexene disproportionation to benzene and cyclohexane or the cyclotrimerization of a wide variety of acetylenes. Stille (36) using a rhodium catalyst prepared from 14 observed activity for the hydrogenation of benzene that increased with reuse, a phenomenon usually associated with metal crystallite formation. Rhodium catalysts of 15 and 16 used to hydroformylate octene-1 revealed a loss of carbonyl adsorptions and a loss in catalytic activity upon reuse (37). 

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