Alcohol and aldehyde decarbonylation

While adsorbed primary alcohols on the Pd( 111) surface dehydrogenate sequentially to form the corresponding adsorbed aldehyde and acyl species prior to their decarbonylation (23), we have found no evidence for aldehyde formation from primary alcohols on Rh(l 11) (2124). Instead, alcohol and aldehyde decarbonylation pathways on Rh(lll) appear to be non-intersecting. This surprising divergence of reaction pathways for such closely related molecules is demonstrated by two critical observations ... 

Acetaldehyde decomposition, reaction pathway control, 14-15 Acetylene, continuous catalytic conversion over metal-modified shape-selective zeolite catalyst, 355-370 Acid-catalyzed shape selectivity in zeolites primary shape selectivity, 209-211 secondary shape selectivity, 211-213 Acid molecular sieves, reactions of m-diisopropylbenzene, 222-230 Activation of C-H, C-C, and C-0 bonds of oxygenates on Rh(l 11) bond-activation sequences, 350-353 divergence of alcohol and aldehyde decarbonylation pathways, 347-351 experimental procedure, 347 Additives, selectivity, 7,8r Adsorption of benzene on NaX and NaY zeolites, homogeneous, See Homogeneous adsorption of benzene on NaX and NaY zeolites... 

Alcohol and aldehyde decarbonylation on Rh(l 11), activation of C-H, C-C, and C-0 bonds, 345-353 Alkane dehydroeyelization with Pt-Sn-alumina catalysts aromatic formation, 120 preparation condition effect, 119... 

Rhodium(II) acetate catalyzes C—H insertion, olefin addition, heteroatom-H insertion, and ylide formation of a-diazocarbonyls via a rhodium carbenoid species (144—147). Intramolecular cyclopentane formation via C—H insertion occurs with retention of stereochemistry (143). Chiral rhodium (TT) carboxamides catalyze enantioselective cyclopropanation and intramolecular C—N insertions of CC-diazoketones (148). Other reactions catalyzed by rhodium complexes include double-bond migration (140), hydrogenation of aromatic aldehydes and ketones to hydrocarbons (150), homologation of esters (151), carbonylation of formaldehyde (152) and amines (140), reductive carbonylation of dimethyl ether or methyl acetate to 1,1-diacetoxy ethane (153), decarbonylation of aldehydes (140), water gas shift reaction (69,154), C—C skeletal rearrangements (132,140), oxidation of olefins to ketones (155) and aldehydes (156), and oxidation of substituted anthracenes to anthraquinones (157). Rhodium-catalyzed hydrosilation of olefins, alkynes, carbonyls, alcohols, and imines is facile and may also be accomplished enantioselectively (140). Rhodium complexes are moderately active alkene and alkyne polymerization catalysts (140). In some cases polymer-supported versions of homogeneous rhodium catalysts have improved activity, compared to their homogenous counterparts. This is the case for the conversion of alkenes direcdy to alcohols under oxo conditions by rhodium—amine polymer catalysts... 

The decarbonylation reaction is not confined to aldehydes, but also embraces those compounds that have aldehyde tautomers. Thus, both carbohydrates and allylic alcohols can be decarbonylated. When glucose is allowed to react with frani -[RhCl(CO)(PPh3)2] in A -methylpyrrolidin-2-one, decarbonylation occurs and arabinitol is formed with retention of configuration. The decarbonylation of fructose to arabinitol is complicated by the simultaneous dehydration to furfinyl alcohol, which is the major product. Analogous reactions occur with lower carbohydrates in the limit, glycolaldehyde is decarbonylated to methanol. Aldose derivatives can also be converted to their C i analogues, but the yields are only about half of those obtained with the parent aldoses. Disaccharides usually give better yields. 

The above reaction is reversible so that primary alcohols may be dehydrogenated to an aldehyde which could decarbonylate to produce CO. It has been shown that the 1-alcohol and corresponding aldehyde are at or near an equilibrium composition when using a doubly promoted iron catalyst at 7 atm. The CO produced by the above reaction could produce CO2 through the WGS reaction ... 

The desired synthon, acetonide 520, is prepared from carbonate 517 by treatment with acetone under acidic conditions. Alkylation of bicyclic lactone 521 with 520 affords 522 as a single isomer. Reduction of the lactone with DIBAL produces an equilibrium mixture of lactol and hydroxy aldehyde 523. Oxidation of the ally lie alcohol and decarbonylation with Wilkinson s catalyst furnishes the crucial enone intermediate 524 common to both natural products. 

Fifth, although the relative inertness of carbonyl componnds excluding acyl halides was emphasized above, most everything in chemistry is relative, and organopalladinm chemistry is no exception. Thus, in the absence of faster reaction paths, Pd and its complexes may react with aldehydes via C—H activation to give acylpalladinm derivatives and snbsequent decarbonylation (Sect. VL5.1), while ketones may be rednced to alcohols and even to hydrocarbons, as discussed in Sect. VII.2.3.1, althongh the presence of proximal 7T- or n-donors may be critical in snch reactions. 

In 2002, Morimoto and Shibata independently reported the use of a rhodium carbonyl complex obtained via aldehyde decarbonylation for a Pauson-Khand type reaction (Scheme 2-17). This success prompted further investigation into CO gas-free carbonylation reactions. Lee et al. reported the use of a formate ester in the CO gas-free asymmetric Pauson-Khand type reaction. Park et reported the use of alcohol as a CO source, and Ikeda and co-workers used aldoses as a source of CO. 

Waxes are synthesised by reduction of fatty acids to primary alcohols via aldehydes. Primary alcohols react with acyl-CoAs to form esters, aldehydes eliminate carbon monoxide (by decarbonylation) giving rise to hydrocarbons (alkanes). Oxidation of alkanes yields secondary alcohols, and oxidation of secondary alcohols gives rise to ketones. 

CO into a metal-hydrogen bond, apparently analogous to the common insertion of CO into a metal-alkyl bond (6). Step (c) is the reductive elimination of an acyl group and a hydride, observed in catalytic decarbonylation of aldehydes (7,8). Steps (d-f) correspond to catalytic hydrogenation of an organic carbonyl compound to an alcohol that can be achieved by several mononuclear complexes (9JO). Schemes similar to this one have been proposed for the mechanism of CO reduction by heterogeneous catalysts, the latter considered to consist of effectively separate, one-metal atom centers (11,12). As noted earlier, however, this may not be a reasonable model. 

Decarbonylation of higher oxygenates on the Rh(l 11) surface leads to volatile hydrocarbons only in the case of aldehydes. Higher alcohols do not form adsorbed aldehydes, but appear to undergo (J-CH scission toformsurfaceoxametallacycles. These postulated intermediates can also be formed by C-0 scission in epoxides. Of the ten C2 and C3 oxygenates examined, elimination of atleastfivedifferenthydrocarbonligandsmustbeinvolvedintiiedecarbonylation step to explain the variations observed in the identity of adsorbed and volatile products. 

The production of hydrocarbons from aromatic alcohols is most readily explained by the hydrogenolysis of the alcohol, but an alternate possibility should be considered. The formation of an aldehyde and its subsequent decarbonylation under reaction conditions could lead to the hydrocarbon. Both toluene and 2-phenylethanol, the mixture of products secured from benzyl alcohol, may be regarded as derived from phenylacetaldehyde as an intermediate ... 

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