Hydrogenation unsaturated alcohol

The use of copper chromite at 40°C and atmospheric pressure was not very effective for selective carbonyl group hydrogenation. Unsaturated alcohols were produced from unsaturated aldehydes in low yields at low conversions and not at all from methyl vinyl ketone. 28 With unconjugated, unsaturated aldehydes, copper chromite is effective as a selective hydrogenation catalyst. Hydrogenation of 46 at 140°-160°C and 200 atmospheres gave better than 70% of the diene diol, 47. Increasing the temperature to 240°C resulted in the complete saturation of 46 (Eqn. 18.28). 29... 

The 7, i5-unsaturated alcohol 99 is cyclized to 2-vinyl-5-phenyltetrahydro-furan (100) by exo cyclization in aqueous alcohol[124]. On the other hand, the dihydropyran 101 is formed by endo cyclization from a 7, (5-unsaturated alcohol substituted by two methyl groups at the i5-position. The direction of elimination of /3-hydrogen to give either enol ethers or allylic ethers can be controlled by using DMSO as a solvent and utilized in the synthesis of the tetronomycin precursor 102[125], The oxidation of the optically active 3-alkene-l,2-diol 103 affords the 2,5-dihydrofuran 104 in high ee. It should be noted that /3-OH is eliminated rather than /3-H at the end of the reac-tion[126]. 

Allyl alcohol, CH2=CH—CH2OH (2-propen-l-ol) [107-18-6] is the simplest unsaturated alcohol. One hydrogen atom can easily be abstracted from the aHyhc methylene (—CH2—) to form a radical. Since the radical is stabilized by resonance with the C=C double bond, it is very difficult to get high molecular weight polymers by radical polymerization. In spite of the fact that aHyl alcohol has been produced commercially for some years (1), it has not found use as a monomer in large volumes as have other vinyl monomers. 

Selective hydrogenation of the carboxyl or ester group in preference to the olefinic unsaturation also produces unsaturated alcohols. 

Osmium makes a sluggish carbonyl hydrogenation catalyst but has the unusual property of reducing a, -unsaturated aldehydes to the unsaturated alcohol in good yield (85). The system has proved erratic high selectivity can only be obtained through prereduction of the catalyst just before use. 

These pentahydrides have attracted attention as catalysts for hydrogenation of the double bond in alkenes. IrH5(PPr3)2 catalyses vinylic H-D exchange between terminal alkenes and benzene, the isomerization of a,f3-ynones, isomerization of unsaturated alcohols and dehydrogenation of molecules such as secondary alcohols [176],... 

Ir catalysts supported on binary oxides of Ti/Si and Nb/Si were prepared and essayed for the hydrogenation of a,P-unsaturated aldehydes reactions. The results of characterization revealed that monolayers of Ti/Si and Nb/Si allow a high metal distribution with a small size crystallite of Ir. The activity test indicates that the catalytic activity of these solids is dependent on the dispersion obtained and acidity of the solids. For molecules with a ring plane such as furfural and ciimamaldehyde, the adsorption mode can iirfluence the obtained products. SMSI effect (evidenced for H2 chemisorption) favors the formation of unsaturated alcohol. 

The hydrogenation of p-unsaturated alcohols is a classical example of competing reaction processes in heterogeneous catalysis. In principle, either isomerization to an enol followed by tautomerization to the ketone can occur, or direct hydrogenation to the saturated alcohol is possible (1). It is fair to state that interest in this type of chemistry is derived from both basic scientific... 

Considerable effort has gone into learning how to hydrogenate the C=0 bond and retain the C=C bond to produce a,p-unsaturated alcohols (allylic alcohols), which are useful in the fine chemicals industry. Early works toward selectively hydrogenating the C=0 bond have been reviewed and discussed.146 An excellent review was published in 1995.147... 

A bimetallic catalyst can be obtained by the reaction of tetrabutyltin with Rh/Si02 catalyst. The partial hydrogenolysis leads to the Rhs[Sn(n-C4H9)2]/ Si02 surface organometallic complexes, which proved to be fully selective in the hydrogenation of unsaturated aldehydes into the corresponding unsaturated alcohols.318... 

Rosenthal and co-workers (91, 92) studied the cobalt hydroformylation of various unsaturated carbohydrates. As with other a,j8-unsaturated ethers, addition of the formyl group occurred almost exclusively at the double-bond carbon a to the oxygen. High yields of product were obtained, but hydrogenation to alcohol was facile, even under mild conditions, as noted in Eq. (43) ... 

Other advances over the past few years have been the development of (a) homogeneous hydrogenation catalysts for substrates normally not readily reduced, e.g., aromatics, isonitriles, and nitro compounds, and (b) a number of catalyst systems with unusual selectivity properties, e.g., with the capability of reducing a,/3-unsaturated aldehydes to the corresponding a,/3-unsaturated alcohols (see Sections II,B,2 and VII). 

The very unusual selective hydrogenation of ,/3-unsaturated aldehydes to the unsaturated alcohols, Eq. (30), has been accomplished using [RhCl(CO)2]2 in the presence of tertiary amines under oxo conditions (162). RhCl(PPh3)3 systems under similar conditions reduce the olefinic bond (162), as do Co2(CO)8 systems in the presence of amines or phosphites (163). Further details on the versatile Rh(BH4)(amide)py2Cl2 systems (/, p. 280) have appeared (164, 165) ketones are also slowly hydrogenated (166), and 1,5,9-cyclododecatriene has been selectively reduced to cyclododecene (167). 

The aqueous Co(CN)52- solutions under H2 have been found to catalyze hydrogenolysis of C4-unsaturated alcohols to butenes but, more remarkably, with acetylenic alcohols besides hydrogenated products secondary nitriles are also formed by addition of HCN (stoichiometric with respect to cobalt) (195) ... 

The [RhCl(CO)2]2 dimer immobilized on a cross-linked polystyrene containing pyrrolidine effects the same novel selectivity as the homogeneous analog in hydrogenation of a,/3-unsaturated aldehydes to the unsaturated alcohols, Eq. (30) (162). 

In 1996, Liu et al. reported the selective hydrogenation of cinnamaldehyde, an a,/ -unsaturated aldehyde, to cinnamyl alcohol, an a,/ -unsaturated alcohol, by means of PVP-protected Pt/Co bimetallic colloids prepared by the polyol process [111]. The colloids were obtained as a dark-brown homogeneous dispersion in a mixture of ethylene glycol and diethylene glycol, and characterized by TEM and XRD. These authors prepared different samples of nanoparticles with Pt Co ratios of 3 1 and 1 1, the mean diameters of which measured 1.7 and 2.2 nm, respectively. These colloidal systems were also compared with the single metal-... 

The Osmium cluster Os3(CO)12 and clusters in the presence of various phosphines and triphenylphosphite have been utilized for the hydrogenation of cinnamaldehyde and crotonaldehyde (Table 15.7) [36]. The results show that good yields of unsaturated alcohols can be obtained by using a large excess of phosphine at elevated hydrogenation temperatures. 

As for some of the monodentate phosphine-based catalysts, ds-[Ru(6,6 -Cl2bpy)2(0H2)2][CF3S03]2 was found to require water for the best catalytic activity in the reduction of aldehydes and ketones [57]. Aldehydes and ketones were found to be hydrogenated, with reasonable yields. Unsaturated aldehydes were reduced with selectivity towards the unsaturated alcohol, whereas unsaturated ketones showed selectivity towards the saturated ketones. 

In these reactions, the major diastereomer is formed by the addition of hydrogen syn to the hydroxyl group in the substrate. The cationic iridium catalyst [Ir(PCy3)(py)(nbd)]+ is very effective in hydroxy-directive hydrogenation of cyclic alcohols to afford high diastereoselectivity, even in the case of bishomoallyl alcohols (Table 21.4, entries 10-13) [5, 34, 35]. An intermediary dihydride species is not observed in the case of rhodium complexes, but iridium dihydride species are observed and the interaction of the hydroxyl unit of an unsaturated alcohol with iridium is detected spectrometrically through the presence of diastereotopic hydrides using NMR spectroscopy [21]. 

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