Olefin hydrogenation unsaturated alcohols

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

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). 

In fine chemical manufacturing, the application of promoted platinum catalysts is less known. Maxted and Akhar have reported that the addition of stannous, manganous, ceric and ferric chloride to platinum oxide (Adams catalyst) facilitates the hydrogenation of aldehydes, ketones and olefins (ref. 1). The selective hydrogenation of unsaturated aldehydes or ketones to unsaturated alcohols has been achieved by the addition of ferrous sulfate and zinc acetate to platinum catalysts (ref. 2). 

The oxidahon of olefins with aqueous hydrogen peroxide in methanol can produce several products, by different reachon paths double bond epoxidation, allylic H-abstraction, epoxide solvolysis, alcohol and glycol oxidation (Scheme 18.6). Normally, oxide catalysts of Group IV-Vl metals are poorly selechve, because of their acidic properhes, the inhibition they are subject to in aqueous media and homo-lytic side reachons with hydrogen peroxide. The only excephon concerns the epoxidahon of a,(3-unsaturated alcohols and acids, which are able to bind on the... 

Epoxidation of olefins with hydrogen peroxide in the presence of Fe(acac)3 has been examined in the cases of stilbene, unsaturated alcohols, and fatty acids. From cis- and trans-olefins the main product is the trans isomer, formed via a biradical intermediate. Cholesterol undergoes /3-epoxidation. ... 

Of the cases described so far, the presence of a third compound had the strongest effect on the selectivity of hydrogenation of two olefinic substrates in the pair olefin-unsaturated alcohol. This influence appeared both in cases where the third compound was unsaturated, was adsorbed competitively and reacted on the catalyst surface, and in cases where the third compound was represented by an inert solvent not undergoing competitive adsorption (was not entering equations of the Langmuir-Hinshelwood type, which were degraded to pseudo-zero order) and obviously operated through interactions of molecules from the bulk phase with adsorbed molecules of the substrate. 

While the effect of a third olefinic substrate on the selectivity of hydrogenation of a binary olefinic mixture could be investigated only at comparable concentrations of all three substrates, because the use of a single olefinic substrate in a considerable excess would lead to its preferential hydrogenation, the inert solvent was mainly used in a much higher concentration. An attempt to solve the problem of the effect of solvent concentration on the selectivity of hydrogenation was made (101). The measurements were again carried out in olefin-unsaturated alcohol systems. 

Platinum, Pd, and Ni hydrogenate gaseous or easily volatilized olefins in the vapor. Noble metal catalysts, finely divided and activated prove efficient for liquid olefins, unsaturated alcohols, and cycloalkenes at atm P, in ethanol, glacial acetic acid or ethyl acetate. Other Ni catalysts require H2 P. Side chains of aromatic compounds can be hydrogenated in the liquid phase with Ni or Pt and in the gas phase with Cu catalysts. ... 

Rhenium compounds such as Re2Sc7 are more reactive hydrogenation catalysts for the reduction of carbonyls than for olefins, except in conjugated systems . Unsaturated carbonyls have been selectively hydrogenated to unsaturated alcohols, catalyzed by a chromium-promoted finely divided Ni (Raney Ni) catalyst" ... 

Carbonyl hydrogenation is generally less facile than olefin hydrogenation, making selective hydrogenation of a, -unsaturated aldehydes to the allyl alcohol a special challenge. Substitution of the carbon atom attached to the carbonyl (i. e. from the aldehyde to the ketone), substantially increases the steric hindrance to carbonyl adsorption, hence the lack of reports in the literature of selective unsaturated ke-... 

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