Platinum aldehyde hydrogenation

Aldehydes and ketones are usually hydrogenated to the alcohol over platinum, rhodium or ruthenium catalysts at 25 -60°C and 1-5 atmospheres pressure. Platinum catalyzed hydrogenations are generally best run in acidic media while with rhodium or ruthenium neutral or basic solvents are preferred. Hydrogenations run over ruthenium catalysts are facilitated by the presence of water which makes ruthenium a particularly effective catalyst for the hydrogenation of sugars and other water soluble aldehydes and ketones.2... 

When a stream of air is passed over liquid ether and then over a red hot platinum spiral, hydrogen peroxide may be continuously obtained by scrubbing the vapors with water. Ether apparently forms a peroxide under the conditions, which is decomposed by the scrubbing water. If the products are condensed and the liquid product slowly evaporated over sulfuric acid, a crystalline material remains which is slowly volatile and is capable of detonation. It is also capable of liberating iodine from potassium iodide.184 On the other hand, if red hot pumice is substituted for the platinum catalyst, the scrubbing water shows no peroxide formation, and aldehyde and acetone are the chief products.180... 

Palladium is usually the prefeired metal of choice for aromatic aldehyde hydrogenation in neutral non-polar solvents such as hexane, DMF, or ethyl acetate (5-100 °C and 1-10 bar) although ruthenium, which is less active, can be considered and run in aqueous alcohol at similar temperatures and pressures. If higher pressures are accessible ruthenium may be preferable because of its lower (historical) cost. Its use has recently been reviewed [4]. Although platinum and rhodium could... 

Vanillin (3.04 g, 0.02 mol), dissolved in a minimum amount of absolute ethanol, was combined with 2.66 g of aminoacetaldehyde diethylacetal (0.02 mol), and the mixture was diluted to 15 mL with absolute ethanol and hydrogenated at atmospheric pressure and room temperature over 200 mg of previously reduced platinum oxide. Hydrogen consumption stopped at about 90% completion after about 3 h. The catalyst was removed by filtration and the solvent was evaporated under vacuum. The residual oil was dissolved in 50 mL concentrated hydrochloric acid. The solution which had become hot was cooled and washed with three 30-mL portions of 3 2 ether-benzene to remove starting aldehyde. A two-fold excess of benzaldehyde (4.24 g, 0.04 mole) dissolved in 50 mL of ethanol was added to the acidic solution which was subsequently boiled for 30 min. The cooled solution was diluted with an equal volume of water and washed with three 50-mL portions of ether to remove the excess benzaldehyde. The solution was made basic with ammonium hydroxide to pH 8. The precipitate was removed by filtration and crystallized once from water-ethanol to give 3.33 g of 4-benzyl-6-hydroxy-7-methoxyisoquinoline, in a yield of 63%, m.p. 185-190°C. The analytical sample has m.p. at 192-193°C. 

The present work was undertaken to examine this possibility by trying a new method of low-temperature catalyst preparation. The method studied involves the adsorption of metal precursors on supports and the reduction by sodium tetrahydroborate solution for the preparation of supported platinum catalysts. The adsorption and reduction of platinum precursors are carried out at room temperature and the highest temperature during the preparation is 390 K for the removal of solvent. The activities of the catalysts prepared were examined for liquid-phase hydrogenation of cinnamaldehyde under mild conditions. Our attention was directed to not only total activity but also selectivity to cinnamyl alcohol, since it is difficult for platinum to hydrogenate the C=0 bond of this a, -unsaturated aldehyde compared to the C=C bond [2]. We examined the dependence of the catalytic activity and selectivity on preparation variables including metal precursor species, support materials and reduction conditions. In addition, the prepared catalysts were characterized by several techniques to clarify their catalytic features. The activity of the alumina-supported platinum catalyst prepared by the present method was briefly reported in a recent communication [3]. 

Reductive amination of aldehydes and ketones gives primary, secondary, and tertiary amines. Sodium triacetoxyborohydride (STAB-H) [93] or platinum-catalyzed hydrogenations are used as shown in Equations 6.59 [94] and 6.60 [95]. 

The most obvious way to reduce an aldehyde or a ketone to an alcohol is by hydro genation of the carbon-oxygen double bond Like the hydrogenation of alkenes the reac tion IS exothermic but exceedingly slow m the absence of a catalyst Finely divided metals such as platinum palladium nickel and ruthenium are effective catalysts for the hydrogenation of aldehydes and ketones Aldehydes yield primary alcohols... 

Styrene oxide [96-09-3] M 120.2, b 84-86 /16.5mm, d 1.053, n 1.535. Fractional distn at reduced pressure does not remove phenylacetaldehyde. If this material is present, the styrene oxide is treated with hydrogen under 3 atmospheres pressure in the presence of platinum oxide. The aldehyde, but not the oxide, is reduced to 6-phenylethanol) and separation is now readily achieved by fractional distn. [Schenck and Kaizermen J Am Chem Soc 75 1636 1953.]... 

Reduction of unsaturated aldehydes seems more influenced by the catalyst than is that of unsaturated ketones, probably because of the less hindered nature of the aldehydic function. A variety of special catalysts, such as unsupported (96), or supported (SJ) platinum-iron-zinc, plalinum-nickel-iron (47), platinum-cobalt (90), nickel-cobalt-iron (42-44), osmium (<55), rhenium heptoxide (74), or iridium-on-carbon (49), have been developed for selective hydrogenation of the carbonyl group in unsaturated aldehydes. None of these catalysts appears to reduce an a,/3-unsaturated ketonic carbonyl selectively. 

In certain reductions it is an advantage to reduce the platinum oxide to platinum black by shaking with hydrogen in the presence of solvent only, before the substance to be reduced is added to the mixture. More often the catalyst is reduced in the presence of the substance to be reduced with aldehydes for example the platinum black is usually more finely divided and generally more active if prepared in presence of the aldehyde. 

Aldehydes and ketones can be converted to ethers by treatment with an alcohol and triethylsilane in the presence of a strong acid or by hydrogenation in alcoholic acid in the presence of platinum oxide. The process can formally be regarded as addition of ROH to give a hemiacetal RR C(OH)OR", followed by reduction of the OH. In this respect, it is similar to 16-14. In a similar reaction, ketones can be converted to carboxylic esters (reductive acylation of ketones) by treatment with an acyl chloride and triphenyltin hydride. " ... 

As mentioned in Section 3.2, hydrogenation is by far the most investigated catalytic reaction and palladium the most commonly employed metal, followed by platinum. The most common substrates for catalytic hydrogenation tests are simple alkenes, cyclic alkenes and unsaturated carbonylic compounds. In the latter case, conjugated substrates (a,P-unsaturated aldehydes, acrylic acid) have received particular attention. 

During hydrogenation of aldehydes, especially over platinum oxide, catalyst deactivation occurs. The reasons for this deactivation are not well understood and several theories exist.6... 

The electrochemical oxidation is often more sensitive to the reaction conditions than to the substituents. Platinum electrodes are recommended for methoxylation and the equivalent acetoxylation procedures.290 In acetonitrile buffered by hydrogen carbonate ion, 3,4-diethylfuran affords the 2,5-dihydroxy-2,5-dihydro derivative (84%) and Jones oxidation readily leads to diethylmaleic anhydride in what is claimed to be the best general method for such conversions.291 In unbuffered methanol and under current density control, the oxidation of 2-methylfuran appears to eliminate the methyl group since the product is the acetal-ester 111 also obtained from methyl 2-furoate.292 If sodium acetate buffer is used, however, the methyl group is retained but oxidized in part to the aldehyde diacetate 112 in a... 

Attempted reaction of 1,3-pentadiene with the optically active diboron derived from dialkyl tartrate in the presence of a phosphine-free platinum catalyst gave poor diastereoselectivity (20% de).63 Better selectivity has been attained with a modified platinum catalyst bearing a PCy3 ligand (Scheme 6).64 The reaction of allylborane thus obtained with an aldehyde followed by oxidation with basic hydrogen peroxide affords the corresponding diol derivative with moderate ee. 

However, platinum catalysts have several disadvantages they have low reaction rates, they hydrogenate the substrate and their regioselectivity to the branched aldehyde is low. The selectivity of Pt-diphosphite/SnCl2 systems is also low. When the appropriate diphosphite is used, ee s can be as high as 90% [13]. In the early 90s, several reports were published which described the state of the art in hydroformylation with both rhodium and platinum systems [14-16]. 

Hydrosilylation can be applied to alkenes, alkynes, and aldehydes or ketones. A wide range of metal compounds can be used as a catalyst. The most common and active ones for alkenes and alkynes are undoubtedly based on platinum. Hydrosilylation of C-0 double bonds gives silyl ethers, which are subsequently hydrolysed to their alcohols. The reaction is of interest in its enantioselective version in organic synthesis for making chiral alcohols, as the achiral hydrogenation of aldehydes or ketones does not justify the use of expensive silanes as a reagent. 

Stern showed rather conclusively that the palladium does not depart to leave a carbonium ion but that both hydride migration and collapse to an aldehyde proceed simultaneously. The removal of the /3 hydrogen in a complexes by the heavier Group VIII metals has been documented. Thus Chatt and Shaw (63) showed that a platinum hydride complex could undergo the reversible addition of ethylene ... 

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